Humacyte (HUMA) POS AM 19 Nov 21 Prospectus update (post-effective amendment) Financial data

Document and Entity Information

Document and Entity Information	9 Months Ended
	Sep. 30, 2021
Document and Entity Information [Abstract]
Document Type	POS AM
Entity Registrant Name	Humacyte, Inc.
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Central Index Key	0001818382
Amendment Flag	true
Amendment Description	Humacyte, Inc., a Delaware corporation, filed with the Securities and Exchange Commission (the "SEC") a Registration Statement on Form S-1 on September 17, 2021, as amended on October 22, 2021 by Pre-Effective Amendment No. 1 to the Registration Statement on Form S-1, which was declared effective by the SEC on October 25, 2021 (as amended, the "Registration Statement"). This Post-Effective Amendment No. 1 to the Registration Statement is being filed in order to update disclosures in the registration statement reflecting the filing by Humacyte, Inc. of its Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2021, and to make certain other updates. Unless otherwise noted, all common and preferred share and related price information has been retroactively adjusted to give effect to the Exchange Ratio established in the Business Combination Agreement (each as defined in this prospectus).

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019
Current assets
Cash and cash equivalents	$ 240,449	$ 39,929	$ 93,713
Accounts receivable	240	113	601
Prepaid expenses	3,490	1,407	640
Total current assets	244,179	41,449	94,954
Finance lease right-of-use assets, net	21,947	23,492	25,552
Operating lease right-of-use assets, net	738	769	897
Property and equipment, net	36,499	40,978	47,288
Total assets	303,363	106,688	168,691
Current liabilities
Accounts payable	5,830	2,274	3,272
Accrued expenses	9,422	4,592	6,000	$ 7,049
PPP loan payable, current portion		2,451
Deferred payroll tax, current portion	145	145
Finance lease obligation, current portion	1,915	1,729	1,500
Operating lease obligation, current portion	44	42	70
SVB loan payable, current portion	3,889
Total current liabilities	21,245	11,233	10,842
PPP loan payable, net of current portion		822
Deferred payroll tax, net of current portion	144	144
Finance lease obligation, net of current portion	21,627	23,090	24,819
Operating lease obligation, net of current portion	693	727	829
Contingent earnout liability	169,200
SVB loan payable, net of current portion	14,038
Common stock warrant liabilities	555
Total liabilities	227,502	36,016	36,490
Commitments and contingencies (Note 11)
Redeemable convertible preferred stock (Series A, B, C and D) $0.001 par value, 0 and 69,613,565 shares authorized as of September 30, 2021 and December 31, 2020, respectively; 0 and 69,613,562 shares outstanding as of September 30, 2021 and December 31, 2020, respectively; liquidation preference of $0 and $435,579 as of September 30, 2021 and December 31, 2020, respectively.		420,989	420,989
Stockholders' equity (deficit)
Preferred stock, $0.0001 par value; 20,000,000 and 0 shares designated as of September 30, 2021 and December 31, 2020; 0 shares issued and outstanding as of September 30, 2021 and December 31, 2020
Common stock, $0.0001 and $0.0001 par value as of September 30, 2021 and December 31, 2020, respectively; 250,000,000 and 340,216,780 shares authorized as of September 30, 2021 and December 31, 2020, respectively; 103,003,384 and 5,822,396 shares issued and outstanding as of September 30, 2021 and December 31, 2020, respectively.	10	1	1
Additional paid-in capital	533,009	37,778	32,783
Accumulated deficit	(457,158)	(388,096)	(321,572)	$ (234,289)
Total stockholders' equity (deficit)	75,861	(350,317)	(288,788)
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	$ 303,363	$ 106,688	$ 168,691

Balance sheet (Parenthetical)

Balance sheet (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Aug. 26, 2021	Dec. 31, 2020	Dec. 31, 2019
Balance Sheets
Redeemable convertible preferred stock, par value	$ 0.001		$ 0.001	$ 0.001
Redeemable convertible preferred stock, shares authorized	0		69,613,565	69,613,565
Redeemable convertible preferred stock, shares outstanding	0		69,613,562	69,613,562
Redeemable convertible preferred stock, liquidation preference	$ 0		$ 435,579	$ 435,579
Preferred stock, par value	$ 0.0001		$ 0.0001
Preferred stock, shares designated	20,000,000		0
Preferred stock, shares issued	0		0
Preferred stock, shares outstanding	0		0
Common stock, par value	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001
Common stock, shares authorized	250,000,000		340,216,780	340,216,780
Common stock, shares issued	103,003,384		5,822,396	5,627,157
Common stock, shares outstanding	103,003,384	103,003,384	5,822,396	5,627,157

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Condensed Consolidated Statements of Operations and Comprehensive Loss
Grant Revenue	$ 241	$ 914	$ 1,086	$ 1,367	$ 1,491	$ 6,187
Operating expenses:
Research and development (includes related party expenses of $2 and $149 for the three months ended September 30, 2021 and 2020 and $168 and $462 for the nine months ended September 30, 2021 and 2020)	15,386	14,692	45,091	40,879	54,078	75,603
General and administrative	5,398	3,435	15,576	9,416	12,013	16,275
Total operating expenses	20,784	18,127	60,667	50,295	66,091	91,878
Loss from operations	(20,543)	(17,213)	(59,581)	(48,928)	(64,600)	(85,691)
Other expenses, net:
Interest income	3	2	6	277	278	2,567
Change in fair value of contingent earnout liability	(9,768)		(9,768)
Interest expense	(1,204)	(549)	(2,952)	(1,661)	(2,202)	(2,298)
Transaction costs expensed	(49)		(49)
Change in fair value of common stock warrant liabilities	(2)		(2)
Gain on PPP loan forgiveness			3,284
Total other expenses, net	(11,020)	(547)	(9,481)	(1,384)	(1,924)	269
Net loss and comprehensive loss	$ (31,563)	$ (17,760)	$ (69,062)	$ (50,312)	$ (66,524)	$ (85,422)
Net loss per share attributable to common stockholders, basic	$ (0.72)	$ (3.07)	$ (3.69)	$ (8.74)
Net loss per share attributable to common stockholders, diluted	$ (0.72)	$ (3.07)	$ (3.69)	$ (8.74)
Weighted-average shares outstanding used in computing net loss per share attributable to common stockholders, basic	43,950,856	5,788,130	18,728,471	5,755,418
Weighted-average shares outstanding used in computing net loss per share attributable to common stockholders, diluted	43,950,856	5,788,130	18,728,471	5,755,418
Net loss per share attributable to common stockholders, basic and diluted					$ (11.54)	$ (16.17)
Weighted-average shares outstanding used in computing net loss per share attributable to common stockholders, basic and diluted					5,765,688	5,283,628

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Condensed Consolidated Statements of Operations and Comprehensive Loss
Related party expenses	$ 2	$ 149	$ 168	$ 462	$ 620	$ 571

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Changes in Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Redeemable Convertible Preferred Stock.	Common Stock	Additional Paid-in Capital	Accumulated DeficitCumulative Effect Adjustment	Accumulated Deficit	Cumulative Effect Adjustment	Total
Balance at the beginning at Dec. 31, 2018	$ 420,989
Balance at the beginning (in shares) at Dec. 31, 2018	69,613,562
Balance at the end at Dec. 31, 2019	$ 420,989						$ 420,989
Balance at the end (in shares) at Dec. 31, 2019	69,613,562						69,613,562
Balance at the beginning at Dec. 31, 2018		$ 1	$ 27,108		$ (234,289)		$ (207,180)
Balance at the beginning (in shares) at Dec. 31, 2018		5,006,326
Equity
Proceeds from the exercise of stock options			1,218				$ 1,218
Proceeds from the exercise of stock options (in shares)		620,831					620,831
Net loss					(85,422)		$ (85,422)
Stock-based compensation			4,457				4,457
Balance at the end (ASU 2016-02) at Dec. 31, 2019				$ (1,861)		$ (1,861)
Balance at the end at Dec. 31, 2019		$ 1	32,783		(321,572)		(288,788)
Balance at the end (in shares) at Dec. 31, 2019		5,627,157
Balance at the end at Mar. 31, 2020	$ 420,989
Balance at the end (in shares) at Mar. 31, 2020	69,613,562
Equity
Proceeds from the exercise of stock options			175				175
Proceeds from the exercise of stock options (in shares)		148,159
Net loss					(17,674)		(17,674)
Stock-based compensation			1,182				1,182
Balance at the end at Mar. 31, 2020		$ 1	34,140		(339,246)		(305,105)
Balance at the end (in shares) at Mar. 31, 2020		5,775,316
Balance at the beginning at Dec. 31, 2019	$ 420,989						$ 420,989
Balance at the beginning (in shares) at Dec. 31, 2019	69,613,562						69,613,562
Balance at the end at Sep. 30, 2020	$ 420,989
Balance at the end (in shares) at Sep. 30, 2020	69,613,562
Balance at the beginning (ASU 2016-02) at Dec. 31, 2019				(1,861)		(1,861)
Balance at the beginning at Dec. 31, 2019		$ 1	32,783		(321,572)		$ (288,788)
Balance at the beginning (in shares) at Dec. 31, 2019		5,627,157
Equity
Net loss							(50,312)
Balance at the end at Sep. 30, 2020		$ 1	36,484		(371,884)		(335,399)
Balance at the end (in shares) at Sep. 30, 2020		5,788,877
Balance at the beginning at Dec. 31, 2019	$ 420,989						$ 420,989
Balance at the beginning (in shares) at Dec. 31, 2019	69,613,562						69,613,562
Balance at the end at Dec. 31, 2020	$ 420,989						$ 420,989
Balance at the end (in shares) at Dec. 31, 2020	69,613,562						69,613,562
Balance at the beginning (ASU 2016-02) at Dec. 31, 2019				$ (1,861)		$ (1,861)
Balance at the beginning at Dec. 31, 2019		$ 1	32,783		(321,572)		$ (288,788)
Balance at the beginning (in shares) at Dec. 31, 2019		5,627,157
Equity
Proceeds from the exercise of stock options			301				$ 301
Proceeds from the exercise of stock options (in shares)		195,239					195,239
Net loss					(66,524)		$ (66,524)
Stock-based compensation			4,694				4,694
Balance at the end at Dec. 31, 2020		$ 1	37,778		(388,096)		(350,317)
Balance at the end (in shares) at Dec. 31, 2020		5,822,396
Balance at the beginning at Mar. 31, 2020	$ 420,989
Balance at the beginning (in shares) at Mar. 31, 2020	69,613,562
Balance at the end at Jun. 30, 2020	$ 420,989
Balance at the end (in shares) at Jun. 30, 2020	69,613,562
Balance at the beginning at Mar. 31, 2020		$ 1	34,140		(339,246)		(305,105)
Balance at the beginning (in shares) at Mar. 31, 2020		5,775,316
Equity
Proceeds from the exercise of stock options			48				48
Proceeds from the exercise of stock options (in shares)		11,761
Net loss					(14,878)		(14,878)
Stock-based compensation			1,114				1,114
Balance at the end at Jun. 30, 2020		$ 1	35,302		(354,124)		(318,821)
Balance at the end (in shares) at Jun. 30, 2020		5,787,077
Balance at the end at Sep. 30, 2020	$ 420,989
Balance at the end (in shares) at Sep. 30, 2020	69,613,562
Equity
Proceeds from the exercise of stock options			12				12
Proceeds from the exercise of stock options (in shares)		1,800
Net loss					(17,760)		(17,760)
Stock-based compensation			1,170				1,170
Balance at the end at Sep. 30, 2020		$ 1	36,484		(371,884)		(335,399)
Balance at the end (in shares) at Sep. 30, 2020		5,788,877
Balance at the beginning at Dec. 31, 2020	$ 420,989						$ 420,989
Balance at the beginning (in shares) at Dec. 31, 2020	69,613,562						69,613,562
Balance at the end at Mar. 31, 2021	$ 420,989
Balance at the end (in shares) at Mar. 31, 2021	69,613,562
Balance at the beginning at Dec. 31, 2020		$ 1	37,778		(388,096)		$ (350,317)
Balance at the beginning (in shares) at Dec. 31, 2020		5,822,396
Equity
Proceeds from the exercise of stock options			206				206
Proceeds from the exercise of stock options (in shares)		116,149
Net loss					(20,301)		(20,301)
Stock-based compensation			2,528				2,528
Issuance of warrants in conjunction with debt			2,360				2,360
Balance at the end at Mar. 31, 2021		$ 1	42,872		(408,397)		(365,524)
Balance at the end (in shares) at Mar. 31, 2021		5,938,545
Balance at the beginning at Dec. 31, 2020	$ 420,989						$ 420,989
Balance at the beginning (in shares) at Dec. 31, 2020	69,613,562						69,613,562
Balance at the end (in shares) at Sep. 30, 2021							0
Balance at the beginning at Dec. 31, 2020		$ 1	37,778		(388,096)		$ (350,317)
Balance at the beginning (in shares) at Dec. 31, 2020		5,822,396
Equity
Proceeds from the exercise of stock options (in shares)							188,006
Net loss							$ (69,062)
Balance at the end at Sep. 30, 2021		$ 10	533,009		(457,158)		75,861
Balance at the end (in shares) at Sep. 30, 2021		103,003,384
Balance at the beginning at Mar. 31, 2021	$ 420,989
Balance at the beginning (in shares) at Mar. 31, 2021	69,613,562
Balance at the end at Jun. 30, 2021	$ 420,989
Balance at the end (in shares) at Jun. 30, 2021	69,613,562
Balance at the beginning at Mar. 31, 2021		$ 1	42,872		(408,397)		(365,524)
Balance at the beginning (in shares) at Mar. 31, 2021		5,938,545
Equity
Proceeds from the exercise of stock options			30				30
Proceeds from the exercise of stock options (in shares)		5,204
Net loss					(17,198)		(17,198)
Stock-based compensation			2,930				2,930
Balance at the end at Jun. 30, 2021		$ 1	45,832		(425,595)		$ (379,762)
Balance at the end (in shares) at Jun. 30, 2021		5,943,749
Redeemable convertible preferred Stock
Conversion of redeemable convertible preferred stock into common stock in connection with the Merger and related PIPE financing	$ (420,989)
Conversion of redeemable convertible preferred stock into common stock in connection with the Merger and related PIPE financing (in shares)	(69,613,562)
Balance at the end (in shares) at Sep. 30, 2021							0
Equity
Proceeds from the exercise of stock options			360				$ 360
Proceeds from the exercise of stock options (in shares)		99,624
Conversion of redeemable convertible preferred stock into common stock in connection with the Merger and related PIPE financing		$ 7	420,982				420,989
Conversion of redeemable convertible preferred stock into common stock in connection with the Merger and related PIPE financing (in shares)		69,613,562
The merger and related PIPE financing, net of transaction costs and acquired liabilities		$ 2	209,478				209,480
Public warrants assumed upon the merger, net of transaction costs			13,912				13,912
Issuance of common stock upon the Merger and related PIPE Financing, net of issuance costs (in shares)		27,346,449
Net loss					(31,563)		(31,563)
Stock-based compensation			1,877				1,877
Contingent consideration liability recognized upon closing of the reverse recapitalization			159,432				159,432
Balance at the end at Sep. 30, 2021		$ 10	$ 533,009		$ (457,158)		$ 75,861
Balance at the end (in shares) at Sep. 30, 2021		103,003,384

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities
Net loss	$ (66,524)	$ (85,422)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	6,291	4,689
Stock-based compensation expense	4,694	4,457
Loss on disposal of property and equipment	177	69
Amortization expense	2,060	2,060
Non-cash operating lease costs	81	62
Accrued interest on PPP loan obligation	22
Changes in operating assets and liabilities:
Accounts receivable	488	(185)
Prepaid expenses	(767)	216
Other assets		112
Accounts payable	(889)	2,434
Accrued expenses	(1,408)	372
Operating lease obligation	(82)	(62)
Deferred payroll taxes	289
Deferred revenue		(589)
Net cash used in operating activities	(55,568)	(71,787)
Cash flows from investing activities
Purchase of property and equipment	(318)	(8,125)
Proceeds from sale of property and equipment	50
Net cash used in investing activities	(268)	(8,125)
Cash flows from financing activities
Proceeds from the exercise of stock options	301	1,218
Proceeds from PPP loan	3,251
Payment of finance lease principal	(1,500)	(1,292)
Net cash provided by financing activities	2,052	(74)
Net increase (decrease) in cash and cash equivalents	(53,784)	(79,986)
Cash and cash equivalents at the beginning of the period	93,713	173,699
Cash and cash equivalents at the end of the period	39,929	93,713
Supplemental disclosure of noncash activities:
Operating lease right-of-use assets obtained in exchange for lease obligations	36	36
Accrued property and equipment	$ 4	$ 113

Organization and Description of

Organization and Description of Business	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Organization and Description of Business
Organization and Description of Business	1. Organization and Description of Business Organization Humacyte, Inc.and subsidiary, or the Company, is pioneering the development and manufacture of off-the-shelf, universally implantable, bioengineered human tissues designed to improve the lives of patients and transform the practice of medicine. The Company is leveraging its technology platform to develop proprietary, bioengineered, acellular human tissues for use in the treatment of diseases and conditions across a range of anatomic locations in multiple therapeutic areas. On August 26, 2021 (the “ ” “ ” “ ” “ ” “ ” “ ” “ ” Refer to Note 3 — Liquidity and Going Concern Since its inception in 2004, the Company has generated no product revenue and has incurred net losses and negative cash flows from operations in each year. To date, the Company has financed its operations primarily through the sale of equity securities and convertible debt and, to a lesser extent, through governmental and other grants. At December 31, 2020 and September 30, 2021, the Company had an accumulated deficit of $388.1 million and $457.2 million, respectively. The Company ’ ’ ’ ’ As of September 30, 2021, the Company had cash and cash equivalents of $240.4 million. Based on the cash and cash equivalents on hand, the Company believes its combined cash and cash equivalents will be sufficient to fund operations, including clinical trial expenses and capital expenditure requirements, for at least 12 months from the issuance date of these interim financial statements. Impact of COVID-19 The COVID-19 pandemic, which began in December ’ ’ ’ ’ ’ To date, the COVID-19 pandemic has not resulted in material financial impacts or impairment losses in the carrying values of the Company ’ ’	1. Organization and Description of Business Organization Humacyte, Inc., or the Company, is pioneering the development and manufacture of off-the-shelf, universally implantable, bioengineered human tissues to improve the lives of patients and transform the practice of medicine. The Company is leveraging its technology platform to develop proprietary, bioengineered, acellular human tissues for use in the treatment of diseases and conditions across a range of anatomic locations in multiple therapeutic areas. Liquidity and Going Concern Since its inception in 2004, the Company has generated no product revenue and has incurred net losses and negative cash flows from operations in each year. To date, the Company has financed its operations primarily through the sale of equity securities and convertible debt and, to a lesser extent, through governmental and other grants. At December 31, 2019 and December 31, 2020, the Company had an accumulated deficit of $321.6 million and $388.1 million, respectively. The Company ’ ’ ’ ’ The Company does not believe its existing cash and cash equivalents will be sufficient to fund its anticipated operating expenses, including clinical trial expenses, and capital expenditure requirements for at least twelve months following the date these financial statements were issued. Until such time, if ever, as the Company is able to successfully develop and commercialize one or more of its product candidates, it expects to fund its operations through the sale of equity, debt, borrowing under credit facilities or through potential collaborations with other companies, other strategic transactions or government contracts and grants. The Company ’ ’ substantial doubt about its ability to continue as a going concern within one year The accompanying financial statements do not include any adjustments that might result from the outcome of this uncertainty. Accordingly, the financial statements have been prepared on a basis that assumes the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the ordinary course of business. Impact of COVID-19 The COVID-19 pandemic, which began in December ’ ’ ’ ’ ’ 1. Organization and Description of Business (continued) To date, the COVID-19 pandemic has not resulted in material financial impacts or impairment losses in the carrying values of the Company ’ ’

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The Company has prepared the accompanying financial statements in conformity with accounting principles generally accepted in the United ’ Unless otherwise noted, the Company has retroactively adjusted all common and preferred share and related price information to give effect to the Exchange Ratio established in the Merger Agreement. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Significant estimates in the financial statements include stock-based compensation costs, right-of-use, or ROU, assets, accruals for research and development activities, contingent earnout liability, fair value of common stock warrants, redeemable convertible preferred stock and income taxes. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates. Unaudited Interim Condensed Consolidated Financial Statements The accompanying interim condensed consolidated financial statements and the related footnote disclosures are unaudited. These unaudited interim financial statements have been prepared on the same basis as the audited financial statements, and in management ’ ’ Certain information and footnote disclosures normally included in consolidated financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements for the year ended December 31, 2020 and the related notes included elsewhere in this prospectus, which provides a more complete discussion of the Company’s accounting policies and certain other information. Other than the policies noted below, there have been no significant changes to the significant accounting policies disclosed in Note 2 of the audited consolidated financial statements as of and for the years ended December 31, 2019 and 2020 included elsewhere in this prospectus. Common Stock Warrants The Company assumed 5,000,000 publicly-traded warrants ( “ ” “ ” ’ “ ” “ ” ’ “ ” The Company evaluated the Common Stock Warrants to determine the appropriate financial statement classification upon the consummation of the Merger. The Common Stock Warrants are not mandatorily redeemable and are considered to be freestanding instruments as they are separately exercisable into common shares. As such, the Common Stock Warrants were not classified as liabilities under FASB ASC Topic 480, Distinguishing Liabilities from Equity Derivatives and Hedging The agreement governing the Common Stock Warrants includes a provision ( “ ” ’ “ ’ ” ’ The Public Warrants are considered to be “indexed to the Company’s own stock”. The agreement provides that in the event of a tender or exchange offer made to and accepted by holders of more than 50% of the outstanding shares of the Company ’ ’ ’ Contingent Earnout Liability In connection with the Reverse Recapitalization and pursuant to the Business Combination Agreement dated as of February 17, 2021 by and among Legacy Humacyte, Merger Sub, and AHAC (the “ ” ’ “ ” The estimated fair value of the Contingent Earnout Shares was determined using a Monte Carlo simulation using a distribution of potential outcomes on a monthly basis over a ten-year period prioritizing the most reliable information available. The assumptions utilized in the calculation were based on the achievement of certain stock price milestones, including the current Company common stock price, expected volatility, risk-free rate, expected term and expected dividend yield. The Contingent Earnout Shares are categorized as a Level Segments The Company operates and manages its business as one reportable and operating segment. The Company is developing proprietary, bioengineered, acellular human tissues that are designed to be used in the treatment of diseases and conditions across a range of anatomic locations in multiple therapeutic areas. The Company ’ Revenue Recognition The Company ’ Under ASC 606, revenue is recognized when a customer obtains control of promised goods or services and is recognized in an amount that reflects the consideration that an entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) In addition, ASC 606 requires disclosure of the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. For contracts where the period between when the Company transfers a promised good or service to the customer and when the customer pays is one year or less, the Company has elected the practical expedient to not adjust the promised amount of consideration for the effects of a significant financing component. Grant Revenue The Company generates revenue primarily from government and other awarded grants that reimburse the Company for certain allowable costs related to research and development efforts. These grants include the following terms: The Department of Defense grants are for an award of $4.0 million, all of which was recognized as revenue before the program ended, for work on bioengineered blood vessels for vascular trauma, which was awarded to the Company in September 2017 and ended in February 2020, and an award of $7.1 million for work to support human tissue engineered blood vessels for vascular reconstruction in the injured warfighter, which was awarded to the Company in August 2017 and is ongoing. The Company has recognized revenue of $0.6 million and $1.0 million during the three and nine months ended September 30, 2020,respectively, and $0.2 million and $1.1 million during the three and nine months ended September 30, 2021, respectively, for reimbursement of certain allowable costs related to these grants. The National Institutes of Health grant is for $1.6 million for work to support bioengineered grafts for peripheral vascular disease, which was awarded to the Company in November 2013. The Company recognized $1.6 million for the reimbursement of certain allowable costs related to the grant before this program ended in 2020. The Company recognized $0.3 million during the three and nine months ended September 30, 2020, and no revenue during the three and nine months ended September 30, 2021, for reimbursement of certain allowable costs related to these grants. The Company has determined that the grants are not within the scope of ASC 606 as they do not meet the definition of a contract with a customer. The Company has concluded that the grants meet the definition of a contribution and are nonexchange transactions and has applied the contribution accounting model in Subtopic 958-605, Not-for-Profit-Entities-Revenue Recognition by analogy. The Company recognizes funding received from grants as revenue, rather than as a reduction of research and development expenses, because the Company is the principal in conducting the research and development activities and these grants are central to the Company ’ ’ Revenue from grants not within the scope of ASC 606 was $0.9 million and $1.4 million for the three and nine months ended September 30, 2020, respectively, and $0.2 million and $1.1 million for the three and nine months ended September 30, 2021, respectively. Concentration of Credit Risk Financial instruments which potentially subject the Company to concentrations of credit risk consist principally of cash and cash equivalents. Total cash balances exceeded insured balances by the Federal Deposit Insurance Corporation as of December 31, 2020 and September 30, 2021. Cash equivalents are invested in highly rated money market funds invested only in obligations of the U.S. government and its agencies. The majority of the Company ’ ’ ’ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue Accounts Receivable ​ ​ Three Months ​ Nine Months ​ December 31, ​ September 30, ​ ​ 2020 2021 2020 2021 2020 2021 Grant A ​ — ​ — ​ — ​ — ​ — ​ — ​ Grant B 0 ​ — % 11 ​ — % — ​ — Grant C 68 % 100 % 65 % 100 % 100 % 100 % Grant D 30 — % 20 ​ — % — — Total 98 % 100 % 96 % 100 % 100 % 100 % ​ All of the Company ’ Other Risks and Uncertainties The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, successful discovery and development of its product candidates, the success of clinical trials and other studies for its product candidates, including for its ongoing V005 Phase II/III clinical trial and V007 Phase III clinical trial, the regulatory approval and commercialization of its HAVs and other product candidates, ’ ’ ’ Product candidates currently under development will require extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel, and infrastructure and extensive compliance-reporting capabilities. Even if the Company ’ ’ Net Loss per Share Attributable to Common Stockholders The Company follows the two-class method to compute basic and diluted net loss per share attributable to common stockholders when shares met the definition of participating securities. The two-class method determines net loss per common share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to share in the earnings as if all income for the period had been distributed. During periods of loss, there is no allocation required under the two-class method since the redeemable convertible preferred stock did not have a contractual obligation to share in the Company ’ Basic net loss per share attributable to common stockholders is computed by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period without consideration of potentially dilutive common stock. Diluted net loss per share attributable to common stockholders reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock or resulted in the issuance of common stock that then shared in the earnings of the Company unless inclusion of such shares would be anti-dilutive. As the Company has only incurred losses, basic and diluted net loss per share is the same. The potential shares of common stock that were excluded from the computation of diluted net loss per share for each period because including them would have had an antidilutive effect were as follows: ​ ​ ​ ​ ​ ​ ​ September 30, ​ 2020 2021 ​ ​ ​ ​ ​ Shares issuable upon conversion of Series A redeemable convertible preferred stock 18,421,897 — Shares issuable upon conversion of Series B redeemable convertible preferred stock 24,137,647 — Shares issuable upon conversion of Series C redeemable convertible preferred stock 11,241,283 — Shares issuable upon conversion of Series D redeemable convertible preferred stock 15,812,735 — Exercise of options under stock plan 4,516,907 6,399,888 Warrants to purchase common stock 32,961 5,465,204 ​ The 15,000,000 Contingent Earnout shares are excluded from the anti-dilutive table for all the periods presented as such shares are contingently issuable until the share price of the Company exceeds specified thresholds that have not yet been achieved, or upon the occurrence of a change in control. Impairment of Long-Lived Assets The Company reviews the carrying value of property and equipment for indicators of possible impairment whenever events and circumstances indicate that the carrying value of an asset or asset group may not be recoverable from the estimated future net undiscounted cash flows expected to result from its use and eventual disposition. In cases where estimated future net undiscounted cash flows are less than the carrying value, an impairment loss is recognized equal to an amount by which the carrying value exceeds the fair value of the asset or asset group. The factors considered by management in performing this assessment include current operating results, trends and prospects, the manner in which the property is used, and the effects of obsolescence, demand, competition, and other economic factors. Based on this assessment, during the nine months ended September 30, 2020 and 2021, respectively, the Company concluded there were no such events or changes in circumstances requiring review of the carrying amount of the Company ’ Recently Adopted Accounting Pronouncements In August 2020, the FASB issued ASU No. 2020-06, “ ’ ’ ” “ ” ’ Recently Issued Accounting Pronouncements In May 2021, the FASB issued “ ’ ” “ ” ’	2. Summary of Significant Accounting Policies Basis of Presentation The Company has prepared the accompanying financial statements in conformity with accounting principles generally accepted in the United Reverse Recapitalization On August 26, 2021 (the “ ” “ ” “ ” “ ” “ ” “ ” “ ” “ ” Unless otherwise noted, the Company has retroactively adjusted all common and preferred share and related price information to give effect to the Exchange Ratio of approximately 0.26260 established in the Merger Agreement. Segments The Company operates and manages its business as one reportable and operating ’ Comprehensive loss Comprehensive loss includes net loss as well as other changes in stockholders ’ Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Significant estimates in the financial statements include stock-based compensation costs, right-of-use, or ROU assets, accruals for research and development activities, fair value of common stock, useful lives of property and equipment, redeemable convertible preferred stock and income taxes. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates. ​ 2. Summary of Significant Accounting Policies (continued) Cash and Cash Equivalents The Company considers all short-term, highly liquid investments purchased with an original maturity of three months or less at the date of purchase to be cash equivalents. Cash deposits are held with financial institutions with investment-grade ratings in the United Redeemable Convertible Preferred Stock The Company analyzes all issued equity instruments to determine the appropriate accounting and classification. The Company evaluates its equity instruments under Accounting Standards Codification, or ASC 480, Distinguishing liabilities from equity The Company records equity instruments that are classified as temporary equity at fair value upon issuance, net of issuance costs. The Company accretes the carrying value of its redeemable convertible preferred stock to the redemption or liquidation amount once the Company has determined that it is probable that it will become redeemable or be liquidated. The accretion will be recorded as charges against additional paid-in capital until the additional paid-in capital balance is reduced to zero. At that time, additional accretion adjustments will be recorded as additions to accumulated deficit. The Company also analyzes instances where the equity instrument has a conversion feature pursuant to ASC 815, Derivatives and hedging Revenue Recognition The Company ’ In 2014, the Financial Accounting Standards Board, or FASB issued Accounting Standards Update No. Under ASC 606, revenue is recognized when a customer obtains control of promised goods or services and is recognized in an amount that reflects the consideration that an entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) In addition, ASC 606 requires disclosure of the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. ​ 2. Summary of Significant Accounting Policies (continued) For contracts where the period between when the Company transfers a promised good or service to the customer and when the customer pays is one year or less, the Company has elected the practical expedient to not adjust the promised amount of consideration for the effects of a significant financing component. Grant Revenue We generate revenue primarily from government and other awarded grants that reimburse us for certain allowable costs related to research and development efforts. The Company has determined that the grants are not within the scope of ASC 606 as they do not meet the definition of a contract with a customer. The Company has concluded that the grants meet the definition of a contribution and are nonexchange transactions and has applied the contribution accounting model in Subtopic 958-605, Not-for-Profit-Entities-Revenue Recognition by analogy. The Company recognizes funding received from grants as revenue, rather than as a reduction of research and development expenses, because the Company is the principal in conducting the research and development activities and these grants are central to the Company ’ Revenue from grants not within the scope of ASC 606 was $6.2 million and $1.5 million for the years ending December 31, 2019 and 2020, respectively. Concentration of Credit Risk Financial instruments which potentially subject the Company to concentrations of credit risk consist principally of cash and cash equivalents. Total cash balances exceeded insured balances by the Federal Depository Insurance Corporation as of December 31, 2019 and 2020. Cash equivalents are invested in highly rated money market funds invested only in obligations of the US government and its agencies. The majority of the Company ’ ’ ’ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2020 ​ ​ ​ ​ ​ Accounts ​ ​ ​ Accounts ​ ​ Revenue Receivable Revenue Receivable ​ Grant A ​ 28 % — ​ — ​ — ​ Grant B 38 % 67 % 10 % — Grant C 34 % 33 % 67 % 100 % Grant D — — 18 % — Total 100 % 100 % 95 % 100 % ​ All of the Company ’ ​ 2. Summary of Significant Accounting Policies (continued) Other Risks and Uncertainties The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, successful discovery and development of its product candidates, the success of clinical trials and other studies for its product candidates, including for its ongoing V005 Phase II/III clinical trial and V007 Phase III clinical trial, the regulatory approval and commercialization of its HAVs and other product candidates, ’ ’ ’ Product candidates currently under development will require extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel, and infrastructure and extensive compliance-reporting capabilities. Even if the Company ’ ’ Net Loss per Share Attributable to Common Stockholders The Company applies the two-class method to compute basic and diluted net loss per share attributable to common stockholders when shares meet the definition of participating securities. The two-class method determines net loss per share for each class of common and redeemable convertible preferred stock according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income (loss) available to common stockholders for the period to be allocated between common and redeemable convertible preferred stock based upon their respective rights to share in the earnings as if all income (loss) for the period had been distributed. During periods of loss, there is no allocation required under the two-class method since the redeemable convertible preferred stock does not have a contractual obligation to share in the Company ’ ​ 2. Summary of Significant Accounting Policies (continued) Basic net loss per share attributable to common stockholders is computed by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period without consideration of potentially dilutive common stock. Diluted net loss per share attributable to common stockholders reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock or resulted in the issuance of common stock that then shared in the earnings of the Company unless inclusion of such shares would be anti-dilutive. Since the Company has only incurred losses, basic and diluted net loss per share is the same. Securities that could potentially dilute net loss per share in the future that were not included in the computation of diluted net loss per share are as follows: ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2020 ​ ​ ​ ​ ​ Shares issuable upon conversion of Series A redeemable convertible preferred stock 18,421,897 18,421,897 Shares issuable upon conversion of Series B redeemable convertible preferred stock 24,137,647 24,137,647 Shares issuable upon conversion of Series C redeemable convertible preferred stock 11,241,283 11,241,283 Shares issuable upon conversion of Series D redeemable convertible preferred stock 15,812,735 15,812,735 Options to purchase common stock 5,220,236 4,813,262 Warrant to purchase common stock 32,961 32,961 ​ Fair Value of Financial Instruments Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in the principal or most advantageous market in an orderly transaction between market participants at the measurement date. ASC 820, Fair Value Measurement and Disclosures ● Level 1 — Observable inputs that reflect unadjusted quoted prices for identical assets or liabilities in active markets. ● Level 2 — Inputs other than quoted prices included in Level 1 that are observable for the asset or liability, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. ● Level 3 — Unobservable inputs in which little or no market data exists, therefore requiring the Company to develop its own assumptions. The Company evaluates assets and liabilities subject to fair value measurements on a recurring basis to determine the appropriate level at which to classify them for each reporting period, utilizing valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible. The determination requires significant judgments to be made by the Company. The Company ’ ​ 2. Summary of Significant Accounting Policies (continued) Property and Equipment, Net Property and equipment, net are recorded at cost less accumulated depreciation. Expenditures for major additions and improvements are capitalized and minor replacements, maintenance, and repairs are charged to expense as incurred. When property and equipment are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the balance sheet accounts and any resulting gain or loss is included in the results of operations for the respective period. Depreciation is calculated using the straight-line method over the estimated useful lives of the related assets. The estimated useful lives for significant asset categories are as follows: ​ ​ ​ ​ ​ Estimated Useful Property and equipment ​ Lives (Years) Scientific equipment ​ 5 – 7 Computer equipment 5 Software 3 Furniture and fixtures 5 – 7 Leasehold improvements Lesser of useful life or life of lease Construction in progress N/A ​ Impairment of Long-Lived Assets The Company reviews the carrying value of property and equipment for indicators of possible impairment whenever events and circumstances indicate that the carrying value of an asset or asset group may not be recoverable from the estimated future net undiscounted cash flows expected to result from its use and eventual disposition. In cases where estimated future net undiscounted cash flows are less than the carrying value, an impairment loss is recognized equal to an amount by which the carrying value exceeds the fair value of the asset or asset group. The factors considered by management in performing this assessment include current operating results, trends and prospects, the manner in which the property is used, and the effects of obsolescence, demand, competition, and other economic factors. Based on this assessment, there was no impairment at December 31, 2019 and 2020. Income Taxes Income taxes are computed using the asset and liability approach that requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the Company ’ ​ 2. Summary of Significant Accounting Policies (continued) The Company recognizes the benefit of an income tax position only if it is more likely than not (greater than 50%) that the tax position will be sustained upon tax examination, based solely on the technical merits of the tax position. Otherwise, no benefit can be recognized. Assessing an uncertain tax position begins with the initial determination of the sustainability of the position and is measured at the largest amount of benefit that is greater than 50% likely of being realized upon ultimate settlement. As of each balance sheet date, unresolved uncertain tax positions must be reassessed. Additionally, the Company must accrue interest and related penalties, if applicable, on all tax exposures for which reserves have been established consistent with jurisdictional tax laws. The Company has analyzed its filing positions in all significant Federal and state jurisdictions where it is required to file income tax returns, as well as open tax years in these jurisdictions. As of December 31, 2019 and 2020, the Company has determined that no uncertain tax positions would have a material impact on the financials statements of the Company. The Company is no longer subject to Federal, state, and local tax examinations by tax authorities for years before 2017 although carry-forward attributes that were generated prior to 2017 may still be adjusted upon examination by the taxing authorities if they either have been or will be used in a future period. No income tax returns are currently under examination by taxing authorities. As of December 31, 2019 and 2020, the Company had not recorded any amounts for unrecognized tax benefits. The Company ’ ’ Intellectual Property The Company seeks to protect its intellectual property by filing patent applications in the United ’ Research and Development The Company expenses research and development costs as operating expenses as incurred. Research and development expenses consist primarily of: ● salaries and related overhead expenses for personnel in research and development functions, including stock-based compensation and benefits; ● fees paid to consultants and CROs, including in connection with clinical trials, and other related clinical trial fees, such as for investigator grants, patient screening, laboratory work and statistical compilation and analysis; ● allocation of facility lease and maintenance costs; ● depreciation of leasehold improvements, laboratory equipment and computers; ● costs related to purchasing raw materials for and producing product candidates for clinical trials; ● costs related to compliance with regulatory requirements; ● costs related to the manufacturing scale-out initiative; and ● license fees related to in-licensed technologies. 2. Summary of Significant Accounting Policies (continued) Accrued Research and Development The Company has entered into various agreements with CROs and a CMO, which conduct preclinical studies and clinical trials and contract manufacturing activities. The Company ’ Stock-Based Compensation The Company accounts for stock-based compensation for employees and non-employees measured at grant date, based on the fair value of the award. The Company measures the fair value of awards granted using the Black-Scholes option pricing model and recognizes the expense over the requisite service period using the straight-line method. Option valuation models, including the Black-Scholes option-pricing model, require the input of highly subjective assumptions, and changes in the assumptions used can materially affect the grant-date fair value of an award. These assumptions include the risk-free rate of interest, expected dividend yield, expected volatility, the expected term of the award, and the fair value of the underlying common stock on the date of grant. Forfeitures are accounted for as they occur. Leases Effective January 1, 2019, the Company accounts for its leases under ASC 842, Leases ’ “ ” “ ” “ ” ’ “ ” “ ” “ ” Under this guidance, arrangements meeting the definition of a lease are classified as operating or finance leases, and are recorded on the balance sheet as both a right-of-use asset and lease liability, calculated by discounting fixed lease payments over the lease term at the rate implicit in the lease or the Company ’ ​ 2. Summary of Significant Accounting Policies (continued) Lease expenses for minimum lease payments for operating leases are recognized on a straight-line basis over the lease term. Amortization expense of the right-of-use asset for finance leases is recognized on a straight-line basis over the lease term and interest expense for finance leases is recognized based on the incremental borrowing rate. Lease liabilities are increased by interest and reduced by payments each period, and the right of use asset is amortized over the lease term. In calculating the right-of-use assets and lease liabilities, the Company has elected to combine lease and non-lease components for all asset classes. The Company excludes short-term leases, if any, having initial terms of 12 months or less from the new guidance as an accounting policy election, and recognizes rent expense on a straight-line basis over the lease term. Prior to the adoption of ASC 842 on January 1, 2019 the Company was deemed to be the accounting owner of leased space during the construction of its headquarters in a build-to-suit arrangement. Upon substantial completion of construction in June ’ ’ each The cumulative effect of initially applying the new lease guidance on January 1, 2019 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ January 1, 2019 ​ ​ ​ ​ ​ Cumulative ​ Beginning ​ ​ Beginning ​ Effect ​ Balance, ($ in thousands) Balance Adjustment As Adjusted Assets ​ ​ ​ ​ ​ ​ Building asset ​ $ 25,091 ​ $ (25,091) ​ $ — Finance lease right-of-use assets, net ​ $ — ​ $ 27,612 ​ $ 27,612 Operating lease right-of-use assets, net ​ $ — ​ $ 923 ​ $ 923 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Liabilities and stockholders’ deficit ​ ​ ​ Accrued expenses ​ $ 7,049 ​ $ (1) ​ $ 7,048 Facility financing obligation, current portion ​ $ 276 ​ $ (276) ​ $ — Finance lease obligation, current portion ​ $ — ​ $ 1,292 ​ $ 1,292 Operating lease obligation, current portion ​ $ — ​ $ 55 ​ $ 55 Facility financing obligation, net of current portion ​ $ 22,955 ​ $ (22,955) ​ $ — Finance lease obligation, net of current portion ​ $ — ​ $ 26,319 ​ $ 26,319 Operating lease obligation, net of current portion ​ $ — ​ $ 870 ​ $ 870 Accumulated deficit ​ $ (234,289) ​ $ (1,861) ​ $ (236,150) ​ ​ 2. Summary of Significant Accounting Policies (continued) Recently Adopted Accounting Pronouncements In August — Recently Issued Accounting Pronouncements In August 2020, the FASB issued ASU No. 2020-06, “  –  ’  –  ’ “ ”

