Ocular Therapeutix (OCUL) 10-K 28 Feb 22 2021 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Feb. 24, 2022	Jun. 30, 2021
Document And Entity Information [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Document Transition Report	false
Entity File Number	001-36554
Entity Registrant Name	Ocular Therapeutix, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-5560161
Entity Address, Address Line One	24 Crosby Drive
Entity Address, City or Town	Bedford
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01730
City Area Code	781
Local Phone Number	357-4000
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	OCUL
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		76,754,160
Auditor Name	PricewaterhouseCoopers LLP
Auditor Firm ID	238
Auditor Location	Boston, Massachusetts
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Entity Central Index Key	0001393434
Amendment Flag	false
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Public Float			$ 1,079

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 164,164	$ 228,057
Accounts receivable, net	21,135	12,252
Inventory	1,250	1,201
Prepaid expenses and other current assets	4,751	4,650
Total current assets	191,300	246,160
Property and equipment, net	6,956	8,095
Restricted cash	1,764	1,764
Operating lease assets	4,867	5,844
Total assets	204,887	261,863
Current liabilities:
Accounts payable	4,592	2,709
Accrued expenses and other current liabilities	20,121	14,307
Operating lease liabilities	1,624	1,358
Notes payable, net of discount, current		8,290
Total current liabilities	26,337	26,664
Other liabilities:
Operating lease liabilities, net of current portion	5,924	7,548
Derivative liability	20,192	98,313
Deferred revenue	13,000	12,000
Notes payable, net of discount	25,000	16,936
2026 convertible notes, net	26,435	24,307
Total liabilities	116,888	185,768
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.0001 par value; 5,000,000 shares authorized and no shares issued or outstanding at December 31, 2021 and December 31, 2020, respectively
Common stock, $0.0001 par value; 200,000,000 and 100,000,000 shares authorized and 76,731,940 and 75,996,732 shares issued and outstanding at December 31, 2021 and December 31, 2020, respectively	8	8
Additional paid-in capital	633,795	615,338
Accumulated deficit	(545,804)	(539,251)
Total stockholders' equity	87,999	76,095
Total liabilities and stockholders' equity	$ 204,887	$ 261,863

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
CONSOLIDATED BALANCE SHEETS
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	100,000,000
Common stock, shares issued	76,731,940	75,996,732
Common stock, shares outstanding	76,731,940	75,996,732

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenue:
Product revenue, net	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Total revenue, net	$ 43,522	$ 17,403	$ 4,227
Costs and operating expenses:
Cost, Product and Service [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Cost of product revenue	$ 4,406	$ 2,083	$ 2,325
Research and development	50,083	28,694	41,091
Selling and marketing	35,190	26,614	24,491
General and administrative	31,880	22,859	22,122
Total costs and operating expenses	121,559	80,250	90,029
Loss from operations	(78,037)	(62,847)	(85,802)
Other income (expense):
Interest income	33	168	1,229
Interest expense	(6,671)	(6,768)	(6,101)
Change in fair value of derivative liability	78,121	(86,189)	4,310
Other income (expense), net	1		(8)
Total other income (expense), net	71,484	(92,789)	(570)
Net loss and comprehensive loss	$ (6,553)	$ (155,636)	$ (86,372)
Net loss per share, basic	$ (0.09)	$ (2.56)	$ (1.91)
Weighted average common shares outstanding, basic	76,392,870	60,752,225	45,273,231
Net loss per share, diluted	$ (0.98)	$ (2.56)	$ (1.91)
Weighted average common shares outstanding, diluted	82,162,102	60,752,225	45,273,231

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Total
Balance at Dec. 31, 2018	$ 4	$ 333,114	$ (297,243)	$ 35,875
Balance, shares at Dec. 31, 2018	41,518,091
Stockholders' Equity (Deficit)
Issuance of common stock upon exercise of stock options		78		78
Issuance of common stock upon exercise of stock options, shares	28,583
Issuance of common stock in connection with employee stock purchase plan		451		451
Issuance of common stock in connection with employee stock purchase plan, shares	130,945
Issuance of common stock upon public offering, net of issuance costs	$ 1	37,578		37,579
Issuance of common stock upon public offering, net of issuance costs, shares	8,655,940
Stock-based compensation expense		8,759		8,759
Net loss			(86,372)	(86,372)
Balance at Dec. 31, 2019	$ 5	379,980	(383,615)	(3,630)
Balance, shares at Dec. 31, 2019	50,333,559
Stockholders' Equity (Deficit)
Issuance of common stock upon exercise of stock options	$ 1	2,585		2,586
Issuance of common stock upon exercise of stock options, shares	567,776
Issuance of common stock in connection with employee stock purchase plan		747		747
Issuance of common stock in connection with employee stock purchase plan, shares	161,175
Issuance of common stock upon public offering, net of issuance costs	$ 2	224,495		224,497
Issuance of common stock upon public offering, net of issuance costs, shares	24,934,222
Stock-based compensation expense		7,531		7,531
Net loss			(155,636)	(155,636)
Balance at Dec. 31, 2020	$ 8	615,338	(539,251)	76,095
Balance, shares at Dec. 31, 2020	75,996,732
Stockholders' Equity (Deficit)
Issuance of common stock upon exercise of stock options		2,586		$ 2,586
Issuance of common stock upon exercise of stock options, shares	598,923			598,924
Issuance of common stock upon cashless exercise of warrant, shares	11,737
Common stock issuance costs		(91)		$ (91)
Issuance of common stock in connection with employee stock purchase plan		985		985
Issuance of common stock in connection with employee stock purchase plan, shares	124,548
Stock-based compensation expense		14,977		14,977
Net loss			(6,553)	(6,553)
Balance at Dec. 31, 2021	$ 8	$ 633,795	$ (545,804)	$ 87,999
Balance, shares at Dec. 31, 2021	76,731,940

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (6,553)	$ (155,636)	$ (86,372)
Adjustments to reconcile net loss to net cash used in operating activities
Stock-based compensation expense	14,977	7,531	8,759
Non-cash interest expense	4,628	4,415	3,683
Change in fair value of derivative liability	(78,121)	86,189	(4,310)
Depreciation and amortization expense	2,421	2,773	2,530
Gain on disposal of property and equipment	(1)		7
Changes in operating assets and liabilities:
Accounts receivable	(8,883)	(9,704)	(2,347)
Prepaid expenses and other current assets	(101)	(2,419)	(518)
Inventory	(49)	(247)	(737)
Operating lease assets	977	811	733
Accounts payable	1,796	(452)	124
Accrued expenses	3,717	2,311	1,714
Deferred revenue	1,000	12,000
Operating lease liabilities	(1,358)	(1,125)	(844)
Net cash used in operating activities	(65,550)	(53,554)	(77,578)
Cash flows from investing activities:
Purchases of property and equipment	(1,194)	(841)	(2,238)
Net cash used in investing activities	(1,194)	(841)	(2,238)
Cash flows from financing activities:
Proceeds from issuance of notes payable, net	3,722
Proceeds from issuance of 2026 convertible notes, net of issuance costs			37,275
Proceeds from exercise of stock options	2,586	2,585	78
Proceeds from issuance of common stock pursuant to employee stock purchase plan	985	747	451
Proceeds from the Paycheck Protection Program Loan		3,201
Repayment of the Paycheck Protection Program Loan		(3,201)
Proceeds from issuance of common stock upon public offering, net of issuance costs		224,682	37,537
Issuance costs from the issuance of common stock upon public offering	(275)
Repayment of notes payable	(4,167)
Net cash provided by financing activities	2,851	228,014	75,341
Net (decrease) increase in cash, cash equivalents and restricted cash	(63,893)	173,620	(4,475)
Cash, cash equivalents and restricted cash at beginning of period	229,821	56,201	60,676
Cash, cash equivalents and restricted cash at end of period	165,928	229,821	56,201
Supplemental disclosure of cash flow information:
Cash paid for interest	1,932	2,354	2,298
Supplemental disclosure of non-cash investing and financing activities:
Additional right of use asset and related lease liability			2,044
Additions to property and equipment included in accounts payable and accrued expenses at balance sheet dates	$ 181	91	214
Derivative liability in connection with issuance of 2026 convertible notes			16,434
Public offering costs included in accounts payable and accrued expenses at balance sheet dates		$ 184	$ 42