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Property and Equipment, Net
Property and Equipment, Net	5. Property and Equipment, Net Property and equipment, net consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ September 30, ($ in thousands) 2020 2021 ​ ​ ​ ​ ​ ​ Scientific equipment ​ $ 27,412 ​ $ 27,578 Computer equipment ​ 149 ​ 154 Software ​ 335 ​ 335 Furniture and fixtures ​ 988 ​ 988 Leasehold improvements ​ 26,355 ​ 26,355 ​ ​ 55,239 ​ 55,410 Accumulated depreciation ​ (14,261) ​ (18,911) Property and equipment, net ​ $ 40,978 ​ $ 36,499 ​ Depreciation expense totaled $1.6 million and $4.7 million for the three and nine months ended September 30, 2020, respectively, and $1.5 million and $4.7 million for the three and nine months ended September 30, 2021, respectively. All long-lived assets are maintained in the United	3. Property and Equipment, Net Property and equipment, net consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ($ in thousands) 2019 2020 ​ ​ ​ ​ ​ ​ Scientific equipment ​ $ 27,822 ​ $ 27,412 Computer equipment ​ 218 ​ 149 Software ​ 340 ​ 335 Furniture and fixtures ​ 988 ​ 988 Leasehold improvements ​ 26,337 ​ 26,355 ​ ​ 55,705 ​ 55,239 Accumulated depreciation ​ (8,417) ​ (14,261) Property and equipment, net ​ $ 47,288 ​ $ 40,978 ​ Depreciation expense totaled $4.7 million and $6.3 million for the years ended December 31, 2019 and 2020, respectively. All long-lived assets are maintained in the United

Accrued Expenses

Accrued Expenses	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Accrued Expenses
Accrued Expenses	6. Accrued Expenses Accrued expenses consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ September 30, ($ in thousands) 2020 2021 ​ ​ ​ ​ ​ ​ Accrued external research, development and manufacturing costs ​ $ 2,615 ​ $ 2,685 Accrued employee compensation and benefits ​ 1,009 ​ 4,025 Accrued professional fees ​ 968 ​ 2,712 Total ​ $ 4,592 ​ $ 9,422 ​	4. Accrued Expenses Accrued expenses consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ($ in thousands) 2019 2020 Accrued external research, development and manufacturing costs ​ $ 3,872 ​ $ 2,615 Accrued employee compensation and benefits ​ 1,260 ​ 1,009 Accrued professional fees ​ 868 ​ 968 Total ​ $ 6,000 ​ $ 4,592 ​

Debt

Debt	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Debt
Debt	7. Debt On April 30, 2020, the Company received loan proceeds in the amount of approximately $3.3 million under the Paycheck Protection Program ( “ ” In March 2021, the Company entered into a term loan agreement with Silicon Valley Bank and SVB Innovation Credit Fund VIII, L.P., which provides a term loan facility of up to $50.0 million with a maturity date of March 1, 2025, or the Loan Agreement. The Company ’ The Loan Agreement provides that the term loans will be distributed in tranches. The initial term loan tranche of $20.0 million was drawn in March 2021 and is accounted for net of issuance costs which are being accreted to interest expense over the term of the loan using the effective interest method. As of September 30, 2021, three subsequent $10.0 million term loan tranches were eligible to be disbursed at the request of the Company during specified draw periods between now and 2023 if certain business development milestones and other specified requirements are met by the dates specified in the Loan Agreement. Borrowings bear interest at the greater of 7.5% or the Wall Street Journal Prime Rate plus 4.25% (7.5% as of September 30, 2021). Interest only payments on the principal amount outstanding are due monthly beginning in the first month after the loan is dispersed. Repayment of principal may begin as soon as April 1, 2022 under the level of borrowing outstanding at September 30, 2021, and no later than April 1, 2024. The term loans may only be prepaid in full, and such prepayment requires 30 days ’ On October 13, 2021, the Company borrowed an additional $10.0 million under the Loan Agreement. As a result of the additional borrowing, the commencement of repayment of principal was deferred to no earlier than July 2023. In connection with the Loan Agreement, the Company granted warrants to the lenders to purchase shares of common stock at an exercise price of $10.28 per share, of which 287,704 warrants were immediately exercisable. The warrants are classified within stockholders ’ ’ ’ At issuance, the Company initially determined that the funding of an additional tranche was not probable, and therefore no value was ascribed to the remaining 123,302 warrants that were only exercisable upon the funding of the additional tranche. As a result of the Company ’ ’ SVB loan payable and net discount or premium balances are as follows: ​ ​ ​ ​ ​ ​ September 30, ($ in thousands) 2021 Principal amount of SVB loan payable ​ $ 20,000 Final payment amount of SVB loan payable ​ 1,000 Net premium associated with accretion of final payment and other debt issuance costs ​ (3,073) SVB loan payable, current and noncurrent ​ 17,927 Less SVB loan payable, current portion ​ (3,889) SVB loan payable, noncurrent portion ​ $ 14,038 ​ Future minimum payments of principal on the Company ’ ​ ​ ​ ​ ​ Year ending December 31: ($ in thousands) 2021 (remainder) ​ $ — 2022 ​ 5,555 2023 ​ 6,667 2024 ​ 6,667 2025 ​ 1,111 Total future payments ​ 20,000 ​	5. Debt On April 30, 2020, the Company received loan proceeds in the amount of approximately $3.3 million under the Paycheck Protection Program ( “ ” “ ” In September 2020, the Company applied for forgiveness of the outstanding amount under its PPP loan. The Company used the proceeds for purposes it believes were consistent with the requirements of the PPP. The Company determined that loan forgiveness would become probable upon approval by the Small Business Administration of the Company ’ ​

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases
Leases	6. Leases The Company ’ ’ At December 31, 2019 and 2020, the Company had finance lease liabilities of $26.3 million and $24.8 million, respectively, and right-of-use assets of $25.6 million and $23.5 million, respectively, and operating lease liabilities of $0.9 million and $0.8 million, respectively, and right-of-use assets of $0.9 million and $0.8 million, respectively, all of which were included in the balance sheet. The Company ’ ’ renewal options have been included in the calculation of the lease liabilities and right of use assets as the Company is reasonably certain to exercise the options due to the specialized nature of the leased building. Variable expenses generally represent the Company ’ ’ The following summarizes quantitative information about the Company ’ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ($in thousands) 2019 2020 Finance lease cost ​ ​ ​ ​ ​ ​ Amortization of right-of-use assets ​ $ 2,060 ​ $ 2,060 Interest on lease liabilities ​ 2,298 ​ 2,180 Total finance lease cost ​ 4,358 ​ 4,240 Operating lease cost ​ 137 ​ 152 Total lease cost ​ $ 4,495 ​ $ 4,392 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ Year Ended ​ ​ ​ December 31, 2019 ​ December 31, 2020 ​ ​ ​ Finance ​ Operating ​ Finance ​ Operating ​ ($ in thousands) Leases Leases Leases Leases Operating cash flows from leases ​ $ (2,298) ​ $ (137) ​ $ (2,180) ​ $ (182) ​ Financing cash flows from leases ​ $ (1,292) ​ $ — ​ $ (1,500) ​ $ — ​ Weighted-average remaining lease term ​ 6.02 ​ 6.38 ​ 5.52 ​ 6.24 ​ Weighted-average discount rate ​ 8.50 % ​ 8.50 % ​ 8.50 % ​ 8.50 % ​ As of December 31, 2020, the maturities of the Company ’ ​ ​ ​ ​ ​ ​ ​ ​ ($ in thousands) Finance Operating Year Ended December 31, 2021 ​ $ 3,773 ​ $ 105 Year Ended December 31, 2022 ​ 3,868 ​ 105 Year Ended December 31, 2023 ​ 3,965 ​ 105 Year Ended December 31, 2024 ​ 4,065 ​ 106 Year Ended December 31, 2025 ​ 4,167 ​ 106 Thereafter ​ 16,937 ​ 678 Total ​ 36,775 ​ 1,205 Less: present value discount ​ (11,956) ​ (436) Lease liabilities ​ $ 24,819 ​ $ 769 ​

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2020
Redeemable Convertible Preferred Stock
Redeemable Convertible Preferred Stock	7. Redeemable Convertible Preferred Stock Redeemable Convertible Preferred Stock and Preferred Stock Terms The Company has outstanding series A redeemable convertible preferred stock, series B redeemable convertible preferred stock, series C redeemable convertible preferred stock and series D redeemable convertible preferred stock, which are collectively referred to as “ ” “ ” As of December 31, 2019 and December 31, 2020, redeemable convertible preferred stock consisted of the following (in thousands, except share amounts): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Redeemable Redeemable ​ ​ ​ ​ ​ ​ ​ ​ Convertible ​ Convertible ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Preferred ​ Preferred Stock ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock ​ Issued and ​ ​ Carrying ​ Liquidation ​ Issuance ​ Authorized Outstanding Value Preference Price Series A redeemable convertible preferred stock ​ 18,421,897 ​ 18,421,897 ​ $ 74,079 ​ $ 74,079 ​ $ 4.0212 Series B redeemable convertible preferred stock ​ 24,137,647 ​ 24,137,647 ​ ​ 127,358 ​ ​ 136,500 ​ $ 5.6550 Series C redeemable convertible preferred stock ​ 11,241,286 ​ 11,241,283 ​ ​ 70,704 ​ ​ 75,000 ​ $ 6.6717 Series D redeemable convertible preferred stock ​ 15,812,735 ​ 15,812,735 ​ ​ 148,848 ​ ​ 150,000 ​ $ 9.4859 ​ 69,613,565 69,613,562 ​ $ 420,989 ​ $ 435,579 ​ ​ ​ ​ In connection with the series D redeemable convertible preferred stock financing, the Company granted Fresenius Medical Care the right to purchase up to an aggregate of $30.0 million of its common stock in a private placement effected concurrently with its initial public offering at a price per share equal to the initial public offering price. See Note 13: Related Party Transactions for further discussion of the Company ’ Election of Directors The holders of the series A redeemable convertible preferred stock and the series B redeemable convertible preferred stock may designate one individual and two individuals, respectively, to the Board of Directors. The holders of the series C redeemable convertible preferred stock may designate one individual to the Board of Directors and Fresenius Medical Care may designate one representative to attend, in a non-voting observer capacity, all meetings of the Company ’ Conversion to Common Stock Each share of redeemable convertible preferred stock is convertible, at the option of the holder thereof, into that number of the fully paid and nonassessable shares of common stock determined by dividing the original issue price for the relevant shares by the conversion price. Each share of redeemable convertible preferred stock will automatically be converted into that number of fully-paid, nonassessable shares of common stock at the then effective conversion rate for such shares (i) ​ 7. Redeemable Convertible Preferred Stock   (continued) The following are the conversion prices for each series of the redeemable convertible preferred stock as of December 31, 2020: ​ ​ ​ ​ ​ Series Conversion Series A redeemable convertible preferred stock ​ $ 4.0212 Series B redeemable convertible preferred stock ​ $ 5.6550 Series C redeemable convertible preferred stock ​ $ 6.6717 Series D redeemable convertible preferred stock ​ $ 9.4859 ​ These conversion prices are subject to adjustment from time to time including for certain share issuances made without consideration or for consideration less than the then applicable conversion price of a series of redeemable convertible preferred stock, dividends, stock splits, and combinations. As of December 31, 2020, each series of redeemable convertible preferred stock is convertible on a one-for-one basis. The series A, series B, series C and series D redeemable convertible preferred stock includes an anti-dilution feature that adjusts the conversion price, in certain scenarios, if the Company sells shares at a price below the stated conversion price. The anti-dilution provision is considered a contingent beneficial conversion feature. Due to the inability of the Company to determine the price of the shares sold, the Company is unable to determine the number of shares that the holder would receive if the contingency occurs. Therefore, the beneficial conversion feature is not recognized until the contingent event occurs. Dividends Any dividends on the redeemable convertible preferred stock are not cumulative. The holders of the redeemable convertible preferred stock are entitled to receive dividends pro rata with the holders of common stock on an as-converted basis, when and if declared and paid by the Board of Directors, out of any assets at the time legally available. Any declared and unpaid dividends on the redeemable convertible preferred stock are payable upon certain voluntary or involuntary acquisition or sale transactions or the liquidation, dissolution or winding up of the Company as described below under “ ” ​ 7. Redeemable Convertible Preferred Stock   (continued) Liquidation In the event of certain voluntary or involuntary acquisition or sale transactions or upon the liquidation, dissolution or winding up of the Company, each, a Reorganization, in which the holders of the series D redeemable convertible preferred stock receive less than $9.4859 per share plus any declared but unpaid dividends, referred to as the Series D Liquidation Preference, or such lesser amount approved in writing by the holders of a majority of the then outstanding series D redeemable convertible preferred stock, the series D stockholders will receive the series D liquidation preference before the holders of the series C, series B, series A redeemable convertible preferred stock or common stockholders would receive any proceeds relating to such Reorganization, and the entire assets of the Company available for distribution would be distributed pro rata among holders of the series D redeemable convertible preferred stock. In the event that, after the payment to the holders of the series D redeemable convertible preferred stock, the holders of the series C redeemable convertible preferred stock would receive less than $6.6717 per share plus any declared but unpaid dividends or such lesser amount approved by the holders of at least 80% of the then outstanding series C redeemable convertible preferred stock, the entire remaining assets of the Company available for distribution would be distributed pro rata among holders of the series C redeemable convertible preferred stock. In the event that, after the payment to the holders of the series D redeemable convertible preferred stock and series C redeemable convertible preferred stock, the holders of the series B redeemable convertible preferred stock would receive less than $5.6550 per share plus any declared but unpaid dividends or such lesser amount approved by the holders of a majority of the then outstanding series B redeemable convertible preferred stock, the entire remaining assets of the Company available for distribution would be distributed pro rata among holders of the series B redeemable convertible preferred stock. However, in the event of any Reorganization, if the holders of the series D redeemable convertible preferred stock, series C redeemable convertible preferred stock or series B redeemable convertible preferred stock would receive less than 1.25 times their respective liquidation preference per share, the holders of each such series will be entitled to receive, in preference to any distribution of assets to the holders of any junior series, an amount per share equal to 1.25 times such liquidation preference. In the event that, after the payment to the holders of the series D redeemable convertible preferred stock, series Voting Except as provided in the Company ’ ’ ​ 7. Redeemable Convertible Preferred Stock (continued) Redemption and Balance Sheet Classification In accordance with the Company ’

Stockholders, Equity (Deficit)

Stockholders, Equity (Deficit)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Stockholders' Equity (Deficit)
Stockholders' Equity (Deficit)	8. Stockholders ’ Equity (Deficit) Redeemable Convertible Preferred Stock As of December 31, 2020 and immediately prior to the Merger, Legacy Humacyte had outstanding series A redeemable convertible preferred stock, series B redeemable convertible preferred stock, series C redeemable convertible preferred stock and series D redeemable convertible preferred stock, which are collectively referred to as “ ” In connection with the Merger, all previously issued and outstanding redeemable convertible preferred stock was converted into an equivalent number of shares of common stock of the Company on a one-to-one basis, then multiplied by the Exchange Ratio pursuant to the Merger Agreement. Common Stock On August 26, 2021, the Merger and related PIPE Financing was consummated and the Company issued 27,346,449 shares of common stock for proceeds of $242.4 million. The Company incurred $3.9 million of transaction costs, consisting of banking, legal, and other professional fees. Legacy Humacyte assumed $15.2 million of liabilities, including PIPE Financing fees and legal fees, and $0.1 million of assets from AHAC. Immediately following the Merger, there were 103,003,384 shares of common stock outstanding with a par value of $0.0001. As of September 30, 2021, the Company ’ The holders of common stock are entitled to receive dividends from time to time as may be declared by the Company ’ The holders of common stock are entitled to one vote for each share held with respect to all matters voted on by the common stockholders of the Company. In the event of a reorganization of the Company, after payment to the preferred stockholders of their liquidation preferences, holders of common stock are entitled to share ratably in all remaining assets of the Company. As of September 30, 2021, the Company had reserved common stock for future issuances as follows: ​ ​ ​ ​ ​ September 30, ​ 2021 Common stock reserved for Contingent Consideration Shares 15,000,000 Exercise of options under stock plans 6,399,888 Issuance of options under stock plans 7,730,503 Shares available for grant under ESPP 1,030,033 Warrants to purchase common stock 5,465,204 ​ ​ 35,625,628 ​ On August 26, 2021, upon the Closing, all of the outstanding redeemable convertible preferred stock was converted to Common Stock pursuant to the conversion rate effective immediately prior to the Merger and the Exchange Ratio and the remaining amount was reclassified to additional paid-in capital. Preferred Stock The Company ’ ’ Warrants Activity of warrants for the nine months ended September 30, 2021 is set forth below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Legacy ​ ​ ​ ​ ​ ​ ​ ​ Humacyte ​ ​ ​ ​ ​ ​ ​ ​ Common Stock ​ Private Placement ​ ​ ​ Total Common ​ Warrants Warrants Public Warrants Stock Warrants ​ ​ ​ ​ ​ ​ ​ ​ ​ Outstanding as of December 31, 2020 ​ 32,961 ​ — ​ — ​ 32,961 Common Stock Warrants issued to SVB ​ 287,704 ​ — ​ — ​ 287,704 Common Stock Warrants as Part of the Merger — 177,500 5,000,000 5,177,500 Warrants Exercised (32,961) — — (32,961) Oustanding as of September 30, 2021 287,704 177,500 5,000,000 5,465,204 ​ In conjunction with a long-term debt agreement entered into on March 15, 2006 and paid in full during 2011, the Company issued a warrant that gave the holder the right to purchase 32,961 shares of the Company ’ See Note 7 — ’ Private Placement Warrants The Private Placement Warrants were initially recognized as a liability on the Closing Date, at a fair value of $0.6 million, and the Private Placement Warrant liability was remeasured to fair value as of September 30, 2021, resulting in a loss of less than $0.1 million for the three and nine months ended September 30, 2021, classified within change in fair value of common stock warrant liabilities in the condensed consolidated statements of operations and comprehensive loss. The Private Placement Warrants were valued using the following assumptions under the Monte Carlo simulation value model: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ August 26, September 30, ​ ​ 2021 ​ 2021 Market price of public stock ​ $ 10.96 ​ $ 11.61 ​ Exercise price ​ $ 11.50 ​ $ 11.50 ​ Expected term (years) ​ 5.00 ​ 4.91 ​ Expected share price volatility ​ 32.5 % 28.5 % Risk-free interest rate ​ 0.68 % 0.96 % Estimated dividend yield ​ 0 % 0 % ​ Public Warrants The Public Warrants may only be exercised for a whole number of shares and will expire five years after the completion of the Merger. The Public Warrants became exercisable 30 days after the completion of the Merger. The Public Warrants were initially recognized as equity on the Closing Date at a fair value of $2.80 per share. There were no exercises of the Public Warrants during the three months ended September 30, 2021. Contingent Earnout Liability Following the Closing, former holders of Legacy Humacyte common and preferred shares may receive up to 15,000,000 additional shares of the Company ’ “ ” stock quoted on the Nasdaq (or the exchange on which the shares of common stock are then listed) is greater or equal to $15.00 and $20.00, respectively, over any twenty trading days within any thirty-day trading period. Upon the Closing, the contingent obligation to issue Contingent Earnout Shares was accounted for as a liability because the triggering events that determine the number of Contingent Earnout Shares required to be issued include events that are not solely indexed to the common stock of Humacyte. The estimated fair value of the total Contingent Earnout Shares at the Closing on August 26, 2021, was $159.4 million based on a Monte Carlo simulation valuation model using a distribution of potential outcomes on a monthly basis over a ten-year period using the most reliable information available. The Contingent Earnout Liability was remeasured to fair value as of September 30, 2021, resulting in the recording of a non-cash loss of $9.8 million for the three and nine months ended September 30, 2021, classified within change in fair value of contingent earnout liability in the condensed consolidated statements of operations and comprehensive loss. Assumptions used in the valuations are described below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ August 26, September 30, ​ ​ 2021 ​ 2021 Current stock price ​ $ 10.96 ​ $ 11.61 ​ Expected share price volatility ​ 79.6 % 78.9 % Risk-free interest rate ​ 1.34 % 1.55 % Estimated dividend yield ​ 0 % 0.0 % Expected term (years) ​ 10.00 ​ 10.00 ​ ​	8. Stockholders ’ Deficit Common Stock As of December 31, 2019 and 2020, the Company ’ ’ The holders of common stock are entitled to receive dividends from time to time as may be declared by the Board of Directors. No cash dividend may be declared or paid to common stockholders until paid on each series of outstanding redeemable convertible preferred stock in accordance with its terms. Through December 31, 2020, no The holders of common stock are entitled to one vote for each share held with respect to all matters voted on by the common stockholders of the Company. Preferred stockholders generally vote together with the holders of common stock as a single class ’ In the event of a Reorganization of the Company, after payment to the preferred stockholders of their liquidation preferences, holders of common stock are entitled, together with holders of redeemable convertible preferred stock, to share ratably in all remaining assets of the Company. 8. Stockholders ’ Deficit (continued) At December 31, 2019 and 2020, the Company had reserved common stock for future issuances as follows: ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2020 ​ ​ ​ ​ ​ Conversion of Series A redeemable convertible preferred stock 18,421,897 18,421,897 Conversion of Series B redeemable convertible preferred stock 24,137,647 24,137,647 Conversion of Series C redeemable convertible preferred stock 11,241,286 11,241,286 Conversion of Series D redeemable convertible preferred stock 15,812,735 15,812,735 Exercise of options under stock plan 5,220,236 4,813,262 Issuance of options under stock plan 2,736,954 2,948,598 Warrant to purchase common stock 32,961 ​ 32,961 ​ ​ 77,603,716 77,408,386 ​ Warrant In conjunction with a long-term debt agreement entered into on March 15, 2006 and paid in full during 2011, the Company issued a warrant that gave the holder the right to purchase 32,961 shares of the Company ’

Stock-based Compensation

Stock-based Compensation	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Stock-based Compensation
Stock-based Compensation	9. Stock-based Compensation At Closing, the 2021 Long-Term Incentive Plan, or the 2021 Plan, and the 2021 Employee Stock Purchase Plan, or the ESPP, became effective. As of September 30, 2021, 7,730,503 and 1,030,033 shares of common stock were available under the 2021 Plan and ESPP, respectively. On January 1 of each year commencing January 1, 2022, the 2021 Plan and the ESPP reserve will automatically increase in an amount equal to the lesser of (a) 5% and 1%, respectively, of the number of shares of the Company ’ ’ Under the 2021 Plan, the Company can grant non-statutory stock options, or NSOs, incentive stock options, or ISOs, stock appreciation rights, restricted stock, restricted stock units, unrestricted stock, performance awards and other forms of awards. Under the ESPP, eligible employees are permitted to purchase shares of the Company ’ ’ Prior to the Closing, Legacy Humacyte had two equity incentive plans, the 2015 Omnibus Incentive Plan, as amended, or the 2015 Plan, and the 2005 Stock Option Plan, or the 2005 Plan. As a result of the Merger, no further awards may be granted under either the 2015 plan or the 2005 Plan. All awards previously granted and outstanding as of the effective date of the Merger, which total The Company ’ ’ ’ The Company has granted options that include either a service-based or performance-based vesting conditions, or both, and a 10-year contractual term. The service-based vesting condition for the plans is generally satisfied over 36 Company recognizes stock-based compensation expense based on the grant date fair value of the awards measured using the Black-Scholes option pricing model. Compensation expense related to awards with service-based vesting conditions is recognized on a straight-line basis over the requisite service period. Option valuation models, including the Black-Scholes option-pricing model, require the input of highly subjective assumptions, and changes in the assumptions used can materially affect the grant-date fair value of an award. These assumptions include the risk-free rate of interest, expected dividend yield, expected volatility, the expected term of the award, and the fair value of the underlying common stock on the date of grant. Forfeitures are accounted for as they occur. Compensation expense related to awards with performance-based vesting conditions is recognized over the requisite service period using the accelerated attribution method to the extent achievement of the performance-based condition is probable. The Company does not recognize compensation expense related to awards with performance-based vesting conditions until it is probable that the performance-based vesting condition will be achieved. Forfeitures are accounted for as they occur. Option awards under the Company ’ ’ ’ Under the terms of her employment agreement, the Company awarded the Company ’ ’ three The Company estimated the fair value of the stock options on the date of grant using the following assumptions in the Black-Scholes option-pricing model: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended September 30, ​ 2020 2021 (1) 2020 2021 Estimated dividend yield ​ 0 % — ​ 0 % 0 % Expected share price volatility (weighted average and range, if applicable) ​ 91.6 % — ​ 91.4% (89.4% to 91.6%) ​ 91.4% (91.0% to 92.1%) ​ Risk-free interest rate (weighted average and range, if applicable) ​ 0.34 % — ​ 0.40% (0.34% to 0.75%) ​ 0.68% (0.62% to 1.02%) ​ Expected term of options (in years) ​ 6.0 ​ — ​ 6.0 ​ 6.0 ​ (1) The Company did not grant any stock options during the three months ended September 30, 2021. ​ ● Fair Value of Common Stock. As the Company ’ s common stock was not publicly traded prior to the Merger, the fair value of the shares of its common stock underlying the options has historically been determined by the Company ’ s board of directors with input from management, after considering independent third-party valuation reports. ● Expected Term. The expected term represents the period that stock options are expected to be outstanding. The Company calculated the expected term using the simplified method for options, which is available where there is insufficient historical data about exercise patterns and post-vesting employment termination behavior. The simplified method is based on the vesting period and the contractual term for each grant, or for each vesting-tranche for awards with graded vesting. The mid-point between the vesting date and the maximum contractual expiration date is used as the expected term under this method. For awards with multiple vesting-tranches, the times from grant until the mid-points for each of the tranches may be averaged to provide an overall expected term. ● Expected Volatility. The expected volatility was based on the historical share volatility of several publicly traded peer companies over a period of time equal to the expected term of the options, as the Company does not have any trading history to use the volatility of its common stock. For purposes of identifying these peer companies, the Company considered the industry, stage of development, size and financial leverage of potential comparable companies. ● Risk-Free Interest Rate. The risk-free interest rate was based on the yields of U.S. Treasury zero-coupon securities with maturities similar in duration to the expected term of the options. ● Expected Dividend Yield. The Company has not paid dividends on its common stock nor does it expect to pay dividends in the foreseeable future. Accordingly, the Company has estimated the dividend yield to be zero. At September 30, 2021, there were 7,730,503 options remaining available for grant under the 2021 Plan. The Company has sufficient authorized and unissued shares to make all issuances currently available under the 2021 Plan. The following tables show a summary of stock-based compensation expense included in the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2021, and the three and nine months ended September 30, 2020, and remaining unrecognized cost as of September 30, 2021 and 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ($ in thousands) ​ 2020 ​ 2021 ​ 2020 ​ 2021 Research and development ​ $ 308 ​ $ 486 ​ $ 781 ​ $ 1,837 General and administrative ​ ​ 862 ​ ​ 1,391 ​ ​ 2,685 ​ ​ 5,498 Total ​ $ 1,170 ​ $ 1,877 ​ $ 3,466 ​ $ 7,335 ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ September 30, ($ in thousands) ​ 2020 ​ 2021 Unrecognized share-based compensation cost ​ $ 5,789 ​ $ 12,480 Expected weighted average period compensation costs to be recognized (years) ​ 1.7 ​ 2.1 ​ A summary of option activity under the Company ’ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ ​ ​ Weighted ​ Remaining ​ Aggregate ​ ​ ​ ​ Average Exercise ​ Contractual Term ​ Intrinsic Value ​ ​ Number of Shares ​ Price Per Share ​ (years) ​ (in thousands) Options outstanding at December 31, 2020 4,813,262 ​ $ 6.04 6.6 ​ $ 20,422 Granted 1,838,029 ​ $ 10.28 ​ Exercised (188,006) ​ $ 2.97 ​ Forfeited (63,397) ​ $ 7.87 ​ Options outstanding at September 30, 2021 6,399,888 ​ $ 7.33 6.6 ​ $ 26,705 Vested and exercisable, September 30, 2021 4,092,342 ​ $ 5.74 5.1 ​ $ 23,345 Vested and expected to vest, September 30, 2021 6,399,888 ​ $ 7.33 6.6 ​ $ 26,705 ​ The Company did not grant any stock options during the three months ended September 30, 2021.	9. Stock-based Compensation The Company has adopted the 2015 Omnibus Incentive Plan, as amended, or the 2015 Plan, which allows for the grant of nonstatutory stock options, or NSOs, and incentive stock options, or ISOs, stock appreciation rights, restricted stock, restricted stock units and unrestricted stock awards to employees, officers, directors, and consultants in the service of the Company. The Company believes that such awards aid in aligning the interests of these persons with those of its stockholders. The Board of Directors determines the specific terms of equity incentive grants, including the exercise price per share and vesting period for option awards. Option awards are granted with an exercise price equal to the fair market value of the Company ’ The Company has granted options that include either a service-based or performance-based vesting condition and a 10-year contractual term. The service-based vesting condition is generally satisfied over 36 months from the date of grant. The performance-based vesting conditions are satisfied upon the attainment of certain product development milestones. The Company recognizes stock-based compensation expense based on the grant date fair value of the awards. Compensation expense related to awards with service-based vesting conditions is recognized on a straight-line basis over the requisite service period. Compensation expense related to awards with performance-based vesting conditions is recognized over the requisite service period using the accelerated attribution method to the extent achievement of the performance-based condition is probable. The Company does not recognize compensation expense related to awards with performance-based vesting conditions until it is probable that the performance-based vesting condition will be achieved. Forfeitures are accounted for as they occur. Option awards under the 2015 Plan generally provide for accelerated vesting of the unvested portions of any option award in the event of an involuntary termination, as such term is defined in the relevant stock option agreement, of a grantee ’ ’ ​ 9. Stock-based Compensation (continued) The Company used the following assumptions on the date of grant to estimate the fair value of the stock options in the Black-Scholes option-pricing model as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ 2019 2020 ​ Estimated dividend yield ​ 0 % 0 % Expected share price volatility ​ 70.1%-87.7 % 89.4% - 91.6 % Risk-free interest rate ​ 1.76% - 2.46 % 0.34% - 0.75 % Expected term of options (in years) ​ 6.00 ​ 6.00 ​ ​ ● Fair Value of Common Stock. As the Company ’ s common stock has not historically been publicly traded, the fair value of the shares of its common stock underlying the options has historically been determined by the Company ’ s board of directors with input from management, after considering independent third-party valuation reports. ● Expected Term. The expected term represents the period that stock options are expected to be outstanding. The Company calculated the expected term using the simplified method for options, which is available where there is insufficient historical data about exercise patterns and post-vesting employment termination behavior. The simplified method is based on the vesting period and the contractual term for each grant, or for each vesting-tranche for awards with graded vesting. The mid-point between the vesting date and the maximum contractual expiration date is used as the expected term under this method. For awards with multiple vesting-tranches, the times from grant until the mid-points for each of the tranches may be averaged to provide an overall expected term. ● Expected Volatility. The expected volatility was based on the historical share volatility of several publicly traded peer companies over a period of time equal to the expected term of the options, as the Company does not have any trading history to use the volatility of its common stock. For purposes of identifying these peer companies, the Company considered the industry, stage of development, size and financial leverage of potential comparable companies. ● Risk-Free Interest Rate. The risk-free interest rate was based on the yields of US Treasury zero-coupon securities with maturities similar in duration to the expected term of the options. ● Expected Dividend Yield. The Company has not paid dividends on its common stock nor does it expect to pay dividends in the foreseeable future. Accordingly, the Company has estimated the dividend yield to be zero. At December 31, 2020, there were 2,948,598 options remaining available for grant under the 2015 Plan. The Company has sufficient authorized and unissued shares to make all issuances currently contemplated under the 2015 Plan. ​ 9. Stock-based Compensation (continued) The following tables show a summary of stock-based compensation expense included in the statements of operations and comprehensive loss for the years ended December 31, 2019 and 2020, and remaining unrecognized cost as of December 31, 2019 and 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ($ in thousands) ​ 2019 ​ 2020 Research and development ​ $ 914 ​ $ 1,135 General and administrative ​ 3,543 ​ 3,559 Total ​ $ 4,457 ​ $ 4,694 ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ($ in thousands) ​ 2019 ​ 2020 Unrecognized share-based compensation cost ​ $ 7,919 ​ $ 5,789 Expected weighted average period compensation costs to be recognized (years) ​ 1.8 ​ 1.7 ​ A summary of option activity under the 2015 Plan during the years ended December 31, 2019 and 2020 is presented below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ ​ ​ Weighted ​ Remaining ​ Aggregate ​ ​ Number of ​ Average Exercise ​ Contractual Term ​ Intrinsic Value ​ ​ Shares ​ Price Per Share ​ (years) ​ (in thousands) Options outstanding at December 31, 2018 5,638,773 ​ $ 4.69 7.4 ​ $ 21,354 Granted 621,031 ​ ​ 8.49 ​ Exercised (620,831) ​ ​ 1.97 ​ Forfeited (418,737) ​ ​ 7.62 ​ Options outstanding at December 31, 2019 5,220,236 ​ $ 5.22 6.5 ​ $ 17,044 Granted 480,856 ​ ​ 9.79 ​ Exercised (195,239) ​ ​ 1.55 ​ Forfeited (692,591) ​ ​ 3.76 ​ Options outstanding at December 31, 2020 4,813,262 ​ $ 6.04 6.6 ​ $ 20,422 Vested and exercisable, December 31, 2020 3,392,302 ​ $ 4.99 5.9 ​ $ 17,925 Vested and expected to vest, December 31, 2020 4,813,262 ​ $ 6.04 6.6 ​ $ 20,422 ​ The total intrinsic value of options exercised during the years ended December 31, 2019 and 2020 was $4.0 million and $1.4 million, respectively. The weighted-average grant-date fair value per share of options granted during the years ended December 31, 2019 and 2020 was $5.84 and $7.26, respectively. ​

Income Taxes

Income Taxes	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Income Taxes
Income Taxes	10. Income Taxes The Company ’ ’ The Company did not record any income tax expense or benefit during the three and nine months ended September 30, 2020 and 2021. The Company has a net operating loss and has provided a valuation allowance against net deferred tax assets due to uncertainties regarding the Company ’ On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security ( “ ” ’	10. Income Taxes The Company did not record any income tax expense or benefit during the years ended December 31, 2019 and 2020. The Company has a net operating loss and has provided a valuation allowance against net deferred tax assets due to uncertainties regarding the Company ’ Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company ’ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ($ in thousands) 2019 2020 Deferred tax assets: ​ ​ ​ ​ ​ ​ Net operating loss ​ $ 50,616 ​ $ 53,515 Capitalized research and development ​ 19,660 ​ ​ 32,337 Research credits ​ 10,658 ​ 15,056 Share-based compensation ​ 1,669 ​ 2,519 Right of use lease liability ​ 207 ​ 177 Accrued expenses ​ 71 ​ 57 Other ​ 1 ​ 1 Total deferred tax asset ​ 82,882 ​ 103,662 Less: valuation allowance ​ (82,193) ​ (101,757) Total net deferred tax asset ​ 689 ​ 1,905 ​ ​ ​ ​ ​ ​ ​ Deferred tax liabilities: ​ ​ Basis difference in fixed assets ​ (482) ​ (1,728) Right of use lease assets ​ (207) ​ (177) Total deferred tax liability ​ (689) ​ (1,905) Total net deferred tax asset/(liability) ​ $ — ​ $ — ​ A valuation allowance is provided for deferred tax assets where the recoverability of the assets is uncertain. The determination to provide a valuation allowance is dependent upon the assessment of whether it is more likely than not that sufficient future taxable income will be generated to utilize the deferred tax assets. Based on the weight of the available evidence, which includes the Company ’ ​ 10. Income Taxes (continued) The reasons for the difference between the actual income tax benefit for the years ended December 31, 2019 and 2020, and the amount computed by applying the statutory Federal income tax rate to losses before income taxes are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2020 ($ in thousands) ​ Amount Rate Amount Rate Income tax benefit at statutory rate ​ $ (17,939) 21.0 % $ (13,970) 21.0 % State income taxes, net of federal benefit ​ (1,739) 2.0 % (1,338) 2.0 % Tax credits ​ (1,821) 2.1 % (2,625) 3.9 % Other nondeductible expenses ​ 54 0.0 % 90 (0.1) % Deferred rate changes ​ 16 0.0 % 16 0.0 % Other ​ 449 (0.5) % (1,736) 2.6 % Change in valuation allowance ​ 20,980 (24.6) % 19,563 (29.4) % Provision for income taxes ​ $ — 0.0 % $ — 0.0 % ​ As of December 31, 2020 the Company had approximately $232.7 million and $232.6 million of Federal and state net operating losses, respectively. Of this amount, $71.5 million of Federal net operating losses are carried over indefinitely, while the remaining amount begins to expire in 2025. The Company ’ As of December 31, 2019 and December 31, 2020 the Company had Federal and state research tax credit carryforwards of $10.7 million and $15.1 million, respectively. These credit carryforwards begin to expire in 2021. Net operating loss carryforwards and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service, or IRS, and may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant stockholders or groups over a three-year period in excess of 50% as defined under Sections The Company applies the accounting guidance for uncertainties in income taxes, which prescribes a recognition threshold and measurement process for recording uncertain tax positions taken, or expected to be taken, in a tax return in the financial statements. Additionally, the guidance also prescribes the treatment for derecognition, classification, accounting in interim periods and disclosure requirements for uncertain tax positions. The Company accrues for the estimated amount of taxes for uncertain tax positions if it is more likely than not that the Company would be required to pay such additional taxes. On March 27, 2020, the CARES Act was passed by the U.S. Congress and signed into United ’

Retirement Plan

Retirement Plan	12 Months Ended
	Dec. 31, 2020
Retirement Plan
Retirement Plan	11. Retirement Plan The Company maintains two defined contribution employee retirement plans, or 401(k) plans, for all employees upon their date of hire. The 401(k) plans are intended to qualify as tax-qualified plans under Section ’ ’

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Commitments and Contingencies
Commitments and Contingencies	11. Commitments and Contingencies Patent License Agreements Duke University In March In connection with the Company ’ ’ ● a low single-digit percentage royalty on eligible sales of licensed products and licensed services, plus a low double-digit percentage of any sublicensing revenue; ● an annual minimum royalty beginning in 2012, which increases in the calendar year immediately following the first commercial sale of licensed products or licensed services (whichever occurs first); and ● an additional amount in license fees, as certain milestones are met. The license agreement remains effective until the last of the patent rights expires or four years after the Company ’ ’ Yale University In February – ’ fee, increasing between the first and fourth anniversaries of the agreement up to a maximum of less than $0.1 million per year for this license. In August ’ In August ’ The Company has agreed to use reasonable commercial efforts to develop and commercialize the licensed patents and any licensed products and methods, and to use reasonable efforts to make the licensed products available to patients in low and low-middle income countries. The Company is also obligated to provide Yale periodically an updated and revised copy of its plan for each license, which must indicate progress of its development and commercialization. The Company may also sublicense the Company ’ ’ In connection with its entry into the license agreement, the Company paid Yale upfront cash fees. The Company has also agreed to pay Yale: ● annual maintenance fees, increasing between the first anniversary of the agreement until the fifth anniversary for the coating and BVP licenses and until the fourth anniversary for the tubular prostheses license up to a maximum of less than $0.1 million per year; ● milestone payments upon achievement of certain regulatory and commercial milestones of $0.2 million and $0.6 million; ● a low single-digit percentage royalty on worldwide net sales, subject to reductions for third-party license fees; and ● a low double-digit percentage of sublicensing income. If the Company or any of its future sublicensees bring a patent challenge against Yale or assists another party in bringing a patent challenge against Yale, the license fees described above will be subject to certain increases and penalties. The agreements expire on a country-by-country basis on the date on which the last of the patents in such country expires, lapses or is declared invalid. Yale may terminate the agreements if the Company fails to (i) ’ ’ ’ ’ respect to the licensed patents. The Company has agreed to indemnify Yale against certain third-party claims. Payments to Yale under the license agreement were immaterial during the periods presented. Legal Matters The Company currently is not aware of any legal proceedings or claims that management believes will have, individually or in the aggregate, a material adverse effect on the Company ’ Indemnification To the extent permitted under Delaware law, the Company has agreed to indemnify its directors and officers for certain events or occurrences while the director or officer is, or was serving, at the Company ’ ’ ’	12. Commitments and Contingencies Patent License Agreements Duke University In March In connection with the Company ’ ’ ● a low single-digit percentage royalty on eligible sales of licensed products and licensed services, plus a low double-digit percentage of any sublicensing revenue; ● an annual minimum royalty beginning in 2012, which increases in the calendar year immediately following the first commercial sale of licensed products or licensed services (whichever occurs first); and ● an additional amount in license fees, as certain milestones are met. The license agreement remains effective until the last of the patent rights expires or four years after our first commercial sale, unless earlier terminated. Either party may terminate the agreement for fraud, willful misconduct or illegal conduct, or uncured material breach. Duke may terminate the agreement if the Company becomes insolvent. Duke may also terminate the license, convert the license into a non-exclusive license or seek assignment of any sublicense if the Company fails to reach diligence milestones within the applicable time period. If the Company abandons any claim, patent or patent application, its rights under the license with respect to such patent rights will be terminated in the territory in which the Company abandons such rights. The Company may terminate the license agreement unilaterally upon three months ’ ​ 12. Commitments and Contingencies (continued) Yale University In February – ’ In August ’ In August ’ The Company has agreed to use reasonable commercial efforts to develop and commercialize the licensed patents and any licensed products and methods, and to use reasonable efforts to make the licensed products available to patients in low and low-middle income countries. The Company is also obligated to provide Yale periodically an updated and revised copy of its plan for each license, which must indicate progress of its development and commercialization. The Company may also sublicense the Company ’ ’ In connection with its entry into the license agreement, the Company paid Yale upfront cash fees. The Company has also agreed to pay Yale: ● annual maintenance fees, increasing between the first anniversary of the agreement until the fifth anniversary for the coating and BVP licenses and until the fourth anniversary for the tubular prostheses license; ● milestone payments upon achievement of certain regulatory and commercial milestones; ● a low single-digit percentage royalty on worldwide net sales, subject to reductions for third-party license fees; and ● a low double-digit percentage of sublicensing income. If the Company or any of its future sublicensees bring a patent challenge against Yale or assists another party in bringing a patent challenge against Yale, the license fees described above will be subject to certain increases and penalties. ​ 12. Commitments and Contingencies (continued) The agreements expire on a country-by-country basis on the date on which the last of the patents in such country expires, lapses or is declared invalid. Yale may terminate the agreements if the Company fails to (i) ’ ’ ’ ’ Legal Matters The Company currently is not aware of any legal proceedings or claims that management believes will have, individually or in the aggregate, a material adverse effect on the Company ’ Indemnification To the extent permitted under Delaware law, the Company has agreed to indemnify its directors and officers for certain events or occurrences while the director or officer is, or was serving, at the Company ’ ’ ’

Related Party Transactions

Related Party Transactions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Related Party Transactions
Related Party Transactions	12. Related Party Transactions Fresenius Medical Care investments and distribution agreement In June 2018, the Company completed a $150 million financing transaction pursuant to which Fresenius Medical Care purchased shares of series D redeemable convertible preferred stock that at the Closing of the Merger converted into 15,812,735 shares of the Company ’ ’ In addition, the Company entered into a distribution agreement with Fresenius Medical Care in June 2018 which, as amended as of February 16, 2021, granted Fresenius Medical Care and its affiliates exclusive rights to develop outside the United States and EU and commercialize outside of the United States the Company ’ The Company is responsible for developing and seeking regulatory approval for the distribution product in the field in the United States. For countries outside the United States, the parties agreed to use commercially reasonable efforts to satisfy certain agreed minimum market entry criteria for the distribution product in the field in such country. For the EU, once such criteria have been satisfied for the applicable country, or if the parties otherwise mutually agree to obtain regulatory approval for the distribution product in the field in the applicable country, the Company agreed to use commercially reasonable efforts to obtain such regulatory approval (other than pricing approval), and Fresenius Medical Care agreed to use commercially reasonable efforts to obtain the corresponding pricing approval. For the rest of the world (i.e., outside the United States and the EU), once such criteria have been satisfied for the applicable country, or if the parties otherwise mutually agree to obtain regulatory and pricing approval for the distribution product in the field in the applicable country, Fresenius Medical Care agreed to use commercially reasonable efforts to obtain such approvals, and the Company agreed to use commercially reasonable efforts to support Fresenius Medical Care in its efforts. Under the distribution agreement, the Company grants an exclusive, sublicensable license to Fresenius Medical Care under the patents, know-how and regulatory materials controlled by the Company during the term to commercialize the distribution product in the field outside the United States, subject to the Company ’ and regulatory materials controlled by the Company during the term to develop the distribution product in accordance with the terms of the distribution agreement. In addition, the Company grants to Fresenius Medical Care, among other things, a perpetual, irrevocable, non-exclusive sublicensable license under the patents and know-how that primarily relate to the distribution product or its manufacture and that were created, conceived or developed solely or jointly by or on behalf of Fresenius Medical Care in the performance of its activities under the distribution agreement. The distribution agreement provides that the Company will own all know-how and patents that primarily relate to the distribution product or its manufacture that are created, conceived or developed by or on behalf of either party in the performance of activities under the distribution agreement. Ownership of all other know-how, patents, materials and other intellectual property created, conceived or developed during the performance of activities under the distribution agreement will be determined in accordance with U.S. patent laws for determining inventorship. The Company is obligated to make payments to Fresenius Medical Care based on a share of aggregate net sales by or on behalf of the Company of the distribution product in the United States in the field. Such revenue-share payments will be a percentage of net sales in the low double digits, without regard to the calendar year in which such net sales are attributable, until such time that the Company has paid to Fresenius Medical Care a certain total amount, at which time the revenue-share will decrease to a percentage of net sales in the mid-single digits. The amounts that Fresenius Medical Care will be obligated to pay the Company under the distribution agreement for sales of the distribution product in the field outside of the United States will vary. Fresenius Medical Care agreed to pay the Company initially, on a country-by-country basis for sales outside of the United States, the amount equal to the average cost of manufacturing the Company ’ The distribution agreement will generally continue on a country-by-country basis until the later of (a) the tenth anniversary of the launch date of the distribution product in the relevant country or (b) the expiration of the last-to-expire valid claim of specified patents in such country. Each party is permitted to terminate the distribution agreement for insolvency of, or, under certain circumstances, including various cure periods, material breach by the other party. Subject to a cure period, Fresenius Medical Care may also terminate the distribution agreement in its entirety or on a country-by-country basis (i) for certain withdrawals of regulatory approval or (ii) for termination or expiration of any of our in-licenses that is necessary for the exercise of Fresenius Medical Care ’ ’ Arrangements with Dr. Niklason and Yale University In September The MOU provided for the Company to make a payment each year through 2023 to the academic institution with which Dr. ’ ’ The following table shows a summary of related party expenses included in the statements of operations and comprehensive loss for the three and nine months ended September 30, 2020 and 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months ​ Nine Months ($ in thousands) 2020 2021 2020 2021 Expenses under MOU 125 — 375 — License expenses 20 — 70 85 Other 4 2 17 83 Total 149 2 462 168 ​ As of December 31, 2020 and September 30, 2021, the Company was a party to license agreements with Yale University, as described in Note 11 —	13. Related Party Transactions Fresenius Medical Care distribution agreement In addition to Fresenius Medical Care ’ ’ The Company is responsible for developing and seeking regulatory approval for the distribution product in the field in the United States. For countries outside the United States, the parties agreed to use commercially reasonable efforts to satisfy certain agreed minimum market entry criteria for the distribution product in the field in such country. For the EU, once such criteria have been satisfied for the applicable country, or if the parties otherwise mutually agree to obtain regulatory approval for the distribution product in the field in the applicable country, the Company agreed to use commercially reasonable efforts to obtain such regulatory approval (other than pricing approval), and Fresenius Medical Care agreed to use commercially reasonable efforts to obtain the corresponding pricing approval. For the rest of the world (i.e., outside the United States and the EU), once such criteria have been satisfied for the applicable country, or if the parties otherwise mutually agree to obtain regulatory and pricing approval for the distribution product in the field in the applicable country, Fresenius Medical Care agreed to use commercially reasonable efforts to obtain such approvals, and the Company agreed to use commercially reasonable efforts to support Fresenius Medical Care in its efforts. Under the distribution agreement, the Company grants an exclusive, sublicensable license to Fresenius Medical Care under the patents, know-how and regulatory materials controlled by the Company during the term to commercialize the distribution product in the field outside the United States, subject to the Company ’ The distribution agreement provides that the Company will own all know-how and patents that primarily relate to the distribution product or its manufacture that are created, conceived or developed by or on behalf of either party in the performance of activities under the distribution agreement. Ownership of all other know-how, patents, materials and other intellectual property created, conceived or developed during the performance of activities under the distribution agreement will be determined in accordance with U.S. patent laws for determining inventorship. ​ 13. Related Party Transactions (continued) The Company is obligated to make payments to Fresenius Medical Care based on a share of aggregate net sales by or on behalf of the Company of the distribution product in the United States in the field. Such revenue-share payments will be a percentage of net sales in the low double digits, without regard to the calendar year in which such net sales are attributable, until such time that the Company has paid to Fresenius Medical Care a certain total amount, at which time the revenue-share will decrease to a percentage of net sales in the mid-single digits. The amounts that Fresenius Medical Care will be obligated to pay the Company under the distribution agreement for sales of the distribution product in the field outside of the United States will vary. Fresenius Medical Care agreed to pay the Company initially, on a country-by-country basis for sales outside of the United States, the amount equal to the average cost of manufacturing the Company ’ The distribution agreement will generally continue on a country-by-country basis until the later of (a) the tenth anniversary of the launch date of the distribution product in the relevant country or (b) the expiration of the last-to-expire valid claim of specified patents in such country. Each party is permitted to terminate the distribution agreement for insolvency of, or, under certain circumstances, including various cure periods, material breach by the other party. Subject to a cure period, Fresenius Medical Care may also terminate the distribution agreement in its entirety or on a country-by-country basis (i) for certain withdrawals of regulatory approval or (ii) for termination or expiration of any of our in-licenses that is necessary for the exercise of Fresenius Medical Care ’ ’ Arrangements with Dr. Niklason and Yale University In September The MOU provided for the Company to make a payment each year through 2023 to the academic institution with which Dr. ’ ’ The following table shows a summary of related party expenses included in the statements of operations and comprehensive loss for the years ended December 31, 2019 and 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ($ in thousands) 2019 2020 Expenses under MOU $ 422 $ 500 License expenses 110 92 Other 39 28 Total $ 571 $ 620 ​ As of December 31, 2019 and December 31, 2020, the Company was a party to license agreements with Yale University, as described in Note 12 —

Subsequent Events

Subsequent Events	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	13. Subsequent Events In preparing the condensed consolidated financial statements as of September 30, 2021 and for the three and nine months ended September 30, 2021, the Company evaluated the effect subsequent events would have on the financial statements through the date the financial statements were issued. On October 13, 2021, the Company borrowed an additional $10.0 million under the Loan Agreement, and the warrants to purchase an additional 123,302 shares of the Company ’ — — ’	14. Subsequent Events The Company evaluated the effect subsequent events would have on the financial statements through March 22, 2021, which is the date the financial statements were issued. Under the terms of her employment agreement, the Company awarded Dr. Niklason an additional stock option award in January 2021 entitling her to purchase 1,312,984 shares of the Company ’ none three Under the terms of his consulting agreement, the Company awarded Mr. Sander an additional stock option award in January 2021 entitling him to purchase 183,817 shares of the Company ’ three On February 17, 2021, the Company entered into a business combination agreement with AHAC and Merger Sub, a wholly owned subsidiary of AHAC, pursuant to which Merger Sub will merge with the Company, with the Company surviving the Merger as a wholly owned subsidiary of AHAC. As a result of the Merger, AHAC will immediately be renamed New Humacyte. Immediately prior to the consummation of the Merger, the Company ’ ’ ’ ’ ’ No

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation The Company has prepared the accompanying financial statements in conformity with accounting principles generally accepted in the United ’ Unless otherwise noted, the Company has retroactively adjusted all common and preferred share and related price information to give effect to the Exchange Ratio established in the Merger Agreement.	Basis of Presentation The Company has prepared the accompanying financial statements in conformity with accounting principles generally accepted in the United Reverse Recapitalization
Unaudited Interim Condensed Consolidated Financial Statements	Unaudited Interim Condensed Consolidated Financial Statements The accompanying interim condensed consolidated financial statements and the related footnote disclosures are unaudited. These unaudited interim financial statements have been prepared on the same basis as the audited financial statements, and in management ’ ’ Certain information and footnote disclosures normally included in consolidated financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements for the year ended December 31, 2020 and the related notes included elsewhere in this prospectus, which provides a more complete discussion of the Company’s accounting policies and certain other information. Other than the policies noted below, there have been no significant changes to the significant accounting policies disclosed in Note 2 of the audited consolidated financial statements as of and for the years ended December 31, 2019 and 2020 included elsewhere in this prospectus.	On August 26, 2021 (the “ ” “ ” “ ” “ ” “ ” “ ” “ ” “ ” Unless otherwise noted, the Company has retroactively adjusted all common and preferred share and related price information to give effect to the Exchange Ratio of approximately 0.26260 established in the Merger Agreement.
Common Stock Warrants	Common Stock Warrants The Company assumed 5,000,000 publicly-traded warrants ( “ ” “ ” ’ “ ” “ ” ’ “ ” The Company evaluated the Common Stock Warrants to determine the appropriate financial statement classification upon the consummation of the Merger. The Common Stock Warrants are not mandatorily redeemable and are considered to be freestanding instruments as they are separately exercisable into common shares. As such, the Common Stock Warrants were not classified as liabilities under FASB ASC Topic 480, Distinguishing Liabilities from Equity Derivatives and Hedging The agreement governing the Common Stock Warrants includes a provision ( “ ” ’ “ ’ ” ’ The Public Warrants are considered to be “indexed to the Company’s own stock”. The agreement provides that in the event of a tender or exchange offer made to and accepted by holders of more than 50% of the outstanding shares of the Company ’ ’ ’
Contingent Earnout Liability	Contingent Earnout Liability In connection with the Reverse Recapitalization and pursuant to the Business Combination Agreement dated as of February 17, 2021 by and among Legacy Humacyte, Merger Sub, and AHAC (the “ ” ’ “ ” The estimated fair value of the Contingent Earnout Shares was determined using a Monte Carlo simulation using a distribution of potential outcomes on a monthly basis over a ten-year period prioritizing the most reliable information available. The assumptions utilized in the calculation were based on the achievement of certain stock price milestones, including the current Company common stock price, expected volatility, risk-free rate, expected term and expected dividend yield. The Contingent Earnout Shares are categorized as a Level
Segments	Segments The Company operates and manages its business as one reportable and operating segment. The Company is developing proprietary, bioengineered, acellular human tissues that are designed to be used in the treatment of diseases and conditions across a range of anatomic locations in multiple therapeutic areas. The Company ’	Segments The Company operates and manages its business as one reportable and operating ’
Comprehensive loss		Comprehensive loss Comprehensive loss includes net loss as well as other changes in stockholders ’
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Significant estimates in the financial statements include stock-based compensation costs, right-of-use, or ROU, assets, accruals for research and development activities, contingent earnout liability, fair value of common stock warrants, redeemable convertible preferred stock and income taxes. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates.	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Significant estimates in the financial statements include stock-based compensation costs, right-of-use, or ROU assets, accruals for research and development activities, fair value of common stock, useful lives of property and equipment, redeemable convertible preferred stock and income taxes. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates. ​ 2. Summary of Significant Accounting Policies (continued)
Cash and Cash Equivalents		Cash and Cash Equivalents The Company considers all short-term, highly liquid investments purchased with an original maturity of three months or less at the date of purchase to be cash equivalents. Cash deposits are held with financial institutions with investment-grade ratings in the United
Redeemable Convertible Preferred Stock		Redeemable Convertible Preferred Stock The Company analyzes all issued equity instruments to determine the appropriate accounting and classification. The Company evaluates its equity instruments under Accounting Standards Codification, or ASC 480, Distinguishing liabilities from equity The Company records equity instruments that are classified as temporary equity at fair value upon issuance, net of issuance costs. The Company accretes the carrying value of its redeemable convertible preferred stock to the redemption or liquidation amount once the Company has determined that it is probable that it will become redeemable or be liquidated. The accretion will be recorded as charges against additional paid-in capital until the additional paid-in capital balance is reduced to zero. At that time, additional accretion adjustments will be recorded as additions to accumulated deficit. The Company also analyzes instances where the equity instrument has a conversion feature pursuant to ASC 815, Derivatives and hedging
Revenue Recognition	Revenue Recognition The Company ’ Under ASC 606, revenue is recognized when a customer obtains control of promised goods or services and is recognized in an amount that reflects the consideration that an entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) In addition, ASC 606 requires disclosure of the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. For contracts where the period between when the Company transfers a promised good or service to the customer and when the customer pays is one year or less, the Company has elected the practical expedient to not adjust the promised amount of consideration for the effects of a significant financing component.	Revenue Recognition The Company ’ In 2014, the Financial Accounting Standards Board, or FASB issued Accounting Standards Update No. Under ASC 606, revenue is recognized when a customer obtains control of promised goods or services and is recognized in an amount that reflects the consideration that an entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) In addition, ASC 606 requires disclosure of the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. ​ 2. Summary of Significant Accounting Policies (continued) For contracts where the period between when the Company transfers a promised good or service to the customer and when the customer pays is one year or less, the Company has elected the practical expedient to not adjust the promised amount of consideration for the effects of a significant financing component.
Grant Revenue	Grant Revenue The Company generates revenue primarily from government and other awarded grants that reimburse the Company for certain allowable costs related to research and development efforts. These grants include the following terms: The Department of Defense grants are for an award of $4.0 million, all of which was recognized as revenue before the program ended, for work on bioengineered blood vessels for vascular trauma, which was awarded to the Company in September 2017 and ended in February 2020, and an award of $7.1 million for work to support human tissue engineered blood vessels for vascular reconstruction in the injured warfighter, which was awarded to the Company in August 2017 and is ongoing. The Company has recognized revenue of $0.6 million and $1.0 million during the three and nine months ended September 30, 2020,respectively, and $0.2 million and $1.1 million during the three and nine months ended September 30, 2021, respectively, for reimbursement of certain allowable costs related to these grants. The National Institutes of Health grant is for $1.6 million for work to support bioengineered grafts for peripheral vascular disease, which was awarded to the Company in November 2013. The Company recognized $1.6 million for the reimbursement of certain allowable costs related to the grant before this program ended in 2020. The Company recognized $0.3 million during the three and nine months ended September 30, 2020, and no revenue during the three and nine months ended September 30, 2021, for reimbursement of certain allowable costs related to these grants. The Company has determined that the grants are not within the scope of ASC 606 as they do not meet the definition of a contract with a customer. The Company has concluded that the grants meet the definition of a contribution and are nonexchange transactions and has applied the contribution accounting model in Subtopic 958-605, Not-for-Profit-Entities-Revenue Recognition by analogy. The Company recognizes funding received from grants as revenue, rather than as a reduction of research and development expenses, because the Company is the principal in conducting the research and development activities and these grants are central to the Company ’ ’ Revenue from grants not within the scope of ASC 606 was $0.9 million and $1.4 million for the three and nine months ended September 30, 2020, respectively, and $0.2 million and $1.1 million for the three and nine months ended September 30, 2021, respectively.	Grant Revenue We generate revenue primarily from government and other awarded grants that reimburse us for certain allowable costs related to research and development efforts. The Company has determined that the grants are not within the scope of ASC 606 as they do not meet the definition of a contract with a customer. The Company has concluded that the grants meet the definition of a contribution and are nonexchange transactions and has applied the contribution accounting model in Subtopic 958-605, Not-for-Profit-Entities-Revenue Recognition by analogy. The Company recognizes funding received from grants as revenue, rather than as a reduction of research and development expenses, because the Company is the principal in conducting the research and development activities and these grants are central to the Company ’ Revenue from grants not within the scope of ASC 606 was $6.2 million and $1.5 million for the years ending December 31, 2019 and 2020, respectively.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments which potentially subject the Company to concentrations of credit risk consist principally of cash and cash equivalents. Total cash balances exceeded insured balances by the Federal Deposit Insurance Corporation as of December 31, 2020 and September 30, 2021. Cash equivalents are invested in highly rated money market funds invested only in obligations of the U.S. government and its agencies. The majority of the Company ’ ’ ’ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue Accounts Receivable ​ ​ Three Months ​ Nine Months ​ December 31, ​ September 30, ​ ​ 2020 2021 2020 2021 2020 2021 Grant A ​ — ​ — ​ — ​ — ​ — ​ — ​ Grant B 0 ​ — % 11 ​ — % — ​ — Grant C 68 % 100 % 65 % 100 % 100 % 100 % Grant D 30 — % 20 ​ — % — — Total 98 % 100 % 96 % 100 % 100 % 100 % ​ All of the Company ’	Concentration of Credit Risk Financial instruments which potentially subject the Company to concentrations of credit risk consist principally of cash and cash equivalents. Total cash balances exceeded insured balances by the Federal Depository Insurance Corporation as of December 31, 2019 and 2020. Cash equivalents are invested in highly rated money market funds invested only in obligations of the US government and its agencies. The majority of the Company ’ ’ ’ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2020 ​ ​ ​ ​ ​ Accounts ​ ​ ​ Accounts ​ ​ Revenue Receivable Revenue Receivable ​ Grant A ​ 28 % — ​ — ​ — ​ Grant B 38 % 67 % 10 % — Grant C 34 % 33 % 67 % 100 % Grant D — — 18 % — Total 100 % 100 % 95 % 100 % ​ All of the Company ’
Other Risks and Uncertainties	Other Risks and Uncertainties The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, successful discovery and development of its product candidates, the success of clinical trials and other studies for its product candidates, including for its ongoing V005 Phase II/III clinical trial and V007 Phase III clinical trial, the regulatory approval and commercialization of its HAVs and other product candidates, ’ ’ ’ Product candidates currently under development will require extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel, and infrastructure and extensive compliance-reporting capabilities. Even if the Company ’ ’	​ 2. Summary of Significant Accounting Policies (continued) Other Risks and Uncertainties The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, successful discovery and development of its product candidates, the success of clinical trials and other studies for its product candidates, including for its ongoing V005 Phase II/III clinical trial and V007 Phase III clinical trial, the regulatory approval and commercialization of its HAVs and other product candidates, ’ ’ ’ Product candidates currently under development will require extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel, and infrastructure and extensive compliance-reporting capabilities. Even if the Company ’ ’
Net Loss per Share Attributable to Common Stockholders	Net Loss per Share Attributable to Common Stockholders The Company follows the two-class method to compute basic and diluted net loss per share attributable to common stockholders when shares met the definition of participating securities. The two-class method determines net loss per common share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to share in the earnings as if all income for the period had been distributed. During periods of loss, there is no allocation required under the two-class method since the redeemable convertible preferred stock did not have a contractual obligation to share in the Company ’ Basic net loss per share attributable to common stockholders is computed by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period without consideration of potentially dilutive common stock. Diluted net loss per share attributable to common stockholders reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock or resulted in the issuance of common stock that then shared in the earnings of the Company unless inclusion of such shares would be anti-dilutive. As the Company has only incurred losses, basic and diluted net loss per share is the same. The potential shares of common stock that were excluded from the computation of diluted net loss per share for each period because including them would have had an antidilutive effect were as follows: ​ ​ ​ ​ ​ ​ ​ September 30, ​ 2020 2021 ​ ​ ​ ​ ​ Shares issuable upon conversion of Series A redeemable convertible preferred stock 18,421,897 — Shares issuable upon conversion of Series B redeemable convertible preferred stock 24,137,647 — Shares issuable upon conversion of Series C redeemable convertible preferred stock 11,241,283 — Shares issuable upon conversion of Series D redeemable convertible preferred stock 15,812,735 — Exercise of options under stock plan 4,516,907 6,399,888 Warrants to purchase common stock 32,961 5,465,204 ​ The 15,000,000 Contingent Earnout shares are excluded from the anti-dilutive table for all the periods presented as such shares are contingently issuable until the share price of the Company exceeds specified thresholds that have not yet been achieved, or upon the occurrence of a change in control.	Net Loss per Share Attributable to Common Stockholders The Company applies the two-class method to compute basic and diluted net loss per share attributable to common stockholders when shares meet the definition of participating securities. The two-class method determines net loss per share for each class of common and redeemable convertible preferred stock according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income (loss) available to common stockholders for the period to be allocated between common and redeemable convertible preferred stock based upon their respective rights to share in the earnings as if all income (loss) for the period had been distributed. During periods of loss, there is no allocation required under the two-class method since the redeemable convertible preferred stock does not have a contractual obligation to share in the Company ’ ​ 2. Summary of Significant Accounting Policies (continued) Basic net loss per share attributable to common stockholders is computed by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period without consideration of potentially dilutive common stock. Diluted net loss per share attributable to common stockholders reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock or resulted in the issuance of common stock that then shared in the earnings of the Company unless inclusion of such shares would be anti-dilutive. Since the Company has only incurred losses, basic and diluted net loss per share is the same. Securities that could potentially dilute net loss per share in the future that were not included in the computation of diluted net loss per share are as follows: ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2020 ​ ​ ​ ​ ​ Shares issuable upon conversion of Series A redeemable convertible preferred stock 18,421,897 18,421,897 Shares issuable upon conversion of Series B redeemable convertible preferred stock 24,137,647 24,137,647 Shares issuable upon conversion of Series C redeemable convertible preferred stock 11,241,283 11,241,283 Shares issuable upon conversion of Series D redeemable convertible preferred stock 15,812,735 15,812,735 Options to purchase common stock 5,220,236 4,813,262 Warrant to purchase common stock 32,961 32,961 ​ Fair Value of Financial Instruments Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in the principal or most advantageous market in an orderly transaction between market participants at the measurement date. ASC 820, Fair Value Measurement and Disclosures ● Level 1 — Observable inputs that reflect unadjusted quoted prices for identical assets or liabilities in active markets. ● Level 2 — Inputs other than quoted prices included in Level 1 that are observable for the asset or liability, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. ● Level 3 — Unobservable inputs in which little or no market data exists, therefore requiring the Company to develop its own assumptions. The Company evaluates assets and liabilities subject to fair value measurements on a recurring basis to determine the appropriate level at which to classify them for each reporting period, utilizing valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible. The determination requires significant judgments to be made by the Company. The Company ’ ​ 2. Summary of Significant Accounting Policies (continued)
Fair Value of Financial Instruments		​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2020 ​ ​ ​ ​ ​ Shares issuable upon conversion of Series A redeemable convertible preferred stock 18,421,897 18,421,897 Shares issuable upon conversion of Series B redeemable convertible preferred stock 24,137,647 24,137,647 Shares issuable upon conversion of Series C redeemable convertible preferred stock 11,241,283 11,241,283 Shares issuable upon conversion of Series D redeemable convertible preferred stock 15,812,735 15,812,735 Options to purchase common stock 5,220,236 4,813,262 Warrant to purchase common stock 32,961 32,961
Property and Equipment, Net		Property and Equipment, Net Property and equipment, net are recorded at cost less accumulated depreciation. Expenditures for major additions and improvements are capitalized and minor replacements, maintenance, and repairs are charged to expense as incurred. When property and equipment are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the balance sheet accounts and any resulting gain or loss is included in the results of operations for the respective period. Depreciation is calculated using the straight-line method over the estimated useful lives of the related assets. The estimated useful lives for significant asset categories are as follows: ​ ​ ​ ​ ​ Estimated Useful Property and equipment ​ Lives (Years) Scientific equipment ​ 5 – 7 Computer equipment 5 Software 3 Furniture and fixtures 5 – 7 Leasehold improvements Lesser of useful life or life of lease Construction in progress N/A
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews the carrying value of property and equipment for indicators of possible impairment whenever events and circumstances indicate that the carrying value of an asset or asset group may not be recoverable from the estimated future net undiscounted cash flows expected to result from its use and eventual disposition. In cases where estimated future net undiscounted cash flows are less than the carrying value, an impairment loss is recognized equal to an amount by which the carrying value exceeds the fair value of the asset or asset group. The factors considered by management in performing this assessment include current operating results, trends and prospects, the manner in which the property is used, and the effects of obsolescence, demand, competition, and other economic factors. Based on this assessment, during the nine months ended September 30, 2020 and 2021, respectively, the Company concluded there were no such events or changes in circumstances requiring review of the carrying amount of the Company ’	​ ​ ​ ​ ​ Estimated Useful Property and equipment ​ Lives (Years) Scientific equipment ​ 5 – 7 Computer equipment 5 Software 3 Furniture and fixtures 5 – 7 Leasehold improvements Lesser of useful life or life of lease Construction in progress N/A
Income Taxes		Income Taxes Income taxes are computed using the asset and liability approach that requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the Company ’ ​ 2. Summary of Significant Accounting Policies (continued) The Company recognizes the benefit of an income tax position only if it is more likely than not (greater than 50%) that the tax position will be sustained upon tax examination, based solely on the technical merits of the tax position. Otherwise, no benefit can be recognized. Assessing an uncertain tax position begins with the initial determination of the sustainability of the position and is measured at the largest amount of benefit that is greater than 50% likely of being realized upon ultimate settlement. As of each balance sheet date, unresolved uncertain tax positions must be reassessed. Additionally, the Company must accrue interest and related penalties, if applicable, on all tax exposures for which reserves have been established consistent with jurisdictional tax laws. The Company has analyzed its filing positions in all significant Federal and state jurisdictions where it is required to file income tax returns, as well as open tax years in these jurisdictions. As of December 31, 2019 and 2020, the Company has determined that no uncertain tax positions would have a material impact on the financials statements of the Company. The Company is no longer subject to Federal, state, and local tax examinations by tax authorities for years before 2017 although carry-forward attributes that were generated prior to 2017 may still be adjusted upon examination by the taxing authorities if they either have been or will be used in a future period. No income tax returns are currently under examination by taxing authorities. As of December 31, 2019 and 2020, the Company had not recorded any amounts for unrecognized tax benefits. The Company ’ ’
Intellectual Property		Intellectual Property The Company seeks to protect its intellectual property by filing patent applications in the United ’
Research and Development		Research and Development The Company expenses research and development costs as operating expenses as incurred. Research and development expenses consist primarily of: ● salaries and related overhead expenses for personnel in research and development functions, including stock-based compensation and benefits; ● fees paid to consultants and CROs, including in connection with clinical trials, and other related clinical trial fees, such as for investigator grants, patient screening, laboratory work and statistical compilation and analysis; ● allocation of facility lease and maintenance costs; ● depreciation of leasehold improvements, laboratory equipment and computers; ● costs related to purchasing raw materials for and producing product candidates for clinical trials; ● costs related to compliance with regulatory requirements; ● costs related to the manufacturing scale-out initiative; and ● license fees related to in-licensed technologies.
Accrued Research and Development		Accrued Research and Development The Company has entered into various agreements with CROs and a CMO, which conduct preclinical studies and clinical trials and contract manufacturing activities. The Company ’
Leases		Leases Effective January 1, 2019, the Company accounts for its leases under ASC 842, Leases ’ “ ” “ ” “ ” ’ “ ” “ ” “ ” Under this guidance, arrangements meeting the definition of a lease are classified as operating or finance leases, and are recorded on the balance sheet as both a right-of-use asset and lease liability, calculated by discounting fixed lease payments over the lease term at the rate implicit in the lease or the Company ’ ​ 2. Summary of Significant Accounting Policies (continued) Lease expenses for minimum lease payments for operating leases are recognized on a straight-line basis over the lease term. Amortization expense of the right-of-use asset for finance leases is recognized on a straight-line basis over the lease term and interest expense for finance leases is recognized based on the incremental borrowing rate. Lease liabilities are increased by interest and reduced by payments each period, and the right of use asset is amortized over the lease term. In calculating the right-of-use assets and lease liabilities, the Company has elected to combine lease and non-lease components for all asset classes. The Company excludes short-term leases, if any, having initial terms of 12 months or less from the new guidance as an accounting policy election, and recognizes rent expense on a straight-line basis over the lease term. Prior to the adoption of ASC 842 on January 1, 2019 the Company was deemed to be the accounting owner of leased space during the construction of its headquarters in a build-to-suit arrangement. Upon substantial completion of construction in June ’ ’ each The cumulative effect of initially applying the new lease guidance on January 1, 2019 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ January 1, 2019 ​ ​ ​ ​ ​ Cumulative ​ Beginning ​ ​ Beginning ​ Effect ​ Balance, ($ in thousands) Balance Adjustment As Adjusted Assets ​ ​ ​ ​ ​ ​ Building asset ​ $ 25,091 ​ $ (25,091) ​ $ — Finance lease right-of-use assets, net ​ $ — ​ $ 27,612 ​ $ 27,612 Operating lease right-of-use assets, net ​ $ — ​ $ 923 ​ $ 923 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Liabilities and stockholders’ deficit ​ ​ ​ Accrued expenses ​ $ 7,049 ​ $ (1) ​ $ 7,048 Facility financing obligation, current portion ​ $ 276 ​ $ (276) ​ $ — Finance lease obligation, current portion ​ $ — ​ $ 1,292 ​ $ 1,292 Operating lease obligation, current portion ​ $ — ​ $ 55 ​ $ 55 Facility financing obligation, net of current portion ​ $ 22,955 ​ $ (22,955) ​ $ — Finance lease obligation, net of current portion ​ $ — ​ $ 26,319 ​ $ 26,319 Operating lease obligation, net of current portion ​ $ — ​ $ 870 ​ $ 870 Accumulated deficit ​ $ (234,289) ​ $ (1,861) ​ $ (236,150)
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In August 2020, the FASB issued ASU No. 2020-06, “ ’ ’ ” “ ” ’	Recently Adopted Accounting Pronouncements In August —
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In May 2021, the FASB issued “ ’ ” “ ” ’	Recently Issued Accounting Pronouncements In August 2020, the FASB issued ASU No. 2020-06, “  –  ’  –  ’ “ ”

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Summary of Significant Accounting Policies
Summary of 10% or more of the Company's total revenue or accounts receivable balance	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue Accounts Receivable ​ ​ Three Months ​ Nine Months ​ December 31, ​ September 30, ​ ​ 2020 2021 2020 2021 2020 2021 Grant A ​ — ​ — ​ — ​ — ​ — ​ — ​ Grant B 0 ​ — % 11 ​ — % — ​ — Grant C 68 % 100 % 65 % 100 % 100 % 100 % Grant D 30 — % 20 ​ — % — — Total 98 % 100 % 96 % 100 % 100 % 100 %	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2020 ​ ​ ​ ​ ​ Accounts ​ ​ ​ Accounts ​ ​ Revenue Receivable Revenue Receivable ​ Grant A ​ 28 % — ​ — ​ — ​ Grant B 38 % 67 % 10 % — Grant C 34 % 33 % 67 % 100 % Grant D — — 18 % — Total 100 % 100 % 95 % 100 %
Summary of securities that could potentially dilute net loss per share in the future that were not included in the computation of diluted net loss per share	​ ​ ​ ​ ​ ​ ​ September 30, ​ 2020 2021 ​ ​ ​ ​ ​ Shares issuable upon conversion of Series A redeemable convertible preferred stock 18,421,897 — Shares issuable upon conversion of Series B redeemable convertible preferred stock 24,137,647 — Shares issuable upon conversion of Series C redeemable convertible preferred stock 11,241,283 — Shares issuable upon conversion of Series D redeemable convertible preferred stock 15,812,735 — Exercise of options under stock plan 4,516,907 6,399,888 Warrants to purchase common stock 32,961 5,465,204	​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2020 ​ ​ ​ ​ ​ Shares issuable upon conversion of Series A redeemable convertible preferred stock 18,421,897 18,421,897 Shares issuable upon conversion of Series B redeemable convertible preferred stock 24,137,647 24,137,647 Shares issuable upon conversion of Series C redeemable convertible preferred stock 11,241,283 11,241,283 Shares issuable upon conversion of Series D redeemable convertible preferred stock 15,812,735 15,812,735 Options to purchase common stock 5,220,236 4,813,262 Warrant to purchase common stock 32,961 32,961
Summary of estimated useful lives for significant asset		​ ​ ​ ​ ​ Estimated Useful Property and equipment ​ Lives (Years) Scientific equipment ​ 5 – 7 Computer equipment 5 Software 3 Furniture and fixtures 5 – 7 Leasehold improvements Lesser of useful life or life of lease Construction in progress N/A
Summary of cumulative effect of initially applying the new lease guidance		​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ January 1, 2019 ​ ​ ​ ​ ​ Cumulative ​ Beginning ​ ​ Beginning ​ Effect ​ Balance, ($ in thousands) Balance Adjustment As Adjusted Assets ​ ​ ​ ​ ​ ​ Building asset ​ $ 25,091 ​ $ (25,091) ​ $ — Finance lease right-of-use assets, net ​ $ — ​ $ 27,612 ​ $ 27,612 Operating lease right-of-use assets, net ​ $ — ​ $ 923 ​ $ 923 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Liabilities and stockholders’ deficit ​ ​ ​ Accrued expenses ​ $ 7,049 ​ $ (1) ​ $ 7,048 Facility financing obligation, current portion ​ $ 276 ​ $ (276) ​ $ — Finance lease obligation, current portion ​ $ — ​ $ 1,292 ​ $ 1,292 Operating lease obligation, current portion ​ $ — ​ $ 55 ​ $ 55 Facility financing obligation, net of current portion ​ $ 22,955 ​ $ (22,955) ​ $ — Finance lease obligation, net of current portion ​ $ — ​ $ 26,319 ​ $ 26,319 Operating lease obligation, net of current portion ​ $ — ​ $ 870 ​ $ 870 Accumulated deficit ​ $ (234,289) ​ $ (1,861) ​ $ (236,150)

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Property and Equipment, Net
Schedule of Property and equipment	​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ September 30, ($ in thousands) 2020 2021 ​ ​ ​ ​ ​ ​ Scientific equipment ​ $ 27,412 ​ $ 27,578 Computer equipment ​ 149 ​ 154 Software ​ 335 ​ 335 Furniture and fixtures ​ 988 ​ 988 Leasehold improvements ​ 26,355 ​ 26,355 ​ ​ 55,239 ​ 55,410 Accumulated depreciation ​ (14,261) ​ (18,911) Property and equipment, net ​ $ 40,978 ​ $ 36,499	​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ($ in thousands) 2019 2020 ​ ​ ​ ​ ​ ​ Scientific equipment ​ $ 27,822 ​ $ 27,412 Computer equipment ​ 218 ​ 149 Software ​ 340 ​ 335 Furniture and fixtures ​ 988 ​ 988 Leasehold improvements ​ 26,337 ​ 26,355 ​ ​ 55,705 ​ 55,239 Accumulated depreciation ​ (8,417) ​ (14,261) Property and equipment, net ​ $ 47,288 ​ $ 40,978

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Accrued Expenses
Schedule of Accrued Expenses	​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ September 30, ($ in thousands) 2020 2021 ​ ​ ​ ​ ​ ​ Accrued external research, development and manufacturing costs ​ $ 2,615 ​ $ 2,685 Accrued employee compensation and benefits ​ 1,009 ​ 4,025 Accrued professional fees ​ 968 ​ 2,712 Total ​ $ 4,592 ​ $ 9,422	​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ($ in thousands) 2019 2020 Accrued external research, development and manufacturing costs ​ $ 3,872 ​ $ 2,615 Accrued employee compensation and benefits ​ 1,260 ​ 1,009 Accrued professional fees ​ 868 ​ 968 Total ​ $ 6,000 ​ $ 4,592

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2021
Debt
Summary of SVB loan payable and net discount or premium balances	​ ​ ​ ​ ​ ​ September 30, ($ in thousands) 2021 Principal amount of SVB loan payable ​ $ 20,000 Final payment amount of SVB loan payable ​ 1,000 Net premium associated with accretion of final payment and other debt issuance costs ​ (3,073) SVB loan payable, current and noncurrent ​ 17,927 Less SVB loan payable, current portion ​ (3,889) SVB loan payable, noncurrent portion ​ $ 14,038
Summary of future minimum payments of principal and estimated payments of interest	​ ​ ​ ​ ​ Year ending December 31: ($ in thousands) 2021 (remainder) ​ $ — 2022 ​ 5,555 2023 ​ 6,667 2024 ​ 6,667 2025 ​ 1,111 Total future payments ​ 20,000