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	12 Months Ended
	Dec. 31, 2021
Nature of the Business and Basis of Presentation
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation ​ Ocular Therapeutix, Inc. (the “Company”) was incorporated on September 12, 2006 under the laws of the State of Delaware. The Company is a biopharmaceutical company focused on the formulation, development and commercialization of innovative therapies for diseases and conditions of the eye using its proprietary, bioresorbable hydrogel platform technology. The Company’s product pipeline candidates provide differentiated drug delivery solutions that reduce the complexity and burden of the current standard of care by creating local programmed-release alternatives. Since inception, the Company’s operations have been primarily focused on organizing and staffing the Company, acquiring rights to intellectual property, business planning, raising capital, developing its technology, identifying product candidates, undertaking preclinical studies and clinical trials, manufacturing initial quantities of its products and product candidates and building the initial sales and marketing infrastructure for the commercialization of the Company’s approved products and product candidates and launching its initial product. ​ The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations, regulatory approval and compliance, reimbursement, uncertainty of market acceptance of products and the need to obtain additional financing. Recently approved products will require significant sales, marketing and distribution support up to and including upon their launch. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval, prior to commercialization. ​ As of December 31, 2021, the Company had two FDA-approved products in commercialization in the United States: DEXTENZA® (dexamethasone insert) 0.4mg, an intracanalicular insert for the treatment of post-surgical ocular inflammation and pain and ReSure® Sealant, an ophthalmic device designed to prevent wound leaks in corneal incisions following cataract surgery. In October 2021, DEXTENZA received approval for the treatment of ocular itching associated with allergic conjunctivitis. While ReSure Sealant is commercially available in the United States, it does not receive sales support, is not currently being manufactured by the Company, and has not in the past generated, nor is it anticipated to in the future to generate, material revenues. The Company’s most advanced product candidates are in either Phase 1 or Phase 2 of clinical stage development. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, that any products developed will obtain necessary government regulatory approval and adequate reimbursement or that any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapidly changing technology and substantial competition from pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees and consultants. The Company may not be able to generate significant revenue from sales of any product for several years, if at all. Accordingly, the Company will need to obtain additional capital to finance its operations. ​ The Company has incurred losses and negative cash flows from operations since its inception, and the Company expects to continue to generate operating losses and negative cash flows from operations in the foreseeable future. As of December 31, 2021, the Company had an accumulated deficit of $545,804. The Company believes that its existing cash and cash equivalents of $164,164, as of December 31, 2021, along with its current operating plan, which includes revenues from the sale of DEXTENZA, will enable it to fund its planned operating expenses, debt service obligations and capital expenditure at least through the next 12 months. The future viability of the Company beyond that point is dependent on its ability to generate cash flows from the sale of DEXTENZA and raise additional capital to finance its operations. The Company will need to finance its operations through public or private securities offerings, debt financings or other sources, which may include licensing, collaborations or other strategic transactions or arrangements. Although the Company has been successful in raising capital in the past, there is no assurance that it will be successful in obtaining such additional financing on terms acceptable to the Company, if at all. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate some or all of its research and development programs for product candidates, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations. ​ The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). ​ Risks and Uncertainties ​ The Company is monitoring the potential impact of the COVID-19 pandemic, if any, on the carrying value of certain assets. To date, the Company has not experienced a material business disruption, nor has it incurred impairment of any assets as a result of the COVID-19 pandemic. The extent to which these events may impact the Company’s business will depend on future developments, which are highly uncertain and cannot be predicted at this time. The duration and intensity of the COVID-19 pandemic and any resulting disruption to the Company’s operations is uncertain, and the Company will continue to assess the impact of the COVID-19 pandemic on its financial position.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2021
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies ​ Basis of Presentation and Principles of Consolidation The accompanying consolidated financial statements reflect the operations of the Company and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated. ​ Use of Estimates ​ The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of revenues and expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, revenue recognition, and the fair value of derivatives. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates. ​ Cash Equivalents ​ The Company considers all short-term, highly liquid investments with original maturities of ninety days or less at date of purchase to be cash equivalents. Cash equivalents, which primarily consist of money market accounts, are stated at fair value. ​ Revenue Recognition ​ Product Revenue ​ The Company recognizes product revenue from DEXTENZA for the treatment of post-surgical ocular inflammation and pain, which it began selling to customers in June 2019, and ReSure Sealant. The Company has generated limited revenues from ReSure Sealant to date and does not expect significant future sales. ​ In November 2018, the FDA approved DEXTENZA for the treatment of ocular pain following ophthalmic surgery. The Company entered into a limited number of arrangements with specialty distributors in the United States to distribute DEXTENZA. The Company recognizes revenue in accordance with Accounting Standards Codification 606 – Revenue from Contracts with Customers ​ To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity performs the following five steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract, and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to arrangements that meet the definition of a contract with a customer under Topic 606, including when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, the Company assesses the goods or services promised within each contract, determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. For a complete discussion of accounting for product revenue, see Product Revenue, Net (below). ​ Product Revenue, Net ​ The Company recognizes revenue on product sales when the customer obtains control of the Company's product, which occurs at a point in time (upon delivery to the customer). The Company has determined that the delivery of DEXTENZA to its customers constitutes a single performance obligation. There are no other promises to deliver goods or services beyond what is specified in each accepted customer order. The Company has assessed the existence of a significant financing component in the agreements with its customers. The trade payment terms with the Company’s customers do not exceed one year and therefore the Company has elected to apply the practical expedient and no amount of consideration has been allocated as a financing component. Product revenues are recorded net of applicable reserves for variable consideration, including discounts and allowances. ​ Transaction Price, including Variable Consideration ​ The amount of variable consideration which is included in the transaction price may be constrained, and is included in the net sales price, only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized under the contract will not occur in a future period. Actual amounts of consideration ultimately received may differ from the Company’s estimates. If actual results in the future vary from the Company’s original estimates, the Company will adjust these estimates, which would affect net product revenue and earnings in the period such variances become known. ​ Trade Discounts and Allowances ​ Product Returns The Company estimates the amount of its product sales that may be returned by its customers and records this estimate as a reduction of revenue in the period the related product revenue is recognized, as well as within accrued expenses and other current liabilities, in the accompanying consolidated balance sheets. The Company currently estimates product return reserves using available industry data and its own sales information, including its visibility into the inventory remaining in the distribution channel. The Company has received no returns to date and believes the returns of DEXTENZA will be minimal. ​ Government Chargebacks U.S. The 340B Drug Discount Program is a U.S. federal government program created in 1992 that requires drug manufacturers to provide outpatient drugs to eligible health care organizations and covered entities at significantly reduced prices. Customers charge the Company for the difference between what they pay for the product and the statutory selling price to the qualified government entity. These allowances are established in the same period that the related revenue is recognized, resulting in a reduction of product revenue and accounts receivables, net. Chargeback amounts are generally determined at the time of resale to the qualified government healthcare provider by customers, and the Company generally issues credits for such amounts within a few weeks of the Customer’s notification to the Company of the resale. Allowance for chargebacks consist of credits that the Company expects to issue for units that remain in the distribution channel inventories at each reporting period-end that the Company expects will be sold to qualified healthcare providers, and chargebacks that customers have claimed, but for which the Company has not yet issued a credit. ​ Government Rebates ​ Rebates ​ Other Incentives ​ Collaboration Revenue ​ To determine the appropriate amount of revenue to be recognized for arrangements the Company determines are within the scope of Topic 606, the Company performs the following steps: (i) identify the contract(s) with its customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when or as each performance obligation is satisfied. ​ The Company accounts for a contract with a customer that is within the scope of Topic 606 when all of the following criteria are met: (i) the arrangement has been approved by the parties and the parties are committed to perform their respective obligations; (ii) each party’s rights regarding the goods and/or services to be transferred can be identified; (iii) the payment terms for the goods and/or services to be transferred can be identified; (iv) the arrangement has commercial substance; and (v) collection of substantially all of the consideration to which the Company will be entitled in exchange for the goods and/or services that will be transferred to the customer is probable. The Company also determines the term of the contract based on the period in which the Company and its customer have present and enforceable rights and obligations for purposes of identifying the performance obligations and determining the transaction price. ​ The Company evaluates contracts that contain multiple promises to determine which promises are distinct. Promises are considered to be distinct and therefore, accounted for as separate performance obligations, provided that: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer and (ii) the promise to transfer the good or service to the customer is separately identifiable from other promises in the contract. In assessing whether a promise is distinct, the Company considers factors such as whether: (i) the Company provides a significant service of integrating goods and/or services with other goods and/or services promised in the contract; (ii) one or more of the goods and/or services significantly modifies or customizes, or are significantly modified or customized by one or more of the other goods and/or services promised in the contract; and (iii) the goods and/or services are highly interdependent or highly interrelated. Individual goods or services (or bundles of goods and/or services) that meet both criteria for being distinct are accounted for as separate performance obligations. Promises that are not distinct at contract inception are combined and accounted for as a single performance obligation. Options to acquire additional goods and/or services are evaluated to determine if such option provides a material right to the customer that it would not have received without entering into the contract. If so, the option is accounted for as a separate performance obligation. If not, the option is considered a marketing offer which would be accounted for as a separate contract upon the customer’s election. ​ The transaction price is generally comprised of an upfront payment due at contract inception and variable consideration in the form of payments for the Company’s goods and services and materials and milestone payments due upon the achievement of specified events. Other payments the Company could be entitled to include tiered royalties earned when customers recognize net sales of licensed products. The Company considers the existence of any significant financing component within its arrangements and have determined that a significant financing component does not exist in its arrangements as substantive business purposes exist to support the payment structure other than to provide a significant benefit of financing. The Company measures the transaction price based on the amount of consideration to which the Company expects to be entitled in exchange for transferring the promised goods and/or services to the customer. The Company utilizes either the expected value method or the most likely amount method to estimate the amount of variable consideration, depending on which method is expected to better predict the amount of consideration to which the Company will be entitled. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. With respect to arrangements that include payments for a development or regulatory milestone payment, the Company evaluates whether the associated event is considered likely of achievement and estimates the amount to be included in the transaction price using the most likely amount method. Milestone payments that are not within the Company’s control or the licensee, such as those dependent upon receipt of regulatory approval, are not considered to be likely of achievement until the triggering event occurs. At the end of each reporting period, the Company re-evaluates the probability of achievement of each milestone and any related constraint, and if necessary, adjust its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenue and net loss in the period of adjustment. For arrangements that include sales-based royalties, including milestone payments based upon the achievement of a certain level of product sales, wherein the license is deemed to be the sole or predominant item to which the payments relate, the Company recognizes revenue upon the later of: (i) when the related sales occur or (ii) when the performance obligation to which some or all of the payment has been allocated has been satisfied (or partially satisfied). Consideration that would be received for optional goods and/or services is excluded from the transaction price at contract inception. ​ The Company recognizes as an asset the incremental costs of obtaining a contract with a customer if the costs are expected to be recovered. The Company has elected a practical expedient wherein it recognizes the incremental costs of obtaining a contract as an expense when incurred if the amortization period of the asset that it otherwise would have recognized is one year or less. To date, the Company has not incurred any incremental costs of obtaining a contract with a customer. ​ Inventory ​ The Company values its inventories at the lower of cost or estimated net realizable value. The Company determines the cost of its inventories, which includes amounts related to materials and manufacturing overhead, on a first-in, first-out basis. The Company performs an assessment of the recoverability of capitalized inventory during each reporting period, and it writes down any excess and obsolete inventories to their estimated realizable value in the period in which the impairment is first identified. Such impairment charges, should they occur, are recorded within cost of product revenue. The determination of whether inventory costs will be realizable requires estimates by management. If actual market conditions are less favorable than projected by management, additional write-downs of inventory may be required, which would be recorded as a cost of product revenue in the consolidated statements of operations and comprehensive loss. The Company capitalizes inventory costs associated with the Company’s products after regulatory approval when, based on management’s judgment, future commercialization is considered probable and the future economic benefit is expected to be realized. Inventory acquired prior to receipt of marketing approval of a product candidate is expensed as research and development expense as incurred. Inventory that can be used in either the production of clinical or commercial product is expensed as research and development expense when selected for use in a clinical manufacturing campaign. Inventory produced that will be used in promotional marketing campaigns is expensed to selling and marketing expense when it is selected for use in a marketing program. ​ Inventory consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ December 31, ​ ​ 2021 2020 Raw materials ​ $ 388 ​ $ 384 Work-in-process ​ 605 ​ 232 Finished goods ​ ​ 257 ​ ​ 585 ​ ​ $ 1,250 ​ $ 1,201 ​ Restricted Cash ​ As of December 31, 2021, 2020 and 2019, the Company held restricted cash of $1,764 , respectively, on its consolidated balance sheet. The Company held restricted cash as security deposits for the lease of its manufacturing space and corporate headquarters. ​ The Company’s statements of cash flows include restricted cash with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on such statements. A reconciliation of the cash, cash equivalents, and restricted cash reported within the balance sheet that sum to the total of the same amounts shown in the statement of cash flows is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ December 31, ​ 2021 2020 2019 Cash and cash equivalents ​ $ 164,164 ​ $ 228,057 ​ $ 54,437 Restricted cash ​ ​ 1,764 ​ ​ 1,764 ​ ​ 1,764 Total cash, cash equivalents and restricted cash as shown on the statements of cash flows ​ $ 165,928 ​ $ 229,821 ​ $ 56,201 ​ Concentration of Credit Risk and of Significant Suppliers and Customers ​ Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents and accounts receivable. The Company has all cash and cash equivalents balances at one accredited financial institution, in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. ​ ​ The Company is dependent on a small number of third-party manufacturers to supply products for research and development activities in its preclinical and clinical programs and for sales of its products. The Company’s development programs as well as revenue from future sales of its product sales could be adversely affected by a significant interruption in the supply of any of the components of these products. ​ For the year ended December 31, 2021, three specialty distributor customers accounted for 42%, 26% and 17% of the Company’s total revenue and three specialty distributor customers accounted for 42%, 26% and 21% of the Company’s total accounts receivable. No other customer accounted for more than 10% of total revenue or accounts receivable for the year ended December 31, 2021. ​ For the year ended December 31, 2020, three specialty distributor customers accounted for 42%, 29% and 12% of the Company’s total revenue and three specialty distributor customers accounted for 42%, 33% and 15% of the Company’s total accounts receivable. No other customer accounted for more than 10% of total revenue or accounts receivable for the year ended December 31, 2020. ​ Fair Value Measurements ​ Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: ​ ● Level 1—Quoted prices in active markets for identical assets or liabilities. ​ ● Level 2—Observable inputs (other than Level 1 quoted prices) such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. ​ ● Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. ​ The Company’s cash equivalents at December 31, 2021 and 2020 were carried at fair value determined according to the fair value hierarchy described above (Note 3). ​ The carrying value of the Company’s variable interest rate notes payable (Note 9) are recorded at amortized costs, which approximates fair value due to their short-term nature. ​ On March 1, 2019, the Company issued $37,500 aggregate principal amount of unsecured senior subordinated convertible notes (the “2026 Convertible Notes”) (Note 5) which is carried, net of derivative liability, at its amortized cost of $26,435 at December 31, 2021. The estimated fair value of the 2026 Convertible Notes was $52,790 and $129,362 at December 31, 2021 and 2020. The fair value of the 2026 Convertible Notes was estimated utilizing a binomial lattice model which requires the use of Level 3 unobservable inputs. The main input when determining the fair value of the 2026 Convertible Notes is the bond yield that pertains to the host instrument without the conversion option. The significant assumption used in determining the bond yield is the market yield movements of a comparable instrument issued as of the valuation date, which is assessed and updated each period. The main input when determining the fair value for disclosure purposes is the bond yield which is updated each period to reflect the yield of a comparable instrument issued as of the valuation date. The estimated fair value presented is not necessarily indicative of an amount that could be realized in a current market exchange. The use of alternative inputs and estimation methodologies could have a material effect on these estimates of fair value. ​ Derivative Liability ​ The 2026 Convertible Notes allow the holders to convert all or part of the outstanding principal of their 2026 Convertible Notes into shares of the Company’s common stock provided that no conversion results in a holder beneficially owning more than 19.99% of the issued and outstanding common stock of the Company. The entire embedded conversion option is required to be separated from the 2026 Convertible Notes and accounted for as a freestanding derivative instrument subject to derivative accounting. The main input when determining the fair value of the 2026 Convertible Notes is the bond yield that pertains to the host instrument without the conversion option. The significant assumption used in determining the bond yield is the market yield movements of a comparable instrument issued as of the valuation date, which is assessed and updated each period. Therefore, the entire conversion option is bifurcated from the underlying debt instrument and accounted for and valued separately from the host instrument. The Company measures the value of the embedded conversion option at its estimated fair value and recognizes changes in the estimated fair value in other income (expense), net in the consolidated statements of operations and comprehensive loss during the period of change. The embedded conversion is recognized as a derivative liability in the Company’s consolidated balance sheet. ​ Property and Equipment ​ Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over a three ​ Impairment of Long-Lived Assets and Right of Use Assets ​ Long-lived assets consist of property and equipment and right-of-use assets. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends, and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. The Company has had no impairment triggers of long-lived assets. ​ Research and Development Costs ​ Research and development costs are expensed as incurred. Included in research and development expenses are salaries, stock-based compensation and benefits of employees and other operational costs related to the Company’s research and development activities, including external costs of outside vendors engaged to conduct preclinical studies and clinical trials, manufacturing costs of the Company’s products prior to regulatory approval, costs related to collaboration agreements and facility-related expenses. ​ Research Contract Costs and Accruals ​ The Company has entered into various research and development contracts with research institutions and other companies both inside and outside of the United States. Certain of these agreements have cancellation clauses, and related payments are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs. ​ ​ Patent Costs ​ All patent-related costs incurred in connection with filing and prosecuting patent applications are recorded as general and administrative expenses as incurred, as recoverability of such expenditures is uncertain. ​ Accounting for Stock-Based Compensation ​ The Company measures all stock options and other stock-based awards granted to employees and directors at the fair value on the date of the grant using the Black-Scholes option-pricing model. The fair value of the awards is recognized as expense, net of estimated forfeitures, over the requisite service period, which is generally the vesting period of the respective award. The straight-line method of expense recognition is applied to all awards with service-only conditions. ​ Following the Company’s adoption of Accounting Standards Update (“ASU”) 2018-07, Compensation—Stock Compensation (Topic 718), Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-07”), on January 1, 2019, for stock-based awards issued to non-employees, the Company no longer revalues non-employee awards at each reporting date and instead calculates the fair value of the awards as of the grant date using the Black-Scholes option-pricing model. Compensation expense for these awards is recognized over the related service period. ​ The Company classifies stock-based compensation expense in its consolidated statement of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified. ​ The Company recognizes compensation expense for only the portion of awards that are expected to vest. In developing a forfeiture rate estimate, the Company has considered its historical experience to estimate pre-vesting forfeitures for service-based awards. The impact of a forfeiture rate adjustment will be recognized in full in the period of adjustment, and if the actual forfeiture rate is materially different from the Company’s estimate, the Company may be required to record adjustments to stock-based compensation expense in future periods. ​ Income Taxes ​ The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. ​ The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties. ​ ​ Segment Data ​ The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on advancing its bioresorbable hydrogel product candidates for the programed-release delivery of therapeutic agents, specifically for ophthalmology. All tangible assets are held in the United States. Revenue to date has been generated through product sales, all of which has been earned in the United States. ​ Comprehensive Loss ​ Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the years ended December 31, 2021, 2020 and 2019, there were no items that gave rise to other comprehensive loss and therefore, there was no difference between net loss and comprehensive loss. ​ Net Loss Per Share ​ Basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net loss attributable to common stockholders is computed by adjusting net loss attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities, including the assumed conversion of the Company’s 2026 Convertible Notes, outstanding stock options and common stock warrants, except where the result would be anti-dilutive. Diluted net loss per share attributable to common stockholders is computed by dividing the diluted net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period, including potential dilutive common shares assuming the dilutive effect of the conversion of the 2026 Convertible Notes, the exercise of outstanding stock options and common stock warrants. In the diluted net loss per share calculation, net loss would also be adjusted for the elimination of interest expense on the 2026 Convertible Notes (which includes amortization of the discount created upon bifurcation of the conversion option from the debt) and, the mark-to-market gain or loss each period to the bifurcated conversion option, if the impact was not anti-dilutive. ​ Recently Adopted Accounting Pronouncements ​ In December 2019, the FASB issued ASU No. 2019-12, Income Taxes Topic 740, Simplifying the Accounting for Income Taxes (“ASU 2019-12”). ASU 2019-12 removes certain exceptions for investments, intra-period allocations and interim calculations, and adds guidance to reduce complexity in accounting for income taxes. The guidance is effective for fiscal years beginning after December 15, 2020, including interim periods within those fiscal years. The Company adopted this accounting pronouncement as required effective January 1, 2021 and its adoption did not have a material impact on the consolidated financial statements. ​ In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (‘‘ASU 2016-13’’), which requires the measurement and recognition of expected credit losses for financial assets held at amortized cost. ASU 2016-13 replaces the existing incurred loss impairment