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases
Summary of quantitative information about the leases	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ($in thousands) 2019 2020 Finance lease cost ​ ​ ​ ​ ​ ​ Amortization of right-of-use assets ​ $ 2,060 ​ $ 2,060 Interest on lease liabilities ​ 2,298 ​ 2,180 Total finance lease cost ​ 4,358 ​ 4,240 Operating lease cost ​ 137 ​ 152 Total lease cost ​ $ 4,495 ​ $ 4,392 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ Year Ended ​ ​ ​ December 31, 2019 ​ December 31, 2020 ​ ​ ​ Finance ​ Operating ​ Finance ​ Operating ​ ($ in thousands) Leases Leases Leases Leases Operating cash flows from leases ​ $ (2,298) ​ $ (137) ​ $ (2,180) ​ $ (182) ​ Financing cash flows from leases ​ $ (1,292) ​ $ — ​ $ (1,500) ​ $ — ​ Weighted-average remaining lease term ​ 6.02 ​ 6.38 ​ 5.52 ​ 6.24 ​ Weighted-average discount rate ​ 8.50 % ​ 8.50 % ​ 8.50 % ​ 8.50 %
Schedule of maturities of lease liabilities	​ ​ ​ ​ ​ ​ ​ ​ ($ in thousands) Finance Operating Year Ended December 31, 2021 ​ $ 3,773 ​ $ 105 Year Ended December 31, 2022 ​ 3,868 ​ 105 Year Ended December 31, 2023 ​ 3,965 ​ 105 Year Ended December 31, 2024 ​ 4,065 ​ 106 Year Ended December 31, 2025 ​ 4,167 ​ 106 Thereafter ​ 16,937 ​ 678 Total ​ 36,775 ​ 1,205 Less: present value discount ​ (11,956) ​ (436) Lease liabilities ​ $ 24,819 ​ $ 769

Redeemable Convertible Prefer_2

Redeemable Convertible Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2020
Redeemable Convertible Preferred Stock
Summary of redeemable convertible preferred stock	As of December 31, 2019 and December 31, 2020, redeemable convertible preferred stock consisted of the following (in thousands, except share amounts): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Redeemable Redeemable ​ ​ ​ ​ ​ ​ ​ ​ Convertible ​ Convertible ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Preferred ​ Preferred Stock ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock ​ Issued and ​ ​ Carrying ​ Liquidation ​ Issuance ​ Authorized Outstanding Value Preference Price Series A redeemable convertible preferred stock ​ 18,421,897 ​ 18,421,897 ​ $ 74,079 ​ $ 74,079 ​ $ 4.0212 Series B redeemable convertible preferred stock ​ 24,137,647 ​ 24,137,647 ​ ​ 127,358 ​ ​ 136,500 ​ $ 5.6550 Series C redeemable convertible preferred stock ​ 11,241,286 ​ 11,241,283 ​ ​ 70,704 ​ ​ 75,000 ​ $ 6.6717 Series D redeemable convertible preferred stock ​ 15,812,735 ​ 15,812,735 ​ ​ 148,848 ​ ​ 150,000 ​ $ 9.4859 ​ 69,613,565 69,613,562 ​ $ 420,989 ​ $ 435,579 ​ ​ ​
Summary of conversion prices for each series of the redeemable convertible preferred stock	​ ​ ​ ​ ​ Series Conversion Series A redeemable convertible preferred stock ​ $ 4.0212 Series B redeemable convertible preferred stock ​ $ 5.6550 Series C redeemable convertible preferred stock ​ $ 6.6717 Series D redeemable convertible preferred stock ​ $ 9.4859

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit) (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Schedule of activity of warrants	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Legacy ​ ​ ​ ​ ​ ​ ​ ​ Humacyte ​ ​ ​ ​ ​ ​ ​ ​ Common Stock ​ Private Placement ​ ​ ​ Total Common ​ Warrants Warrants Public Warrants Stock Warrants ​ ​ ​ ​ ​ ​ ​ ​ ​ Outstanding as of December 31, 2020 ​ 32,961 ​ — ​ — ​ 32,961 Common Stock Warrants issued to SVB ​ 287,704 ​ — ​ — ​ 287,704 Common Stock Warrants as Part of the Merger — 177,500 5,000,000 5,177,500 Warrants Exercised (32,961) — — (32,961) Oustanding as of September 30, 2021 287,704 177,500 5,000,000 5,465,204
Summary of common stock reserved for future issuances	​ ​ ​ ​ ​ September 30, ​ 2021 Common stock reserved for Contingent Consideration Shares 15,000,000 Exercise of options under stock plans 6,399,888 Issuance of options under stock plans 7,730,503 Shares available for grant under ESPP 1,030,033 Warrants to purchase common stock 5,465,204 ​ ​ 35,625,628	​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2020 ​ ​ ​ ​ ​ Conversion of Series A redeemable convertible preferred stock 18,421,897 18,421,897 Conversion of Series B redeemable convertible preferred stock 24,137,647 24,137,647 Conversion of Series C redeemable convertible preferred stock 11,241,286 11,241,286 Conversion of Series D redeemable convertible preferred stock 15,812,735 15,812,735 Exercise of options under stock plan 5,220,236 4,813,262 Issuance of options under stock plan 2,736,954 2,948,598 Warrant to purchase common stock 32,961 ​ 32,961 ​ ​ 77,603,716 77,408,386
Private Placement Warrants
Schedule of assumptions used in the valuations	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ August 26, September 30, ​ ​ 2021 ​ 2021 Market price of public stock ​ $ 10.96 ​ $ 11.61 ​ Exercise price ​ $ 11.50 ​ $ 11.50 ​ Expected term (years) ​ 5.00 ​ 4.91 ​ Expected share price volatility ​ 32.5 % 28.5 % Risk-free interest rate ​ 0.68 % 0.96 % Estimated dividend yield ​ 0 % 0 %
Contingent earnout liability
Schedule of assumptions used in the valuations	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ August 26, September 30, ​ ​ 2021 ​ 2021 Current stock price ​ $ 10.96 ​ $ 11.61 ​ Expected share price volatility ​ 79.6 % 78.9 % Risk-free interest rate ​ 1.34 % 1.55 % Estimated dividend yield ​ 0 % 0.0 % Expected term (years) ​ 10.00 ​ 10.00 ​

Stock-based Compensation (Table

Stock-based Compensation (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Stock-based Compensation
Summary of assumptions on the date of grant to estimate the fair value of the stock options in the Black-Scholes option-pricing model	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended September 30, ​ 2020 2021 (1) 2020 2021 Estimated dividend yield ​ 0 % — ​ 0 % 0 % Expected share price volatility (weighted average and range, if applicable) ​ 91.6 % — ​ 91.4% (89.4% to 91.6%) ​ 91.4% (91.0% to 92.1%) ​ Risk-free interest rate (weighted average and range, if applicable) ​ 0.34 % — ​ 0.40% (0.34% to 0.75%) ​ 0.68% (0.62% to 1.02%) ​ Expected term of options (in years) ​ 6.0 ​ — ​ 6.0 ​ 6.0 ​	​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ 2019 2020 ​ Estimated dividend yield ​ 0 % 0 % Expected share price volatility ​ 70.1%-87.7 % 89.4% - 91.6 % Risk-free interest rate ​ 1.76% - 2.46 % 0.34% - 0.75 % Expected term of options (in years) ​ 6.00 ​ 6.00 ​
Summary of stock-based compensation expense included in the statements of operations and comprehensive loss	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ($ in thousands) ​ 2020 ​ 2021 ​ 2020 ​ 2021 Research and development ​ $ 308 ​ $ 486 ​ $ 781 ​ $ 1,837 General and administrative ​ ​ 862 ​ ​ 1,391 ​ ​ 2,685 ​ ​ 5,498 Total ​ $ 1,170 ​ $ 1,877 ​ $ 3,466 ​ $ 7,335 ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ September 30, ($ in thousands) ​ 2020 ​ 2021 Unrecognized share-based compensation cost ​ $ 5,789 ​ $ 12,480 Expected weighted average period compensation costs to be recognized (years) ​ 1.7 ​ 2.1	​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ($ in thousands) ​ 2019 ​ 2020 Research and development ​ $ 914 ​ $ 1,135 General and administrative ​ 3,543 ​ 3,559 Total ​ $ 4,457 ​ $ 4,694 ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ($ in thousands) ​ 2019 ​ 2020 Unrecognized share-based compensation cost ​ $ 7,919 ​ $ 5,789 Expected weighted average period compensation costs to be recognized (years) ​ 1.8 ​ 1.7
Summary of option activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ ​ ​ Weighted ​ Remaining ​ Aggregate ​ ​ ​ ​ Average Exercise ​ Contractual Term ​ Intrinsic Value ​ ​ Number of Shares ​ Price Per Share ​ (years) ​ (in thousands) Options outstanding at December 31, 2020 4,813,262 ​ $ 6.04 6.6 ​ $ 20,422 Granted 1,838,029 ​ $ 10.28 ​ Exercised (188,006) ​ $ 2.97 ​ Forfeited (63,397) ​ $ 7.87 ​ Options outstanding at September 30, 2021 6,399,888 ​ $ 7.33 6.6 ​ $ 26,705 Vested and exercisable, September 30, 2021 4,092,342 ​ $ 5.74 5.1 ​ $ 23,345 Vested and expected to vest, September 30, 2021 6,399,888 ​ $ 7.33 6.6 ​ $ 26,705	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ ​ ​ Weighted ​ Remaining ​ Aggregate ​ ​ Number of ​ Average Exercise ​ Contractual Term ​ Intrinsic Value ​ ​ Shares ​ Price Per Share ​ (years) ​ (in thousands) Options outstanding at December 31, 2018 5,638,773 ​ $ 4.69 7.4 ​ $ 21,354 Granted 621,031 ​ ​ 8.49 ​ Exercised (620,831) ​ ​ 1.97 ​ Forfeited (418,737) ​ ​ 7.62 ​ Options outstanding at December 31, 2019 5,220,236 ​ $ 5.22 6.5 ​ $ 17,044 Granted 480,856 ​ ​ 9.79 ​ Exercised (195,239) ​ ​ 1.55 ​ Forfeited (692,591) ​ ​ 3.76 ​ Options outstanding at December 31, 2020 4,813,262 ​ $ 6.04 6.6 ​ $ 20,422 Vested and exercisable, December 31, 2020 3,392,302 ​ $ 4.99 5.9 ​ $ 17,925 Vested and expected to vest, December 31, 2020 4,813,262 ​ $ 6.04 6.6 ​ $ 20,422

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Taxes
Schedule of components of Company's deferred tax assets and deferred tax liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ($ in thousands) 2019 2020 Deferred tax assets: ​ ​ ​ ​ ​ ​ Net operating loss ​ $ 50,616 ​ $ 53,515 Capitalized research and development ​ 19,660 ​ ​ 32,337 Research credits ​ 10,658 ​ 15,056 Share-based compensation ​ 1,669 ​ 2,519 Right of use lease liability ​ 207 ​ 177 Accrued expenses ​ 71 ​ 57 Other ​ 1 ​ 1 Total deferred tax asset ​ 82,882 ​ 103,662 Less: valuation allowance ​ (82,193) ​ (101,757) Total net deferred tax asset ​ 689 ​ 1,905 ​ ​ ​ ​ ​ ​ ​ Deferred tax liabilities: ​ ​ Basis difference in fixed assets ​ (482) ​ (1,728) Right of use lease assets ​ (207) ​ (177) Total deferred tax liability ​ (689) ​ (1,905) Total net deferred tax asset/(liability) ​ $ — ​ $ —
Schedule of difference between the actual income tax benefit and amount computed by applying the statutory Federal income tax rate to losses before income taxes	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2020 ($ in thousands) ​ Amount Rate Amount Rate Income tax benefit at statutory rate ​ $ (17,939) 21.0 % $ (13,970) 21.0 % State income taxes, net of federal benefit ​ (1,739) 2.0 % (1,338) 2.0 % Tax credits ​ (1,821) 2.1 % (2,625) 3.9 % Other nondeductible expenses ​ 54 0.0 % 90 (0.1) % Deferred rate changes ​ 16 0.0 % 16 0.0 % Other ​ 449 (0.5) % (1,736) 2.6 % Change in valuation allowance ​ 20,980 (24.6) % 19,563 (29.4) % Provision for income taxes ​ $ — 0.0 % $ — 0.0 %

Related Party Transactions (Tab

Related Party Transactions (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Related Party Transactions
Summary of related party expenses included in statements of operations and comprehensive loss	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months ​ Nine Months ($ in thousands) 2020 2021 2020 2021 Expenses under MOU 125 — 375 — License expenses 20 — 70 85 Other 4 2 17 83 Total 149 2 462 168	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ($ in thousands) 2019 2020 Expenses under MOU $ 422 $ 500 License expenses 110 92 Other 39 28 Total $ 571 $ 620

Organization and Description _2

Organization and Description of Business (Details) - USD ($) $ in Thousands	Aug. 26, 2021	Mar. 22, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019
Organization and Description of Business
Proceeds from merger	$ 242,400								$ 242,400
Accumulated deficit			$ 457,158						457,158		$ 388,096	$ 321,572	$ 234,289
Net loss			31,563	$ 17,198	$ 20,301	$ 17,760	$ 14,878	$ 17,674	69,062	$ 50,312	66,524	85,422
Cash and cash equivalents			$ 240,449						$ 240,449		$ 39,929	$ 93,713
Substantial Doubt about Going Concern, within One Year [true false]		true

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Basis of Presentation (Details) - shares	Aug. 26, 2021	Dec. 31, 2020
Summary of Significant Accounting Policies
Exchange ratio		0.2626%
Public warrants assumed	5,000,000
Private placement warrants assumed	177,500
Share accepting a tender offer entitles warrants to receive cash (as a percent)	50.00%

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Segment (Details) - segment	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Segments
Number of reportable segment	1	1	1	1	1	1
Number of operating segment					1

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Grant Revenue (Details) - USD ($) $ in Thousands	1 Months Ended			3 Months Ended		9 Months Ended		12 Months Ended		86 Months Ended
	Sep. 30, 2017	Aug. 31, 2017	Nov. 30, 2013	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue from grants not within the scope of ASC 606				$ 200	$ 900	$ 1,100	$ 1,400	$ 1,500	$ 6,200	$ 1,600
Department of Defense grants | Work on bioengineered blood vessels for vascular trauma
Disaggregation of Revenue [Line Items]
Grants	$ 4,000
Department of Defense grants | Work to support human tissue engineered blood vessels for vascular reconstruction
Disaggregation of Revenue [Line Items]
Grants		$ 7,100
Department of Defense grants | Reimbursement of certain allowable costs related to grants
Disaggregation of Revenue [Line Items]
Recognized revenue				200	600	1,100	1,000
National Institutes of Health grant | Reimbursement of certain allowable costs related to grants
Disaggregation of Revenue [Line Items]
Recognized revenue				$ 0	$ 300	$ 0	$ 300
National Institutes of Health grant | Work to support bioengineered grafts for peripheral vascular disease
Disaggregation of Revenue [Line Items]
Grants			$ 1,600

Summary of Significant Accoun_7

Summary of Significant Accounting Policies -Concentration of Credit Risk (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Revenue | Customer concentration
Concentration Risk [Line Items]
Concentration of Credit Risk	100.00%	98.00%	100.00%	96.00%	95.00%	100.00%
Revenue | Customer concentration | Grant A
Concentration Risk [Line Items]
Concentration of Credit Risk						28.00%
Revenue | Customer concentration | Grant B
Concentration Risk [Line Items]
Concentration of Credit Risk		0.00%		11.00%	10.00%	38.00%
Revenue | Customer concentration | Grant C
Concentration Risk [Line Items]
Concentration of Credit Risk	100.00%	68.00%	100.00%	65.00%	67.00%	34.00%
Revenue | Customer concentration | Grant D
Concentration Risk [Line Items]
Concentration of Credit Risk		30.00%		20.00%	18.00%
Accounts Receivable | Credit concentration
Concentration Risk [Line Items]
Concentration of Credit Risk			100.00%		100.00%	100.00%
Accounts Receivable | Credit concentration | Grant B
Concentration Risk [Line Items]
Concentration of Credit Risk						67.00%
Accounts Receivable | Credit concentration | Grant C
Concentration Risk [Line Items]
Concentration of Credit Risk			100.00%		100.00%	33.00%

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Net Loss per Share Attributable to Common Stockholders (Details) - shares	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Contingent consideration (in shares)	15,000,000
Series A redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities that were not included in the computation of diluted net loss per share		18,421,897	18,421,897	18,421,897
Series B redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities that were not included in the computation of diluted net loss per share		24,137,647	24,137,647	24,137,647
Series C redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities that were not included in the computation of diluted net loss per share		11,241,283	11,241,283	11,241,283
Series D redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities that were not included in the computation of diluted net loss per share		15,812,735	15,812,735	15,812,735
Exercise of options under stock plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities that were not included in the computation of diluted net loss per share	6,399,888	4,516,907	4,813,262	5,220,236
Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities that were not included in the computation of diluted net loss per share	5,465,204	32,961	32,961	32,961

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Property and Equipment, Net (Details)	12 Months Ended
	Dec. 31, 2020
Scientific equipment. | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years
Scientific equipment. | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	7 years
Computer equipment
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years
Software
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Furniture and fixtures | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years
Furniture and fixtures | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	7 years

Summary of Significant Accou_10

Summary of Significant Accounting Policies - Impairment of Long-Lived Assets and Income Taxes (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended		24 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020
Impairment of Long-Lived Assets
Impairment of long-lived assets	$ 0	$ 0	$ 0
Income Taxes
Uncertain tax positions		0		$ 0
Accrued interest or penalties related to uncertain tax positions		$ 0		0
interest or penalties related to uncertain tax positions expensed				$ 0

Summary of Significant Accou_11

Summary of Significant Accounting Policies - Leases (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit	$ (457,158)	$ (388,096)	$ (321,572)	$ (234,289)
Lease liabilities, Finance leases		24,819	26,300
Finance lease right-of-use assets	21,947	23,492	25,552
Operating right-of-use assets	$ 738	769	897
Lease liabilities, Operating leases		$ 769	$ 900
Cumulative Effect Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit				(1,861)
Lease liabilities, Finance leases				27,600
Finance lease right-of-use assets				27,612
Operating right-of-use assets				923
Lease liabilities, Operating leases				900
ASU 2016-02 | Cumulative Effect Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit				$ 1,900

Summary of Significant Accou_12

Summary of Significant Accounting Policies - New lease guidance on January 1, 2019 (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019
Assets
Building asset				$ 25,091
Finance lease right-of-use assets, net	$ 21,947	$ 23,492	$ 25,552
Operating lease right-of-use assets, net	738	769	897
Liabilities and stockholders' deficit
Accrued expenses	9,422	4,592	6,000	7,049
Facility financing obligation, current portion				276
Finance lease obligation, current portion	1,915	1,729	1,500
Operating lease obligation, current portion	44	42	70
Facility financing obligation, net of current portion				22,955
Finance lease obligation, net of current portion	21,627	23,090	24,819
Operating lease obligation, net of current portion	693	727	829
Accumulated deficit	$ (457,158)	$ (388,096)	$ (321,572)	(234,289)
Cumulative Effect Adjustment
Assets
Building asset				(25,091)
Finance lease right-of-use assets, net				27,612
Operating lease right-of-use assets, net				923
Liabilities and stockholders' deficit
Accrued expenses				(1)
Facility financing obligation, current portion				(276)
Finance lease obligation, current portion				1,292
Operating lease obligation, current portion				55
Facility financing obligation, net of current portion				(22,955)
Finance lease obligation, net of current portion				26,319
Operating lease obligation, net of current portion				870
Accumulated deficit				(1,861)
Beginning Balance, As Adjusted
Assets
Finance lease right-of-use assets, net				27,612
Operating lease right-of-use assets, net				923
Liabilities and stockholders' deficit
Accrued expenses				7,048
Finance lease obligation, current portion				1,292
Operating lease obligation, current portion				55
Finance lease obligation, net of current portion				26,319
Operating lease obligation, net of current portion				870
Accumulated deficit				(236,150)
ASU 2016-02 | Cumulative Effect Adjustment
Liabilities and stockholders' deficit
Accumulated deficit				$ 1,900

Property and Equipment, Net (De

Property and Equipment, Net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 55,410		$ 55,410		$ 55,239	$ 55,705
Accumulated depreciation	(18,911)		(18,911)		(14,261)	(8,417)
Property and equipment, net	36,499		36,499		40,978	47,288
Depreciation expense	1,500	$ 1,600	4,650	$ 4,729	6,291	4,689
Scientific equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	27,578		27,578		27,412	27,822
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	154		154		149	218
Software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	335		335		335	340
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	988		988		988	988
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 26,355		$ 26,355		$ 26,355	$ 26,337

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019
Accrued Expenses
Accrued external research, development and manufacturing costs	$ 2,685	$ 2,615	$ 3,872
Accrued employee compensation and benefits	4,025	1,009	1,260
Accrued professional fees	2,712	968	868
Total	$ 9,422	$ 4,592	$ 6,000	$ 7,049

Debt - PPP (Details)

Debt - PPP (Details) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended		12 Months Ended
	Apr. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Debt Instrument [Line Items]
Proceeds from debt instruments			$ 3,251	$ 3,251
Gain on PPP loan forgiveness		$ 3,284
Paycheck Protection Program
Debt Instrument [Line Items]
Proceeds from debt instruments	$ 3,300
Gain on PPP loan forgiveness		$ 3,284

Leases - Paragraphs (Details)

Leases - Paragraphs (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating Lease, Liability			$ 769	$ 900
Finance Lease, Liability			24,819	26,300
Operating Lease, Right-of-Use Asset		$ 738	769	897
Finance lease right-of-use assets, net		$ 21,947	$ 23,492	$ 25,552
Maximum
Gain (Loss) on Termination of Lease	$ 100

Leases - Costs (Details)

Leases - Costs (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Finance lease cost
Amortization of right-of-use assets			$ 2,060	$ 2,060
Interest on lease liabilities			2,180	2,298
Total finance lease cost			4,240	4,358
Operating lease cost	$ 31	$ 71	152	137
Total lease cost			$ 4,392	$ 4,495

Leases - Cash flows (Details)

Leases - Cash flows (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Leases
Operating cash flows from leases, Operating Leases			$ (182)	$ (137)
Operating cash flows from leases, Finance Leases			(2,180)	(2,298)
Financing cash flows from leases	$ (1,277)	$ (1,107)	$ (1,500)	$ (1,292)
Weighted-average remaining lease term, Operating Leases			6 years 2 months 26 days	6 years 4 months 17 days
Weighted-average remaining lease term, Finance Leases			5 years 6 months 7 days	6 years 7 days
Weighted-average discount rate, Operating Leases			8.50%	8.50%
Weighted-average discount rate, Finance Leases			8.50%	8.50%

Leases - Maturities (Details)

Leases - Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Operating leases
2021	$ 105
2022	105
2023	105
2024	106
2025	106
Thereafter	678
Total, Operating leases	1,205
Less: present value discount, Operating leases	436
Lease liabilities, Operating leases	769	$ 900
Finance leases
2021	3,773
2022	3,868
2023	3,965
2024	4,065
2025	4,167
Thereafter	16,937
Total, Finance leases	36,775
Less: present value discount, Finance leases	11,956
Lease liabilities, Finance leases	$ 24,819	$ 26,300

Redeemable Convertible Prefer_3

Redeemable Convertible Preferred Stock - Preferred Stock Terms (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Temporary Equity [Line Items]
Redeemable Convertible Preferred Stock, Authorized	0	69,613,565	69,613,565
Redeemable Convertible Preferred Stock, Issued and Outstanding	0	69,613,562	69,613,562
Redeemable Convertible Preferred Stock, Carrying Value		$ 420,989	$ 420,989
Redeemable Convertible Preferred Stock, Liquidation Preference	$ 0	$ 435,579	$ 435,579
Series A redeemable convertible preferred stock
Temporary Equity [Line Items]
Redeemable Convertible Preferred Stock, Authorized		18,421,897
Redeemable Convertible Preferred Stock, Issued and Outstanding		18,421,897
Redeemable Convertible Preferred Stock, Carrying Value		$ 74,079
Redeemable Convertible Preferred Stock, Liquidation Preference		$ 74,079
Redeemable Convertible Preferred Stock, Issuance Price		$ 4.0212
Series B redeemable convertible preferred stock
Temporary Equity [Line Items]
Redeemable Convertible Preferred Stock, Authorized		24,137,647
Redeemable Convertible Preferred Stock, Issued and Outstanding		24,137,647
Redeemable Convertible Preferred Stock, Carrying Value		$ 127,358
Redeemable Convertible Preferred Stock, Liquidation Preference		$ 136,500
Redeemable Convertible Preferred Stock, Issuance Price		$ 5.6550
Series C redeemable convertible preferred stock
Temporary Equity [Line Items]
Redeemable Convertible Preferred Stock, Authorized		11,241,286
Redeemable Convertible Preferred Stock, Issued and Outstanding		11,241,283
Redeemable Convertible Preferred Stock, Carrying Value		$ 70,704
Redeemable Convertible Preferred Stock, Liquidation Preference		$ 75,000
Redeemable Convertible Preferred Stock, Issuance Price		$ 6.6717
Series D redeemable convertible preferred stock
Temporary Equity [Line Items]
Redeemable Convertible Preferred Stock, Authorized		15,812,735
Redeemable Convertible Preferred Stock, Issued and Outstanding		15,812,735
Redeemable Convertible Preferred Stock, Carrying Value		$ 148,848
Redeemable Convertible Preferred Stock, Liquidation Preference		$ 150,000
Redeemable Convertible Preferred Stock, Issuance Price		$ 9.4859

Redeemable Convertible Prefer_4

Redeemable Convertible Preferred Stock (Details)	Dec. 31, 2020USD ($)
Fresenius Medical Care | Private placement
Class of Stock [Line Items]
Right to purchase common stock granted	$ 30

Redeemable Convertible Prefer_5

Redeemable Convertible Preferred Stock - Election of Directors (Details)	12 Months Ended
	Dec. 31, 2020individual
Fresenius Medical Care
Temporary Equity [Line Items]
Number of representative to attend, in a non-voting observer capacity designated by related party	1
Series A redeemable convertible preferred stock
Temporary Equity [Line Items]
Number of individual designated for board of director by holder of stock	1
Series B redeemable convertible preferred stock
Temporary Equity [Line Items]
Number of individual designated for board of director by holder of stock	2
Series C redeemable convertible preferred stock
Temporary Equity [Line Items]
Number of individual designated for board of director by holder of stock	1

Redeemable Convertible Prefer_6

Redeemable Convertible Preferred Stock - Conversion to Common Stock (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)$ / shares
Redeemable Convertible Preferred Stock
Minimum offering price required for automatic conversion | $ / shares	$ 2.7401
Minimum aggregate gross proceeds required for automatic conversion | $	$ 100
Percentage of written request of holder required for automatic conversion	60.00%

Redeemable Convertible Prefer_7

Redeemable Convertible Preferred Stock- Conversion prices (Details)	Dec. 31, 2020$ / shares
Temporary Equity [Line Items]
Conversion ratio	1
Series A redeemable convertible preferred stock
Temporary Equity [Line Items]
Conversion Price	$ 4.0212
Series B redeemable convertible preferred stock
Temporary Equity [Line Items]
Conversion Price	5.6550
Series C redeemable convertible preferred stock
Temporary Equity [Line Items]
Conversion Price	6.6717
Series D redeemable convertible preferred stock
Temporary Equity [Line Items]
Conversion Price	$ 9.4859

Redeemable Convertible Prefer_8

Redeemable Convertible Preferred Stock - Liquidation (Details)	12 Months Ended
	Dec. 31, 2020$ / shares
Temporary Equity [Line Items]
Number of times of liquidation preference per share holder is entitled to receive	1.25
Series A redeemable convertible preferred stock
Temporary Equity [Line Items]
Liquidation preference per share	$ 4.0212
Series B redeemable convertible preferred stock
Temporary Equity [Line Items]
Liquidation preference per share	5.6550
Series C redeemable convertible preferred stock
Temporary Equity [Line Items]
Liquidation preference per share	$ 6.6717
Percentage of holders required for approval of liquidation preference	80.00%
Series D redeemable convertible preferred stock
Temporary Equity [Line Items]
Liquidation preference per share	$ 9.4859

Stockholders' Equity (Deficit_2

Stockholders' Equity (Deficit) - Common Stock (Details) $ / shares in Units, $ in Thousands	Aug. 26, 2021USD ($)$ / sharesshares	Sep. 30, 2021$ / sharesshares	Sep. 30, 2021USD ($)Vote$ / sharesshares	Dec. 31, 2020Vote$ / sharesshares	Dec. 31, 2019$ / sharesshares
Proceeds from merger	$ 242,400		$ 242,400
Assets	$ 100
Common stock, shares outstanding | shares	103,003,384	103,003,384	103,003,384	5,822,396	5,627,157
Common stock, par value | $ / shares	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001
Dividends declared | $ / shares			$ 0	$ 0
Number of vote per common share held | Vote				1
Common stock, authorized | shares		250,000,000	250,000,000	340,216,780	340,216,780
Common Stock
Issuance of common stock upon the Merger and related PIPE Financing, net of issuance costs | shares	27,346,449	27,346,449
Proceeds from merger	$ 242,400
Transaction costs	$ 3,900
Common stock, shares outstanding | shares	103,003,384
Common stock, par value | $ / shares	$ 0.0001	$ 0.0001	$ 0.0001
Number of vote per common share held | Vote			1
Common stock, authorized | shares		250,000,000	250,000,000
Alpha Healthcare Acquisition Corp. and Hunter Merger Sub, Inc. | Common Stock
Contingent consideration liability	$ 15,200
Assets	$ 100

Stockholders' Equity (Deficit_3

Stockholders' Equity (Deficit) - Common stock for future issuances (Details) - shares	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Reserved common stock for future issuances	35,625,628	77,408,386	77,603,716
Series A redeemable convertible preferred stock
Class of Stock [Line Items]
Reserved common stock for future issuances		18,421,897	18,421,897
Series B redeemable convertible preferred stock
Class of Stock [Line Items]
Reserved common stock for future issuances		24,137,647	24,137,647
Series C redeemable convertible preferred stock
Class of Stock [Line Items]
Reserved common stock for future issuances		11,241,286	11,241,286
Series D redeemable convertible preferred stock
Class of Stock [Line Items]
Reserved common stock for future issuances		15,812,735	15,812,735
Common stock reserved for Contingent Consideration Shares
Class of Stock [Line Items]
Reserved common stock for future issuances	15,000,000
Exercise of options under stock plan
Class of Stock [Line Items]
Reserved common stock for future issuances	6,399,888	4,813,262	5,220,236
Issuance of options under stock plan
Class of Stock [Line Items]
Reserved common stock for future issuances	7,730,503	2,948,598	2,736,954
Shares available for grant under ESPP
Class of Stock [Line Items]
Reserved common stock for future issuances	1,030,033
Warrants to purchase common stock
Class of Stock [Line Items]
Reserved common stock for future issuances	5,465,204	32,961	32,961

Stock-based Compensation (Detai

Stock-based Compensation (Details) - $ / shares	1 Months Ended	9 Months Ended	12 Months Ended
	Jan. 31, 2021	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of options remaining available for grant		7,730,503	2,948,598
Outstanding awards		6,399,888	4,813,262	5,220,236	5,638,773
Contractual term		10 years	10 years
Vesting period	3 years		36 months
Commencement of involuntary termination term prior to effective date of corporate transaction		30 days	30 days
End of involuntary termination term after effective date of corporate transaction		12 months	12 months
Granted		1,838,029	480,856	621,031
Exercise price		$ 10.28	$ 9.79	$ 8.49
Minimum
Vesting period		36 months
Maximum
Vesting period		48 months
Chief Executive Officer [Member]
Vesting period	3 years
Granted	1,312,984
Exercise price	$ 10.28

Stock-based Compensation - Fair

Stock-based Compensation - Fair value of the stock options (Details)	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Assumptions on the date of grant to estimate the fair value of the stock options
Estimated dividend yield	0.00%	0.00%	0.00%	0.00%	0.00%
Expected price volatility	91.60%	91.40%	91.40%
Expected share price volatility, minimum		91.00%	89.40%		89.40%	70.10%
Expected share price volatility, maximum		92.10%	91.60%		91.60%	87.70%
Risk-free interest rate	0.34%	0.68%	0.40%
Risk-free interest rate, minimum		0.62%	0.34%		0.34%	1.76%
Risk-free interest rate, maximum		1.02%	0.75%		0.75%	2.46%
Expected term of options (in years)	6 years	6 years	6 years		6 years	6 years

Stock-based Compensation - Avai

Stock-based Compensation - Available options (Details) - shares	Sep. 30, 2021	Dec. 31, 2020
Stock-based Compensation
Number of options remaining available for grant	7,730,503	2,948,598

Stock-based Compensation - Expe

Stock-based Compensation - Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 1,877	$ 1,170	$ 7,335	$ 3,466	$ 4,694	$ 4,457
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	486	308	1,837	781	1,135	914
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 1,391	$ 862	$ 5,498	$ 2,685	$ 3,559	$ 3,543

Stock-based Compensation - Unre

Stock-based Compensation - Unrecognized cost (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock-based Compensation
Unrecognized share-based compensation cost	$ 12,480	$ 5,789	$ 7,919
Expected weighted average period compensation costs to be recognized (years)	2 years 1 month 6 days	1 year 8 months 12 days	1 year 9 months 18 days

Stock-based Compensation - Opti

Stock-based Compensation - Option activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Shares
Options outstanding at the beginning	4,813,262	5,220,236	5,638,773
Granted	1,838,029	480,856	621,031
Exercised	(188,006)	(195,239)	(620,831)
Forfeited	(63,397)	(692,591)	(418,737)
Options outstanding at the end	6,399,888	4,813,262	5,220,236	5,638,773
Vested and exercisable at the end of period	4,092,342	3,392,302
Vested and expected to vest at the end	6,399,888	4,813,262
Weighted Average Exercise Price Per Share
Options outstanding at the beginning (in dollars per share)	$ 6.04	$ 5.22	$ 4.69
Granted (in dollars per share)	10.28	9.79	8.49
Exercised (in dollars per share)	2.97	1.55	1.97
Forfeited (in dollars per share)	7.87	3.76	7.62
Options outstanding at the end (in dollars per share)	7.33	6.04	$ 5.22	$ 4.69
Vested and exercisable at the end of period (in dollars per share)	5.74	4.99
Vested and expected to vest at the end (in dollars per share)	$ 7.33	$ 6.04
Weighted Average Remaining Contractual Term and Aggregate Intrinsic Value
Options outstanding (in years)	6 years 7 months 6 days	6 years 7 months 6 days	6 years 6 months	7 years 4 months 24 days
Vested and exercisable at the end of period (in years)	5 years 1 month 6 days	5 years 10 months 24 days
Vested and expected to vest at the end (in years)	6 years 7 months 6 days	6 years 7 months 6 days
Options outstanding at the beginning (in dollars)	$ 20,422	$ 17,044	$ 21,354
Options outstanding at the end (in dollars)	26,705	20,422	$ 17,044	$ 21,354
Vested and exercisable at the end of period (in years)	23,345	17,925
Vested and expected to vest at the end (in dollars)	$ 26,705	$ 20,422

Stock-based Compensation - Othe

Stock-based Compensation - Other information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Stock-based Compensation
Total intrinsic value of options exercised	$ 1.4	$ 4
Weighted-average grant-date fair value per share of options granted	$ 7.26	$ 5.84

Income Taxes - Deferred tax ass

Income Taxes - Deferred tax assets and deferred tax liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating loss	$ 53,515	$ 50,616
Intangible assets	32,337	19,660
Research credits	15,056	10,658
Share-based compensation	2,519	1,669
Right of use lease liability	177	207
Accrued expenses	57	71
Other	1	1
Total deferred tax asset	103,662	82,882
Less: valuation allowance	(101,757)	(82,193)
Total net deferred tax asset	1,905	689
Deferred tax liabilities:
Basis difference in fixed assets	(1,728)	(482)
Right of Use Lease Assets	(177)	(207)
Total deferred tax liability	$ (1,905)	$ (689)

Income Taxes - Tax reconciliati

Income Taxes - Tax reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Income Taxes
Income tax benefit at statutory rate, Amount					$ (13,970)	$ (17,939)
State income taxes, net of federal benefit, Amount					(1,338)	(1,739)
Tax credits, Amount					(2,625)	(1,821)
Other nondeductible expenses, Amount					90	54
Deferred rate changes, Amount					16	16
Other, Amount					(1,736)	449
Change in valuation allowance, Amount					$ 19,563	$ 20,980
Income tax benefit at statutory rate, Rate					21.00%	21.00%
State income taxes, net of federal benefit, Rate					2.00%	2.00%
Tax credits, Rate					3.90%	2.10%
Other nondeductible expenses, Rate					(0.10%)	0.00%
Deferred rate changes, Rate					0.00%	0.00%
Other, Rate					2.60%	(0.50%)
Change in valuation allowance, Rate					(29.40%)	(24.60%)
Effective tax rate	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%

Income Taxes - Additional infor

Income Taxes - Additional information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating Loss Carryforwards [Line Items]
Percent of limitation on taxable income	80.00%
Effective federal tax rate	$ (13,970)	$ (17,939)
Effective federal tax rate	21.00%	21.00%
Foreign
Operating Loss Carryforwards [Line Items]
Operating loss	$ 232,700
Operating loss	71,500
Tax credit carryforwards		$ 10,700
State
Operating Loss Carryforwards [Line Items]
Operating loss	232,600
Tax credit carryforwards	$ 15,100

Retirement Plan (Details)

Retirement Plan (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)plan	Dec. 31, 2019USD ($)
Defined Contribution Plan Disclosure [Line Items]
Number of plans | plan	2,000
Qualified Plan
Defined Contribution Plan Disclosure [Line Items]
Employer's contribution for retirement plan | $	$ 0.6	$ 0.6
Plan 401 (K)
Defined Contribution Plan Disclosure [Line Items]
Employer's contribution Percentage for retirement plan	4.00%

Commitments and Contingencies -

Commitments and Contingencies - Duke University (Details) - Duke university - License agreement - shares	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Agreement expiration term after first commercial sale	4 years	4 years
Threshold notice period required to terminate the agreement	3 months	3 months
Collaborative Arrangement, Shares Issued In Connection With License Agreement	52,693	52,693

Commitments and Contingencies_2

Commitments and Contingencies - Yale University (Details) - Yale university - USD ($) $ in Millions	1 Months Ended		9 Months Ended	12 Months Ended
	Aug. 31, 2019	Feb. 28, 2014	Sep. 30, 2021	Dec. 31, 2020
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payments upon achievement of certain regulatory milestones			$ 0.2
Milestone payments upon achievement of certain commercial milestones			$ 0.6
License agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Threshold notice period required to terminate the agreement			90 days	90 days
License agreement related to coatings for small diameter vessels to inhibit clotting
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative Arrangement, Maximum Annual Maintenance Fee	$ 0.1	$ 0.1
License agreement related to bioartificial vascular pancreas
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative Arrangement, Maximum Annual Maintenance Fee			$ 0.1
License agreement related to tubular prostheses
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative Arrangement, Maximum Annual Maintenance Fee	$ 0.1

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Millions	Aug. 26, 2021	Aug. 31, 2021	Jun. 30, 2018	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2023	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2021
Related Party Transaction [Line Items]
Proceeds from PIPE	$ 175
Common stock, shares issued							5,822,396	5,627,157	103,003,384
Fresenius Medical Care
Related Party Transaction [Line Items]
Financing amount			$ 150
Shares issued for conversion of preferred shares	15,812,735
Proceeds from PIPE		$ 25
Common stock, shares issued		2,500,000
Dr. Niklason, President, CEO and member of board of directors
Related Party Transaction [Line Items]
Aggregate amount						$ 2.5
Payments made				$ 0.1	$ 0.4		$ 0.5	$ 0.4

Related Party Transactions - Ex

Related Party Transactions - Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Total	$ 2	$ 149	$ 168	$ 462	$ 620	$ 571
Expenses under MOU
Related Party Transaction [Line Items]
Total		125		375	500	422
License expenses
Related Party Transaction [Line Items]
Total		20	85	70	92	110
Other
Related Party Transaction [Line Items]
Total	$ 2	$ 4	$ 83	$ 17	$ 28	$ 39

Subsequent Events - Stock optio

Subsequent Events - Stock option grants (Details) - $ / shares	1 Months Ended	9 Months Ended	12 Months Ended
	Jan. 31, 2021	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019	Mar. 22, 2021
Subsequent Event [Line Items]
Option to purchase shares of common stock		1,838,029	480,856	621,031
Exercise price		$ 10.28	$ 9.79	$ 8.49
Number of shares vested as of the issuance date		6,399,888	4,813,262
Vesting period	3 years		36 months
Dr. Niklason
Subsequent Event [Line Items]
Option to purchase shares of common stock	1,312,984
Exercise price	$ 10.28
Vesting period	3 years
Subsequent event | Dr. Niklason
Subsequent Event [Line Items]
Option to purchase shares of common stock	1,312,984
Exercise price	$ 10.28
Number of shares vested as of the issuance date					0
Vesting period	3 years
Subsequent event | Mr. Sander
Subsequent Event [Line Items]
Option to purchase shares of common stock	183,817
Exercise price	$ 10.28
Number of shares vested as of the issuance date					0