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	12 Months Ended
	Dec. 31, 2021
Fair Value of Financial Assets and Liabilities
Fair Value of Financial Assets and Liabilities	3. Fair Value of Financial Assets and Liabilities ​ The following tables present information about the Company’s financial assets and liabilities that are measured at fair value on a recurring basis as of December 31, 2021 and 2020 and indicate the level of the fair value hierarchy utilized to determine such fair value: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements as of ​ ​ December 31, 2021 Using: ​ Level 1 Level 2 Level 3 Total Assets: ​ ​ ​ ​ Cash equivalents: ​ ​ ​ ​ Money market funds ​ $ 62,392 ​ $ — ​ $ — ​ $ 62,392 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Liability: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Derivative liability (Note 4) ​ $ — ​ $ — ​ $ 20,192 ​ $ 20,192 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements as of ​ ​ December 31, 2020 Using: ​ Level 1 Level 2 Level 3 Total Assets: ​ ​ ​ ​ Cash equivalents: ​ ​ ​ ​ Money market funds ​ $ 213,372 ​ $ — ​ $ — ​ $ 213,372 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Liability: ​ ​ ​ ​ Derivative liability (Note 4) ​ $ — ​ $ — ​ $ 98,313 ​ $ 98,313 ​ During the year ended December 31, 2021 and 2020, there were no transfers between Level 1 and 2.

Derivative Liability

Derivative Liability	12 Months Ended
	Dec. 31, 2021
Derivative Liability
Derivative Liability	4. Derivative Liability ​ The 2026 Convertible Notes (Note 5) contained an embedded conversion option that met the criteria to be bifurcated and accounted for separately from the 2026 Convertible Notes (the "Derivative Liability"). The Derivative Liability was recorded at fair value upon the issuance of the 2026 Convertible Notes and is subsequently remeasured to fair value at each reporting period. The Derivative Liability was initially valued and remeasured using a "with-and-without" method. The "with-and-without" methodology involves valuing the whole instrument on an as-is basis and then valuing the instrument without the embedded conversion option. The difference between the entire instrument with the embedded conversion option compared to the instrument without the embedded conversion option is the fair value of the derivative, recorded as the Derivative Liability. ​ The fair value of the 2026 Convertible Notes with and without the conversion option is estimated using a binomial lattice approach. The main inputs to valuing the 2026 Convertible Notes with the conversion option are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of ​ ​ ​ December 31, ​ December 31, ​ ​ ​ 2021 ​ 2020 ​ Company's stock price ​ $ 6.97 ​ $ 20.70 ​ Expected annual volatility ​ ​ 82.6 % ​ 105.5 % Bond yield ​ ​ 12.6 % ​ 12.0 % ​ The bond yield was derived by making the fair value of the 2026 Convertible Notes equal to the face value on the issuance date. Fair value measurements are highly sensitive to changes in these inputs and significant changes in these inputs would result in a significantly higher or lower fair value. ​ A roll forward of the derivative liability is as follows: ​ ​ ​ ​ ​ ​ ​ As of Balance at December 31, 2019 ​ $ 12,124 Change in fair value ​ ​ 86,189 Balance at December 31, 2020 ​ ​ 98,313 Change in fair value ​ ​ (78,121) Balance at December 31, 2021 ​ $ 20,192 ​

Convertible Notes

Convertible Notes	12 Months Ended
	Dec. 31, 2021
Convertible Notes
Convertible Notes	5. Convertible Notes ​ On March 1, 2019, the Company issued $37,500 of 2026 Convertible Notes. Each 2026 Convertible Note accrues interest at an annual rate of 6% of its outstanding principal amount, which is payable, along with the principal amount at maturity, on March 1, 2026, unless earlier converted, repurchased or redeemed. The Company presents accrued interest in accrued current liabilities because the notes are currently convertible and the interest is payable in cash. The effective annual interest rate for the 2026 Convertible Notes was ​ The holders of the 2026 Convertible Notes may convert all or part of the outstanding principal amount of their 2026 Convertible Notes into shares of the Company’s common stock, par value $0.0001 per share, prior to maturity and provided that no conversion results in a holder beneficially owning more than 19.99% of the issued and outstanding common stock of the Company. The conversion rate is initially 153.8462 shares of the Company’s common stock per $1,000 principal amount of the 2026 Convertible Notes, which is equivalent to an initial conversion price of $6.50 per share. The conversion rate is subject to adjustment in customary circumstances such as stock splits or similar changes to the Company’s capitalization. ​ At its election, the Company may choose to make such conversion payment in cash, in shares of common stock, or a combination thereof. Upon any conversion of any 2026 Convertible Note, the Company is obligated to make a cash payment to the holder of such 2026 Convertible Note for any interest accrued but unpaid on the principal amount converted. Upon the occurrence of a Corporate Transaction (as defined below), each holder has the option to require the Company to repurchase all or part of the outstanding principal amount of such note at a repurchase price equal to 100% of the outstanding principal amount of the 2026 Convertible Note to be repurchased, plus accrued and unpaid interest to, but excluding the repurchase date. In addition, each holder is entitled to receive an additional make-whole cash payment in accordance with a table set forth in each 2026 Convertible Note. ​ Upon conversion by the holder, the Company has the right to select the settlement of the conversion in either shares of common stock, cash, or in a combination thereof. In addition, the Company is obligated to make a cash payment to the holder of such 2026 Convertible Note for any interest accrued but unpaid on the principal amount converted. ​ ● If the Company elects to satisfy such conversion by shares of common stock, the Company shall deliver to the converting holder in respect of each $1,000 principal amount of 2026 Convertible Notes being converted a number of common shares equal to the conversion rate in effect on the conversion date; ● If the Company elects to satisfy such conversion by cash settlement, the Company shall pay to the converting holder in respect of each $1,000 principal amount of 2026 Convertible Notes being converted cash in an amount equal to the sum of the Daily Conversion Values (as defined below) for each of the twenty (20 ) consecutive trading days during a specified period. The “Daily Conversion Values” is defined as each of the 20 consecutive trading days during the specified period, 5.0% of the product of (a) the conversion rate on such trading day and (b) the Daily VWAP on such trading day. The Daily VWAP is defined as each of the 20 consecutive trading days during the applicable Observation Period, the per share volume-weighted average price as displayed under the heading “Bloomberg VWAP” on the Bloomberg page for the Company. ● If the Company elects to satisfy such conversion by combination, the Company shall pay or deliver, as the case may be, in respect of each $1,000 principal amount of 2026 Convertible Notes being converted, a settlement amount equal to the sum of the Daily Settlement Amounts (as defined below) for each of the twenty (20) consecutive trading days during the specified period. The “Daily Settlement Amount” is defined as, for each of the 20 consecutive trading days during the specified period: (a) cash in an amount equal to the lesser of (i) the Daily Measurement Value (as defined below) and (ii) the Daily Conversion Value on such Trading Day; and (b) if the Daily Conversion Value on such trading day exceeds the Daily Measurement Value, a number of Shares equal to (i) the difference between the Daily Conversion Value and the Daily Measurement Value, divided by (ii) the Daily VWAP for such Trading Day. The “Daily Measurement Value” is defined as the Specified Dollar Amount (as defined below) , if any, divided by 20. The “Specified Dollar Amount” is defined as the maximum cash amount per $1,000 principal amount of Notes to be received upon conversion as specified in the notice specifying the Company’s chosen settlement method. In the event of a Corporate Transaction, the noteholder shall have the right to either (a) convert all of the unpaid principal at the conversion rate and receive a cash payment equal to (i) the outstanding accrued but unpaid interest under the 2026 Convertible Note to, but excluding, the corporate transaction conversion date (to the extent such date occurs prior to March 1, 2026, the maturity date of the 2026 Convertible Notes) plus (ii) and an additional amount of consideration based on a sliding scale depending on the date of such as Corporate transaction or (b) require the Company to repurchase all or part of the outstanding principal amount of such 2026 Convertible Note at a repurchase price equal to 100% of the outstanding principal amount of the 2026 Convertible Note to be repurchased, plus accrued and unpaid interest to, but excluding, the repurchase date. ​ A corporate transaction includes (i) a merger or consolidation executed through a tender offer or change of control (other than one in which stockholders of the Company own a majority by voting power of the outstanding shares of the surviving or acquiring corporation); (ii) a sale, lease, transfer, of all or substantially all of the assets of the Company; or (iii) if the Company’s common stock ceases to be listed or quoted on any of the New York Stock Exchange, the Nasdaq Global Select Market, the Nasdaq Global Market or the Nasdaq Capital Market (the “Corporate Transaction”). ​ On or after March 1, 2022, if the last reported sale price of the common stock has been at least 130% of the conversion rate then in effect for 20 of the preceding 30 trading days (including the last trading day of such period), the Company is entitled, at its option, to redeem all or part of the outstanding principal amount of the 2026 Convertible Notes, on a pro rata basis, at an optional redemption price equal to 100% of the outstanding principal amount of the 2026 Convertible Notes to be redeemed, plus accrued and unpaid interest to, but excluding, the optional redemption date. ​ The 2026 Convertible Notes are subject to acceleration upon the occurrence of specified events of default, including a default or breach of certain contracts material to the Company and the delisting and deregistration of the Company’s common stock. ​ As discussed in Note 4, the Company determined that the embedded conversion option is required to be separated from the 2026 Convertible Notes and accounted for as a freestanding derivative instrument subject to derivative accounting. The allocation of proceeds to the conversion option results in a discount on the 2026 Convertible Notes. The Company is amortizing the discount to interest expense over the term of the 2026 Convertible Notes using the effective interest method. ​ A summary of the 2026 Convertible Notes at December 31, 2021 and 2020 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2021 2020 2026 Convertible Notes ​ $ 37,500 ​ $ 37,500 Less: unamortized discount ​ ​ (11,065) ​ ​ (13,193) Total ​ $ 26,435 ​ $ 24,307 ​

Property and Equipment, net

Property and Equipment, net	12 Months Ended
	Dec. 31, 2021
Property and Equipment, net
Property and Equipment, net	6. Property and Equipment, net ​ Property and equipment, net consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2021 2020 Equipment ​ $ 10,989 ​ $ 10,186 Leasehold improvements ​ 9,074 ​ 9,074 Furniture and fixtures ​ 1,286 ​ 1,281 Software ​ 236 ​ 220 Construction in progress ​ 578 ​ 120 ​ ​ 22,163 ​ 20,881 Less: Accumulated depreciation and amortization ​ (15,207) ​ (12,786) ​ ​ $ 6,956 ​ $ 8,095 ​ Depreciation and amortization expense was $2,421, $2,773 and $2,530 for the years ended December 31, 2021, 2020 and 2019, respectively.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2021
Accrued Expenses
Accrued Expenses	7. Accrued Expenses ​ Accrued expenses consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2021 2020 Accrued payroll and related expenses ​ $ 6,597 ​ $ 5,853 Accrued rebates and programs ​ ​ 3,615 ​ ​ 1,438 Accrued professional fees ​ 1,227 ​ 868 Accrued research and development expenses ​ 1,102 ​ 1,013 Accrued interest payable on 2026 convertible notes ​ 6,475 ​ 4,194 Accrued other ​ 1,105 ​ 941 ​ ​ $ 20,121 ​ $ 14,307 ​