Subsequent Events - Merger (Det

Subsequent Events - Merger (Details) - Subsequent event	Feb. 17, 2021USD ($)
Subsequent Event [Line Items]
Amount of common stock investors have agreed to purchase	$ 175,000,000
Intangible Assets, Net (Including Goodwill)	$ 0

Balance Sheets_2

Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019
Current assets
Cash and cash equivalents	$ 240,449	$ 39,929	$ 93,713
Accounts receivable	240	113	601
Prepaid expenses	3,490	1,407	640
Total current assets	244,179	41,449	94,954
Finance lease right-of-use assets, net	21,947	23,492	25,552
Operating lease right-of-use assets, net	738	769	897
Property and equipment, net	36,499	40,978	47,288
Total assets	303,363	106,688	168,691
Current liabilities
Accounts payable	5,830	2,274	3,272
Accrued expenses	9,422	4,592	6,000	$ 7,049
SVB loan payable, current portion	3,889
Finance lease obligation, current portion	1,915	1,729	1,500
Deferred payroll tax, current portion	145	145
Operating lease obligation, current portion	44	42	70
PPP loan payable, current portion		2,451
Total current liabilities	21,245	11,233	10,842
Contingent earnout liability	169,200
Finance lease obligation, net of current portion	21,627	23,090	24,819
SVB loan payable, net of current portion	14,038
Operating lease obligation, net of current portion	693	727	829
Common stock warrant liabilities	555
Deferred payroll tax, net of current portion	144	144
PPP loan payable, net of current portion		822
Total liabilities	227,502	36,016	36,490
Commitments and contingencies (Note 11)
Redeemable convertible preferred stock (Series A, B, C and D) $0.001 par value, 0 and 69,613,565 shares authorized as of September 30, 2021 and December 31, 2020, respectively; 0 and 69,613,562 shares outstanding as of September 30, 2021 and December 31, 2020, respectively; liquidation preference of $0 and $435,579 as of September 30, 2021 and December 31, 2020, respectively.		420,989	420,989
Stockholders' equity (deficit)
Preferred stock, $0.0001 par value; 20,000,000 and 0 shares designated as of September 30, 2021 and December 31, 2020; 0 shares issued and outstanding as of September 30, 2021 and December 31, 2020
Common stock, $0.0001 and $0.0001 par value as of September 30, 2021 and December 31, 2020, respectively; 250,000,000 and 340,216,780 shares authorized as of September 30, 2021 and December 31, 2020, respectively; 103,003,384 and 5,822,396 shares issued and outstanding as of September 30, 2021 and December 31, 2020, respectively.	10	1	1
Additional paid-in capital	533,009	37,778	32,783
Accumulated deficit	(457,158)	(388,096)	(321,572)	$ (234,289)
Total stockholders' equity (deficit)	75,861	(350,317)	(288,788)
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	$ 303,363	$ 106,688	$ 168,691

Balance sheet (Parenthetical)_2

Balance sheet (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Aug. 26, 2021	Dec. 31, 2020	Dec. 31, 2019
Balance Sheets
Redeemable convertible preferred stock, par value	$ 0.001		$ 0.001	$ 0.001
Redeemable convertible preferred stock, shares authorized	0		69,613,565	69,613,565
Redeemable convertible preferred stock, shares outstanding	0		69,613,562	69,613,562
Redeemable convertible preferred stock, liquidation preference	$ 0		$ 435,579	$ 435,579
Preferred stock, par value	$ 0.0001		$ 0.0001
Preferred stock, shares designated	20,000,000		0
Preferred stock, shares issued	0		0
Preferred stock, shares outstanding	0		0
Common stock, par value	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001
Common stock, shares authorized	250,000,000		340,216,780	340,216,780
Common stock, shares issued	103,003,384		5,822,396	5,627,157
Common stock, shares outstanding	103,003,384	103,003,384	5,822,396	5,627,157

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Condensed Consolidated Statements of Operations and Comprehensive Loss
Grant Revenue	$ 241	$ 914	$ 1,086	$ 1,367	$ 1,491	$ 6,187
Operating expenses:
Research and development (includes related party expenses of $2 and $149 for the three months ended September 30, 2021 and 2020 and $168 and $462 for the nine months ended September 30, 2021 and 2020)	15,386	14,692	45,091	40,879	54,078	75,603
General and administrative	5,398	3,435	15,576	9,416	12,013	16,275
Total operating expenses	20,784	18,127	60,667	50,295	66,091	91,878
Loss from operations	(20,543)	(17,213)	(59,581)	(48,928)	(64,600)	(85,691)
Other expenses, net:
Interest income	3	2	6	277	278	2,567
Change in fair value of contingent earnout liability	(9,768)		(9,768)
Interest expense	(1,204)	(549)	(2,952)	(1,661)	(2,202)	(2,298)
Transaction costs expensed	(49)		(49)
Change in fair value of common stock warrant liabilities	(2)		(2)
Gain on PPP loan forgiveness			3,284
Total other expenses, net	(11,020)	(547)	(9,481)	(1,384)	(1,924)	269
Net loss and comprehensive loss	$ (31,563)	$ (17,760)	$ (69,062)	$ (50,312)	$ (66,524)	$ (85,422)
Net loss per share attributable to common stockholders, basic	$ (0.72)	$ (3.07)	$ (3.69)	$ (8.74)
Net loss per share attributable to common stockholders, diluted	$ (0.72)	$ (3.07)	$ (3.69)	$ (8.74)
Weighted-average shares outstanding used in computing net loss per share attributable to common stockholders, basic	43,950,856	5,788,130	18,728,471	5,755,418
Weighted-average shares outstanding used in computing net loss per share attributable to common stockholders, diluted	43,950,856	5,788,130	18,728,471	5,755,418
Net loss per share attributable to common stockholders, basic and diluted					$ (11.54)	$ (16.17)
Weighted-average shares outstanding used in computing net loss per share attributable to common stockholders, basic and diluted					5,765,688	5,283,628

Condensed Consolidated Statem_6

Condensed Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Condensed Consolidated Statements of Operations and Comprehensive Loss
Related party expenses	$ 2	$ 149	$ 168	$ 462	$ 620	$ 571

Condensed Consolidated Statem_7

Condensed Consolidated Statements of Changes in Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Redeemable Convertible Preferred Stock.	Common Stock	Additional Paid-in Capital	Accumulated DeficitCumulative Effect Adjustment	Accumulated Deficit	Cumulative Effect Adjustment	Total
Balance at the beginning at Dec. 31, 2018	$ 420,989
Balance at the beginning (in shares) at Dec. 31, 2018	69,613,562
Balance at the end at Dec. 31, 2019	$ 420,989						$ 420,989
Balance at the end (in shares) at Dec. 31, 2019	69,613,562						69,613,562
Balance at the beginning at Dec. 31, 2018		$ 1	$ 27,108		$ (234,289)		$ (207,180)
Balance at the beginning (in shares) at Dec. 31, 2018		5,006,326
Equity
Proceeds from the exercise of stock options			1,218				$ 1,218
Proceeds from the exercise of stock options (in shares)		620,831					620,831
Net loss					(85,422)		$ (85,422)
Stock-based compensation			4,457				4,457
Balance at the end (ASU 2016-02) at Dec. 31, 2019				$ (1,861)		$ (1,861)
Balance at the end at Dec. 31, 2019		$ 1	32,783		(321,572)		(288,788)
Balance at the end (in shares) at Dec. 31, 2019		5,627,157
Balance at the end at Mar. 31, 2020	$ 420,989
Balance at the end (in shares) at Mar. 31, 2020	69,613,562
Equity
Proceeds from the exercise of stock options			175				175
Proceeds from the exercise of stock options (in shares)		148,159
Net loss					(17,674)		(17,674)
Stock-based compensation			1,182				1,182
Balance at the end at Mar. 31, 2020		$ 1	34,140		(339,246)		(305,105)
Balance at the end (in shares) at Mar. 31, 2020		5,775,316
Balance at the beginning at Dec. 31, 2019	$ 420,989						$ 420,989
Balance at the beginning (in shares) at Dec. 31, 2019	69,613,562						69,613,562
Balance at the end at Sep. 30, 2020	$ 420,989
Balance at the end (in shares) at Sep. 30, 2020	69,613,562
Balance at the beginning (ASU 2016-02) at Dec. 31, 2019				(1,861)		(1,861)
Balance at the beginning at Dec. 31, 2019		$ 1	32,783		(321,572)		$ (288,788)
Balance at the beginning (in shares) at Dec. 31, 2019		5,627,157
Equity
Net loss							(50,312)
Balance at the end at Sep. 30, 2020		$ 1	36,484		(371,884)		(335,399)
Balance at the end (in shares) at Sep. 30, 2020		5,788,877
Balance at the beginning at Dec. 31, 2019	$ 420,989						$ 420,989
Balance at the beginning (in shares) at Dec. 31, 2019	69,613,562						69,613,562
Balance at the end at Dec. 31, 2020	$ 420,989						$ 420,989
Balance at the end (in shares) at Dec. 31, 2020	69,613,562						69,613,562
Balance at the beginning (ASU 2016-02) at Dec. 31, 2019				$ (1,861)		$ (1,861)
Balance at the beginning at Dec. 31, 2019		$ 1	32,783		(321,572)		$ (288,788)
Balance at the beginning (in shares) at Dec. 31, 2019		5,627,157
Equity
Proceeds from the exercise of stock options			301				$ 301
Proceeds from the exercise of stock options (in shares)		195,239					195,239
Net loss					(66,524)		$ (66,524)
Stock-based compensation			4,694				4,694
Balance at the end at Dec. 31, 2020		$ 1	37,778		(388,096)		(350,317)
Balance at the end (in shares) at Dec. 31, 2020		5,822,396
Balance at the beginning at Mar. 31, 2020	$ 420,989
Balance at the beginning (in shares) at Mar. 31, 2020	69,613,562
Balance at the end at Jun. 30, 2020	$ 420,989
Balance at the end (in shares) at Jun. 30, 2020	69,613,562
Balance at the beginning at Mar. 31, 2020		$ 1	34,140		(339,246)		(305,105)
Balance at the beginning (in shares) at Mar. 31, 2020		5,775,316
Equity
Proceeds from the exercise of stock options			48				48
Proceeds from the exercise of stock options (in shares)		11,761
Net loss					(14,878)		(14,878)
Stock-based compensation			1,114				1,114
Balance at the end at Jun. 30, 2020		$ 1	35,302		(354,124)		(318,821)
Balance at the end (in shares) at Jun. 30, 2020		5,787,077
Balance at the end at Sep. 30, 2020	$ 420,989
Balance at the end (in shares) at Sep. 30, 2020	69,613,562
Equity
Proceeds from the exercise of stock options			12				12
Proceeds from the exercise of stock options (in shares)		1,800
Net loss					(17,760)		(17,760)
Stock-based compensation			1,170				1,170
Balance at the end at Sep. 30, 2020		$ 1	36,484		(371,884)		(335,399)
Balance at the end (in shares) at Sep. 30, 2020		5,788,877
Balance at the beginning at Dec. 31, 2020	$ 420,989						$ 420,989
Balance at the beginning (in shares) at Dec. 31, 2020	69,613,562						69,613,562
Balance at the end at Mar. 31, 2021	$ 420,989
Balance at the end (in shares) at Mar. 31, 2021	69,613,562
Balance at the beginning at Dec. 31, 2020		$ 1	37,778		(388,096)		$ (350,317)
Balance at the beginning (in shares) at Dec. 31, 2020		5,822,396
Equity
Proceeds from the exercise of stock options			206				206
Proceeds from the exercise of stock options (in shares)		116,149
Net loss					(20,301)		(20,301)
Stock-based compensation			2,528				2,528
Issuance of warrants in conjunction with debt			2,360				2,360
Balance at the end at Mar. 31, 2021		$ 1	42,872		(408,397)		(365,524)
Balance at the end (in shares) at Mar. 31, 2021		5,938,545
Balance at the beginning at Dec. 31, 2020	$ 420,989						$ 420,989
Balance at the beginning (in shares) at Dec. 31, 2020	69,613,562						69,613,562
Balance at the end (in shares) at Sep. 30, 2021							0
Balance at the beginning at Dec. 31, 2020		$ 1	37,778		(388,096)		$ (350,317)
Balance at the beginning (in shares) at Dec. 31, 2020		5,822,396
Equity
Proceeds from the exercise of stock options (in shares)							188,006
Net loss							$ (69,062)
Balance at the end at Sep. 30, 2021		$ 10	533,009		(457,158)		75,861
Balance at the end (in shares) at Sep. 30, 2021		103,003,384
Balance at the beginning at Mar. 31, 2021	$ 420,989
Balance at the beginning (in shares) at Mar. 31, 2021	69,613,562
Balance at the end at Jun. 30, 2021	$ 420,989
Balance at the end (in shares) at Jun. 30, 2021	69,613,562
Balance at the beginning at Mar. 31, 2021		$ 1	42,872		(408,397)		(365,524)
Balance at the beginning (in shares) at Mar. 31, 2021		5,938,545
Equity
Proceeds from the exercise of stock options			30				30
Proceeds from the exercise of stock options (in shares)		5,204
Net loss					(17,198)		(17,198)
Stock-based compensation			2,930				2,930
Balance at the end at Jun. 30, 2021		$ 1	45,832		(425,595)		$ (379,762)
Balance at the end (in shares) at Jun. 30, 2021		5,943,749
Redeemable convertible preferred Stock
Conversion of redeemable convertible preferred stock into common stock in connection with the Merger and related PIPE financing	$ (420,989)
Conversion of redeemable convertible preferred stock into common stock in connection with the Merger and related PIPE financing (in shares)	(69,613,562)
Balance at the end (in shares) at Sep. 30, 2021							0
Equity
Proceeds from the exercise of stock options			360				$ 360
Proceeds from the exercise of stock options (in shares)		99,624
Conversion of redeemable convertible preferred stock into common stock in connection with the Merger and related PIPE financing		$ 7	420,982				420,989
Conversion of redeemable convertible preferred stock into common stock in connection with the Merger and related PIPE financing (in shares)		69,613,562
The merger and related PIPE financing, net of transaction costs and acquired liabilities		$ 2	209,478				209,480
Public warrants assumed upon the merger, net of transaction costs			13,912				13,912
Issuance of common stock upon the Merger and related PIPE Financing, net of issuance costs (in shares)		27,346,449
Net loss					(31,563)		(31,563)
Stock-based compensation			1,877				1,877
Contingent consideration liability recognized upon closing of the reverse recapitalization			159,432				159,432
Balance at the end at Sep. 30, 2021		$ 10	$ 533,009		$ (457,158)		$ 75,861
Balance at the end (in shares) at Sep. 30, 2021		103,003,384

Condensed Consolidated Statem_8

Condensed Consolidated Statements of Cash Flows $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Cash flows from operating activities
Net loss	$ (69,062)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	4,650
Stock-based compensation expense	7,335
Change in fair value of contingent earnout liability	9,768
Change in fair value of common stock warrant liabilities	2
Amortization expense	1,545
Non-cash operating lease costs	31
Amortization of SVB debt discount	628
Accrued interest on PPP loan obligation	11
Gain on PPP loan forgiveness	(3,284)
Payment of liabilities acquired in Merger	(12,363)
Changes in operating assets and liabilities:
Accounts receivable	(127)
Prepaid expenses	(2,002)
Accounts payable	757
Accrued expenses	2,401
Operating lease obligation	(32)
Net cash used in operating activities	(59,742)
Cash flows from investing activities
Purchase of property and equipment	(175)
Net cash used in investing activities	(175)
Cash flows from financing activities
Proceeds from merger	242,400
Payment of transaction costs related to Merger	(941)
Proceeds from the exercise of stock options	596
Proceeds from SVB loan	19,659
Payment of finance lease principal	(1,277)
Net cash provided by financing activities	260,437
Net increase (decrease) in cash and cash equivalents	200,520
Cash and cash equivalents at the beginning of the period	39,929
Cash and cash equivalents at the end of the period	240,449
Supplemental disclosure
Cash paid for interest on SVB loan	642
Supplemental disclosure of noncash activities:
Issuance of warrants in conjunction with debt	2,360
Unpaid liabilities assumed in connection with Merger	2,228
Unpaid transaction costs in connection with Merger	3,004
Conversion of redeemable convertible preferred stock into common stock in connection with the reverse capitalization	420,989
Contingent Consideration Liability recognized upon the closing of the reverse recapitalization	$ 159,432

Organization and Description _3

Organization and Description of Business	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Organization and Description of Business
Organization and Description of Business	1. Organization and Description of Business Organization Humacyte, Inc.and subsidiary, or the Company, is pioneering the development and manufacture of off-the-shelf, universally implantable, bioengineered human tissues designed to improve the lives of patients and transform the practice of medicine. The Company is leveraging its technology platform to develop proprietary, bioengineered, acellular human tissues for use in the treatment of diseases and conditions across a range of anatomic locations in multiple therapeutic areas. On August 26, 2021 (the “ ” “ ” “ ” “ ” “ ” “ ” “ ” Refer to Note 3 — Liquidity and Going Concern Since its inception in 2004, the Company has generated no product revenue and has incurred net losses and negative cash flows from operations in each year. To date, the Company has financed its operations primarily through the sale of equity securities and convertible debt and, to a lesser extent, through governmental and other grants. At December 31, 2020 and September 30, 2021, the Company had an accumulated deficit of $388.1 million and $457.2 million, respectively. The Company ’ ’ ’ ’ As of September 30, 2021, the Company had cash and cash equivalents of $240.4 million. Based on the cash and cash equivalents on hand, the Company believes its combined cash and cash equivalents will be sufficient to fund operations, including clinical trial expenses and capital expenditure requirements, for at least 12 months from the issuance date of these interim financial statements. Impact of COVID-19 The COVID-19 pandemic, which began in December ’ ’ ’ ’ ’ To date, the COVID-19 pandemic has not resulted in material financial impacts or impairment losses in the carrying values of the Company ’ ’	1. Organization and Description of Business Organization Humacyte, Inc., or the Company, is pioneering the development and manufacture of off-the-shelf, universally implantable, bioengineered human tissues to improve the lives of patients and transform the practice of medicine. The Company is leveraging its technology platform to develop proprietary, bioengineered, acellular human tissues for use in the treatment of diseases and conditions across a range of anatomic locations in multiple therapeutic areas. Liquidity and Going Concern Since its inception in 2004, the Company has generated no product revenue and has incurred net losses and negative cash flows from operations in each year. To date, the Company has financed its operations primarily through the sale of equity securities and convertible debt and, to a lesser extent, through governmental and other grants. At December 31, 2019 and December 31, 2020, the Company had an accumulated deficit of $321.6 million and $388.1 million, respectively. The Company ’ ’ ’ ’ The Company does not believe its existing cash and cash equivalents will be sufficient to fund its anticipated operating expenses, including clinical trial expenses, and capital expenditure requirements for at least twelve months following the date these financial statements were issued. Until such time, if ever, as the Company is able to successfully develop and commercialize one or more of its product candidates, it expects to fund its operations through the sale of equity, debt, borrowing under credit facilities or through potential collaborations with other companies, other strategic transactions or government contracts and grants. The Company ’ ’ substantial doubt about its ability to continue as a going concern within one year The accompanying financial statements do not include any adjustments that might result from the outcome of this uncertainty. Accordingly, the financial statements have been prepared on a basis that assumes the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the ordinary course of business. Impact of COVID-19 The COVID-19 pandemic, which began in December ’ ’ ’ ’ ’ 1. Organization and Description of Business (continued) To date, the COVID-19 pandemic has not resulted in material financial impacts or impairment losses in the carrying values of the Company ’ ’

Summary of Significant Accou_13

Summary of Significant Accounting Policies	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The Company has prepared the accompanying financial statements in conformity with accounting principles generally accepted in the United ’ Unless otherwise noted, the Company has retroactively adjusted all common and preferred share and related price information to give effect to the Exchange Ratio established in the Merger Agreement. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Significant estimates in the financial statements include stock-based compensation costs, right-of-use, or ROU, assets, accruals for research and development activities, contingent earnout liability, fair value of common stock warrants, redeemable convertible preferred stock and income taxes. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates. Unaudited Interim Condensed Consolidated Financial Statements The accompanying interim condensed consolidated financial statements and the related footnote disclosures are unaudited. These unaudited interim financial statements have been prepared on the same basis as the audited financial statements, and in management ’ ’ Certain information and footnote disclosures normally included in consolidated financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements for the year ended December 31, 2020 and the related notes included elsewhere in this prospectus, which provides a more complete discussion of the Company’s accounting policies and certain other information. Other than the policies noted below, there have been no significant changes to the significant accounting policies disclosed in Note 2 of the audited consolidated financial statements as of and for the years ended December 31, 2019 and 2020 included elsewhere in this prospectus. Common Stock Warrants The Company assumed 5,000,000 publicly-traded warrants ( “ ” “ ” ’ “ ” “ ” ’ “ ” The Company evaluated the Common Stock Warrants to determine the appropriate financial statement classification upon the consummation of the Merger. The Common Stock Warrants are not mandatorily redeemable and are considered to be freestanding instruments as they are separately exercisable into common shares. As such, the Common Stock Warrants were not classified as liabilities under FASB ASC Topic 480, Distinguishing Liabilities from Equity Derivatives and Hedging The agreement governing the Common Stock Warrants includes a provision ( “ ” ’ “ ’ ” ’ The Public Warrants are considered to be “indexed to the Company’s own stock”. The agreement provides that in the event of a tender or exchange offer made to and accepted by holders of more than 50% of the outstanding shares of the Company ’ ’ ’ Contingent Earnout Liability In connection with the Reverse Recapitalization and pursuant to the Business Combination Agreement dated as of February 17, 2021 by and among Legacy Humacyte, Merger Sub, and AHAC (the “ ” ’ “ ” The estimated fair value of the Contingent Earnout Shares was determined using a Monte Carlo simulation using a distribution of potential outcomes on a monthly basis over a ten-year period prioritizing the most reliable information available. The assumptions utilized in the calculation were based on the achievement of certain stock price milestones, including the current Company common stock price, expected volatility, risk-free rate, expected term and expected dividend yield. The Contingent Earnout Shares are categorized as a Level Segments The Company operates and manages its business as one reportable and operating segment. The Company is developing proprietary, bioengineered, acellular human tissues that are designed to be used in the treatment of diseases and conditions across a range of anatomic locations in multiple therapeutic areas. The Company ’ Revenue Recognition The Company ’ Under ASC 606, revenue is recognized when a customer obtains control of promised goods or services and is recognized in an amount that reflects the consideration that an entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) In addition, ASC 606 requires disclosure of the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. For contracts where the period between when the Company transfers a promised good or service to the customer and when the customer pays is one year or less, the Company has elected the practical expedient to not adjust the promised amount of consideration for the effects of a significant financing component. Grant Revenue The Company generates revenue primarily from government and other awarded grants that reimburse the Company for certain allowable costs related to research and development efforts. These grants include the following terms: The Department of Defense grants are for an award of $4.0 million, all of which was recognized as revenue before the program ended, for work on bioengineered blood vessels for vascular trauma, which was awarded to the Company in September 2017 and ended in February 2020, and an award of $7.1 million for work to support human tissue engineered blood vessels for vascular reconstruction in the injured warfighter, which was awarded to the Company in August 2017 and is ongoing. The Company has recognized revenue of $0.6 million and $1.0 million during the three and nine months ended September 30, 2020,respectively, and $0.2 million and $1.1 million during the three and nine months ended September 30, 2021, respectively, for reimbursement of certain allowable costs related to these grants. The National Institutes of Health grant is for $1.6 million for work to support bioengineered grafts for peripheral vascular disease, which was awarded to the Company in November 2013. The Company recognized $1.6 million for the reimbursement of certain allowable costs related to the grant before this program ended in 2020. The Company recognized $0.3 million during the three and nine months ended September 30, 2020, and no revenue during the three and nine months ended September 30, 2021, for reimbursement of certain allowable costs related to these grants. The Company has determined that the grants are not within the scope of ASC 606 as they do not meet the definition of a contract with a customer. The Company has concluded that the grants meet the definition of a contribution and are nonexchange transactions and has applied the contribution accounting model in Subtopic 958-605, Not-for-Profit-Entities-Revenue Recognition by analogy. The Company recognizes funding received from grants as revenue, rather than as a reduction of research and development expenses, because the Company is the principal in conducting the research and development activities and these grants are central to the Company ’ ’ Revenue from grants not within the scope of ASC 606 was $0.9 million and $1.4 million for the three and nine months ended September 30, 2020, respectively, and $0.2 million and $1.1 million for the three and nine months ended September 30, 2021, respectively. Concentration of Credit Risk Financial instruments which potentially subject the Company to concentrations of credit risk consist principally of cash and cash equivalents. Total cash balances exceeded insured balances by the Federal Deposit Insurance Corporation as of December 31, 2020 and September 30, 2021. Cash equivalents are invested in highly rated money market funds invested only in obligations of the U.S. government and its agencies. The majority of the Company ’ ’ ’ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue Accounts Receivable ​ ​ Three Months ​ Nine Months ​ December 31, ​ September 30, ​ ​ 2020 2021 2020 2021 2020 2021 Grant A ​ — ​ — ​ — ​ — ​ — ​ — ​ Grant B 0 ​ — % 11 ​ — % — ​ — Grant C 68 % 100 % 65 % 100 % 100 % 100 % Grant D 30 — % 20 ​ — % — — Total 98 % 100 % 96 % 100 % 100 % 100 % ​ All of the Company ’ Other Risks and Uncertainties The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, successful discovery and development of its product candidates, the success of clinical trials and other studies for its product candidates, including for its ongoing V005 Phase II/III clinical trial and V007 Phase III clinical trial, the regulatory approval and commercialization of its HAVs and other product candidates, ’ ’ ’ Product candidates currently under development will require extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel, and infrastructure and extensive compliance-reporting capabilities. Even if the Company ’ ’ Net Loss per Share Attributable to Common Stockholders The Company follows the two-class method to compute basic and diluted net loss per share attributable to common stockholders when shares met the definition of participating securities. The two-class method determines net loss per common share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to share in the earnings as if all income for the period had been distributed. During periods of loss, there is no allocation required under the two-class method since the redeemable convertible preferred stock did not have a contractual obligation to share in the Company ’ Basic net loss per share attributable to common stockholders is computed by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period without consideration of potentially dilutive common stock. Diluted net loss per share attributable to common stockholders reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock or resulted in the issuance of common stock that then shared in the earnings of the Company unless inclusion of such shares would be anti-dilutive. As the Company has only incurred losses, basic and diluted net loss per share is the same. The potential shares of common stock that were excluded from the computation of diluted net loss per share for each period because including them would have had an antidilutive effect were as follows: ​ ​ ​ ​ ​ ​ ​ September 30, ​ 2020 2021 ​ ​ ​ ​ ​ Shares issuable upon conversion of Series A redeemable convertible preferred stock 18,421,897 — Shares issuable upon conversion of Series B redeemable convertible preferred stock 24,137,647 — Shares issuable upon conversion of Series C redeemable convertible preferred stock 11,241,283 — Shares issuable upon conversion of Series D redeemable convertible preferred stock 15,812,735 — Exercise of options under stock plan 4,516,907 6,399,888 Warrants to purchase common stock 32,961 5,465,204 ​ The 15,000,000 Contingent Earnout shares are excluded from the anti-dilutive table for all the periods presented as such shares are contingently issuable until the share price of the Company exceeds specified thresholds that have not yet been achieved, or upon the occurrence of a change in control. Impairment of Long-Lived Assets The Company reviews the carrying value of property and equipment for indicators of possible impairment whenever events and circumstances indicate that the carrying value of an asset or asset group may not be recoverable from the estimated future net undiscounted cash flows expected to result from its use and eventual disposition. In cases where estimated future net undiscounted cash flows are less than the carrying value, an impairment loss is recognized equal to an amount by which the carrying value exceeds the fair value of the asset or asset group. The factors considered by management in performing this assessment include current operating results, trends and prospects, the manner in which the property is used, and the effects of obsolescence, demand, competition, and other economic factors. Based on this assessment, during the nine months ended September 30, 2020 and 2021, respectively, the Company concluded there were no such events or changes in circumstances requiring review of the carrying amount of the Company ’ Recently Adopted Accounting Pronouncements In August 2020, the FASB issued ASU No. 2020-06, “ ’ ’ ” “ ” ’ Recently Issued Accounting Pronouncements In May 2021, the FASB issued “ ’ ” “ ” ’	2. Summary of Significant Accounting Policies Basis of Presentation The Company has prepared the accompanying financial statements in conformity with accounting principles generally accepted in the United Reverse Recapitalization On August 26, 2021 (the “ ” “ ” “ ” “ ” “ ” “ ” “ ” “ ” Unless otherwise noted, the Company has retroactively adjusted all common and preferred share and related price information to give effect to the Exchange Ratio of approximately 0.26260 established in the Merger Agreement. Segments The Company operates and manages its business as one reportable and operating ’ Comprehensive loss Comprehensive loss includes net loss as well as other changes in stockholders ’ Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Significant estimates in the financial statements include stock-based compensation costs, right-of-use, or ROU assets, accruals for research and development activities, fair value of common stock, useful lives of property and equipment, redeemable convertible preferred stock and income taxes. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates. ​ 2. Summary of Significant Accounting Policies (continued) Cash and Cash Equivalents The Company considers all short-term, highly liquid investments purchased with an original maturity of three months or less at the date of purchase to be cash equivalents. Cash deposits are held with financial institutions with investment-grade ratings in the United Redeemable Convertible Preferred Stock The Company analyzes all issued equity instruments to determine the appropriate accounting and classification. The Company evaluates its equity instruments under Accounting Standards Codification, or ASC 480, Distinguishing liabilities from equity The Company records equity instruments that are classified as temporary equity at fair value upon issuance, net of issuance costs. The Company accretes the carrying value of its redeemable convertible preferred stock to the redemption or liquidation amount once the Company has determined that it is probable that it will become redeemable or be liquidated. The accretion will be recorded as charges against additional paid-in capital until the additional paid-in capital balance is reduced to zero. At that time, additional accretion adjustments will be recorded as additions to accumulated deficit. The Company also analyzes instances where the equity instrument has a conversion feature pursuant to ASC 815, Derivatives and hedging Revenue Recognition The Company ’ In 2014, the Financial Accounting Standards Board, or FASB issued Accounting Standards Update No. Under ASC 606, revenue is recognized when a customer obtains control of promised goods or services and is recognized in an amount that reflects the consideration that an entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) In addition, ASC 606 requires disclosure of the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. ​ 2. Summary of Significant Accounting Policies (continued) For contracts where the period between when the Company transfers a promised good or service to the customer and when the customer pays is one year or less, the Company has elected the practical expedient to not adjust the promised amount of consideration for the effects of a significant financing component. Grant Revenue We generate revenue primarily from government and other awarded grants that reimburse us for certain allowable costs related to research and development efforts. The Company has determined that the grants are not within the scope of ASC 606 as they do not meet the definition of a contract with a customer. The Company has concluded that the grants meet the definition of a contribution and are nonexchange transactions and has applied the contribution accounting model in Subtopic 958-605, Not-for-Profit-Entities-Revenue Recognition by analogy. The Company recognizes funding received from grants as revenue, rather than as a reduction of research and development expenses, because the Company is the principal in conducting the research and development activities and these grants are central to the Company ’ Revenue from grants not within the scope of ASC 606 was $6.2 million and $1.5 million for the years ending December 31, 2019 and 2020, respectively. Concentration of Credit Risk Financial instruments which potentially subject the Company to concentrations of credit risk consist principally of cash and cash equivalents. Total cash balances exceeded insured balances by the Federal Depository Insurance Corporation as of December 31, 2019 and 2020. Cash equivalents are invested in highly rated money market funds invested only in obligations of the US government and its agencies. The majority of the Company ’ ’ ’ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2020 ​ ​ ​ ​ ​ Accounts ​ ​ ​ Accounts ​ ​ Revenue Receivable Revenue Receivable ​ Grant A ​ 28 % — ​ — ​ — ​ Grant B 38 % 67 % 10 % — Grant C 34 % 33 % 67 % 100 % Grant D — — 18 % — Total 100 % 100 % 95 % 100 % ​ All of the Company ’ ​ 2. Summary of Significant Accounting Policies (continued) Other Risks and Uncertainties The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, successful discovery and development of its product candidates, the success of clinical trials and other studies for its product candidates, including for its ongoing V005 Phase II/III clinical trial and V007 Phase III clinical trial, the regulatory approval and commercialization of its HAVs and other product candidates, ’ ’ ’ Product candidates currently under development will require extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel, and infrastructure and extensive compliance-reporting capabilities. Even if the Company ’ ’ Net Loss per Share Attributable to Common Stockholders The Company applies the two-class method to compute basic and diluted net loss per share attributable to common stockholders when shares meet the definition of participating securities. The two-class method determines net loss per share for each class of common and redeemable convertible preferred stock according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income (loss) available to common stockholders for the period to be allocated between common and redeemable convertible preferred stock based upon their respective rights to share in the earnings as if all income (loss) for the period had been distributed. During periods of loss, there is no allocation required under the two-class method since the redeemable convertible preferred stock does not have a contractual obligation to share in the Company ’ ​ 2. Summary of Significant Accounting Policies (continued) Basic net loss per share attributable to common stockholders is computed by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period without consideration of potentially dilutive common stock. Diluted net loss per share attributable to common stockholders reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock or resulted in the issuance of common stock that then shared in the earnings of the Company unless inclusion of such shares would be anti-dilutive. Since the Company has only incurred losses, basic and diluted net loss per share is the same. Securities that could potentially dilute net loss per share in the future that were not included in the computation of diluted net loss per share are as follows: ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2020 ​ ​ ​ ​ ​ Shares issuable upon conversion of Series A redeemable convertible preferred stock 18,421,897 18,421,897 Shares issuable upon conversion of Series B redeemable convertible preferred stock 24,137,647 24,137,647 Shares issuable upon conversion of Series C redeemable convertible preferred stock 11,241,283 11,241,283 Shares issuable upon conversion of Series D redeemable convertible preferred stock 15,812,735 15,812,735 Options to purchase common stock 5,220,236 4,813,262 Warrant to purchase common stock 32,961 32,961 ​ Fair Value of Financial Instruments Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in the principal or most advantageous market in an orderly transaction between market participants at the measurement date. ASC 820, Fair Value Measurement and Disclosures ● Level 1 — Observable inputs that reflect unadjusted quoted prices for identical assets or liabilities in active markets. ● Level 2 — Inputs other than quoted prices included in Level 1 that are observable for the asset or liability, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. ● Level 3 — Unobservable inputs in which little or no market data exists, therefore requiring the Company to develop its own assumptions. The Company evaluates assets and liabilities subject to fair value measurements on a recurring basis to determine the appropriate level at which to classify them for each reporting period, utilizing valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible. The determination requires significant judgments to be made by the Company. The Company ’ ​ 2. Summary of Significant Accounting Policies (continued) Property and Equipment, Net Property and equipment, net are recorded at cost less accumulated depreciation. Expenditures for major additions and improvements are capitalized and minor replacements, maintenance, and repairs are charged to expense as incurred. When property and equipment are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the balance sheet accounts and any resulting gain or loss is included in the results of operations for the respective period. Depreciation is calculated using the straight-line method over the estimated useful lives of the related assets. The estimated useful lives for significant asset categories are as follows: ​ ​ ​ ​ ​ Estimated Useful Property and equipment ​ Lives (Years) Scientific equipment ​ 5 – 7 Computer equipment 5 Software 3 Furniture and fixtures 5 – 7 Leasehold improvements Lesser of useful life or life of lease Construction in progress N/A ​ Impairment of Long-Lived Assets The Company reviews the carrying value of property and equipment for indicators of possible impairment whenever events and circumstances indicate that the carrying value of an asset or asset group may not be recoverable from the estimated future net undiscounted cash flows expected to result from its use and eventual disposition. In cases where estimated future net undiscounted cash flows are less than the carrying value, an impairment loss is recognized equal to an amount by which the carrying value exceeds the fair value of the asset or asset group. The factors considered by management in performing this assessment include current operating results, trends and prospects, the manner in which the property is used, and the effects of obsolescence, demand, competition, and other economic factors. Based on this assessment, there was no impairment at December 31, 2019 and 2020. Income Taxes Income taxes are computed using the asset and liability approach that requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the Company ’ ​ 2. Summary of Significant Accounting Policies (continued) The Company recognizes the benefit of an income tax position only if it is more likely than not (greater than 50%) that the tax position will be sustained upon tax examination, based solely on the technical merits of the tax position. Otherwise, no benefit can be recognized. Assessing an uncertain tax position begins with the initial determination of the sustainability of the position and is measured at the largest amount of benefit that is greater than 50% likely of being realized upon ultimate settlement. As of each balance sheet date, unresolved uncertain tax positions must be reassessed. Additionally, the Company must accrue interest and related penalties, if applicable, on all tax exposures for which reserves have been established consistent with jurisdictional tax laws. The Company has analyzed its filing positions in all significant Federal and state jurisdictions where it is required to file income tax returns, as well as open tax years in these jurisdictions. As of December 31, 2019 and 2020, the Company has determined that no uncertain tax positions would have a material impact on the financials statements of the Company. The Company is no longer subject to Federal, state, and local tax examinations by tax authorities for years before 2017 although carry-forward attributes that were generated prior to 2017 may still be adjusted upon examination by the taxing authorities if they either have been or will be used in a future period. No income tax returns are currently under examination by taxing authorities. As of December 31, 2019 and 2020, the Company had not recorded any amounts for unrecognized tax benefits. The Company ’ ’ Intellectual Property The Company seeks to protect its intellectual property by filing patent applications in the United ’ Research and Development The Company expenses research and development costs as operating expenses as incurred. Research and development expenses consist primarily of: ● salaries and related overhead expenses for personnel in research and development functions, including stock-based compensation and benefits; ● fees paid to consultants and CROs, including in connection with clinical trials, and other related clinical trial fees, such as for investigator grants, patient screening, laboratory work and statistical compilation and analysis; ● allocation of facility lease and maintenance costs; ● depreciation of leasehold improvements, laboratory equipment and computers; ● costs related to purchasing raw materials for and producing product candidates for clinical trials; ● costs related to compliance with regulatory requirements; ● costs related to the manufacturing scale-out initiative; and ● license fees related to in-licensed technologies. 2. Summary of Significant Accounting Policies (continued) Accrued Research and Development The Company has entered into various agreements with CROs and a CMO, which conduct preclinical studies and clinical trials and contract manufacturing activities. The Company ’ Stock-Based Compensation The Company accounts for stock-based compensation for employees and non-employees measured at grant date, based on the fair value of the award. The Company measures the fair value of awards granted using the Black-Scholes option pricing model and recognizes the expense over the requisite service period using the straight-line method. Option valuation models, including the Black-Scholes option-pricing model, require the input of highly subjective assumptions, and changes in the assumptions used can materially affect the grant-date fair value of an award. These assumptions include the risk-free rate of interest, expected dividend yield, expected volatility, the expected term of the award, and the fair value of the underlying common stock on the date of grant. Forfeitures are accounted for as they occur. Leases Effective January 1, 2019, the Company accounts for its leases under ASC 842, Leases ’ “ ” “ ” “ ” ’ “ ” “ ” “ ” Under this guidance, arrangements meeting the definition of a lease are classified as operating or finance leases, and are recorded on the balance sheet as both a right-of-use asset and lease liability, calculated by discounting fixed lease payments over the lease term at the rate implicit in the lease or the Company ’ ​ 2. Summary of Significant Accounting Policies (continued) Lease expenses for minimum lease payments for operating leases are recognized on a straight-line basis over the lease term. Amortization expense of the right-of-use asset for finance leases is recognized on a straight-line basis over the lease term and interest expense for finance leases is recognized based on the incremental borrowing rate. Lease liabilities are increased by interest and reduced by payments each period, and the right of use asset is amortized over the lease term. In calculating the right-of-use assets and lease liabilities, the Company has elected to combine lease and non-lease components for all asset classes. The Company excludes short-term leases, if any, having initial terms of 12 months or less from the new guidance as an accounting policy election, and recognizes rent expense on a straight-line basis over the lease term. Prior to the adoption of ASC 842 on January 1, 2019 the Company was deemed to be the accounting owner of leased space during the construction of its headquarters in a build-to-suit arrangement. Upon substantial completion of construction in June ’ ’ each The cumulative effect of initially applying the new lease guidance on January 1, 2019 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ January 1, 2019 ​ ​ ​ ​ ​ Cumulative ​ Beginning ​ ​ Beginning ​ Effect ​ Balance, ($ in thousands) Balance Adjustment As Adjusted Assets ​ ​ ​ ​ ​ ​ Building asset ​ $ 25,091 ​ $ (25,091) ​ $ — Finance lease right-of-use assets, net ​ $ — ​ $ 27,612 ​ $ 27,612 Operating lease right-of-use assets, net ​ $ — ​ $ 923 ​ $ 923 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Liabilities and stockholders’ deficit ​ ​ ​ Accrued expenses ​ $ 7,049 ​ $ (1) ​ $ 7,048 Facility financing obligation, current portion ​ $ 276 ​ $ (276) ​ $ — Finance lease obligation, current portion ​ $ — ​ $ 1,292 ​ $ 1,292 Operating lease obligation, current portion ​ $ — ​ $ 55 ​ $ 55 Facility financing obligation, net of current portion ​ $ 22,955 ​ $ (22,955) ​ $ — Finance lease obligation, net of current portion ​ $ — ​ $ 26,319 ​ $ 26,319 Operating lease obligation, net of current portion ​ $ — ​ $ 870 ​ $ 870 Accumulated deficit ​ $ (234,289) ​ $ (1,861) ​ $ (236,150) ​ ​ 2. Summary of Significant Accounting Policies (continued) Recently Adopted Accounting Pronouncements In August — Recently Issued Accounting Pronouncements In August 2020, the FASB issued ASU No. 2020-06, “  –  ’  –  ’ “ ”