Collaboration Agreements

Collaboration Agreements	12 Months Ended
	Dec. 31, 2021
Collaboration Agreements
Collaboration Agreements	8. Collaboration Agreements ​ AffaMed License Agreement ​ On October 29, 2020, the Company entered into license agreement (“License Agreement”) with AffaMed Therapeutic Limited (“AffaMed”) for the development and commercialization of the Company’s DEXTENZA product regarding ocular inflammation and pain following cataract surgery and allergic conjunctivitis (collectively, the “DEXTENZA Field”) and for the Company’s OTX-TIC product candidate (collectively with DEXTENZA, the “AffaMed Licensed Products”) regarding open-angle glaucoma or ocular hypertension (collectively, the “TIC Field” and, with the DEXTENZA Field, each a “Field”), in each case in mainland China, Taiwan, Hong Kong, Macau, South Korea, and the countries of the Association of Southeast Asian Nations (collectively, the “Territories”). The Company retains development and commercialization rights for the AffaMed Licensed Products in the rest of the world. ​ Under the License Agreement, the Company received a non-refundable upfront payment of $12,000 in December 2020 and additional $1,000 milestone in the fourth quarter of 2021. The Company is also eligible to receive up to an additional $90,000 in aggregate, inclusive of a low-seven-figure clinical support payment, upon the achievement of certain regulatory, development and commercial milestones. The Company is also entitled to receive tiered, escalating royalties on the net sales of the AffaMed Licensed Products ranging from a low-teen to low-twenties percentage. Royalties under the License Agreement are payable on an AffaMed Licensed Product-by-AffaMed Licensed Product and jurisdiction-by-jurisdiction basis and are subject to potential reductions in specified circumstances, subject to a specified floor. ​ Under the License Agreement, the Company is generally responsible for expenses related to the development of the AffaMed Licensed Products in the applicable Fields in the Territories, provided that AffaMed (i) reimburse the Company a low-teen percentage of expenses incurred in connection with certain clinical trials conducted by the Company and designed to support marketing approval of the AffaMed Licensed Product by the FDA or the European Medicines Agency (“Global Studies”); (ii) is solely responsible for expenses incurred in connection with territory-specific clinical trials that it conducts in furtherance of the development plan agreed between the parties in the applicable Fields in the Territories (“Local Studies”); and (iii) reimburse the Company in full for expenses incurred in connection with obtaining and maintaining regulatory approvals of the AffaMed Licensed Products in the applicable Fields in the Territories. In the event AffaMed declines to participate in a Global Study or to conduct a Local Study in any jurisdiction in which the Company determines to conduct such a study, the Company is relieved of its obligation to provide AffaMed clinical data from such study, other than safety data, unless AffaMed subsequently reimburses the Company in the amounts described above plus a prespecified premium. ​ The License Agreement expires upon the expiration of the last royalty term for the last AffaMed Licensed Product in any applicable Field in the Territories. Either party may, subject to specified cure periods, terminate the License Agreement in the event of the other party’s uncured breach. Either party may also terminate the License Agreement under specified circumstances relating to the other party’s insolvency. AffaMed has the right to terminate the License Agreement at any time after completion of a Phase 3 clinical trial for OTX-TIC for any or no reason upon providing the Company three months’ notice. During an established period following its change of control or its entry into a global licensing agreement that includes the Territories with a third party, the Company has the option to terminate the License Agreement, subject to a specified notice period and the repayment of any costs and expenses incurred by AffaMed in connection with the License Agreement, including upfront and milestone payments AffaMed has previously paid to the Company, at a prespecified premium. ​ The Company concluded that AffaMed is a customer in this arrangement, and as such, the arrangement falls within the scope of the revenue recognition guidance in ASC 606. ​ At the inception of the License Agreement, the Company identified the following performance obligations in the agreement: ​ ● the license, regulatory filings and manufacturing of DEXTENZA; ​ ● the license, regulatory filings and manufacturing for the Company’s OTX-TIC product candidate regarding open-angle glaucoma or ocular hypertension in the Territories; ​ ● obligations to participate on various joint research, development and project committees; and ​ ● the conduct of a Phase 2 clinical trial of OTX-TIC ​ The Company has concluded there is a combined performance obligation for a development and commercialization license and manufacturing obligations for DEXTENZA Field and the Company’s OTX-TIC product candidate regarding open-angle glaucoma or ocular hypertension in the Territories. ​ Further, AffaMed cannot exploit the value of the development and commercialization license for DEXTENZA Field and the Company’s OTX-TIC product candidate regarding open-angle glaucoma or ocular hypertension in the Territories without receipt of supply as the development and commercialization license does not convey to AffaMed the right to manufacture and therefore the Company has combined the development and commercialization license and the manufacturing obligations into one performance obligation. ​ The Company has concluded that the right of AffaMed to opt into the Global Studies for DEXTENZA and OTX-TIC are options that do not convey a material right to AffaMed. Therefore, these have not been recognized as performance obligations upon the inception of the License Agreement. ​ With respect to the obligation of the Company to participate in joint research, development and project committees the Company has concluded that these obligations are not material. ​ The transaction price was allocated to the performance obligations based on the relative estimated standalone selling prices of each performance obligation. ​ The Company developed the estimated standalone selling price for the services and/or manufacturing and supply included in each of the performance obligation, as applicable, primarily based on the nature of the services to be performed and/or goods to be manufactured and estimates of the associated costs, adjusted for a reasonable profit margin that would be expected to be realized under similar contracts. ​ The Company has determined that any sales-based royalties and milestones will be recognized as the Company delivers the clinical and commercial manufactured product to AffaMed. Any changes in estimates may result in a cumulative catch-up based on the number of units of manufactured product delivered. ​ As of December 31, 2021, the transaction price was determined to be $13,000. All potential regulatory, development and commercial milestone payments in the amount of $90,000 did not meet the recognition criteria under the most likely method, because their achievement was highly dependent on factors outside the control of the Company and therefore, were excluded from the transaction price as of December 31, 2021. Furthermore, under the expected value method the Company excluded the potential royalties from the transaction price. ​ We recognize revenue related to the amounts allocated to the combined performance obligations for DEXTENZA Field and the Company’s OTX-TIC product candidate based on the point in time upon which control of supply is transferred to AffaMed for each delivery of the associated supply. The Company currently expects to recognize the revenue over a period of approximately seven commencing on the date the Company begins delivering product to AffaMed. This estimate of this period considers the timing of development and commercial activities under the License Agreement and may be reduced or increased based on the various activities as directed by the joint committees, decisions made by AffaMed, regulatory feedback or other factors not currently known. ​ The Company has not recognized any revenue under the License Agreement as of December 31, 2021 and 2020 as there has been an insignificant amount of delivery of product under the License Agreement. The Company does not expect to recognize material revenue from the License Agreement in 2022. The entire transaction price is recorded as deferred revenue as of December 31, 2021 and 2020. ​ Regeneron Collaboration Agreement ​ On October 10, 2016, the Company entered into a Collaboration, Option and License Agreement (the “Collaboration Agreement”) with Regeneron Pharmaceuticals, Inc. (“Regeneron”) for the development and potential commercialization of products using the Company’s hydrogel in combination with Regeneron’s large molecule VEGF-targeting compounds for the treatment of retinal diseases. On August 5, 2021, Regeneron notified the Company of its termination of the Collaboration Agreement. The termination became effective immediately. ​ Under the terms of the Collaboration Agreement, the Company and Regeneron had agreed to conduct a joint research program with the aim of developing a sustained-release formulation of aflibercept, currently marketed under the tradename Eylea, that is suitable for advancement into clinical development. The Company had granted Regeneron an option (the “Option”) to enter into an exclusive, worldwide license to develop and commercialize products using the Company’s hydrogel in combination with Regeneron’s large molecule VEGF-targeting compounds (“Licensed Products”). Under the term of the Collaboration Agreement, Regeneron was responsible for funding an initial preclinical tolerability study. In connection with the termination of the Collaboration Agreement, all licenses, options and other rights granted to either party under the Collaboration Agreement automatically terminated, other than the surviving joint intellectual property rights described below. The Company and Regeneron also became obligated to undertake certain transition activities upon the termination, including the return of specified property of the other party. Each party retains an equal, undivided ownership interest, which may be transferred, licensed and otherwise exploited without a duty to account to the other party, in certain intellectual property rights jointly developed under the collaboration. As a result of the termination, the Company is no longer eligible to receive (i) reimbursement from Regeneron for ongoing research and development activities, (ii) a fee upon exercise of the Option, (iii) payments upon the achievement of specified development and regulatory milestones of the Regeneron Licensed Products, or (iv) tiered, escalating royalties in a range from a high-single digit to a low-to-mid teen percentage of net sales of Regeneron Licensed Products, in each case pursuant to the Collaboration Agreement. The Company is also no longer obligated to reimburse Regeneron for certain development costs, up to an aggregate amount of in certain circumstances, were Regeneron to have exercised the Option. On May 8, 2020, the Company entered into an amendment (the “Regeneron Amendment”) to the Collaboration Agreement. Pursuant to the Regeneron Amendment, the Company and Regeneron have adopted a new work plan to transition joint efforts under the Collaboration Agreement to the research and development of an extended-delivery formulation of aflibercept to be delivered to the suprachoroidal space. Regeneron has agreed to pay personnel and material costs of the Company for specified preclinical development activities in connection with the revised work plan, as well as certain other costs. In addition, the Regeneron Amendment provides for the modification of the terms of the Option previously granted to Regeneron under the Collaboration Agreement. As amended, the Option is exclusive for twenty-four months following May 8, 2020. As of December 31, 2021 and 2020, the Company had recorded $768 and $1,256 related to work performed for preclinical development activities in connection with the revised work plan which the Company has recorded as a reduction of research and development expense as this research is not an output of the Company’s ordinary business activities. As of December 31, 2021 and 2020, the Company had included the

Notes Payable

Notes Payable	12 Months Ended
	Dec. 31, 2021
Notes Payable
Notes Payable	9. Notes Payable ​ The Company entered into a credit and security agreement in 2014 (as amended to date, the “Credit Agreement”) establishing the Company’s credit facility (the “Credit Facility”). The Company has a total borrowing capacity of ​ In December 2018, the Company amended the terms of the Credit Agreement to increase total indebtedness under the Credit Facility to $25,000 which was used primarily to pay-off outstanding balances as of the closing date. The Company was required to make interest-only payments under the Credit Facility until December 2020. Commencing in January 2021, the Company was required to make 36 equal monthly installments of principal in the amount of $694, plus interest, through December 2023. Amounts borrowed under the Credit Facility were at LIBOR base rate, subject to 2.00% floor, plus 7.25%. Prior to the Fourth Amendment (as defined below), the interest rate was 9.25 %. The exit fee equal to 3.5%, or $429 that was previously accrued, has been paid. ​ In June 2021, the Company entered into a Fourth Amended and Restated Credit and Security Agreement (the “Fourth Amendment”) to amend the terms of its debt with existing lenders for total indebtedness of $20,833 and borrowed an incremental $4,167, for a total of $25,000 (the “2021 Amended Credit Facility”). The Company is required to make interest-only payments under the 2021 Amended Credit Facility through April 2024. Commencing in May 2024, the Company is required to make 19 equal monthly installments of principal in the amount of $1,042, plus interest, then on the maturity date, November 30, 2025 the remaining balance of $5,208 plus the exit fee. In the event the Company achieves certain milestones under the 2021 Amended Credit Facility, the Company has the right to extend through April 1, 2026 and make 5 equal monthly installments of principal in the amount of $1,042, plus interest. The Company has not assumed the achievement of these milestones for purposes of disclosures herein. Amounts borrowed under the 2021 Amended Credit Facility are at LIBOR base rate, subject to 1.00% floor, plus 6.75%. The interest rate on the date of the amendment was 8.8%. In addition, a final payment (exit fee) equal to 3.5% of amounts drawn under the Amended Credit Facility, or $875 based on borrowings of $25,000, is due upon the maturity date of November 30, 2025. The Company is accruing the exit fee through November 30, 2025. ​ The Company accounted for the Fourth Amendment as a modification in accordance with the guidance in ASC 470-50, Debt. Amounts paid to the lenders were recorded as debt discount and a new effective interest rate was established. The effective annual interest rate of the outstanding debt under the Fourth Amendment is . ​ There are no financial covenants associated with the Fourth Amendment. However, the Fourth Amendment does contain negative covenants restricting the Company’s activities, including limitations on dispositions, mergers or acquisitions; encumbering its intellectual property; incurring indebtedness or liens; paying dividends; making certain investments; and engaging in certain other business transactions. As of December 31, 2021, the Company was not in violation of any of its covenants under the Fourth Amendment. The obligations under the Fourth Amendment are subject to acceleration upon the occurrence of specified events of default, including a material adverse change in the Company’s business, operations or financial or other condition. The debt is collateralized by substantially all of the Company’s assets, including its intellectual property. ​ In accordance with the Credit Agreement, in connection with the Company’s desire to issue and sell the 2026 Convertible Notes, the Company amended the terms of its debt with existing lenders in February 2019. The amendment added to the Credit Agreement, among other provisions, a negative covenant restricting the Company from paying the holders of the 2026 Convertible Notes ahead in priority to the existing lenders, for so long as indebtedness remains outstanding under the Credit Facility, and a cross-default provision to establish that an event of default under the purchase agreement for the 2026 Convertible Notes also constitutes an event of default under the Credit Agreement. ​ Borrowings outstanding are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ 2021 2020 Borrowings outstanding ​ $ 25,000 ​ $ 25,000 Accrued exit fee ​ ​ 110 ​ ​ 355 Unamortized discount ​ ​ (110) ​ ​ (129) ​ ​ ​ 25,000 ​ ​ 25,226 Less: current portion ​ ​ — ​ ​ (8,290) Long-term notes payable ​ $ 25,000 ​ $ 16,936 ​ As of December 31, 2021, the annual repayment requirements for the Credit Facility, inclusive of the final payment of $875 due at expiration, were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ending December 31, Principal Final Payment Total 2022 ​ ​ — ​ ​ — ​ ​ — 2023 ​ ​ — ​ ​ — ​ ​ — 2024 ​ ​ 8,333 ​ ​ — ​ ​ 8,333 2025 ​ ​ 16,667 ​ ​ 875 ​ ​ 17,542 ​ ​ $ 25,000 ​ $ 875 ​ $ 25,875 ​

Warrants

Warrants	12 Months Ended
	Dec. 31, 2021
Warrants
Warrants	10. Warrants ​ In April 2014, the Company entered into a credit facility with Silicon Valley Bank and MidCap Financial SBIC, LP, and it issued the lenders warrants to purchase 100,000 shares of its Series D-1 redeemable convertible preferred stock with an exercise price of $3.00 per share. Upon the closing of the Company’s IPO in July 2014, the preferred stock warrants became warrants to purchase an aggregate of 37,878 shares of its common stock with an exercise price of $7.92 per share, with Silicon Valley Bank and MidCap Financial SBIC, LP., each holding warrants On January 29, 2021, holders of warrants to purchase 18,939 shares of common stock at an exercise price of $7.92 exercised their right to purchase their warrants. The exercise price of the warrants was paid through a net share settlement mechanism and as a result the Company issued shares of common stock to satisfy the exercise of all the warrants. There are ​ The Company had warrants for the purchase of 18,939 shares of common stock outstanding with MidCap Financial SBIC, LP at December 31, 2020 at a weighted average exercise price of $7.92 per share and an expiration date of April 17, 2021.

Preferred Stock

Preferred Stock	12 Months Ended
	Dec. 31, 2021
Preferred Stock
Preferred Stock	11. Preferred Stock ​ The Amended and Restated Certificate of Incorporation authorized 5,000,000 shares of preferred stock, $0.0001 par value, all of which is undesignated and none of which are issued outstanding

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2021
Common Stock.
Common Stock	12. Common Stock ​ The Amended and Restated Certificate of Incorporation authorized 100,000,000 shares of the Company’s common stock. In June 2021, the Company adopted an amended and restated certificate of incorporation increasing the number of its authorized shares of its common stock to ​ On August 9, 2021, the Company and Jefferies mutually terminated the 2019 Sales Agreement and entered into another Open Market Sale Agreement (the “2021 Sales Agreement”) under which the Company may offer and sell shares of common stock of the Company having an aggregate offering price of up to $100,000 from time to time through Jefferies, acting as agent. As of February 27, 2022, the Company has ​ On December 14, 2020, the Company entered into an underwriting agreement with Jefferies LLC (“Jefferies”) and Piper Sandler & Co. (collectively with Jefferies, “the Underwriters”) in connection with an underwritten public offering of 3,725,000 shares of the Company’s common stock. Under the terms of this underwriting agreement, the Company also granted the Underwriters an option to purchase up to an additional 558,750 shares of common stock at the public offering price, less the underwriting discounts and commissions. The Underwriters subsequently exercised this option to purchase such option shares in full. The public offering price of the shares in this offering was $21.50 per share, and the Underwriters purchased all of the shares from the Company at a price of $20.21 per share. After deducting underwriting discounts and commissions and offering expenses, the Company received net proceeds from the offering of $86,390. ​ On October 13, 2020, the Company entered into an underwriting agreement with the Underwriters, in connection with an underwritten public offering of 7,180,000 shares of the Company’s common stock. Under the terms of this underwriting agreement, the Company also granted the Underwriters an option to purchase up to an additional 1,077,000 shares of common stock at the public offering price, less the underwriting discounts and commissions. The Underwriters subsequently exercised this option to purchase such option shares in full. The public offering price of the shares in this offering was $9.75 per share, and the Underwriters purchased all of the shares from the Company at a price of $9.17 per share. After deducting underwriting discounts and commissions and offering expenses, the Company received net proceeds from the offering of $75,406. ​ In May 2020, the Company entered into an underwriting agreement with the Underwriters, in connection with an underwritten public offering of 8,181,819 shares of the Company’s common stock. Under the terms of this underwriting agreement, the Company also granted the Underwriters an option to purchase up to an additional 1,227,272 shares of common stock at the public offering price, less the underwriting discounts and commissions. The Underwriters subsequently exercised this option to purchase such option shares in full. The public offering price of the shares in this offering was $5.50 per share, and the Underwriters purchased all of the shares from the Company at a price of $5.17 per share. After deducting underwriting discounts and commissions and offering expenses, the Company received net proceeds from the offering of $48,327. ​ On April 5, 2019, the Company entered into an Open Market Sales Agreement SM from time-to-time through Jefferies, acting as agent. In the twelve months ended December 31, 2020, the Company sold 2,984,381 shares of common stock under the 2019 Sales Agreement, resulting in net proceeds of approximately $14,359 ​ As of December 31, 2021, the Company had reserved 10,934,828 shares of common stock for the exercise of outstanding stock options and the number of shares remaining available for grant under the Company’s 2021 Stock Incentive Plan (the “2021 Plan”), 2014 Stock Incentive Plan (the “2014 Plan”) and the 2019 Inducement Stock Incentive Plan (the “2019 Inducement Plan”), and the number of shares available for issuance under the 2014 Employee Stock Purchase Plan (Note 13). ​