Reverse Recapitalization

Reverse Recapitalization	9 Months Ended
	Sep. 30, 2021
Reverse Recapitalization
Reverse Recapitalization	3. Reverse Recapitalization On August 26, 2021, Merger Sub, a wholly-owned subsidiary of AHAC, merged with Legacy Humacyte, with Legacy Humacyte surviving as a wholly-owned subsidiary of AHAC. At the effective time of the Merger: ● each outstanding share of Legacy Humacyte common stock was converted into approximately 0.26260 shares of the Company’s common stock; ​ ● each outstanding share of preferred stock of Legacy Humacyte was cancelled and converted into the aggregate number of shares of New Humacyte’s common stock that would be issued upon conversion of the shares of Legacy Humacyte preferred stock based on the applicable conversion ratio immediately prior to the effective time, multiplied by approximately 0.26260 ; and ​ ● each outstanding option or warrant to purchase Legacy Humacyte common stock was converted into an option or warrant, as applicable, to purchase a number of shares of the Company’s common stock equal to the number of shares of Legacy Humacyte common stock subject to such option or warrant multiplied by approximately 0.26260 , at an exercise price per share equal to the current exercise price per share for such option or warrant divided by approximately 0.26260 ; ​ in each case, rounded down to the nearest whole share. In addition, upon the closing of the merger (the “Closing”), 2,500,000 Class B shares of AHAC (Founder Shares) automatically converted into shares of the Company’s common stock, on a one-for-one Former holders of the Legacy Humacyte common stock and Legacy Humacyte preferred stock are eligible to receive up to an aggregate of 15 million additional shares of the Company’s common stock (the “Contingent Earnout Shares”) in the aggregate in two equal tranches of 7.5 million shares if the volume-weighted average closing sale price of the common stock is greater than or equal to $15.00 and $20.00, respectively, for any 20 trading days within any 30 consecutive trading day period. At the Closing on August 26, 2021, the Company recorded a liability (“Contingent Earnout Liability”) of $159.4 million, based on the estimated fair value of the 15 million Contingent Earnout Shares with a corresponding reduction of additional paid-in capital in the equity section of the Company’s condensed consolidated balance sheet. Concurrently with the execution of the Business Combination Agreement, AHAC entered into subscription agreements (the “Subscription Agreements”) with certain investors (the “PIPE Investors”). Pursuant to the Subscription Agreements, the PIPE Investors purchased an aggregate of 17,500,000 shares of the Company’s common stock (the “PIPE Shares”) in a private placement at a price of $10.00 per share for an aggregate purchase price of $175 million (the “PIPE Financing”). The PIPE Financing was consummated in connection with the Closing. The number of shares of the Company’s common stock outstanding immediately following the consummation of the Merger was: ​ ​ ​ ​ ​ ​ Shares Common stock of AHAC, outstanding prior to Merger 10,355,000 ​ Less redemption of AHAC shares (3,008,551) ​ Common stock of AHAC 7,346,449 ​ AHAC Founder Shares 2,500,000 ​ New Humacyte shares issued to PIPE Investors 17,500,000 ​ Issuance of common stock upon reverse recapitalization and PIPE Financing 27,346,449 ​ New Humacyte shares issued in Merger to Legacy Humacyte stockholders 75,656,935 (1) Total shares of common stock immediately after Merger 103,003,384 ​ (1) Includes 69,613,562 shares of common stock issued upon conversion of Legacy Humacyte ’ The Merger is accounted for as a reverse recapitalization in accordance with U.S. GAAP. Under this method of accounting, AHAC is treated as the acquired company for financial reporting purposes and Legacy Humacyte is treated as the acquiror. This determination is primarily based on the fact that subsequent to the Merger, the Legacy Humacyte stockholders hold a majority of the voting rights of the combined company, Legacy Humacyte comprises all of the ongoing operations of the combined company, Legacy Humacyte comprises a majority of the carryover governing body of the combined company, and Legacy Humacyte’s senior management comprises all of the senior management of the combined company. Accordingly, for accounting purposes, the Merger was treated as the equivalent of Legacy Humacyte issuing shares for the net assets of AHAC, accompanied by a recapitalization. The net assets of AHAC were stated at historical costs. No goodwill or other intangible assets were recorded. Operations prior to the Merger are those of Legacy Humacyte. In connection with the Merger, the Company received $242.4 million in proceeds from the Merger and related PIPE Financing. The Company incurred $3.9 million of transaction costs, consisting of banking, legal, and other professional fees, of which $3.9 million was recorded as a reduction of proceeds to additional paid-in capital, and less than $0.1 million related to the Private Placement Warrants, which are classified as liabilities in the condensed consolidated balance sheets, was expensed in the condensed consolidated statements of operations and comprehensive loss. Legacy Humacyte assumed $15.2 million of liabilities, including PIPE Financing fees and legal fees, and $0.1 million of assets from AHAC. Of the $15.2 million of liabilities assumed from AHAC, as of September 30, 2021, $2.2 million was included in accounts payable and accrued expenses. In addition, there were $3.0 million of unpaid transaction costs included in accounts payable and accrued expenses as of September 30, 2021.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
Fair Value Measurements
Fair Value Measurements	4. Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in the principal or most advantageous market in an orderly transaction between market participants at the measurement date. ASC 820, Fair Value Measurement and Disclosures ● Level 1 — Observable inputs that reflect unadjusted quoted prices for identical assets or liabilities in active markets. ● Level 2 — Inputs other than quoted prices included in Level 1 that are observable for the asset or liability, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. ● Level 3 — Unobservable inputs in which little or no market data exists, therefore requiring the Company to develop its own assumptions. The Company evaluates assets and liabilities subject to fair value measurements on a recurring basis to determine the appropriate level at which to classify them for each reporting period, utilizing valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible. The determination requires significant judgments to be made by the Company. The Company’s assets and liabilities that were measured at fair value on a recurring basis were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measured as of December 31, 2020 ($in thousands) Level 1 Level 2 Level 3 Total Assets: ​ ​ ​ ​ Money market funds ​ $ 35,623 ​ $ — ​ $ — ​ $ 35,623 Total financial assets ​ $ 35,623 ​ $ — ​ $ — ​ $ 35,623 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measured as of September 30, 2021 ($in thousands) Level 1 Level 2 Level 3 Total Assets: ​ ​ ​ ​ ​ ​ Money market funds ​ $ 238,375 ​ $ — ​ $ — ​ $ 238,375 Total financial assets ​ $ 238,375 ​ $ — ​ $ — ​ $ 238,375 Liabilities: ​ ​ ​ ​ Contingent earnout liability ​ $ — ​ $ — ​ $ 169,200 ​ $ 169,200 Common stock warrant liabilities (Private Placement Warrants) ​ — ​ — ​ 555 ​ 555 Total financial liabilities ​ $ — ​ $ — ​ $ 169,755 ​ $ 169,755 ​ The following table presents a summary of the changes in the fair value of the Company’s Level 3 financial instruments: ​ ​ ​ ​ ​ ​ ​ ​ ​ Contingent Private Placement ($in thousands) ​ Earnout Liability ​ Warrants ​ ​ ​ ​ ​ ​ ​ Fair value as of December 31, 2020 ​ $ — ​ $ — Private placement warrant liability acquired as part of the merger ​ — ​ (553) Contingent earount liability recognized upon the closing of the reverse recapitalization ​ (159,432) ​ — Change in fair value included in other (expense) income ​ (9,768) ​ (2) Fair value as of September 30, 2021 ​ $ (169,200) ​ $ (555) ​ The fair value of the Contingent Earnout Liability and Private Placement Warrants liability are based on significant unobservable inputs, which represent Level 3 measurements within the fair value hierarchy. In determining the fair value of the Contingent Earnout Liability, the Company used the Monte Carlo simulation value model using a distribution of potential outcomes on a monthly basis over a ten-year period prioritizing the most reliable information available. The assumptions utilized in the calculation were based on the achievement of certain stock price milestones, including the current Company common stock price, expected volatility, risk-free rate, expected term and expected dividend yield (see Note 8). In determining the fair value of the Private Placement Warrants liability, the Company used the Monte Carlo simulation valuation model to estimate the fair value utilizing assumption including the current Company stock price, expected volatility, risk-free rate, expected term and expected dividend yield (see Note 8). The Company’s cash equivalents are classified within Level 1 of the fair value hierarchy because they are valued using quoted market prices. The carrying values of other receivables, accounts payable and accrued expenses as of December 31, 2020 and September 30, 2021 approximated their fair values due to the short-term nature of these items.

Property and Equipment, Net_2

Property and Equipment, Net	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Property and Equipment, Net
Property and Equipment, Net	5. Property and Equipment, Net Property and equipment, net consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ September 30, ($ in thousands) 2020 2021 ​ ​ ​ ​ ​ ​ Scientific equipment ​ $ 27,412 ​ $ 27,578 Computer equipment ​ 149 ​ 154 Software ​ 335 ​ 335 Furniture and fixtures ​ 988 ​ 988 Leasehold improvements ​ 26,355 ​ 26,355 ​ ​ 55,239 ​ 55,410 Accumulated depreciation ​ (14,261) ​ (18,911) Property and equipment, net ​ $ 40,978 ​ $ 36,499 ​ Depreciation expense totaled $1.6 million and $4.7 million for the three and nine months ended September 30, 2020, respectively, and $1.5 million and $4.7 million for the three and nine months ended September 30, 2021, respectively. All long-lived assets are maintained in the United	3. Property and Equipment, Net Property and equipment, net consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ($ in thousands) 2019 2020 ​ ​ ​ ​ ​ ​ Scientific equipment ​ $ 27,822 ​ $ 27,412 Computer equipment ​ 218 ​ 149 Software ​ 340 ​ 335 Furniture and fixtures ​ 988 ​ 988 Leasehold improvements ​ 26,337 ​ 26,355 ​ ​ 55,705 ​ 55,239 Accumulated depreciation ​ (8,417) ​ (14,261) Property and equipment, net ​ $ 47,288 ​ $ 40,978 ​ Depreciation expense totaled $4.7 million and $6.3 million for the years ended December 31, 2019 and 2020, respectively. All long-lived assets are maintained in the United

Accrued Expenses_2

Accrued Expenses	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Accrued Expenses
Accrued Expenses	6. Accrued Expenses Accrued expenses consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ September 30, ($ in thousands) 2020 2021 ​ ​ ​ ​ ​ ​ Accrued external research, development and manufacturing costs ​ $ 2,615 ​ $ 2,685 Accrued employee compensation and benefits ​ 1,009 ​ 4,025 Accrued professional fees ​ 968 ​ 2,712 Total ​ $ 4,592 ​ $ 9,422 ​	4. Accrued Expenses Accrued expenses consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ($ in thousands) 2019 2020 Accrued external research, development and manufacturing costs ​ $ 3,872 ​ $ 2,615 Accrued employee compensation and benefits ​ 1,260 ​ 1,009 Accrued professional fees ​ 868 ​ 968 Total ​ $ 6,000 ​ $ 4,592 ​

Debt_2

Debt	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Debt
Debt	7. Debt On April 30, 2020, the Company received loan proceeds in the amount of approximately $3.3 million under the Paycheck Protection Program ( “ ” In March 2021, the Company entered into a term loan agreement with Silicon Valley Bank and SVB Innovation Credit Fund VIII, L.P., which provides a term loan facility of up to $50.0 million with a maturity date of March 1, 2025, or the Loan Agreement. The Company ’ The Loan Agreement provides that the term loans will be distributed in tranches. The initial term loan tranche of $20.0 million was drawn in March 2021 and is accounted for net of issuance costs which are being accreted to interest expense over the term of the loan using the effective interest method. As of September 30, 2021, three subsequent $10.0 million term loan tranches were eligible to be disbursed at the request of the Company during specified draw periods between now and 2023 if certain business development milestones and other specified requirements are met by the dates specified in the Loan Agreement. Borrowings bear interest at the greater of 7.5% or the Wall Street Journal Prime Rate plus 4.25% (7.5% as of September 30, 2021). Interest only payments on the principal amount outstanding are due monthly beginning in the first month after the loan is dispersed. Repayment of principal may begin as soon as April 1, 2022 under the level of borrowing outstanding at September 30, 2021, and no later than April 1, 2024. The term loans may only be prepaid in full, and such prepayment requires 30 days ’ On October 13, 2021, the Company borrowed an additional $10.0 million under the Loan Agreement. As a result of the additional borrowing, the commencement of repayment of principal was deferred to no earlier than July 2023. In connection with the Loan Agreement, the Company granted warrants to the lenders to purchase shares of common stock at an exercise price of $10.28 per share, of which 287,704 warrants were immediately exercisable. The warrants are classified within stockholders ’ ’ ’ At issuance, the Company initially determined that the funding of an additional tranche was not probable, and therefore no value was ascribed to the remaining 123,302 warrants that were only exercisable upon the funding of the additional tranche. As a result of the Company ’ ’ SVB loan payable and net discount or premium balances are as follows: ​ ​ ​ ​ ​ ​ September 30, ($ in thousands) 2021 Principal amount of SVB loan payable ​ $ 20,000 Final payment amount of SVB loan payable ​ 1,000 Net premium associated with accretion of final payment and other debt issuance costs ​ (3,073) SVB loan payable, current and noncurrent ​ 17,927 Less SVB loan payable, current portion ​ (3,889) SVB loan payable, noncurrent portion ​ $ 14,038 ​ Future minimum payments of principal on the Company ’ ​ ​ ​ ​ ​ Year ending December 31: ($ in thousands) 2021 (remainder) ​ $ — 2022 ​ 5,555 2023 ​ 6,667 2024 ​ 6,667 2025 ​ 1,111 Total future payments ​ 20,000 ​	5. Debt On April 30, 2020, the Company received loan proceeds in the amount of approximately $3.3 million under the Paycheck Protection Program ( “ ” “ ” In September 2020, the Company applied for forgiveness of the outstanding amount under its PPP loan. The Company used the proceeds for purposes it believes were consistent with the requirements of the PPP. The Company determined that loan forgiveness would become probable upon approval by the Small Business Administration of the Company ’ ​

Stockholders, Equity (Deficit_2

Stockholders, Equity (Deficit)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Stockholders' Equity (Deficit)
Stockholders' Equity (Deficit)	8. Stockholders ’ Equity (Deficit) Redeemable Convertible Preferred Stock As of December 31, 2020 and immediately prior to the Merger, Legacy Humacyte had outstanding series A redeemable convertible preferred stock, series B redeemable convertible preferred stock, series C redeemable convertible preferred stock and series D redeemable convertible preferred stock, which are collectively referred to as “ ” In connection with the Merger, all previously issued and outstanding redeemable convertible preferred stock was converted into an equivalent number of shares of common stock of the Company on a one-to-one basis, then multiplied by the Exchange Ratio pursuant to the Merger Agreement. Common Stock On August 26, 2021, the Merger and related PIPE Financing was consummated and the Company issued 27,346,449 shares of common stock for proceeds of $242.4 million. The Company incurred $3.9 million of transaction costs, consisting of banking, legal, and other professional fees. Legacy Humacyte assumed $15.2 million of liabilities, including PIPE Financing fees and legal fees, and $0.1 million of assets from AHAC. Immediately following the Merger, there were 103,003,384 shares of common stock outstanding with a par value of $0.0001. As of September 30, 2021, the Company ’ The holders of common stock are entitled to receive dividends from time to time as may be declared by the Company ’ The holders of common stock are entitled to one vote for each share held with respect to all matters voted on by the common stockholders of the Company. In the event of a reorganization of the Company, after payment to the preferred stockholders of their liquidation preferences, holders of common stock are entitled to share ratably in all remaining assets of the Company. As of September 30, 2021, the Company had reserved common stock for future issuances as follows: ​ ​ ​ ​ ​ September 30, ​ 2021 Common stock reserved for Contingent Consideration Shares 15,000,000 Exercise of options under stock plans 6,399,888 Issuance of options under stock plans 7,730,503 Shares available for grant under ESPP 1,030,033 Warrants to purchase common stock 5,465,204 ​ ​ 35,625,628 ​ On August 26, 2021, upon the Closing, all of the outstanding redeemable convertible preferred stock was converted to Common Stock pursuant to the conversion rate effective immediately prior to the Merger and the Exchange Ratio and the remaining amount was reclassified to additional paid-in capital. Preferred Stock The Company ’ ’ Warrants Activity of warrants for the nine months ended September 30, 2021 is set forth below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Legacy ​ ​ ​ ​ ​ ​ ​ ​ Humacyte ​ ​ ​ ​ ​ ​ ​ ​ Common Stock ​ Private Placement ​ ​ ​ Total Common ​ Warrants Warrants Public Warrants Stock Warrants ​ ​ ​ ​ ​ ​ ​ ​ ​ Outstanding as of December 31, 2020 ​ 32,961 ​ — ​ — ​ 32,961 Common Stock Warrants issued to SVB ​ 287,704 ​ — ​ — ​ 287,704 Common Stock Warrants as Part of the Merger — 177,500 5,000,000 5,177,500 Warrants Exercised (32,961) — — (32,961) Oustanding as of September 30, 2021 287,704 177,500 5,000,000 5,465,204 ​ In conjunction with a long-term debt agreement entered into on March 15, 2006 and paid in full during 2011, the Company issued a warrant that gave the holder the right to purchase 32,961 shares of the Company ’ See Note 7 — ’ Private Placement Warrants The Private Placement Warrants were initially recognized as a liability on the Closing Date, at a fair value of $0.6 million, and the Private Placement Warrant liability was remeasured to fair value as of September 30, 2021, resulting in a loss of less than $0.1 million for the three and nine months ended September 30, 2021, classified within change in fair value of common stock warrant liabilities in the condensed consolidated statements of operations and comprehensive loss. The Private Placement Warrants were valued using the following assumptions under the Monte Carlo simulation value model: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ August 26, September 30, ​ ​ 2021 ​ 2021 Market price of public stock ​ $ 10.96 ​ $ 11.61 ​ Exercise price ​ $ 11.50 ​ $ 11.50 ​ Expected term (years) ​ 5.00 ​ 4.91 ​ Expected share price volatility ​ 32.5 % 28.5 % Risk-free interest rate ​ 0.68 % 0.96 % Estimated dividend yield ​ 0 % 0 % ​ Public Warrants The Public Warrants may only be exercised for a whole number of shares and will expire five years after the completion of the Merger. The Public Warrants became exercisable 30 days after the completion of the Merger. The Public Warrants were initially recognized as equity on the Closing Date at a fair value of $2.80 per share. There were no exercises of the Public Warrants during the three months ended September 30, 2021. Contingent Earnout Liability Following the Closing, former holders of Legacy Humacyte common and preferred shares may receive up to 15,000,000 additional shares of the Company ’ “ ” stock quoted on the Nasdaq (or the exchange on which the shares of common stock are then listed) is greater or equal to $15.00 and $20.00, respectively, over any twenty trading days within any thirty-day trading period. Upon the Closing, the contingent obligation to issue Contingent Earnout Shares was accounted for as a liability because the triggering events that determine the number of Contingent Earnout Shares required to be issued include events that are not solely indexed to the common stock of Humacyte. The estimated fair value of the total Contingent Earnout Shares at the Closing on August 26, 2021, was $159.4 million based on a Monte Carlo simulation valuation model using a distribution of potential outcomes on a monthly basis over a ten-year period using the most reliable information available. The Contingent Earnout Liability was remeasured to fair value as of September 30, 2021, resulting in the recording of a non-cash loss of $9.8 million for the three and nine months ended September 30, 2021, classified within change in fair value of contingent earnout liability in the condensed consolidated statements of operations and comprehensive loss. Assumptions used in the valuations are described below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ August 26, September 30, ​ ​ 2021 ​ 2021 Current stock price ​ $ 10.96 ​ $ 11.61 ​ Expected share price volatility ​ 79.6 % 78.9 % Risk-free interest rate ​ 1.34 % 1.55 % Estimated dividend yield ​ 0 % 0.0 % Expected term (years) ​ 10.00 ​ 10.00 ​ ​	8. Stockholders ’ Deficit Common Stock As of December 31, 2019 and 2020, the Company ’ ’ The holders of common stock are entitled to receive dividends from time to time as may be declared by the Board of Directors. No cash dividend may be declared or paid to common stockholders until paid on each series of outstanding redeemable convertible preferred stock in accordance with its terms. Through December 31, 2020, no The holders of common stock are entitled to one vote for each share held with respect to all matters voted on by the common stockholders of the Company. Preferred stockholders generally vote together with the holders of common stock as a single class ’ In the event of a Reorganization of the Company, after payment to the preferred stockholders of their liquidation preferences, holders of common stock are entitled, together with holders of redeemable convertible preferred stock, to share ratably in all remaining assets of the Company. 8. Stockholders ’ Deficit (continued) At December 31, 2019 and 2020, the Company had reserved common stock for future issuances as follows: ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2020 ​ ​ ​ ​ ​ Conversion of Series A redeemable convertible preferred stock 18,421,897 18,421,897 Conversion of Series B redeemable convertible preferred stock 24,137,647 24,137,647 Conversion of Series C redeemable convertible preferred stock 11,241,286 11,241,286 Conversion of Series D redeemable convertible preferred stock 15,812,735 15,812,735 Exercise of options under stock plan 5,220,236 4,813,262 Issuance of options under stock plan 2,736,954 2,948,598 Warrant to purchase common stock 32,961 ​ 32,961 ​ ​ 77,603,716 77,408,386 ​ Warrant In conjunction with a long-term debt agreement entered into on March 15, 2006 and paid in full during 2011, the Company issued a warrant that gave the holder the right to purchase 32,961 shares of the Company ’

Stock-based Compensation_2

Stock-based Compensation	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Stock-based Compensation
Stock-based Compensation	9. Stock-based Compensation At Closing, the 2021 Long-Term Incentive Plan, or the 2021 Plan, and the 2021 Employee Stock Purchase Plan, or the ESPP, became effective. As of September 30, 2021, 7,730,503 and 1,030,033 shares of common stock were available under the 2021 Plan and ESPP, respectively. On January 1 of each year commencing January 1, 2022, the 2021 Plan and the ESPP reserve will automatically increase in an amount equal to the lesser of (a) 5% and 1%, respectively, of the number of shares of the Company ’ ’ Under the 2021 Plan, the Company can grant non-statutory stock options, or NSOs, incentive stock options, or ISOs, stock appreciation rights, restricted stock, restricted stock units, unrestricted stock, performance awards and other forms of awards. Under the ESPP, eligible employees are permitted to purchase shares of the Company ’ ’ Prior to the Closing, Legacy Humacyte had two equity incentive plans, the 2015 Omnibus Incentive Plan, as amended, or the 2015 Plan, and the 2005 Stock Option Plan, or the 2005 Plan. As a result of the Merger, no further awards may be granted under either the 2015 plan or the 2005 Plan. All awards previously granted and outstanding as of the effective date of the Merger, which total The Company ’ ’ ’ The Company has granted options that include either a service-based or performance-based vesting conditions, or both, and a 10-year contractual term. The service-based vesting condition for the plans is generally satisfied over 36 Company recognizes stock-based compensation expense based on the grant date fair value of the awards measured using the Black-Scholes option pricing model. Compensation expense related to awards with service-based vesting conditions is recognized on a straight-line basis over the requisite service period. Option valuation models, including the Black-Scholes option-pricing model, require the input of highly subjective assumptions, and changes in the assumptions used can materially affect the grant-date fair value of an award. These assumptions include the risk-free rate of interest, expected dividend yield, expected volatility, the expected term of the award, and the fair value of the underlying common stock on the date of grant. Forfeitures are accounted for as they occur. Compensation expense related to awards with performance-based vesting conditions is recognized over the requisite service period using the accelerated attribution method to the extent achievement of the performance-based condition is probable. The Company does not recognize compensation expense related to awards with performance-based vesting conditions until it is probable that the performance-based vesting condition will be achieved. Forfeitures are accounted for as they occur. Option awards under the Company ’ ’ ’ Under the terms of her employment agreement, the Company awarded the Company ’ ’ three The Company estimated the fair value of the stock options on the date of grant using the following assumptions in the Black-Scholes option-pricing model: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended September 30, ​ 2020 2021 (1) 2020 2021 Estimated dividend yield ​ 0 % — ​ 0 % 0 % Expected share price volatility (weighted average and range, if applicable) ​ 91.6 % — ​ 91.4% (89.4% to 91.6%) ​ 91.4% (91.0% to 92.1%) ​ Risk-free interest rate (weighted average and range, if applicable) ​ 0.34 % — ​ 0.40% (0.34% to 0.75%) ​ 0.68% (0.62% to 1.02%) ​ Expected term of options (in years) ​ 6.0 ​ — ​ 6.0 ​ 6.0 ​ (1) The Company did not grant any stock options during the three months ended September 30, 2021. ​ ● Fair Value of Common Stock. As the Company ’ s common stock was not publicly traded prior to the Merger, the fair value of the shares of its common stock underlying the options has historically been determined by the Company ’ s board of directors with input from management, after considering independent third-party valuation reports. ● Expected Term. The expected term represents the period that stock options are expected to be outstanding. The Company calculated the expected term using the simplified method for options, which is available where there is insufficient historical data about exercise patterns and post-vesting employment termination behavior. The simplified method is based on the vesting period and the contractual term for each grant, or for each vesting-tranche for awards with graded vesting. The mid-point between the vesting date and the maximum contractual expiration date is used as the expected term under this method. For awards with multiple vesting-tranches, the times from grant until the mid-points for each of the tranches may be averaged to provide an overall expected term. ● Expected Volatility. The expected volatility was based on the historical share volatility of several publicly traded peer companies over a period of time equal to the expected term of the options, as the Company does not have any trading history to use the volatility of its common stock. For purposes of identifying these peer companies, the Company considered the industry, stage of development, size and financial leverage of potential comparable companies. ● Risk-Free Interest Rate. The risk-free interest rate was based on the yields of U.S. Treasury zero-coupon securities with maturities similar in duration to the expected term of the options. ● Expected Dividend Yield. The Company has not paid dividends on its common stock nor does it expect to pay dividends in the foreseeable future. Accordingly, the Company has estimated the dividend yield to be zero. At September 30, 2021, there were 7,730,503 options remaining available for grant under the 2021 Plan. The Company has sufficient authorized and unissued shares to make all issuances currently available under the 2021 Plan. The following tables show a summary of stock-based compensation expense included in the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2021, and the three and nine months ended September 30, 2020, and remaining unrecognized cost as of September 30, 2021 and 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ($ in thousands) ​ 2020 ​ 2021 ​ 2020 ​ 2021 Research and development ​ $ 308 ​ $ 486 ​ $ 781 ​ $ 1,837 General and administrative ​ ​ 862 ​ ​ 1,391 ​ ​ 2,685 ​ ​ 5,498 Total ​ $ 1,170 ​ $ 1,877 ​ $ 3,466 ​ $ 7,335 ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ September 30, ($ in thousands) ​ 2020 ​ 2021 Unrecognized share-based compensation cost ​ $ 5,789 ​ $ 12,480 Expected weighted average period compensation costs to be recognized (years) ​ 1.7 ​ 2.1 ​ A summary of option activity under the Company ’ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ ​ ​ Weighted ​ Remaining ​ Aggregate ​ ​ ​ ​ Average Exercise ​ Contractual Term ​ Intrinsic Value ​ ​ Number of Shares ​ Price Per Share ​ (years) ​ (in thousands) Options outstanding at December 31, 2020 4,813,262 ​ $ 6.04 6.6 ​ $ 20,422 Granted 1,838,029 ​ $ 10.28 ​ Exercised (188,006) ​ $ 2.97 ​ Forfeited (63,397) ​ $ 7.87 ​ Options outstanding at September 30, 2021 6,399,888 ​ $ 7.33 6.6 ​ $ 26,705 Vested and exercisable, September 30, 2021 4,092,342 ​ $ 5.74 5.1 ​ $ 23,345 Vested and expected to vest, September 30, 2021 6,399,888 ​ $ 7.33 6.6 ​ $ 26,705 ​ The Company did not grant any stock options during the three months ended September 30, 2021.	9. Stock-based Compensation The Company has adopted the 2015 Omnibus Incentive Plan, as amended, or the 2015 Plan, which allows for the grant of nonstatutory stock options, or NSOs, and incentive stock options, or ISOs, stock appreciation rights, restricted stock, restricted stock units and unrestricted stock awards to employees, officers, directors, and consultants in the service of the Company. The Company believes that such awards aid in aligning the interests of these persons with those of its stockholders. The Board of Directors determines the specific terms of equity incentive grants, including the exercise price per share and vesting period for option awards. Option awards are granted with an exercise price equal to the fair market value of the Company ’ The Company has granted options that include either a service-based or performance-based vesting condition and a 10-year contractual term. The service-based vesting condition is generally satisfied over 36 months from the date of grant. The performance-based vesting conditions are satisfied upon the attainment of certain product development milestones. The Company recognizes stock-based compensation expense based on the grant date fair value of the awards. Compensation expense related to awards with service-based vesting conditions is recognized on a straight-line basis over the requisite service period. Compensation expense related to awards with performance-based vesting conditions is recognized over the requisite service period using the accelerated attribution method to the extent achievement of the performance-based condition is probable. The Company does not recognize compensation expense related to awards with performance-based vesting conditions until it is probable that the performance-based vesting condition will be achieved. Forfeitures are accounted for as they occur. Option awards under the 2015 Plan generally provide for accelerated vesting of the unvested portions of any option award in the event of an involuntary termination, as such term is defined in the relevant stock option agreement, of a grantee ’ ’ ​ 9. Stock-based Compensation (continued) The Company used the following assumptions on the date of grant to estimate the fair value of the stock options in the Black-Scholes option-pricing model as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ 2019 2020 ​ Estimated dividend yield ​ 0 % 0 % Expected share price volatility ​ 70.1%-87.7 % 89.4% - 91.6 % Risk-free interest rate ​ 1.76% - 2.46 % 0.34% - 0.75 % Expected term of options (in years) ​ 6.00 ​ 6.00 ​ ​ ● Fair Value of Common Stock. As the Company ’ s common stock has not historically been publicly traded, the fair value of the shares of its common stock underlying the options has historically been determined by the Company ’ s board of directors with input from management, after considering independent third-party valuation reports. ● Expected Term. The expected term represents the period that stock options are expected to be outstanding. The Company calculated the expected term using the simplified method for options, which is available where there is insufficient historical data about exercise patterns and post-vesting employment termination behavior. The simplified method is based on the vesting period and the contractual term for each grant, or for each vesting-tranche for awards with graded vesting. The mid-point between the vesting date and the maximum contractual expiration date is used as the expected term under this method. For awards with multiple vesting-tranches, the times from grant until the mid-points for each of the tranches may be averaged to provide an overall expected term. ● Expected Volatility. The expected volatility was based on the historical share volatility of several publicly traded peer companies over a period of time equal to the expected term of the options, as the Company does not have any trading history to use the volatility of its common stock. For purposes of identifying these peer companies, the Company considered the industry, stage of development, size and financial leverage of potential comparable companies. ● Risk-Free Interest Rate. The risk-free interest rate was based on the yields of US Treasury zero-coupon securities with maturities similar in duration to the expected term of the options. ● Expected Dividend Yield. The Company has not paid dividends on its common stock nor does it expect to pay dividends in the foreseeable future. Accordingly, the Company has estimated the dividend yield to be zero. At December 31, 2020, there were 2,948,598 options remaining available for grant under the 2015 Plan. The Company has sufficient authorized and unissued shares to make all issuances currently contemplated under the 2015 Plan. ​ 9. Stock-based Compensation (continued) The following tables show a summary of stock-based compensation expense included in the statements of operations and comprehensive loss for the years ended December 31, 2019 and 2020, and remaining unrecognized cost as of December 31, 2019 and 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ($ in thousands) ​ 2019 ​ 2020 Research and development ​ $ 914 ​ $ 1,135 General and administrative ​ 3,543 ​ 3,559 Total ​ $ 4,457 ​ $ 4,694 ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ($ in thousands) ​ 2019 ​ 2020 Unrecognized share-based compensation cost ​ $ 7,919 ​ $ 5,789 Expected weighted average period compensation costs to be recognized (years) ​ 1.8 ​ 1.7 ​ A summary of option activity under the 2015 Plan during the years ended December 31, 2019 and 2020 is presented below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ ​ ​ Weighted ​ Remaining ​ Aggregate ​ ​ Number of ​ Average Exercise ​ Contractual Term ​ Intrinsic Value ​ ​ Shares ​ Price Per Share ​ (years) ​ (in thousands) Options outstanding at December 31, 2018 5,638,773 ​ $ 4.69 7.4 ​ $ 21,354 Granted 621,031 ​ ​ 8.49 ​ Exercised (620,831) ​ ​ 1.97 ​ Forfeited (418,737) ​ ​ 7.62 ​ Options outstanding at December 31, 2019 5,220,236 ​ $ 5.22 6.5 ​ $ 17,044 Granted 480,856 ​ ​ 9.79 ​ Exercised (195,239) ​ ​ 1.55 ​ Forfeited (692,591) ​ ​ 3.76 ​ Options outstanding at December 31, 2020 4,813,262 ​ $ 6.04 6.6 ​ $ 20,422 Vested and exercisable, December 31, 2020 3,392,302 ​ $ 4.99 5.9 ​ $ 17,925 Vested and expected to vest, December 31, 2020 4,813,262 ​ $ 6.04 6.6 ​ $ 20,422 ​ The total intrinsic value of options exercised during the years ended December 31, 2019 and 2020 was $4.0 million and $1.4 million, respectively. The weighted-average grant-date fair value per share of options granted during the years ended December 31, 2019 and 2020 was $5.84 and $7.26, respectively. ​

Income Taxes_2

Income Taxes	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Income Taxes
Income Taxes	10. Income Taxes The Company ’ ’ The Company did not record any income tax expense or benefit during the three and nine months ended September 30, 2020 and 2021. The Company has a net operating loss and has provided a valuation allowance against net deferred tax assets due to uncertainties regarding the Company ’ On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security ( “ ” ’	10. Income Taxes The Company did not record any income tax expense or benefit during the years ended December 31, 2019 and 2020. The Company has a net operating loss and has provided a valuation allowance against net deferred tax assets due to uncertainties regarding the Company ’ Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company ’ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ($ in thousands) 2019 2020 Deferred tax assets: ​ ​ ​ ​ ​ ​ Net operating loss ​ $ 50,616 ​ $ 53,515 Capitalized research and development ​ 19,660 ​ ​ 32,337 Research credits ​ 10,658 ​ 15,056 Share-based compensation ​ 1,669 ​ 2,519 Right of use lease liability ​ 207 ​ 177 Accrued expenses ​ 71 ​ 57 Other ​ 1 ​ 1 Total deferred tax asset ​ 82,882 ​ 103,662 Less: valuation allowance ​ (82,193) ​ (101,757) Total net deferred tax asset ​ 689 ​ 1,905 ​ ​ ​ ​ ​ ​ ​ Deferred tax liabilities: ​ ​ Basis difference in fixed assets ​ (482) ​ (1,728) Right of use lease assets ​ (207) ​ (177) Total deferred tax liability ​ (689) ​ (1,905) Total net deferred tax asset/(liability) ​ $ — ​ $ — ​ A valuation allowance is provided for deferred tax assets where the recoverability of the assets is uncertain. The determination to provide a valuation allowance is dependent upon the assessment of whether it is more likely than not that sufficient future taxable income will be generated to utilize the deferred tax assets. Based on the weight of the available evidence, which includes the Company ’ ​ 10. Income Taxes (continued) The reasons for the difference between the actual income tax benefit for the years ended December 31, 2019 and 2020, and the amount computed by applying the statutory Federal income tax rate to losses before income taxes are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2020 ($ in thousands) ​ Amount Rate Amount Rate Income tax benefit at statutory rate ​ $ (17,939) 21.0 % $ (13,970) 21.0 % State income taxes, net of federal benefit ​ (1,739) 2.0 % (1,338) 2.0 % Tax credits ​ (1,821) 2.1 % (2,625) 3.9 % Other nondeductible expenses ​ 54 0.0 % 90 (0.1) % Deferred rate changes ​ 16 0.0 % 16 0.0 % Other ​ 449 (0.5) % (1,736) 2.6 % Change in valuation allowance ​ 20,980 (24.6) % 19,563 (29.4) % Provision for income taxes ​ $ — 0.0 % $ — 0.0 % ​ As of December 31, 2020 the Company had approximately $232.7 million and $232.6 million of Federal and state net operating losses, respectively. Of this amount, $71.5 million of Federal net operating losses are carried over indefinitely, while the remaining amount begins to expire in 2025. The Company ’ As of December 31, 2019 and December 31, 2020 the Company had Federal and state research tax credit carryforwards of $10.7 million and $15.1 million, respectively. These credit carryforwards begin to expire in 2021. Net operating loss carryforwards and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service, or IRS, and may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant stockholders or groups over a three-year period in excess of 50% as defined under Sections The Company applies the accounting guidance for uncertainties in income taxes, which prescribes a recognition threshold and measurement process for recording uncertain tax positions taken, or expected to be taken, in a tax return in the financial statements. Additionally, the guidance also prescribes the treatment for derecognition, classification, accounting in interim periods and disclosure requirements for uncertain tax positions. The Company accrues for the estimated amount of taxes for uncertain tax positions if it is more likely than not that the Company would be required to pay such additional taxes. On March 27, 2020, the CARES Act was passed by the U.S. Congress and signed into United ’

Commitments and Contingencies_3

Commitments and Contingencies	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Commitments and Contingencies
Commitments and Contingencies	11. Commitments and Contingencies Patent License Agreements Duke University In March In connection with the Company ’ ’ ● a low single-digit percentage royalty on eligible sales of licensed products and licensed services, plus a low double-digit percentage of any sublicensing revenue; ● an annual minimum royalty beginning in 2012, which increases in the calendar year immediately following the first commercial sale of licensed products or licensed services (whichever occurs first); and ● an additional amount in license fees, as certain milestones are met. The license agreement remains effective until the last of the patent rights expires or four years after the Company ’ ’ Yale University In February – ’ fee, increasing between the first and fourth anniversaries of the agreement up to a maximum of less than $0.1 million per year for this license. In August ’ In August ’ The Company has agreed to use reasonable commercial efforts to develop and commercialize the licensed patents and any licensed products and methods, and to use reasonable efforts to make the licensed products available to patients in low and low-middle income countries. The Company is also obligated to provide Yale periodically an updated and revised copy of its plan for each license, which must indicate progress of its development and commercialization. The Company may also sublicense the Company ’ ’ In connection with its entry into the license agreement, the Company paid Yale upfront cash fees. The Company has also agreed to pay Yale: ● annual maintenance fees, increasing between the first anniversary of the agreement until the fifth anniversary for the coating and BVP licenses and until the fourth anniversary for the tubular prostheses license up to a maximum of less than $0.1 million per year; ● milestone payments upon achievement of certain regulatory and commercial milestones of $0.2 million and $0.6 million; ● a low single-digit percentage royalty on worldwide net sales, subject to reductions for third-party license fees; and ● a low double-digit percentage of sublicensing income. If the Company or any of its future sublicensees bring a patent challenge against Yale or assists another party in bringing a patent challenge against Yale, the license fees described above will be subject to certain increases and penalties. The agreements expire on a country-by-country basis on the date on which the last of the patents in such country expires, lapses or is declared invalid. Yale may terminate the agreements if the Company fails to (i) ’ ’ ’ ’ respect to the licensed patents. The Company has agreed to indemnify Yale against certain third-party claims. Payments to Yale under the license agreement were immaterial during the periods presented. Legal Matters The Company currently is not aware of any legal proceedings or claims that management believes will have, individually or in the aggregate, a material adverse effect on the Company ’ Indemnification To the extent permitted under Delaware law, the Company has agreed to indemnify its directors and officers for certain events or occurrences while the director or officer is, or was serving, at the Company ’ ’ ’	12. Commitments and Contingencies Patent License Agreements Duke University In March In connection with the Company ’ ’ ● a low single-digit percentage royalty on eligible sales of licensed products and licensed services, plus a low double-digit percentage of any sublicensing revenue; ● an annual minimum royalty beginning in 2012, which increases in the calendar year immediately following the first commercial sale of licensed products or licensed services (whichever occurs first); and ● an additional amount in license fees, as certain milestones are met. The license agreement remains effective until the last of the patent rights expires or four years after our first commercial sale, unless earlier terminated. Either party may terminate the agreement for fraud, willful misconduct or illegal conduct, or uncured material breach. Duke may terminate the agreement if the Company becomes insolvent. Duke may also terminate the license, convert the license into a non-exclusive license or seek assignment of any sublicense if the Company fails to reach diligence milestones within the applicable time period. If the Company abandons any claim, patent or patent application, its rights under the license with respect to such patent rights will be terminated in the territory in which the Company abandons such rights. The Company may terminate the license agreement unilaterally upon three months ’ ​ 12. Commitments and Contingencies (continued) Yale University In February – ’ In August ’ In August ’ The Company has agreed to use reasonable commercial efforts to develop and commercialize the licensed patents and any licensed products and methods, and to use reasonable efforts to make the licensed products available to patients in low and low-middle income countries. The Company is also obligated to provide Yale periodically an updated and revised copy of its plan for each license, which must indicate progress of its development and commercialization. The Company may also sublicense the Company ’ ’ In connection with its entry into the license agreement, the Company paid Yale upfront cash fees. The Company has also agreed to pay Yale: ● annual maintenance fees, increasing between the first anniversary of the agreement until the fifth anniversary for the coating and BVP licenses and until the fourth anniversary for the tubular prostheses license; ● milestone payments upon achievement of certain regulatory and commercial milestones; ● a low single-digit percentage royalty on worldwide net sales, subject to reductions for third-party license fees; and ● a low double-digit percentage of sublicensing income. If the Company or any of its future sublicensees bring a patent challenge against Yale or assists another party in bringing a patent challenge against Yale, the license fees described above will be subject to certain increases and penalties. ​ 12. Commitments and Contingencies (continued) The agreements expire on a country-by-country basis on the date on which the last of the patents in such country expires, lapses or is declared invalid. Yale may terminate the agreements if the Company fails to (i) ’ ’ ’ ’ Legal Matters The Company currently is not aware of any legal proceedings or claims that management believes will have, individually or in the aggregate, a material adverse effect on the Company ’ Indemnification To the extent permitted under Delaware law, the Company has agreed to indemnify its directors and officers for certain events or occurrences while the director or officer is, or was serving, at the Company ’ ’ ’

Related Party Transactions_2

Related Party Transactions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Related Party Transactions
Related Party Transactions	12. Related Party Transactions Fresenius Medical Care investments and distribution agreement In June 2018, the Company completed a $150 million financing transaction pursuant to which Fresenius Medical Care purchased shares of series D redeemable convertible preferred stock that at the Closing of the Merger converted into 15,812,735 shares of the Company ’ ’ In addition, the Company entered into a distribution agreement with Fresenius Medical Care in June 2018 which, as amended as of February 16, 2021, granted Fresenius Medical Care and its affiliates exclusive rights to develop outside the United States and EU and commercialize outside of the United States the Company ’ The Company is responsible for developing and seeking regulatory approval for the distribution product in the field in the United States. For countries outside the United States, the parties agreed to use commercially reasonable efforts to satisfy certain agreed minimum market entry criteria for the distribution product in the field in such country. For the EU, once such criteria have been satisfied for the applicable country, or if the parties otherwise mutually agree to obtain regulatory approval for the distribution product in the field in the applicable country, the Company agreed to use commercially reasonable efforts to obtain such regulatory approval (other than pricing approval), and Fresenius Medical Care agreed to use commercially reasonable efforts to obtain the corresponding pricing approval. For the rest of the world (i.e., outside the United States and the EU), once such criteria have been satisfied for the applicable country, or if the parties otherwise mutually agree to obtain regulatory and pricing approval for the distribution product in the field in the applicable country, Fresenius Medical Care agreed to use commercially reasonable efforts to obtain such approvals, and the Company agreed to use commercially reasonable efforts to support Fresenius Medical Care in its efforts. Under the distribution agreement, the Company grants an exclusive, sublicensable license to Fresenius Medical Care under the patents, know-how and regulatory materials controlled by the Company during the term to commercialize the distribution product in the field outside the United States, subject to the Company ’ and regulatory materials controlled by the Company during the term to develop the distribution product in accordance with the terms of the distribution agreement. In addition, the Company grants to Fresenius Medical Care, among other things, a perpetual, irrevocable, non-exclusive sublicensable license under the patents and know-how that primarily relate to the distribution product or its manufacture and that were created, conceived or developed solely or jointly by or on behalf of Fresenius Medical Care in the performance of its activities under the distribution agreement. The distribution agreement provides that the Company will own all know-how and patents that primarily relate to the distribution product or its manufacture that are created, conceived or developed by or on behalf of either party in the performance of activities under the distribution agreement. Ownership of all other know-how, patents, materials and other intellectual property created, conceived or developed during the performance of activities under the distribution agreement will be determined in accordance with U.S. patent laws for determining inventorship. The Company is obligated to make payments to Fresenius Medical Care based on a share of aggregate net sales by or on behalf of the Company of the distribution product in the United States in the field. Such revenue-share payments will be a percentage of net sales in the low double digits, without regard to the calendar year in which such net sales are attributable, until such time that the Company has paid to Fresenius Medical Care a certain total amount, at which time the revenue-share will decrease to a percentage of net sales in the mid-single digits. The amounts that Fresenius Medical Care will be obligated to pay the Company under the distribution agreement for sales of the distribution product in the field outside of the United States will vary. Fresenius Medical Care agreed to pay the Company initially, on a country-by-country basis for sales outside of the United States, the amount equal to the average cost of manufacturing the Company ’ The distribution agreement will generally continue on a country-by-country basis until the later of (a) the tenth anniversary of the launch date of the distribution product in the relevant country or (b) the expiration of the last-to-expire valid claim of specified patents in such country. Each party is permitted to terminate the distribution agreement for insolvency of, or, under certain circumstances, including various cure periods, material breach by the other party. Subject to a cure period, Fresenius Medical Care may also terminate the distribution agreement in its entirety or on a country-by-country basis (i) for certain withdrawals of regulatory approval or (ii) for termination or expiration of any of our in-licenses that is necessary for the exercise of Fresenius Medical Care ’ ’ Arrangements with Dr. Niklason and Yale University In September The MOU provided for the Company to make a payment each year through 2023 to the academic institution with which Dr. ’ ’ The following table shows a summary of related party expenses included in the statements of operations and comprehensive loss for the three and nine months ended September 30, 2020 and 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months ​ Nine Months ($ in thousands) 2020 2021 2020 2021 Expenses under MOU 125 — 375 — License expenses 20 — 70 85 Other 4 2 17 83 Total 149 2 462 168 ​ As of December 31, 2020 and September 30, 2021, the Company was a party to license agreements with Yale University, as described in Note 11 —	13. Related Party Transactions Fresenius Medical Care distribution agreement In addition to Fresenius Medical Care ’ ’ The Company is responsible for developing and seeking regulatory approval for the distribution product in the field in the United States. For countries outside the United States, the parties agreed to use commercially reasonable efforts to satisfy certain agreed minimum market entry criteria for the distribution product in the field in such country. For the EU, once such criteria have been satisfied for the applicable country, or if the parties otherwise mutually agree to obtain regulatory approval for the distribution product in the field in the applicable country, the Company agreed to use commercially reasonable efforts to obtain such regulatory approval (other than pricing approval), and Fresenius Medical Care agreed to use commercially reasonable efforts to obtain the corresponding pricing approval. For the rest of the world (i.e., outside the United States and the EU), once such criteria have been satisfied for the applicable country, or if the parties otherwise mutually agree to obtain regulatory and pricing approval for the distribution product in the field in the applicable country, Fresenius Medical Care agreed to use commercially reasonable efforts to obtain such approvals, and the Company agreed to use commercially reasonable efforts to support Fresenius Medical Care in its efforts. Under the distribution agreement, the Company grants an exclusive, sublicensable license to Fresenius Medical Care under the patents, know-how and regulatory materials controlled by the Company during the term to commercialize the distribution product in the field outside the United States, subject to the Company ’ The distribution agreement provides that the Company will own all know-how and patents that primarily relate to the distribution product or its manufacture that are created, conceived or developed by or on behalf of either party in the performance of activities under the distribution agreement. Ownership of all other know-how, patents, materials and other intellectual property created, conceived or developed during the performance of activities under the distribution agreement will be determined in accordance with U.S. patent laws for determining inventorship. ​ 13. Related Party Transactions (continued) The Company is obligated to make payments to Fresenius Medical Care based on a share of aggregate net sales by or on behalf of the Company of the distribution product in the United States in the field. Such revenue-share payments will be a percentage of net sales in the low double digits, without regard to the calendar year in which such net sales are attributable, until such time that the Company has paid to Fresenius Medical Care a certain total amount, at which time the revenue-share will decrease to a percentage of net sales in the mid-single digits. The amounts that Fresenius Medical Care will be obligated to pay the Company under the distribution agreement for sales of the distribution product in the field outside of the United States will vary. Fresenius Medical Care agreed to pay the Company initially, on a country-by-country basis for sales outside of the United States, the amount equal to the average cost of manufacturing the Company ’ The distribution agreement will generally continue on a country-by-country basis until the later of (a) the tenth anniversary of the launch date of the distribution product in the relevant country or (b) the expiration of the last-to-expire valid claim of specified patents in such country. Each party is permitted to terminate the distribution agreement for insolvency of, or, under certain circumstances, including various cure periods, material breach by the other party. Subject to a cure period, Fresenius Medical Care may also terminate the distribution agreement in its entirety or on a country-by-country basis (i) for certain withdrawals of regulatory approval or (ii) for termination or expiration of any of our in-licenses that is necessary for the exercise of Fresenius Medical Care ’ ’ Arrangements with Dr. Niklason and Yale University In September The MOU provided for the Company to make a payment each year through 2023 to the academic institution with which Dr. ’ ’ The following table shows a summary of related party expenses included in the statements of operations and comprehensive loss for the years ended December 31, 2019 and 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ($ in thousands) 2019 2020 Expenses under MOU $ 422 $ 500 License expenses 110 92 Other 39 28 Total $ 571 $ 620 ​ As of December 31, 2019 and December 31, 2020, the Company was a party to license agreements with Yale University, as described in Note 12 —

Subsequent Events_2

Subsequent Events	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	13. Subsequent Events In preparing the condensed consolidated financial statements as of September 30, 2021 and for the three and nine months ended September 30, 2021, the Company evaluated the effect subsequent events would have on the financial statements through the date the financial statements were issued. On October 13, 2021, the Company borrowed an additional $10.0 million under the Loan Agreement, and the warrants to purchase an additional 123,302 shares of the Company ’ — — ’	14. Subsequent Events The Company evaluated the effect subsequent events would have on the financial statements through March 22, 2021, which is the date the financial statements were issued. Under the terms of her employment agreement, the Company awarded Dr. Niklason an additional stock option award in January 2021 entitling her to purchase 1,312,984 shares of the Company ’ none three Under the terms of his consulting agreement, the Company awarded Mr. Sander an additional stock option award in January 2021 entitling him to purchase 183,817 shares of the Company ’ three On February 17, 2021, the Company entered into a business combination agreement with AHAC and Merger Sub, a wholly owned subsidiary of AHAC, pursuant to which Merger Sub will merge with the Company, with the Company surviving the Merger as a wholly owned subsidiary of AHAC. As a result of the Merger, AHAC will immediately be renamed New Humacyte. Immediately prior to the consummation of the Merger, the Company ’ ’ ’ ’ ’ No

Summary of Significant Accou_14

Summary of Significant Accounting Policies (Policies)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation The Company has prepared the accompanying financial statements in conformity with accounting principles generally accepted in the United ’ Unless otherwise noted, the Company has retroactively adjusted all common and preferred share and related price information to give effect to the Exchange Ratio established in the Merger Agreement.	Basis of Presentation The Company has prepared the accompanying financial statements in conformity with accounting principles generally accepted in the United Reverse Recapitalization
Unaudited Interim Condensed Consolidated Financial Statements	Unaudited Interim Condensed Consolidated Financial Statements The accompanying interim condensed consolidated financial statements and the related footnote disclosures are unaudited. These unaudited interim financial statements have been prepared on the same basis as the audited financial statements, and in management ’ ’ Certain information and footnote disclosures normally included in consolidated financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements for the year ended December 31, 2020 and the related notes included elsewhere in this prospectus, which provides a more complete discussion of the Company’s accounting policies and certain other information. Other than the policies noted below, there have been no significant changes to the significant accounting policies disclosed in Note 2 of the audited consolidated financial statements as of and for the years ended December 31, 2019 and 2020 included elsewhere in this prospectus.	On August 26, 2021 (the “ ” “ ” “ ” “ ” “ ” “ ” “ ” “ ” Unless otherwise noted, the Company has retroactively adjusted all common and preferred share and related price information to give effect to the Exchange Ratio of approximately 0.26260 established in the Merger Agreement.
Common Stock Warrants	Common Stock Warrants The Company assumed 5,000,000 publicly-traded warrants ( “ ” “ ” ’ “ ” “ ” ’ “ ” The Company evaluated the Common Stock Warrants to determine the appropriate financial statement classification upon the consummation of the Merger. The Common Stock Warrants are not mandatorily redeemable and are considered to be freestanding instruments as they are separately exercisable into common shares. As such, the Common Stock Warrants were not classified as liabilities under FASB ASC Topic 480, Distinguishing Liabilities from Equity Derivatives and Hedging The agreement governing the Common Stock Warrants includes a provision ( “ ” ’ “ ’ ” ’ The Public Warrants are considered to be “indexed to the Company’s own stock”. The agreement provides that in the event of a tender or exchange offer made to and accepted by holders of more than 50% of the outstanding shares of the Company ’ ’ ’
Contingent Earnout Liability	Contingent Earnout Liability In connection with the Reverse Recapitalization and pursuant to the Business Combination Agreement dated as of February 17, 2021 by and among Legacy Humacyte, Merger Sub, and AHAC (the “ ” ’ “ ” The estimated fair value of the Contingent Earnout Shares was determined using a Monte Carlo simulation using a distribution of potential outcomes on a monthly basis over a ten-year period prioritizing the most reliable information available. The assumptions utilized in the calculation were based on the achievement of certain stock price milestones, including the current Company common stock price, expected volatility, risk-free rate, expected term and expected dividend yield. The Contingent Earnout Shares are categorized as a Level
Segments	Segments The Company operates and manages its business as one reportable and operating segment. The Company is developing proprietary, bioengineered, acellular human tissues that are designed to be used in the treatment of diseases and conditions across a range of anatomic locations in multiple therapeutic areas. The Company ’	Segments The Company operates and manages its business as one reportable and operating ’
Comprehensive loss		Comprehensive loss Comprehensive loss includes net loss as well as other changes in stockholders ’
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Significant estimates in the financial statements include stock-based compensation costs, right-of-use, or ROU, assets, accruals for research and development activities, contingent earnout liability, fair value of common stock warrants, redeemable convertible preferred stock and income taxes. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates.	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Significant estimates in the financial statements include stock-based compensation costs, right-of-use, or ROU assets, accruals for research and development activities, fair value of common stock, useful lives of property and equipment, redeemable convertible preferred stock and income taxes. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates. ​ 2. Summary of Significant Accounting Policies (continued)
Cash and Cash Equivalents		Cash and Cash Equivalents The Company considers all short-term, highly liquid investments purchased with an original maturity of three months or less at the date of purchase to be cash equivalents. Cash deposits are held with financial institutions with investment-grade ratings in the United
Redeemable Convertible Preferred Stock		Redeemable Convertible Preferred Stock The Company analyzes all issued equity instruments to determine the appropriate accounting and classification. The Company evaluates its equity instruments under Accounting Standards Codification, or ASC 480, Distinguishing liabilities from equity The Company records equity instruments that are classified as temporary equity at fair value upon issuance, net of issuance costs. The Company accretes the carrying value of its redeemable convertible preferred stock to the redemption or liquidation amount once the Company has determined that it is probable that it will become redeemable or be liquidated. The accretion will be recorded as charges against additional paid-in capital until the additional paid-in capital balance is reduced to zero. At that time, additional accretion adjustments will be recorded as additions to accumulated deficit. The Company also analyzes instances where the equity instrument has a conversion feature pursuant to ASC 815, Derivatives and hedging
Revenue Recognition	Revenue Recognition The Company ’ Under ASC 606, revenue is recognized when a customer obtains control of promised goods or services and is recognized in an amount that reflects the consideration that an entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) In addition, ASC 606 requires disclosure of the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. For contracts where the period between when the Company transfers a promised good or service to the customer and when the customer pays is one year or less, the Company has elected the practical expedient to not adjust the promised amount of consideration for the effects of a significant financing component.	Revenue Recognition The Company ’ In 2014, the Financial Accounting Standards Board, or FASB issued Accounting Standards Update No. Under ASC 606, revenue is recognized when a customer obtains control of promised goods or services and is recognized in an amount that reflects the consideration that an entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) In addition, ASC 606 requires disclosure of the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. ​ 2. Summary of Significant Accounting Policies (continued) For contracts where the period between when the Company transfers a promised good or service to the customer and when the customer pays is one year or less, the Company has elected the practical expedient to not adjust the promised amount of consideration for the effects of a significant financing component.
Grant Revenue	Grant Revenue The Company generates revenue primarily from government and other awarded grants that reimburse the Company for certain allowable costs related to research and development efforts. These grants include the following terms: The Department of Defense grants are for an award of $4.0 million, all of which was recognized as revenue before the program ended, for work on bioengineered blood vessels for vascular trauma, which was awarded to the Company in September 2017 and ended in February 2020, and an award of $7.1 million for work to support human tissue engineered blood vessels for vascular reconstruction in the injured warfighter, which was awarded to the Company in August 2017 and is ongoing. The Company has recognized revenue of $0.6 million and $1.0 million during the three and nine months ended September 30, 2020,respectively, and $0.2 million and $1.1 million during the three and nine months ended September 30, 2021, respectively, for reimbursement of certain allowable costs related to these grants. The National Institutes of Health grant is for $1.6 million for work to support bioengineered grafts for peripheral vascular disease, which was awarded to the Company in November 2013. The Company recognized $1.6 million for the reimbursement of certain allowable costs related to the grant before this program ended in 2020. The Company recognized $0.3 million during the three and nine months ended September 30, 2020, and no revenue during the three and nine months ended September 30, 2021, for reimbursement of certain allowable costs related to these grants. The Company has determined that the grants are not within the scope of ASC 606 as they do not meet the definition of a contract with a customer. The Company has concluded that the grants meet the definition of a contribution and are nonexchange transactions and has applied the contribution accounting model in Subtopic 958-605, Not-for-Profit-Entities-Revenue Recognition by analogy. The Company recognizes funding received from grants as revenue, rather than as a reduction of research and development expenses, because the Company is the principal in conducting the research and development activities and these grants are central to the Company ’ ’ Revenue from grants not within the scope of ASC 606 was $0.9 million and $1.4 million for the three and nine months ended September 30, 2020, respectively, and $0.2 million and $1.1 million for the three and nine months ended September 30, 2021, respectively.	Grant Revenue We generate revenue primarily from government and other awarded grants that reimburse us for certain allowable costs related to research and development efforts. The Company has determined that the grants are not within the scope of ASC 606 as they do not meet the definition of a contract with a customer. The Company has concluded that the grants meet the definition of a contribution and are nonexchange transactions and has applied the contribution accounting model in Subtopic 958-605, Not-for-Profit-Entities-Revenue Recognition by analogy. The Company recognizes funding received from grants as revenue, rather than as a reduction of research and development expenses, because the Company is the principal in conducting the research and development activities and these grants are central to the Company ’ Revenue from grants not within the scope of ASC 606 was $6.2 million and $1.5 million for the years ending December 31, 2019 and 2020, respectively.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments which potentially subject the Company to concentrations of credit risk consist principally of cash and cash equivalents. Total cash balances exceeded insured balances by the Federal Deposit Insurance Corporation as of December 31, 2020 and September 30, 2021. Cash equivalents are invested in highly rated money market funds invested only in obligations of the U.S. government and its agencies. The majority of the Company ’ ’ ’ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue Accounts Receivable ​ ​ Three Months ​ Nine Months ​ December 31, ​ September 30, ​ ​ 2020 2021 2020 2021 2020 2021 Grant A ​ — ​ — ​ — ​ — ​ — ​ — ​ Grant B 0 ​ — % 11 ​ — % — ​ — Grant C 68 % 100 % 65 % 100 % 100 % 100 % Grant D 30 — % 20 ​ — % — — Total 98 % 100 % 96 % 100 % 100 % 100 % ​ All of the Company ’	Concentration of Credit Risk Financial instruments which potentially subject the Company to concentrations of credit risk consist principally of cash and cash equivalents. Total cash balances exceeded insured balances by the Federal Depository Insurance Corporation as of December 31, 2019 and 2020. Cash equivalents are invested in highly rated money market funds invested only in obligations of the US government and its agencies. The majority of the Company ’ ’ ’ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2020 ​ ​ ​ ​ ​ Accounts ​ ​ ​ Accounts ​ ​ Revenue Receivable Revenue Receivable ​ Grant A ​ 28 % — ​ — ​ — ​ Grant B 38 % 67 % 10 % — Grant C 34 % 33 % 67 % 100 % Grant D — — 18 % — Total 100 % 100 % 95 % 100 % ​ All of the Company ’
Other Risks and Uncertainties	Other Risks and Uncertainties The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, successful discovery and development of its product candidates, the success of clinical trials and other studies for its product candidates, including for its ongoing V005 Phase II/III clinical trial and V007 Phase III clinical trial, the regulatory approval and commercialization of its HAVs and other product candidates, ’ ’ ’ Product candidates currently under development will require extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel, and infrastructure and extensive compliance-reporting capabilities. Even if the Company ’ ’	​ 2. Summary of Significant Accounting Policies (continued) Other Risks and Uncertainties The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, successful discovery and development of its product candidates, the success of clinical trials and other studies for its product candidates, including for its ongoing V005 Phase II/III clinical trial and V007 Phase III clinical trial, the regulatory approval and commercialization of its HAVs and other product candidates, ’ ’ ’ Product candidates currently under development will require extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel, and infrastructure and extensive compliance-reporting capabilities. Even if the Company ’ ’
Net Loss per Share Attributable to Common Stockholders	Net Loss per Share Attributable to Common Stockholders The Company follows the two-class method to compute basic and diluted net loss per share attributable to common stockholders when shares met the definition of participating securities. The two-class method determines net loss per common share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to share in the earnings as if all income for the period had been distributed. During periods of loss, there is no allocation required under the two-class method since the redeemable convertible preferred stock did not have a contractual obligation to share in the Company ’ Basic net loss per share attributable to common stockholders is computed by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period without consideration of potentially dilutive common stock. Diluted net loss per share attributable to common stockholders reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock or resulted in the issuance of common stock that then shared in the earnings of the Company unless inclusion of such shares would be anti-dilutive. As the Company has only incurred losses, basic and diluted net loss per share is the same. The potential shares of common stock that were excluded from the computation of diluted net loss per share for each period because including them would have had an antidilutive effect were as follows: ​ ​ ​ ​ ​ ​ ​ September 30, ​ 2020 2021 ​ ​ ​ ​ ​ Shares issuable upon conversion of Series A redeemable convertible preferred stock 18,421,897 — Shares issuable upon conversion of Series B redeemable convertible preferred stock 24,137,647 — Shares issuable upon conversion of Series C redeemable convertible preferred stock 11,241,283 — Shares issuable upon conversion of Series D redeemable convertible preferred stock 15,812,735 — Exercise of options under stock plan 4,516,907 6,399,888 Warrants to purchase common stock 32,961 5,465,204 ​ The 15,000,000 Contingent Earnout shares are excluded from the anti-dilutive table for all the periods presented as such shares are contingently issuable until the share price of the Company exceeds specified thresholds that have not yet been achieved, or upon the occurrence of a change in control.	Net Loss per Share Attributable to Common Stockholders The Company applies the two-class method to compute basic and diluted net loss per share attributable to common stockholders when shares meet the definition of participating securities. The two-class method determines net loss per share for each class of common and redeemable convertible preferred stock according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income (loss) available to common stockholders for the period to be allocated between common and redeemable convertible preferred stock based upon their respective rights to share in the earnings as if all income (loss) for the period had been distributed. During periods of loss, there is no allocation required under the two-class method since the redeemable convertible preferred stock does not have a contractual obligation to share in the Company ’ ​ 2. Summary of Significant Accounting Policies (continued) Basic net loss per share attributable to common stockholders is computed by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period without consideration of potentially dilutive common stock. Diluted net loss per share attributable to common stockholders reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock or resulted in the issuance of common stock that then shared in the earnings of the Company unless inclusion of such shares would be anti-dilutive. Since the Company has only incurred losses, basic and diluted net loss per share is the same. Securities that could potentially dilute net loss per share in the future that were not included in the computation of diluted net loss per share are as follows: ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2020 ​ ​ ​ ​ ​ Shares issuable upon conversion of Series A redeemable convertible preferred stock 18,421,897 18,421,897 Shares issuable upon conversion of Series B redeemable convertible preferred stock 24,137,647 24,137,647 Shares issuable upon conversion of Series C redeemable convertible preferred stock 11,241,283 11,241,283 Shares issuable upon conversion of Series D redeemable convertible preferred stock 15,812,735 15,812,735 Options to purchase common stock 5,220,236 4,813,262 Warrant to purchase common stock 32,961 32,961 ​ Fair Value of Financial Instruments Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in the principal or most advantageous market in an orderly transaction between market participants at the measurement date. ASC 820, Fair Value Measurement and Disclosures ● Level 1 — Observable inputs that reflect unadjusted quoted prices for identical assets or liabilities in active markets. ● Level 2 — Inputs other than quoted prices included in Level 1 that are observable for the asset or liability, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. ● Level 3 — Unobservable inputs in which little or no market data exists, therefore requiring the Company to develop its own assumptions. The Company evaluates assets and liabilities subject to fair value measurements on a recurring basis to determine the appropriate level at which to classify them for each reporting period, utilizing valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible. The determination requires significant judgments to be made by the Company. The Company ’ ​ 2. Summary of Significant Accounting Policies (continued)
Fair Value of Financial Instruments		​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2020 ​ ​ ​ ​ ​ Shares issuable upon conversion of Series A redeemable convertible preferred stock 18,421,897 18,421,897 Shares issuable upon conversion of Series B redeemable convertible preferred stock 24,137,647 24,137,647 Shares issuable upon conversion of Series C redeemable convertible preferred stock 11,241,283 11,241,283 Shares issuable upon conversion of Series D redeemable convertible preferred stock 15,812,735 15,812,735 Options to purchase common stock 5,220,236 4,813,262 Warrant to purchase common stock 32,961 32,961
Property and Equipment, Net		Property and Equipment, Net Property and equipment, net are recorded at cost less accumulated depreciation. Expenditures for major additions and improvements are capitalized and minor replacements, maintenance, and repairs are charged to expense as incurred. When property and equipment are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the balance sheet accounts and any resulting gain or loss is included in the results of operations for the respective period. Depreciation is calculated using the straight-line method over the estimated useful lives of the related assets. The estimated useful lives for significant asset categories are as follows: ​ ​ ​ ​ ​ Estimated Useful Property and equipment ​ Lives (Years) Scientific equipment ​ 5 – 7 Computer equipment 5 Software 3 Furniture and fixtures 5 – 7 Leasehold improvements Lesser of useful life or life of lease Construction in progress N/A
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews the carrying value of property and equipment for indicators of possible impairment whenever events and circumstances indicate that the carrying value of an asset or asset group may not be recoverable from the estimated future net undiscounted cash flows expected to result from its use and eventual disposition. In cases where estimated future net undiscounted cash flows are less than the carrying value, an impairment loss is recognized equal to an amount by which the carrying value exceeds the fair value of the asset or asset group. The factors considered by management in performing this assessment include current operating results, trends and prospects, the manner in which the property is used, and the effects of obsolescence, demand, competition, and other economic factors. Based on this assessment, during the nine months ended September 30, 2020 and 2021, respectively, the Company concluded there were no such events or changes in circumstances requiring review of the carrying amount of the Company ’	​ ​ ​ ​ ​ Estimated Useful Property and equipment ​ Lives (Years) Scientific equipment ​ 5 – 7 Computer equipment 5 Software 3 Furniture and fixtures 5 – 7 Leasehold improvements Lesser of useful life or life of lease Construction in progress N/A
Income Taxes		Income Taxes Income taxes are computed using the asset and liability approach that requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the Company ’ ​ 2. Summary of Significant Accounting Policies (continued) The Company recognizes the benefit of an income tax position only if it is more likely than not (greater than 50%) that the tax position will be sustained upon tax examination, based solely on the technical merits of the tax position. Otherwise, no benefit can be recognized. Assessing an uncertain tax position begins with the initial determination of the sustainability of the position and is measured at the largest amount of benefit that is greater than 50% likely of being realized upon ultimate settlement. As of each balance sheet date, unresolved uncertain tax positions must be reassessed. Additionally, the Company must accrue interest and related penalties, if applicable, on all tax exposures for which reserves have been established consistent with jurisdictional tax laws. The Company has analyzed its filing positions in all significant Federal and state jurisdictions where it is required to file income tax returns, as well as open tax years in these jurisdictions. As of December 31, 2019 and 2020, the Company has determined that no uncertain tax positions would have a material impact on the financials statements of the Company. The Company is no longer subject to Federal, state, and local tax examinations by tax authorities for years before 2017 although carry-forward attributes that were generated prior to 2017 may still be adjusted upon examination by the taxing authorities if they either have been or will be used in a future period. No income tax returns are currently under examination by taxing authorities. As of December 31, 2019 and 2020, the Company had not recorded any amounts for unrecognized tax benefits. The Company ’ ’
Intellectual Property		Intellectual Property The Company seeks to protect its intellectual property by filing patent applications in the United ’
Research and Development		Research and Development The Company expenses research and development costs as operating expenses as incurred. Research and development expenses consist primarily of: ● salaries and related overhead expenses for personnel in research and development functions, including stock-based compensation and benefits; ● fees paid to consultants and CROs, including in connection with clinical trials, and other related clinical trial fees, such as for investigator grants, patient screening, laboratory work and statistical compilation and analysis; ● allocation of facility lease and maintenance costs; ● depreciation of leasehold improvements, laboratory equipment and computers; ● costs related to purchasing raw materials for and producing product candidates for clinical trials; ● costs related to compliance with regulatory requirements; ● costs related to the manufacturing scale-out initiative; and ● license fees related to in-licensed technologies.
Accrued Research and Development		Accrued Research and Development The Company has entered into various agreements with CROs and a CMO, which conduct preclinical studies and clinical trials and contract manufacturing activities. The Company ’
Leases		Leases Effective January 1, 2019, the Company accounts for its leases under ASC 842, Leases ’ “ ” “ ” “ ” ’ “ ” “ ” “ ” Under this guidance, arrangements meeting the definition of a lease are classified as operating or finance leases, and are recorded on the balance sheet as both a right-of-use asset and lease liability, calculated by discounting fixed lease payments over the lease term at the rate implicit in the lease or the Company ’ ​ 2. Summary of Significant Accounting Policies (continued) Lease expenses for minimum lease payments for operating leases are recognized on a straight-line basis over the lease term. Amortization expense of the right-of-use asset for finance leases is recognized on a straight-line basis over the lease term and interest expense for finance leases is recognized based on the incremental borrowing rate. Lease liabilities are increased by interest and reduced by payments each period, and the right of use asset is amortized over the lease term. In calculating the right-of-use assets and lease liabilities, the Company has elected to combine lease and non-lease components for all asset classes. The Company excludes short-term leases, if any, having initial terms of 12 months or less from the new guidance as an accounting policy election, and recognizes rent expense on a straight-line basis over the lease term. Prior to the adoption of ASC 842 on January 1, 2019 the Company was deemed to be the accounting owner of leased space during the construction of its headquarters in a build-to-suit arrangement. Upon substantial completion of construction in June ’ ’ each The cumulative effect of initially applying the new lease guidance on January 1, 2019 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ January 1, 2019 ​ ​ ​ ​ ​ Cumulative ​ Beginning ​ ​ Beginning ​ Effect ​ Balance, ($ in thousands) Balance Adjustment As Adjusted Assets ​ ​ ​ ​ ​ ​ Building asset ​ $ 25,091 ​ $ (25,091) ​ $ — Finance lease right-of-use assets, net ​ $ — ​ $ 27,612 ​ $ 27,612 Operating lease right-of-use assets, net ​ $ — ​ $ 923 ​ $ 923 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Liabilities and stockholders’ deficit ​ ​ ​ Accrued expenses ​ $ 7,049 ​ $ (1) ​ $ 7,048 Facility financing obligation, current portion ​ $ 276 ​ $ (276) ​ $ — Finance lease obligation, current portion ​ $ — ​ $ 1,292 ​ $ 1,292 Operating lease obligation, current portion ​ $ — ​ $ 55 ​ $ 55 Facility financing obligation, net of current portion ​ $ 22,955 ​ $ (22,955) ​ $ — Finance lease obligation, net of current portion ​ $ — ​ $ 26,319 ​ $ 26,319 Operating lease obligation, net of current portion ​ $ — ​ $ 870 ​ $ 870 Accumulated deficit ​ $ (234,289) ​ $ (1,861) ​ $ (236,150)
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In August 2020, the FASB issued ASU No. 2020-06, “ ’ ’ ” “ ” ’	Recently Adopted Accounting Pronouncements In August —
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In May 2021, the FASB issued “ ’ ” “ ” ’	Recently Issued Accounting Pronouncements In August 2020, the FASB issued ASU No. 2020-06, “  –  ’  –  ’ “ ”

Summary of Significant Accou_15

Summary of Significant Accounting Policies (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Summary of Significant Accounting Policies
Summary of 10% or more of the Company's total revenue or accounts receivable balance	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue Accounts Receivable ​ ​ Three Months ​ Nine Months ​ December 31, ​ September 30, ​ ​ 2020 2021 2020 2021 2020 2021 Grant A ​ — ​ — ​ — ​ — ​ — ​ — ​ Grant B 0 ​ — % 11 ​ — % — ​ — Grant C 68 % 100 % 65 % 100 % 100 % 100 % Grant D 30 — % 20 ​ — % — — Total 98 % 100 % 96 % 100 % 100 % 100 %	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2020 ​ ​ ​ ​ ​ Accounts ​ ​ ​ Accounts ​ ​ Revenue Receivable Revenue Receivable ​ Grant A ​ 28 % — ​ — ​ — ​ Grant B 38 % 67 % 10 % — Grant C 34 % 33 % 67 % 100 % Grant D — — 18 % — Total 100 % 100 % 95 % 100 %
Summary of securities that could potentially dilute net loss per share in the future that were not included in the computation of diluted net loss per share	​ ​ ​ ​ ​ ​ ​ September 30, ​ 2020 2021 ​ ​ ​ ​ ​ Shares issuable upon conversion of Series A redeemable convertible preferred stock 18,421,897 — Shares issuable upon conversion of Series B redeemable convertible preferred stock 24,137,647 — Shares issuable upon conversion of Series C redeemable convertible preferred stock 11,241,283 — Shares issuable upon conversion of Series D redeemable convertible preferred stock 15,812,735 — Exercise of options under stock plan 4,516,907 6,399,888 Warrants to purchase common stock 32,961 5,465,204	​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2020 ​ ​ ​ ​ ​ Shares issuable upon conversion of Series A redeemable convertible preferred stock 18,421,897 18,421,897 Shares issuable upon conversion of Series B redeemable convertible preferred stock 24,137,647 24,137,647 Shares issuable upon conversion of Series C redeemable convertible preferred stock 11,241,283 11,241,283 Shares issuable upon conversion of Series D redeemable convertible preferred stock 15,812,735 15,812,735 Options to purchase common stock 5,220,236 4,813,262 Warrant to purchase common stock 32,961 32,961
Summary of estimated useful lives for significant asset		​ ​ ​ ​ ​ Estimated Useful Property and equipment ​ Lives (Years) Scientific equipment ​ 5 – 7 Computer equipment 5 Software 3 Furniture and fixtures 5 – 7 Leasehold improvements Lesser of useful life or life of lease Construction in progress N/A
Summary of cumulative effect of initially applying the new lease guidance		​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ January 1, 2019 ​ ​ ​ ​ ​ Cumulative ​ Beginning ​ ​ Beginning ​ Effect ​ Balance, ($ in thousands) Balance Adjustment As Adjusted Assets ​ ​ ​ ​ ​ ​ Building asset ​ $ 25,091 ​ $ (25,091) ​ $ — Finance lease right-of-use assets, net ​ $ — ​ $ 27,612 ​ $ 27,612 Operating lease right-of-use assets, net ​ $ — ​ $ 923 ​ $ 923 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Liabilities and stockholders’ deficit ​ ​ ​ Accrued expenses ​ $ 7,049 ​ $ (1) ​ $ 7,048 Facility financing obligation, current portion ​ $ 276 ​ $ (276) ​ $ — Finance lease obligation, current portion ​ $ — ​ $ 1,292 ​ $ 1,292 Operating lease obligation, current portion ​ $ — ​ $ 55 ​ $ 55 Facility financing obligation, net of current portion ​ $ 22,955 ​ $ (22,955) ​ $ — Finance lease obligation, net of current portion ​ $ — ​ $ 26,319 ​ $ 26,319 Operating lease obligation, net of current portion ​ $ — ​ $ 870 ​ $ 870 Accumulated deficit ​ $ (234,289) ​ $ (1,861) ​ $ (236,150)

Reverse Recapitalization (Table

Reverse Recapitalization (Tables)	9 Months Ended
	Sep. 30, 2021
Reverse Recapitalization
Schedule of common stock outstanding immediately following the consummation of the Merger	​ ​ ​ ​ ​ ​ Shares Common stock of AHAC, outstanding prior to Merger 10,355,000 ​ Less redemption of AHAC shares (3,008,551) ​ Common stock of AHAC 7,346,449 ​ AHAC Founder Shares 2,500,000 ​ New Humacyte shares issued to PIPE Investors 17,500,000 ​ Issuance of common stock upon reverse recapitalization and PIPE Financing 27,346,449 ​ New Humacyte shares issued in Merger to Legacy Humacyte stockholders 75,656,935 (1) Total shares of common stock immediately after Merger 103,003,384 ​ (1) Includes 69,613,562 shares of common stock issued upon conversion of Legacy Humacyte ’

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Measurements
Schedule of assets and liabilities that were measured at fair value on a recurring basis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measured as of September 30, 2021 ($in thousands) Level 1 Level 2 Level 3 Total Assets: ​ ​ ​ ​ ​ ​ Money market funds ​ $ 238,375 ​ $ — ​ $ — ​ $ 238,375 Total financial assets ​ $ 238,375 ​ $ — ​ $ — ​ $ 238,375 Liabilities: ​ ​ ​ ​ Contingent earnout liability ​ $ — ​ $ — ​ $ 169,200 ​ $ 169,200 Common stock warrant liabilities (Private Placement Warrants) ​ — ​ — ​ 555 ​ 555 Total financial liabilities ​ $ — ​ $ — ​ $ 169,755 ​ $ 169,755
Summary of the changes in the fair value of the Company's Level 3 financial instruments	​ ​ ​ ​ ​ ​ ​ ​ ​ Contingent Private Placement ($in thousands) ​ Earnout Liability ​ Warrants ​ ​ ​ ​ ​ ​ ​ Fair value as of December 31, 2020 ​ $ — ​ $ — Private placement warrant liability acquired as part of the merger ​ — ​ (553) Contingent earount liability recognized upon the closing of the reverse recapitalization ​ (159,432) ​ — Change in fair value included in other (expense) income ​ (9,768) ​ (2) Fair value as of September 30, 2021 ​ $ (169,200) ​ $ (555)

Property and Equipment, Net (_2

Property and Equipment, Net (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Property and Equipment, Net
Schedule of Property and equipment	​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ September 30, ($ in thousands) 2020 2021 ​ ​ ​ ​ ​ ​ Scientific equipment ​ $ 27,412 ​ $ 27,578 Computer equipment ​ 149 ​ 154 Software ​ 335 ​ 335 Furniture and fixtures ​ 988 ​ 988 Leasehold improvements ​ 26,355 ​ 26,355 ​ ​ 55,239 ​ 55,410 Accumulated depreciation ​ (14,261) ​ (18,911) Property and equipment, net ​ $ 40,978 ​ $ 36,499	​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ($ in thousands) 2019 2020 ​ ​ ​ ​ ​ ​ Scientific equipment ​ $ 27,822 ​ $ 27,412 Computer equipment ​ 218 ​ 149 Software ​ 340 ​ 335 Furniture and fixtures ​ 988 ​ 988 Leasehold improvements ​ 26,337 ​ 26,355 ​ ​ 55,705 ​ 55,239 Accumulated depreciation ​ (8,417) ​ (14,261) Property and equipment, net ​ $ 47,288 ​ $ 40,978