Stock-Based Awards

Stock-Based Awards	12 Months Ended
	Dec. 31, 2021
Stock-Based Awards
Stock-Based Awards	13. Stock-Based Awards ​ 2014 Stock Incentive Plan ​ The 2014 Plan provides for the grant of incentive stock options, non-statutory stock options, restricted stock awards, restricted stock units, stock appreciation rights and other stock-based awards. The number of shares initially reserved for issuance under the 2014 Plan was 1,336,907 shares of common stock, which was increased to 2,126,907 on January 1, 2015. The number of shares reserved for issuance may be increased by the number of shares under the 2006 Stock Option Plan (the “2006 Plan”) that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company. The number of shares of common stock that may be issued under the 2014 Plan is subject to increase on the first day of each fiscal year, beginning on January 1, 2015 and ending on December 31, 2024, equal to the least of 1,659,218 shares of the Company’s common stock, 4% of the number of shares of the Company’s common stock outstanding on the first day of the applicable fiscal year, and an amount determined by the Company’s board of directors. On January 1, 2021, the number of shares available for issuance under the 2014 Plan increased by 1,659,218 . On June 18, 2021, the Company’s stockholders approved the adoption of the 2021 Plan previously approved by the board of directors. Effective as of the adoption of the 2021 Plan by the Company’s stockholders, no new awards will be granted under the 2014 Plan. However, as of December 31, 2021, all then-outstanding awards under the 2014 Plan remained in effect and continued to be governed by the terms of the 2014 Plan. ​ ​ 2021 Stock Incentive Plan ​ The 2021 Plan provides for the grant of incentive stock options, non-statutory stock options, restricted stock awards, restricted stock units, stock appreciation rights and other stock-based awards. The number of shares of common stock that may be issued under the 2021 Plan is shares subject to awards granted under the 2014 Plan or the Company’s 2006 Stock Incentive Plan, which awards expire, terminate or are otherwise surrendered, canceled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right (subject to certain limitations). As of December 31, 2021, 6,263,365 shares remained available for issuance under the 2021 Plan. ​ As required by the 2006 Plan, 2014 Plan and 2021 Plan, the exercise price for stock options granted is not to be less than the fair value of common shares as of the date of grant. ​ Inducement Stock Option Awards ​ On June 20, 2017, the Company issued to Antony Mattessich, who became a director of the Company on June 20, 2017 and the Company’s President and Chief Executive Officer on July 26, 2017, a non-statutory stock option to purchase an aggregate of 590,000 shares of the Company’s common stock at an exercise price of $10.94 per share. Subject to Mr. Mattessich’s continued service to the Company, the stock option will vest over a four-year period, with 25% of the shares underlying the option award vesting on the one year anniversary of the grant date and the remaining 75 % of the shares underlying the award vesting monthly thereafter. The stock option was issued outside of the Company’s 2014 Plan as an inducement material to Mr. Mattessich’s acceptance of an offer of employment with the Company in accordance with Nasdaq Listing Rule 5635(c)(4). ​ On July 9, 2019, the Company issued to the Senior Vice President, Head of Business Development, a non-statutory stock option to purchase an aggregate of 60,000 shares of its common stock at an exercise price of $5.13 per share. Subject to his continued service to the Company, the stock option will vest over a four-year period, with 25% of the shares underlying the option award vesting on the one-year anniversary of the grant date and the remaining 75% of the shares underlying the award vesting monthly thereafter. The stock option was issued outside of the Company’s 2014 Plan as an inducement material to the individual’s acceptance of an offer of employment with the Company in accordance with Nasdaq Listing Rule 5635(c)(4). ​ On October 29, 2019, the 2019 Inducement Plan was approved by the Board of Directors of the Company. The 2019 Inducement Plan provides for the following types of awards, each of which is referred to as an “Award”: non- statutory stock options, stock appreciation rights, restricted stock, restricted stock units and other stock-based awards. Awards under the 2019 Inducement Plan may only be granted to persons who (a) were not previously an employee or director of the Company or (b) are commencing employment with the Company following a bona fide period of non-employment, in either case as an inducement material to the individual’s entering into employment with the Company and in accordance with the requirements of Nasdaq Stock Market Rule 5635(c)(4). For the avoidance of doubt, neither consultants nor advisors shall be eligible to participate in the 2019 Inducement Plan. Each person who is granted an Award under the 2019 Inducement Plan is deemed a “Participant.” ​ On February 1, 2021, the Company issued to the Senior Vice President, Clinical Development, a non-statutory stock option to purchase an aggregate of 100,000 shares of its common stock at an exercise price of $18.70 per share subject to a time-based vesting and a non-statutory stock option to purchase 50,000 shares of its common stock at an exercise price of $18.70 per share subject to performance-based vesting. The stock option was issued under the Company’s 2019 Inducement Plan as an inducement material to such individual’s acceptance of an offer of employment with the Company in accordance with Nasdaq Listing Rule 5635(c)(4). Subject to her continued service to the Company, the time-based stock option will vest over a of the shares underlying the award vesting monthly thereafter. The performance-based stock option vests and becomes exercisable in whole or in part if the Company achieves specified milestones, subject to continued service to the Company through the applicable vesting dates. The stock options are subject to the terms and conditions of stock option agreements covering the grant and the Company’s 2019 Inducement Plan, as amended to date. ​ On December 10, 2020, the Board of Directors of the Company amended the 2019 Inducement Plan to increase the aggregate number of shares issuable by 554,000 shares of common stock to 1,054,000 . As of December 31, 2021, ​ 2014 Employee Stock Purchase Plan ​ The Company’s has a 2014 Employee Stock Purchase Plan (the “ESPP”) with a total of 207,402 shares of common stock reserved for issuance under this plan which increased to 232,402 shares of common stock on January 1, 2015. The number of shares of common stock that may be issued under the ESPP will automatically increase on the first day of each fiscal year, commencing on January 1, 2015 and ending on December 31, 2024, in an amount equal to the least of 207,402 shares of the Company’s common stock, 0.5% of the number of shares of the Company’s common stock outstanding on the first day of the applicable fiscal year, and an amount determined by the Company’s board of directors. On January 1, 2020, the number of shares available for issuance under the ESPP increased by 207,402. As of December 31, 2021, 607,048 shares of common stock remained available for issuance. ​ Stock Option Valuation ​ The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The expected life of the options was calculated using the simplified method. The simplified method defines the life as the average of the contractual term of the options and the weighted-average vesting period for all option tranches. The Company utilized the simplified method because the Company did not have sufficient historical exercise data over the life of awards to provide a reasonable basis upon which to estimate expected term. The expected term of stock options granted to nonemployees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. ​ As of December 31, 2021, there were 27,903 outstanding unvested service-based stock options held by nonemployees. ​ The assumptions that the Company used to determine the fair value of the stock options granted to employees and directors are as follows, presented on a weighted average basis: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ 2021 2020 2019 Risk-free interest rate 0.80 % 1.12 % 2.25 % Expected term (in years) 6 6 6 ​ Expected volatility 87.65 % 86.00 % 87 % Expected dividend yield — % — % — % ​ The following table summarizes the Company’s stock option activity: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ Weighted ​ Average ​ ​ ​ ​ ​ ​ ​ Average ​ Remaining ​ Aggregate ​ ​ Shares Issuable ​ Exercise ​ Contractual ​ Intrinsic ​ Under Options Price Term Value ​ ​ ​ ​ ​ ​ ​ (In years) ​ ​ ​ Outstanding as of December 31, 2020 9,114,735 ​ $ 6.66 7.4 ​ $ 16,075 Granted 3,339,974 ​ 17.22 ​ ​ ​ ​ ​ Exercised (598,924) ​ 4.32 ​ ​ ​ ​ ​ Forfeited (920,957) ​ 11.48 ​ ​ ​ ​ ​ Outstanding as of December 31, 2021 10,934,828 ​ $ 9.60 ​ 7.1 ​ ​ 13,283 Options vested and expected to vest as of December 31, 2021 9,504,572 ​ $ 8.93 ​ 6.8 ​ ​ 12,381 Options exercisable as of December 31, 2021 6,570,556 ​ $ 8.22 ​ 6.1 ​ ​ 9,002 ​ The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock. The aggregate intrinsic value of stock options exercised was $6,779, $4,307 and $54 during the years ended December 31, 2021, 2020 and 2019, respectively. ​ The weighted average grant date fair value of stock options granted to employees and directors during the years ended December 31, 2021, 2020 and 2019 was $12.48, $5.93 and $2.99 per share, respectively. ​ Stock-based Compensation ​ The Company recorded stock-based compensation expense related to stock options in the following expense categories of its statements of operations: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2021 2020 2019 Research and development ​ $ 3,750 ​ $ 1,514 ​ $ 2,312 ​ Selling and marketing ​ 4,014 ​ 1,719 ​ 1,013 ​ General and administrative ​ 7,214 ​ 4,298 ​ 5,434 ​ ​ ​ $ 14,978 ​ $ 7,531 ​ $ 8,759 ​ ​ As of December 31, 2021, the Company had an aggregate of $20,382 of unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 2.8 years.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2021
Net Loss Per Share
Net Loss Per Share	14. Net Loss Per Share ​ Basic and diluted net loss per share attributable to common stockholders was calculated as follows for the years ended December 31, 2020 and 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2020 ​ 2019 Numerator: ​ ​ ​ ​ Net loss $ (155,636) ​ $ (86,372) Denominator: ​ ​ Weighted average common shares outstanding, basic and diluted 60,752,225 ​ 45,273,231 Net loss per share - basic and diluted $ (2.56) ​ $ (1.91) ​ ​ ​ ​ ​ ​ ​ ​ For the year ended December 31, 2020 and 2019, there is no dilutive impact. Therefore, diluted net loss per share is the same as basic net loss per share. Basic and diluted net loss per share was calculated as follows for the year ended December 31, 2021: ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2021 Net loss attributable to common stockholders, basic ​ $ (6,553) Interest expense on 2026 Convertible Notes ​ 4,409 Change in fair value of derivative liability ​ ​ (78,121) Net loss attributable to common stockholders, diluted ​ $ (80,265) ​ ​ ​ ​ Weighted average common shares outstanding, basic ​ ​ 76,392,870 Shares issuable upon conversion of 2026 Convertible Notes, as if converted ​ ​ 5,769,232 Weighted average common shares outstanding, diluted ​ 82,162,102 ​ ​ ​ ​ ​ ​ ​ ​ Net loss per share attributable to common stockholders, basic ​ $ (0.09) ​ ​ ​ ​ Net loss per share attributable to common stockholders, diluted ​ $ (0.98) ​ The Company excluded the following common stock equivalents, outstanding as of December 31, 2021, 2020 and 2019 from the computation of diluted net loss per share attributable to common stockholders for the years ended December 31, 2021, 2020 and 2019 because they had an anti-dilutive impact due to the net loss incurred for the periods. The Company also excluded the shares issuable upon conversion of the 2026 Convertible Notes from the computation of diluted net loss per share for the year ended December 31, 2020 and 2019 because they had an anti-dilutive impact. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2021 2020 2019 Options to purchase common stock 10,934,828 9,114,735 7,920,417 Shares issuable upon conversion of 2026 Convertible Notes, if converted — 5,769,232 5,769,232 Warrants for the purchase of common stock — 18,939 18,939 ​ 10,934,828 14,902,906 13,708,588 ​

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies.
Commitments and Contingencies	15. Commitments and Contingencies ​ Intellectual Property Licenses ​ The Company has a license agreement with Incept, LLC (“Incept”) to use and develop certain patent rights (the “Incept License”). Under the Incept License, as amended and restated, the Company was granted a worldwide, perpetual, exclusive license to develop and commercialize products that are delivered to or around the human eye for diagnostic, therapeutic or prophylactic purposes relating to ophthalmic diseases or conditions. The Company is obligated to pay low single-digit royalties on net sales of commercial products developed using the licensed technology, commencing with the date of the first commercial sale of such products and until the expiration of the last to expire of the patents covered by the license. Any of the Company’s sublicensees also will be obligated to pay Incept a royalty equal to a low single-digit percentage of net sales made by it and will be bound by the terms of the agreement to the same extent as the Company. The Company is obligated to reimburse Incept for its share of the reasonable fees and costs incurred by Incept in connection with the prosecution of the patent applications licensed to the Company under the Incept License. From inception through December 31, 2021, royalties paid under this agreement related to product sales were $1,908 and have been charged to cost of product revenue. ​ On September 13, 2018, the Company entered into a second amended and restated license agreement (the “Second Amended Agreement”) with Incept. The Second Amended Agreement amends and restates in full the Company’s prior amended and restated Incept License (the “Prior Agreement” or “Original License”) to expand the scope of the Company’s intellectual property license and modify future intellectual property ownership and other rights thereunder. ​ Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners, and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and senior management team that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. As of December 31, 2021, the Company was not aware of any claims that could have a material effect on its financial position, results of operations or cash flows, and it has not accrued any liabilities related to such obligations in its consolidated financial statements as of December 31, 2021.