Accrued Expenses (Tables)_2

Accrued Expenses (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Accrued Expenses
Schedule of Accrued Expenses	​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ September 30, ($ in thousands) 2020 2021 ​ ​ ​ ​ ​ ​ Accrued external research, development and manufacturing costs ​ $ 2,615 ​ $ 2,685 Accrued employee compensation and benefits ​ 1,009 ​ 4,025 Accrued professional fees ​ 968 ​ 2,712 Total ​ $ 4,592 ​ $ 9,422	​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ($ in thousands) 2019 2020 Accrued external research, development and manufacturing costs ​ $ 3,872 ​ $ 2,615 Accrued employee compensation and benefits ​ 1,260 ​ 1,009 Accrued professional fees ​ 868 ​ 968 Total ​ $ 6,000 ​ $ 4,592

Debt (Tables)_2

Debt (Tables)	9 Months Ended
	Sep. 30, 2021
Debt
Summary of SVB loan payable and net discount or premium balances	​ ​ ​ ​ ​ ​ September 30, ($ in thousands) 2021 Principal amount of SVB loan payable ​ $ 20,000 Final payment amount of SVB loan payable ​ 1,000 Net premium associated with accretion of final payment and other debt issuance costs ​ (3,073) SVB loan payable, current and noncurrent ​ 17,927 Less SVB loan payable, current portion ​ (3,889) SVB loan payable, noncurrent portion ​ $ 14,038
Summary of future minimum payments of principal and estimated payments of interest	​ ​ ​ ​ ​ Year ending December 31: ($ in thousands) 2021 (remainder) ​ $ — 2022 ​ 5,555 2023 ​ 6,667 2024 ​ 6,667 2025 ​ 1,111 Total future payments ​ 20,000

Stockholders' Equity (Deficit_4

Stockholders' Equity (Deficit) (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Schedule of activity of warrants	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Legacy ​ ​ ​ ​ ​ ​ ​ ​ Humacyte ​ ​ ​ ​ ​ ​ ​ ​ Common Stock ​ Private Placement ​ ​ ​ Total Common ​ Warrants Warrants Public Warrants Stock Warrants ​ ​ ​ ​ ​ ​ ​ ​ ​ Outstanding as of December 31, 2020 ​ 32,961 ​ — ​ — ​ 32,961 Common Stock Warrants issued to SVB ​ 287,704 ​ — ​ — ​ 287,704 Common Stock Warrants as Part of the Merger — 177,500 5,000,000 5,177,500 Warrants Exercised (32,961) — — (32,961) Oustanding as of September 30, 2021 287,704 177,500 5,000,000 5,465,204
Summary of common stock reserved for future issuances	​ ​ ​ ​ ​ September 30, ​ 2021 Common stock reserved for Contingent Consideration Shares 15,000,000 Exercise of options under stock plans 6,399,888 Issuance of options under stock plans 7,730,503 Shares available for grant under ESPP 1,030,033 Warrants to purchase common stock 5,465,204 ​ ​ 35,625,628	​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2020 ​ ​ ​ ​ ​ Conversion of Series A redeemable convertible preferred stock 18,421,897 18,421,897 Conversion of Series B redeemable convertible preferred stock 24,137,647 24,137,647 Conversion of Series C redeemable convertible preferred stock 11,241,286 11,241,286 Conversion of Series D redeemable convertible preferred stock 15,812,735 15,812,735 Exercise of options under stock plan 5,220,236 4,813,262 Issuance of options under stock plan 2,736,954 2,948,598 Warrant to purchase common stock 32,961 ​ 32,961 ​ ​ 77,603,716 77,408,386
Private Placement Warrants
Schedule of assumptions used in the valuations	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ August 26, September 30, ​ ​ 2021 ​ 2021 Market price of public stock ​ $ 10.96 ​ $ 11.61 ​ Exercise price ​ $ 11.50 ​ $ 11.50 ​ Expected term (years) ​ 5.00 ​ 4.91 ​ Expected share price volatility ​ 32.5 % 28.5 % Risk-free interest rate ​ 0.68 % 0.96 % Estimated dividend yield ​ 0 % 0 %
Contingent earnout liability
Schedule of assumptions used in the valuations	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ August 26, September 30, ​ ​ 2021 ​ 2021 Current stock price ​ $ 10.96 ​ $ 11.61 ​ Expected share price volatility ​ 79.6 % 78.9 % Risk-free interest rate ​ 1.34 % 1.55 % Estimated dividend yield ​ 0 % 0.0 % Expected term (years) ​ 10.00 ​ 10.00 ​

Stock-based Compensation (Tab_2

Stock-based Compensation (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Stock-based Compensation
Summary of assumptions on the date of grant to estimate the fair value of the stock options in the Black-Scholes option-pricing model	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended September 30, ​ 2020 2021 (1) 2020 2021 Estimated dividend yield ​ 0 % — ​ 0 % 0 % Expected share price volatility (weighted average and range, if applicable) ​ 91.6 % — ​ 91.4% (89.4% to 91.6%) ​ 91.4% (91.0% to 92.1%) ​ Risk-free interest rate (weighted average and range, if applicable) ​ 0.34 % — ​ 0.40% (0.34% to 0.75%) ​ 0.68% (0.62% to 1.02%) ​ Expected term of options (in years) ​ 6.0 ​ — ​ 6.0 ​ 6.0 ​	​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ 2019 2020 ​ Estimated dividend yield ​ 0 % 0 % Expected share price volatility ​ 70.1%-87.7 % 89.4% - 91.6 % Risk-free interest rate ​ 1.76% - 2.46 % 0.34% - 0.75 % Expected term of options (in years) ​ 6.00 ​ 6.00 ​
Summary of stock-based compensation expense included in the statements of operations and comprehensive loss	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ($ in thousands) ​ 2020 ​ 2021 ​ 2020 ​ 2021 Research and development ​ $ 308 ​ $ 486 ​ $ 781 ​ $ 1,837 General and administrative ​ ​ 862 ​ ​ 1,391 ​ ​ 2,685 ​ ​ 5,498 Total ​ $ 1,170 ​ $ 1,877 ​ $ 3,466 ​ $ 7,335 ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ September 30, ($ in thousands) ​ 2020 ​ 2021 Unrecognized share-based compensation cost ​ $ 5,789 ​ $ 12,480 Expected weighted average period compensation costs to be recognized (years) ​ 1.7 ​ 2.1	​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ($ in thousands) ​ 2019 ​ 2020 Research and development ​ $ 914 ​ $ 1,135 General and administrative ​ 3,543 ​ 3,559 Total ​ $ 4,457 ​ $ 4,694 ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ($ in thousands) ​ 2019 ​ 2020 Unrecognized share-based compensation cost ​ $ 7,919 ​ $ 5,789 Expected weighted average period compensation costs to be recognized (years) ​ 1.8 ​ 1.7
Summary of option activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ ​ ​ Weighted ​ Remaining ​ Aggregate ​ ​ ​ ​ Average Exercise ​ Contractual Term ​ Intrinsic Value ​ ​ Number of Shares ​ Price Per Share ​ (years) ​ (in thousands) Options outstanding at December 31, 2020 4,813,262 ​ $ 6.04 6.6 ​ $ 20,422 Granted 1,838,029 ​ $ 10.28 ​ Exercised (188,006) ​ $ 2.97 ​ Forfeited (63,397) ​ $ 7.87 ​ Options outstanding at September 30, 2021 6,399,888 ​ $ 7.33 6.6 ​ $ 26,705 Vested and exercisable, September 30, 2021 4,092,342 ​ $ 5.74 5.1 ​ $ 23,345 Vested and expected to vest, September 30, 2021 6,399,888 ​ $ 7.33 6.6 ​ $ 26,705	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ ​ ​ Weighted ​ Remaining ​ Aggregate ​ ​ Number of ​ Average Exercise ​ Contractual Term ​ Intrinsic Value ​ ​ Shares ​ Price Per Share ​ (years) ​ (in thousands) Options outstanding at December 31, 2018 5,638,773 ​ $ 4.69 7.4 ​ $ 21,354 Granted 621,031 ​ ​ 8.49 ​ Exercised (620,831) ​ ​ 1.97 ​ Forfeited (418,737) ​ ​ 7.62 ​ Options outstanding at December 31, 2019 5,220,236 ​ $ 5.22 6.5 ​ $ 17,044 Granted 480,856 ​ ​ 9.79 ​ Exercised (195,239) ​ ​ 1.55 ​ Forfeited (692,591) ​ ​ 3.76 ​ Options outstanding at December 31, 2020 4,813,262 ​ $ 6.04 6.6 ​ $ 20,422 Vested and exercisable, December 31, 2020 3,392,302 ​ $ 4.99 5.9 ​ $ 17,925 Vested and expected to vest, December 31, 2020 4,813,262 ​ $ 6.04 6.6 ​ $ 20,422

Income Taxes (Tables)_2

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Taxes
Schedule of components of Company's deferred tax assets and deferred tax liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ($ in thousands) 2019 2020 Deferred tax assets: ​ ​ ​ ​ ​ ​ Net operating loss ​ $ 50,616 ​ $ 53,515 Capitalized research and development ​ 19,660 ​ ​ 32,337 Research credits ​ 10,658 ​ 15,056 Share-based compensation ​ 1,669 ​ 2,519 Right of use lease liability ​ 207 ​ 177 Accrued expenses ​ 71 ​ 57 Other ​ 1 ​ 1 Total deferred tax asset ​ 82,882 ​ 103,662 Less: valuation allowance ​ (82,193) ​ (101,757) Total net deferred tax asset ​ 689 ​ 1,905 ​ ​ ​ ​ ​ ​ ​ Deferred tax liabilities: ​ ​ Basis difference in fixed assets ​ (482) ​ (1,728) Right of use lease assets ​ (207) ​ (177) Total deferred tax liability ​ (689) ​ (1,905) Total net deferred tax asset/(liability) ​ $ — ​ $ —
Schedule of difference between the actual income tax benefit and amount computed by applying the statutory Federal income tax rate to losses before income taxes	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2020 ($ in thousands) ​ Amount Rate Amount Rate Income tax benefit at statutory rate ​ $ (17,939) 21.0 % $ (13,970) 21.0 % State income taxes, net of federal benefit ​ (1,739) 2.0 % (1,338) 2.0 % Tax credits ​ (1,821) 2.1 % (2,625) 3.9 % Other nondeductible expenses ​ 54 0.0 % 90 (0.1) % Deferred rate changes ​ 16 0.0 % 16 0.0 % Other ​ 449 (0.5) % (1,736) 2.6 % Change in valuation allowance ​ 20,980 (24.6) % 19,563 (29.4) % Provision for income taxes ​ $ — 0.0 % $ — 0.0 %

Related Party Transactions (T_2

Related Party Transactions (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Related Party Transactions
Summary of related party expenses included in statements of operations and comprehensive loss	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months ​ Nine Months ($ in thousands) 2020 2021 2020 2021 Expenses under MOU 125 — 375 — License expenses 20 — 70 85 Other 4 2 17 83 Total 149 2 462 168	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ($ in thousands) 2019 2020 Expenses under MOU $ 422 $ 500 License expenses 110 92 Other 39 28 Total $ 571 $ 620

Organization and Description _4

Organization and Description of Business (Details) - USD ($) $ in Thousands	Aug. 26, 2021	Mar. 22, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019
Organization and Description of Business
Proceeds from merger	$ 242,400								$ 242,400
Accumulated deficit			$ 457,158						457,158		$ 388,096	$ 321,572	$ 234,289
Net loss			31,563	$ 17,198	$ 20,301	$ 17,760	$ 14,878	$ 17,674	69,062	$ 50,312	66,524	85,422
Cash and cash equivalents			$ 240,449						$ 240,449		$ 39,929	$ 93,713
Substantial Doubt about Going Concern, within One Year [true false]		true

Summary of Significant Accou_16

Summary of Significant Accounting Policies - Common Stock Warrants (Details) - $ / shares	Aug. 26, 2021	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019	Mar. 15, 2006
Summary of Significant Accounting Policies
Public warrants assumed	5,000,000
Private placement warrants assumed	177,500
Common stock, par value	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001
Warrants, exercise price	$ 11.50				$ 1.14
Share accepting a tender offer entitles warrants to receive cash (as a percent)	50.00%

Summary of Significant Accou_17

Summary of Significant Accounting Policies - Contingent Earnout Liability (Details)	Sep. 30, 2021	Aug. 26, 2021trancheshares	Feb. 17, 2021trancheshares
Summary of Significant Accounting Policies
Maximum contingent earnout shares		15,000,000	15,000,000
Number of tranches of contingent earnout shares | tranche		2	2
Number of contingent earnout shares per tranche		7,500,000	7,500,000
Warrants term	10 years

Summary of Significant Accou_18

Summary of Significant Accounting Policies (Details) - segment	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Segments
Exchange ratio					0.2626%
Number of reportable segment	1	1	1	1	1	1
Number of operating segment					1

Summary of Significant Accou_19

Summary of Significant Accounting Policies - Grant Revenue (Details) - USD ($) $ in Thousands	1 Months Ended			3 Months Ended		9 Months Ended		12 Months Ended		86 Months Ended
	Sep. 30, 2017	Aug. 31, 2017	Nov. 30, 2013	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue from grants not within the scope of ASC 606				$ 200	$ 900	$ 1,100	$ 1,400	$ 1,500	$ 6,200	$ 1,600
Department of Defense grants | Work on bioengineered blood vessels for vascular trauma
Disaggregation of Revenue [Line Items]
Grants	$ 4,000
Department of Defense grants | Work to support human tissue engineered blood vessels for vascular reconstruction
Disaggregation of Revenue [Line Items]
Grants		$ 7,100
Department of Defense grants | Reimbursement of certain allowable costs related to grants
Disaggregation of Revenue [Line Items]
Recognized revenue				200	600	1,100	1,000
National Institutes of Health grant | Reimbursement of certain allowable costs related to grants
Disaggregation of Revenue [Line Items]
Recognized revenue				$ 0	$ 300	$ 0	$ 300
National Institutes of Health grant | Work to support bioengineered grafts for peripheral vascular disease
Disaggregation of Revenue [Line Items]
Grants			$ 1,600

Summary of Significant Accou_20

Summary of Significant Accounting Policies -Concentration of Credit Risk (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Revenue | Customer concentration
Concentration Risk [Line Items]
Concentration of Credit Risk	100.00%	98.00%	100.00%	96.00%	95.00%	100.00%
Revenue | Customer concentration | Grant A
Concentration Risk [Line Items]
Concentration of Credit Risk						28.00%
Revenue | Customer concentration | Grant B
Concentration Risk [Line Items]
Concentration of Credit Risk		0.00%		11.00%	10.00%	38.00%
Revenue | Customer concentration | Grant C
Concentration Risk [Line Items]
Concentration of Credit Risk	100.00%	68.00%	100.00%	65.00%	67.00%	34.00%
Revenue | Customer concentration | Grant D
Concentration Risk [Line Items]
Concentration of Credit Risk		30.00%		20.00%	18.00%
Accounts Receivable | Credit concentration
Concentration Risk [Line Items]
Concentration of Credit Risk			100.00%		100.00%	100.00%
Accounts Receivable | Credit concentration | Grant B
Concentration Risk [Line Items]
Concentration of Credit Risk						67.00%
Accounts Receivable | Credit concentration | Grant C
Concentration Risk [Line Items]
Concentration of Credit Risk			100.00%		100.00%	33.00%

Summary of Significant Accou_21

Summary of Significant Accounting Policies - Net Loss per Share Attributable to Common Stockholders (Details) - shares	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Contingent consideration (in shares)	15,000,000
Series A redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities that were not included in the computation of diluted net loss per share		18,421,897	18,421,897	18,421,897
Series B redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities that were not included in the computation of diluted net loss per share		24,137,647	24,137,647	24,137,647
Series C redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities that were not included in the computation of diluted net loss per share		11,241,283	11,241,283	11,241,283
Series D redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities that were not included in the computation of diluted net loss per share		15,812,735	15,812,735	15,812,735
Exercise of options under stock plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities that were not included in the computation of diluted net loss per share	6,399,888	4,516,907	4,813,262	5,220,236
Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities that were not included in the computation of diluted net loss per share	5,465,204	32,961	32,961	32,961

Summary of Significant Accou_22

Summary of Significant Accounting Policies - Property and Equipment, Net (Details)	12 Months Ended
	Dec. 31, 2020
Scientific equipment. | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years
Scientific equipment. | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	7 years
Computer equipment
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years
Software
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Furniture and fixtures | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years
Furniture and fixtures | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	7 years

Summary of Significant Accou_23

Summary of Significant Accounting Policies - Impairment of Long-Lived Assets and Income Taxes (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended		24 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020
Impairment of Long-Lived Assets
Impairment of long-lived assets	$ 0	$ 0	$ 0
Income Taxes
Uncertain tax positions		0		$ 0
Accrued interest or penalties related to uncertain tax positions		$ 0		0
interest or penalties related to uncertain tax positions expensed				$ 0

Reverse Recapitalization (Detai

Reverse Recapitalization (Details)	Aug. 26, 2021USD ($)$ / sharestrancheshares	Sep. 30, 2021USD ($)	Sep. 30, 2021USD ($)	Feb. 17, 2021trancheshares
Business Acquisition [Line Items]
Legacy Humacyte common stock conversion ratio to common stock	0.26260
Founder shares converted to commons stock | shares	2,500,000
Founder shares conversion ratio	1
Maximum contingent earnout shares | shares	15,000,000			15,000,000
Number of tranches of contingent earnout shares | tranche	2			2
Number of contingent earnout shares per tranche | shares	7,500,000			7,500,000
Closing stock price to trigger first trance of contingent earnout shares (USD per share) | $ / shares	$ 15
Closing stock price to trigger second trance of contingent earnout shares (USD per share) | $ / shares	$ 20
Number of days within 30 day period of stock price at $15 or $20 to trigger earnout shares | $ / shares	20
Period of over which 20 days stock price at $15 or $20 to trigger earnout shares	30 days
Contingent Consideration Liability recognized upon the closing of the reverse recapitalization	$ 159,400,000		$ 159,432,000
Proceeds from PIPE	$ 175,000,000
Share Price | $ / shares	$ 10
Proceeds from merger	$ 242,400,000		242,400,000
Transaction costs recorded in APIC	3,900,000
Public warrants assumed upon the merger, net of transaction costs	100,000	$ 13,912,000
Liabilities assumed	15,200,000
Assets	$ 100,000
Accounts Payable and Accrued Liabilities [Member]
Business Acquisition [Line Items]
Unpaid assumed liabilities		2,200,000	2,200,000
Unpaid transaction costs		$ 3,000,000	$ 3,000,000

Reverse Recapitalization - Shar

Reverse Recapitalization - Share After Merger (Details) - shares	Aug. 26, 2021	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Reverse Recapitalization
Common stock of AHAC, outstanding prior to Merger	10,355,000
Less redemption of AHAC shares	(3,008,551)
Common stock of AHAC	7,346,449
AHAC Founder Shares	2,500,000
New Humacyte shares issued to PIPE Investors	17,500,000
Issuance of common stock upon reverse recapitalization and PIPE Financing	27,346,449
New Humacyte shares issued in Merger to Legacy Humacyte stockholders	75,656,935
Total shares of common stock immediately after Merger	103,003,384	103,003,384	5,822,396	5,627,157
Common stock issued upon conversion of Legacy Humacyte's redeemable convertible preferred stock	69,613,562

Fair Value Measurements (Detail

Fair Value Measurements (Details) - Recurring - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets:
Financial assets	$ 238,375	$ 35,623
Liabilities:
Financial liabilities	169,755
Contingent earnout liability
Liabilities:
Financial liabilities	169,200
Private Placement Warrants
Liabilities:
Financial liabilities	555
Money market funds
Assets:
Financial assets	238,375	35,623
Level 1
Assets:
Financial assets	238,375	35,623
Level 1 | Money market funds
Assets:
Financial assets	238,375	$ 35,623
Level 3
Liabilities:
Financial liabilities	169,755
Level 3 | Contingent earnout liability
Liabilities:
Financial liabilities	169,200
Level 3 | Private Placement Warrants
Liabilities:
Financial liabilities	$ 555

Fair Value Measurements - Chang

Fair Value Measurements - Changes in the fair value (Details)	9 Months Ended
	Sep. 30, 2021USD ($)Y	Aug. 26, 2021USD ($)
Contingent earnout liability | Expected term
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Measurement input	10	10
Level 3 | Contingent earnout liability
Changes in the fair value of the Level 3 financial instruments
Fair value of liability recognized	$ (159,432,000)
Change in fair value included in other (expense) income	(9,768,000)
Ending balance	(169,200,000)
Level 3 | Private Placement Warrants
Changes in the fair value of the Level 3 financial instruments
Fair value of liability recognized	(553,000)
Change in fair value included in other (expense) income	(2,000)
Ending balance	$ (555,000)

Property and Equipment, Net (_3

Property and Equipment, Net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 55,410		$ 55,410		$ 55,239	$ 55,705
Accumulated depreciation	(18,911)		(18,911)		(14,261)	(8,417)
Property and equipment, net	36,499		36,499		40,978	47,288
Depreciation expense	1,500	$ 1,600	4,650	$ 4,729	6,291	4,689
Scientific equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	27,578		27,578		27,412	27,822
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	154		154		149	218
Software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	335		335		335	340
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	988		988		988	988
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 26,355		$ 26,355		$ 26,355	$ 26,337

Accrued Expenses (Details)_2

Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019
Accrued Expenses
Accrued external research, development and manufacturing costs	$ 2,685	$ 2,615	$ 3,872
Accrued employee compensation and benefits	4,025	1,009	1,260
Accrued professional fees	2,712	968	868
Total	$ 9,422	$ 4,592	$ 6,000	$ 7,049

Debt - PPP (Details)_2

Debt - PPP (Details) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended		12 Months Ended
	Apr. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Debt Instrument [Line Items]
Proceeds from debt instruments			$ 3,251	$ 3,251
Gain on PPP loan forgiveness		$ 3,284
Paycheck Protection Program
Debt Instrument [Line Items]
Proceeds from debt instruments	$ 3,300
Gain on PPP loan forgiveness		$ 3,284

Debt - Term Loan (Details)

Debt - Term Loan (Details) $ / shares in Units, $ in Millions	Oct. 13, 2021USD ($)$ / sharesshares	Mar. 31, 2021USD ($)shares	Sep. 30, 2021USD ($)tranche$ / sharesshares	Aug. 26, 2021$ / shares	Mar. 15, 2006$ / shares
Line of Credit Facility [Line Items]
Warrants, exercise price | $ / shares				$ 11.50	$ 1.14
Silicon Valley Bank and SVB Innovation Credit Fund VIII, L.P.,
Line of Credit Facility [Line Items]
Percent of outstanding principal and interest collateralized			50.00%
Term loan agreement
Line of Credit Facility [Line Items]
Number of tanches | tranche			3
Amount of loan drawn	$ 10	$ 20
Amount that are eligible to disburse			$ 10
Borrowings bearing interest rate			7.50%
Advance notice period			30 days
Prepayment fee			3.00%
Prepayment fee after March 30, 2022			2.00%
Prepayment fee after March 30, 2023			1.00%
Warrants, exercise price | $ / shares			$ 10.28
Warrants immediately exercisable | shares			287,704
Fair value of warrants			$ 2.4
Final payment fee (as a percent)			5.00%
Final payment fee			$ 1
Debt issuance costs			$ 0.3
Number of warrants with no probable funding that becomes exercisable | shares		123,302
Number of warrants that becomes exercisable for no probable funding | shares	123,302
Exercise price of warrants that became exercisable for no probable funding (USD per share) | $ / shares	$ 10.28
Term loan agreement | Prime Rate
Line of Credit Facility [Line Items]
Borrowings bearing interest rate			7.50%
Basis spread on variable rate			4.25%
Term loan agreement | Silicon Valley Bank and SVB Innovation Credit Fund VIII, L.P.,
Line of Credit Facility [Line Items]
Maximum loan facility amount		$ 50

Debt - SVB loan payable and net

Debt - SVB loan payable and net discount (Details) $ in Thousands	Sep. 30, 2021USD ($)
Debt Instrument [Line Items]
SVB loan payable, current and noncurrent	$ 20,000
SVB Loan payable
Debt Instrument [Line Items]
Principal amount of SVB loan payable	20,000
Final payment amount of SVB loan payable	1,000
Net premium associated with accretion of final payment and other debt issuance costs	(3,073)
SVB loan payable, current and noncurrent	17,927
Less SVB loan payable, current portion	(3,889)
SVB loan payable, noncurrent portion	$ 14,038

Debt - Future minimum payments

Debt - Future minimum payments (Details) $ in Thousands	Sep. 30, 2021USD ($)
Future minimum payments of principal and estimated payments of interest
2022	$ 5,555
2023	6,667
2024	6,667
2025	1,111
Total future payments	20,000
SVB Loan payable
Future minimum payments of principal and estimated payments of interest
Total future payments	17,927
Less final payment	(1,000)
Total principal amount of SVB loan payments	$ 20,000

Stockholders' Equity (Deficit_5

Stockholders' Equity (Deficit) - Common Stock (Details) $ / shares in Units, $ in Thousands	Aug. 26, 2021USD ($)$ / sharesshares	Sep. 30, 2021$ / sharesshares	Sep. 30, 2021USD ($)Vote$ / sharesshares	Dec. 31, 2020Vote$ / sharesshares	Dec. 31, 2019$ / sharesshares
Proceeds from merger	$ 242,400		$ 242,400
Assets	$ 100
Common stock, shares outstanding | shares	103,003,384	103,003,384	103,003,384	5,822,396	5,627,157
Common stock, par value | $ / shares	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001
Dividends declared | $ / shares			$ 0	$ 0
Number of vote per common share held | Vote				1
Common stock, authorized | shares		250,000,000	250,000,000	340,216,780	340,216,780
Common Stock
Issuance of common stock upon the Merger and related PIPE Financing, net of issuance costs | shares	27,346,449	27,346,449
Proceeds from merger	$ 242,400
Transaction costs	$ 3,900
Common stock, shares outstanding | shares	103,003,384
Common stock, par value | $ / shares	$ 0.0001	$ 0.0001	$ 0.0001
Number of vote per common share held | Vote			1
Common stock, authorized | shares		250,000,000	250,000,000
Alpha Healthcare Acquisition Corp. and Hunter Merger Sub, Inc. | Common Stock
Contingent consideration liability	$ 15,200
Assets	$ 100

Stockholders' Equity (Deficit_6

Stockholders' Equity (Deficit) - Common stock for future issuances (Details) - shares	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Reserved common stock for future issuances	35,625,628	77,408,386	77,603,716
Series A redeemable convertible preferred stock
Class of Stock [Line Items]
Reserved common stock for future issuances		18,421,897	18,421,897
Series B redeemable convertible preferred stock
Class of Stock [Line Items]
Reserved common stock for future issuances		24,137,647	24,137,647
Series C redeemable convertible preferred stock
Class of Stock [Line Items]
Reserved common stock for future issuances		11,241,286	11,241,286
Series D redeemable convertible preferred stock
Class of Stock [Line Items]
Reserved common stock for future issuances		15,812,735	15,812,735
Common stock reserved for Contingent Consideration Shares
Class of Stock [Line Items]
Reserved common stock for future issuances	15,000,000
Exercise of options under stock plan
Class of Stock [Line Items]
Reserved common stock for future issuances	6,399,888	4,813,262	5,220,236
Issuance of options under stock plan
Class of Stock [Line Items]
Reserved common stock for future issuances	7,730,503	2,948,598	2,736,954
Shares available for grant under ESPP
Class of Stock [Line Items]
Reserved common stock for future issuances	1,030,033
Warrants to purchase common stock
Class of Stock [Line Items]
Reserved common stock for future issuances	5,465,204	32,961	32,961

Stockholders' Equity (Deficit_7

Stockholders' Equity (Deficit) - Preferred Stock (Details) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred Stock, Shares Authorized	20,000,000	0
Preferred stock, shares outstanding	0	0
Preferred Stock
Preferred stock, par value	$ 0.0001
Preferred Stock, Shares Authorized	20,000,000
Preferred stock, shares outstanding	0

Stockholders' Equity (Deficit_8

Stockholders' Equity (Deficit) - Warrants (Details) - $ / shares	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Aug. 26, 2021	Dec. 31, 2020	Mar. 15, 2006
Warrants to purchase shares of common stock					32,961
Warrants, exercise price			$ 11.50		$ 1.14
Warrants to purchase common stock
Balance, beginning of period		32,961
Common Stock Warrants issued to SVB		287,704
Common Stock Warrants as Part of the Merger		5,177,500
Warrants Exercised		(32,961)
Ending balance	5,465,204	5,465,204
Warrants to purchase shares of common stock				32,961
Warrants, exercise price				$ 1.14
Private Placement Warrants
Common Stock Warrants as Part of the Merger		177,500
Ending balance	177,500	177,500
Public Warrants
Common Stock Warrants as Part of the Merger		5,000,000
Warrants Exercised	0
Ending balance	5,000,000	5,000,000
Humacyte, Inc.
Balance, beginning of period		32,961
Common Stock Warrants issued to SVB		287,704
Warrants Exercised		(32,961)
Ending balance	287,704	287,704

Stockholders' Equity (Deficit_9

Stockholders' Equity (Deficit) - Private Placement Warrants (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2021USD ($)	Sep. 30, 2021USD ($)
Change in fair value of common stock warrant liabilities	$ 2	$ 2
Private Placement Warrants
Fair value of warrant liability	600	600
Change in fair value of common stock warrant liabilities	$ 100	$ 100
Private Placement Warrants | Estimated dividend yield
Measurement input	0	0

Stockholders' Equity (Defici_10

Stockholders' Equity (Deficit) - Public Warrants (Details) - $ / shares	Aug. 26, 2021	Sep. 30, 2021	Sep. 30, 2021
Warrants term		10 years	10 years
Warrants to purchase common stock
Warrants Exercised			(32,961)
Public Warrants
Warrants term	5 years
Number of days warrants become exercisable after the completion of merger	30 days
Fair Value per Share on Closing Date	$ 2.80
Warrants Exercised		0

Stockholders' Equity (Defici_11

Stockholders' Equity (Deficit) - Contingent Earnout Liability (Details)	3 Months Ended	9 Months Ended
	Sep. 30, 2021USD ($)Y	Sep. 30, 2021USD ($)YitemD$ / sharesshares	Aug. 26, 2021USD ($)
Contingent consideration (in shares) | shares		15,000,000
Change in fair value of contingent earnout liability | $	$ 9,768,000	$ 9,768,000
Contingent earnout liability
Contingent consideration (in shares) | shares		15,000,000
Number of equal tranches | item		2
Number of trading days within any 30 consecutive trading day period | D		20
Estimated fair value of contingent consideration shares | $			$ 159,400,000
Change in fair value of contingent earnout liability | $		$ 9,800,000
Contingent earnout liability | Tranche one
shares of common stock per tranche | shares		7,500,000
Volume-weighted average closing sale price | $ / shares		$ 15
Contingent earnout liability | Tranche two
Volume-weighted average closing sale price | $ / shares		$ 20
Current stock price | Contingent earnout liability
Measurement input	11.61	11.61	10.96
Expected share price volatility | Contingent earnout liability
Measurement input	78.9	78.9	79.6
Risk-free interest rate | Contingent earnout liability
Measurement input	1.55	1.55	1.34
Estimated dividend yield | Contingent earnout liability
Measurement input	0	0	0
Expected term | Contingent earnout liability
Measurement input	10	10	10

Stock-based Compensation (Det_2

Stock-based Compensation (Details)	Aug. 25, 2021plan	Jan. 31, 2021$ / sharesshares	Sep. 30, 2021$ / sharesshares	Dec. 31, 2020$ / sharesshares	Dec. 31, 2019$ / sharesshares	Aug. 26, 2021shares	Dec. 31, 2018shares
Number of options remaining available for grant			7,730,503	2,948,598
Outstanding awards			6,399,888	4,813,262	5,220,236		5,638,773
Contractual term			10 years	10 years
Vesting period		3 years		36 months
Commencement of involuntary termination term prior to effective date of corporate transaction			30 days	30 days
End of involuntary termination term after effective date of corporate transaction			12 months	12 months
Granted			1,838,029	480,856	621,031
Exercise price | $ / shares			$ 10.28	$ 9.79	$ 8.49
Long-Term Incentive Plan, 2021 [Member]
Number of options remaining available for grant			7,730,503
Annual increase (as a percent)			5.00%
Employee Stock Purchase Plan, 2021[Member]
Number of options remaining available for grant			1,030,033
Annual increase (as a percent)			1.00%
Purchase price as percent of trading price			85.00%
Minimum
Vesting period			36 months
Maximum
Vesting period			48 months
Chief Executive Officer [Member]
Vesting period		3 years
Granted		1,312,984
Exercise price | $ / shares		$ 10.28
Humacyte, Inc.
Share Based Compensation Number Of Plans | plan	2
Humacyte, Inc. | Omnibus Incentive Plan, 2015 [Member]
Outstanding awards						5,886,706
Humacyte, Inc. | Stock Option Plan, 2005 [Member]
Outstanding awards						518,432

Stock-based Compensation - Fa_2

Stock-based Compensation - Fair value of the stock options (Details)	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Assumptions on the date of grant to estimate the fair value of the stock options
Estimated dividend yield	0.00%	0.00%	0.00%	0.00%	0.00%
Expected price volatility	91.60%	91.40%	91.40%
Expected share price volatility, minimum		91.00%	89.40%		89.40%	70.10%
Expected share price volatility, maximum		92.10%	91.60%		91.60%	87.70%
Risk-free interest rate	0.34%	0.68%	0.40%
Risk-free interest rate, minimum		0.62%	0.34%		0.34%	1.76%
Risk-free interest rate, maximum		1.02%	0.75%		0.75%	2.46%
Expected term of options (in years)	6 years	6 years	6 years		6 years	6 years

Stock-based Compensation - Addi

Stock-based Compensation - Additional information (Details) - shares	Sep. 30, 2021	Dec. 31, 2020
Stock-based Compensation
Number of options remaining available for grant	7,730,503	2,948,598

Stock-based Compensation - Ex_2

Stock-based Compensation - Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 1,877	$ 1,170	$ 7,335	$ 3,466	$ 4,694	$ 4,457
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	486	308	1,837	781	1,135	914
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 1,391	$ 862	$ 5,498	$ 2,685	$ 3,559	$ 3,543

Stock-based Compensation - Un_2

Stock-based Compensation - Unrecognized cost (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock-based Compensation
Unrecognized share-based compensation cost	$ 12,480	$ 5,789	$ 7,919
Expected weighted average period compensation costs to be recognized (years)	2 years 1 month 6 days	1 year 8 months 12 days	1 year 9 months 18 days

Stock-based Compensation - Op_2

Stock-based Compensation - Option activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Shares
Options outstanding at the beginning	4,813,262	5,220,236	5,638,773
Granted	1,838,029	480,856	621,031
Exercised	(188,006)	(195,239)	(620,831)
Forfeited	(63,397)	(692,591)	(418,737)
Options outstanding at the end	6,399,888	4,813,262	5,220,236	5,638,773
Vested and exercisable at the end of period	4,092,342	3,392,302
Vested and expected to vest at the end	6,399,888	4,813,262
Weighted Average Exercise Price Per Share
Options outstanding at the beginning (in dollars per share)	$ 6.04	$ 5.22	$ 4.69
Granted (in dollars per share)	10.28	9.79	8.49
Exercised (in dollars per share)	2.97	1.55	1.97
Forfeited (in dollars per share)	7.87	3.76	7.62
Options outstanding at the end (in dollars per share)	7.33	6.04	$ 5.22	$ 4.69
Vested and exercisable at the end of period (in dollars per share)	5.74	4.99
Vested and expected to vest at the end (in dollars per share)	$ 7.33	$ 6.04
Weighted Average Remaining Contractual Term and Aggregate Intrinsic Value
Options outstanding (in years)	6 years 7 months 6 days	6 years 7 months 6 days	6 years 6 months	7 years 4 months 24 days
Vested and exercisable at the end of period (in years)	5 years 1 month 6 days	5 years 10 months 24 days
Vested and expected to vest at the end (in years)	6 years 7 months 6 days	6 years 7 months 6 days
Options outstanding at the beginning (in dollars)	$ 20,422	$ 17,044	$ 21,354
Options outstanding at the end (in dollars)	26,705	20,422	$ 17,044	$ 21,354
Vested and exercisable at the end of period (in years)	23,345	17,925
Vested and expected to vest at the end (in dollars)	$ 26,705	$ 20,422

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Income Taxes
Income tax benefit at statutory rate, Amount					$ (13,970)	$ (17,939)
State income taxes, net of federal benefit, Amount					(1,338)	(1,739)
Tax credits, Amount					(2,625)	(1,821)
Other nondeductible expenses, Amount					90	54
Deferred rate changes, Amount					16	16
Other, Amount					(1,736)	449
Change in valuation allowance, Amount					$ 19,563	$ 20,980
Income tax benefit at statutory rate, Rate					21.00%	21.00%
State income taxes, net of federal benefit, Rate					2.00%	2.00%
Tax credits, Rate					3.90%	2.10%
Other nondeductible expenses, Rate					(0.10%)	0.00%
Deferred rate changes, Rate					0.00%	0.00%
Other, Rate					2.60%	(0.50%)
Change in valuation allowance, Rate					(29.40%)	(24.60%)
Effective tax rate	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%

Commitments and Contingencies_4

Commitments and Contingencies - Patent License Agreements (Details) - Duke university - License agreement - shares	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Agreement expiration term after first commercial sale	4 years	4 years
Threshold notice period required to terminate the agreement	3 months	3 months
Collaborative Arrangement, Shares Issued In Connection With License Agreement	52,693	52,693

Commitments and Contingencies_5

Commitments and Contingencies - Duke Agreement (Details) - Yale university - USD ($) $ in Millions	1 Months Ended		9 Months Ended	12 Months Ended
	Aug. 31, 2019	Feb. 28, 2014	Sep. 30, 2021	Dec. 31, 2020
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payments upon achievement of certain regulatory milestones			$ 0.2
Milestone payments upon achievement of certain commercial milestones			$ 0.6
License agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Threshold notice period required to terminate the agreement			90 days	90 days
License agreement related to coatings for small diameter vessels to inhibit clotting
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative Arrangement, Maximum Annual Maintenance Fee	$ 0.1	$ 0.1
License agreement related to bioartificial vascular pancreas
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative Arrangement, Maximum Annual Maintenance Fee			$ 0.1
License agreement related to tubular prostheses
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative Arrangement, Maximum Annual Maintenance Fee	$ 0.1

Related Party Transactions (D_2

Related Party Transactions (Details) - USD ($) $ in Millions	Aug. 26, 2021	Aug. 31, 2021	Jun. 30, 2018	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2023	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2021
Related Party Transaction [Line Items]
Proceeds from PIPE	$ 175
Common stock, shares issued							5,822,396	5,627,157	103,003,384
Fresenius Medical Care
Related Party Transaction [Line Items]
Financing amount			$ 150
Shares issued for conversion of preferred shares	15,812,735
Proceeds from PIPE		$ 25
Common stock, shares issued		2,500,000
Dr. Niklason, President, CEO and member of board of directors
Related Party Transaction [Line Items]
Aggregate amount						$ 2.5
Payments made				$ 0.1	$ 0.4		$ 0.5	$ 0.4

Related Party Transactions - _2

Related Party Transactions - Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Total	$ 2	$ 149	$ 168	$ 462	$ 620	$ 571
Expenses under MOU
Related Party Transaction [Line Items]
Total		125		375	500	422
License expenses
Related Party Transaction [Line Items]
Total		20	85	70	92	110
Other
Related Party Transaction [Line Items]
Total	$ 2	$ 4	$ 83	$ 17	$ 28	$ 39

Subsequent Events - (Details)

Subsequent Events - (Details) - USD ($)	Oct. 13, 2021	Mar. 31, 2021
Term loan agreement
Subsequent Event [Line Items]
Amount of loan drawn	$ 10,000,000	$ 20,000,000
Number of warrants that becomes exercisable for no probable funding	123,302
Exercise price of warrants that became exercisable for no probable funding (USD per share)	$ 10.28
Subsequent event
Subsequent Event [Line Items]
Amount of loan drawn	$ 10
Number of warrants that becomes exercisable for no probable funding	123,302
Exercise price of warrants that became exercisable for no probable funding (USD per share)	$ 10.28