Leases

Leases	12 Months Ended
	Dec. 31, 2021
Leases
Leases	16. Leases ​ The Company leases real estate, including laboratory, manufacturing and office space. The Company’s leases have remaining lease terms ranging from less than 1 year to 8 years. Certain leases include one or more options to renew . All of the Company’s leases qualify as operating leases. ​ In October 2017, the Company entered into an amendment to a lease agreement for the Company’s laboratory and manufacturing space located at 34 Crosby Drive and 36 Crosby Drive, each in Bedford, Massachusetts. The lease term commenced on June 30, 2018 and will expire on July 31, 2023. ​ In June 2016, the Company entered into a lease agreement for approximately 70,712 square feet of general office, research and development and manufacturing space located at 15 Crosby Drive in Bedford, Massachusetts. The lease term commenced on February 1, 2017 and will expire on July 31, 2027. The Company has the option to extend the lease for ​ On April 4, 2019, the Company entered into a non-cancelable lease for 30,036 square feet of space located at 24 Crosby Drive in Bedford, Massachusetts to be used for office space. The five-year lease commenced on April 18, 2019 and terminates on March 24, 2024 and does not include any lease renewal options . ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the ​ For the ​ For the ​ ​ Year Ended ​ Year Ended ​ Year Ended ​ ​ December 31, ​ December 31, ​ December 31, ​ ​ 2021 ​ 2020 ​ 2019 Operating lease costs ​ $ 2,482 ​ $ 2,418 ​ $ 2,070 Variable lease costs ​ ​ 629 ​ ​ 677 ​ ​ 538 Total lease costs ​ $ 3,111 ​ $ 3,095 ​ $ 2,608 ​ The following table summarizes the presentation in the Company’s consolidated balance sheet of its operating leases: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ Balance sheet location 2021 ​ 2020 Assets: ​ ​ ​ ​ ​ ​ ​ ​ Operating lease assets ​ Operating lease assets ​ $ 4,867 ​ $ 5,844 ​ ​ ​ ​ ​ ​ ​ ​ ​ Liability: ​ ​ ​ ​ ​ ​ ​ ​ Current operating lease liabilities ​ Operating lease liabilities ​ $ 1,624 ​ $ 1,358 Non-current operating lease liabilities ​ Operating lease liabilities, net of current portion ​ ​ 5,924 ​ ​ 7,548 Total Operating lease liabilities: ​ ​ ​ $ 7,548 ​ $ 8,906 ​ The minimum lease payments for the next five years and thereafter are expected to be as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, Year Ending December 31, ​ ​ 2021 2022 ​ ​ ​ ​ 2,549 2023 ​ ​ ​ ​ 2,355 2024 ​ ​ ​ ​ 1,569 2025 ​ ​ ​ ​ 1,447 2026 ​ ​ ​ ​ 1,482 Thereafter ​ ​ ​ ​ 884 Total lease payments ​ ​ ​ $ 10,286 Less: interest ​ ​ ​ ​ 2,738 Present value of operating lease liabilities ​ ​ ​ $ 7,548 ​ The following table summarizes the weighted average remaining lease term and the weighted average incremental borrowing rate used to determine the operating lease liability: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ December 31, ​ 2021 ​ ​ 2020 Weighted average remaining lease term in years ​ ​ 4.8 ​ ​ 5.6 ​ Weighted average discount rate ​ ​ 13.55 % ​ 13.55 % ​ Supplemental disclosure of cash flow information related to the Company’s operating leases included in cash flows provided by operating activities in its consolidated statements of cash flows is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the ​ ​ For the ​ For the ​ ​ Year Ended ​ ​ Year Ended ​ Year Ended ​ ​ December 31, ​ ​ December 31, ​ December 31, ​ 2021 ​ ​ 2020 ​ 2019 Cash paid for amounts included in the measurement of lease liabilities ​ $ 2,482 ​ $ 2,418 ​ $ 2,215 ​

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Taxes
Income Taxes	17. Income Taxes ​ During the years ended December 31, 2021, 2020 and 2019, the Company recorded no income tax benefits for the net operating losses incurred or the research and development tax credits generated in each year, due to its uncertainty of realizing a benefit from those items. ​ A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2021 2020 2019 Federal statutory income tax rate 21.0 % 21.0 % 21.0 % Research and development tax credits 35.9 ​ 1.0 2.1 ​ State taxes, net of federal benefit 19.3 ​ 1.0 2.7 ​ Stock-based compensation (7.8) ​ — (1.3) ​ Derivative liability ​ 244.7 ​ (11.5) ​ ​ ​ Other (12.2) ​ — (0.5) ​ Change in the valuation allowance (300.9) ​ (11.5) (24.0) ​ Effective income tax rate — % — % — % ​ Changes in the valuation of the derivative liability do not provide a future tax benefit. To the extent the deferred tax asset related to the derivative liability exceeds the deferred tax liability related to the 2026 Convertible Notes, the excess is recorded as a permanent item. Net deferred tax assets consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2021 2020 Deferred tax assets: ​ ​ ​ ​ ​ ​ Net operating loss carryforwards ​ $ 106,265 ​ $ 90,797 Tax credit carryforwards ​ 15,853 ​ 13,514 Capitalized start-up costs ​ 373 ​ 514 Capitalized research and development expenses, net ​ 7,828 ​ 10,657 Operating lease liabilities ​ ​ 1,705 ​ ​ 2,066 Derivative liability ​ ​ 2,499 ​ ​ 3,061 Accrued expenses and other ​ 11,712 ​ 6,828 Total deferred tax assets ​ 146,235 ​ 127,437 Valuation allowance ​ (142,637) ​ (123,020) Net deferred tax assets ​ ​ 3,598 ​ ​ 4,417 ​ ​ ​ ​ ​ ​ ​ Deferred tax liabilities: ​ ​ ​ ​ ​ ​ Operating lease right of use assets ​ ​ (1,099) ​ ​ (1,356) 2026 Convertible Notes ​ ​ (2,499) ​ ​ (3,061) Total deferred tax liabilities ​ ​ (3,598) ​ ​ (4,417) Net deferred tax assets ​ $ — ​ $ — ​ Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2021, 2020 and 2019 related primarily to the increase in net operating loss carryforwards, amortization of capitalized research and development expenses, and increase in research and development tax credit carryforwards were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2021 2020 2019 Valuation allowance as of beginning of year ​ $ 123,020 ​ $ 105,062 ​ $ 84,343 Increases recorded to income tax provision ​ 19,617 ​ 17,958 ​ 20,719 Valuation allowance as of end of year ​ $ 142,637 ​ $ 123,020 ​ $ 105,062 ​ As of December 31, 2021, the Company had net operating loss (“NOL”) carryforwards for federal and state income tax purposes of $423,628 and $296,998 , respectively. The federal and state NOLs generated for annual periods prior to January 1, 2018 begin to expire in 2026. The Company’s federal NOLs generated for the years ended since December 31, 2018, which amounted to a total of $297,823 limitation under Section 382 of the Internal Revenue Code of 1986 due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain shareholders or public groups in the stock of a corporation by more than 50% over a three-year period. The Company has not conducted a study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382, at any time since inception, utilization of the NOL carryforwards or research and development tax credit carryforwards would be subject to an annual limitation under Section 382, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable long-term tax-exempt rate, and then could be subject to additional adjustments, as required. Any limitation may result in expiration of a portion of the NOL carryforwards or research and development tax credit carryforwards before utilization. Further, until a study is completed and any limitation is known, no amounts are being presented as an uncertain tax position. ​ The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. Management considered the Company’s cumulative net losses and concluded that it is more likely than not that the Company would not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance was established against the net deferred tax assets as of December 31, 2021, 2020 and 2019. ​ The Company has not recorded any amounts for unrecognized tax benefits as of December 31, 2021, 2020 or 2019. ​ The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. There are currently no pending income tax examinations. The Company’s tax years are still open under statute from December 31, 2017 to the present. Earlier years may be examined to the extent that tax credit or net operating loss carryforwards are used in future periods. The Company’s policy is to record interest and penalties related to income taxes as part of its income tax provision. As of December 31, 2021 and 2020, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s statements of operations and comprehensive loss.

401(k) Savings Plan

401(k) Savings Plan	12 Months Ended
	Dec. 31, 2021
401(k) Savings Plan
401(k) Savings Plan	18. 401(k) Savings Plan ​ The Company established a defined contribution savings plan under Section 401(k) of the Internal Revenue Code. This plan covers substantially all employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. Company contributions to the plan may be made at the discretion of the board of directors. Through December 31, 2021, the Company has made contributions of $493 made to the plan by the Company.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2021
Related Party Transactions
Related Party Transactions	​ 19. Related Party Transactions ​ Since October 2017, the Company has engaged McCarter English LLP (“McCarter”) to provide legal services to the Company, including with respect to intellectual property matters. Mr. Jonathan M. Sparks, Ph.D., a partner at McCarter & English, served in the capacity as the Company’s in-house counsel from October 2017 through August 31, 2020. The Company incurred fees for legal services rendered by McCarter of $766 and $1,119 for the years ended December 31, 2020 and 2019, respectively. As of December 31, 2020, there was ​ In November 2020, the Company engaged Specialty Pharma Consulting, LLC (“Specialty Pharma”), an entity affiliated with Kevin Coughenour, to provide services for quality engineering and validation activities in the ordinary course of business. Mr. Coughenour is married to the Company’s former Chief Operating Officer Patricia Kitchen. The Company incurred fees for quality engineering and validation activities rendered by Specialty Pharma of $155 , for the for the year ended December 31, 2021. As of December 31, 2020, there was recorded in accrued expenses for Specialty Pharma. On April 26, 2021, the Company and Specialty Pharma terminated their relationship. ​ The Company has engaged Wilmer Cutler Pickering Hale and Dorr LLP (“WilmerHale”) to provide certain legal services to the Company. The Company's Chief Business Officer’s sister is a managing partner at WilmerHale, who has not participated in providing legal services to the Company. The Company incurred fees for legal services rendered by WilmerHale of approximately $1,396 and $1,772 for the year ended December 31, 2021 and 2020, respectively. As of December 31, 2021 and 2020, there was $119 and $114 recorded in accounts payable for WilmerHale. As of December 31, 2021 and 2020, there was $68 and $239 recorded in accrued expenses for WilmerHale. ​

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2021
Subsequent Events
Subsequent Events	20. Subsequent Events ​ The number of shares of common stock that may be issued under the ESPP will automatically increase on the first day of each fiscal year, commencing on January 1, 2015 and ending on December 31, 2024, in an amount equal to the least of 207,402 shares of the Company’s common stock, 0.5% of the number of shares of the Company’s common stock outstanding on the first day of the applicable fiscal year, and an amount determined by the Company’s board of directors. On January 1, 2022, the number of shares available for issuance under the ESPP increased by 207,402.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2021
Summary of Significant Accounting Policies
Basis of Presentation and Principles of Consolidation	Basis of Presentation and Principles of Consolidation The accompanying consolidated financial statements reflect the operations of the Company and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated.
Use of Estimates	Use of Estimates ​ The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of revenues and expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, revenue recognition, and the fair value of derivatives. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.
Cash Equivalents	Cash Equivalents ​ The Company considers all short-term, highly liquid investments with original maturities of ninety days or less at date of purchase to be cash equivalents. Cash equivalents, which primarily consist of money market accounts, are stated at fair value.
Revenue Recognition	Revenue Recognition ​ Product Revenue ​ The Company recognizes product revenue from DEXTENZA for the treatment of post-surgical ocular inflammation and pain, which it began selling to customers in June 2019, and ReSure Sealant. The Company has generated limited revenues from ReSure Sealant to date and does not expect significant future sales. ​ In November 2018, the FDA approved DEXTENZA for the treatment of ocular pain following ophthalmic surgery. The Company entered into a limited number of arrangements with specialty distributors in the United States to distribute DEXTENZA. The Company recognizes revenue in accordance with Accounting Standards Codification 606 – Revenue from Contracts with Customers ​ To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity performs the following five steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract, and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to arrangements that meet the definition of a contract with a customer under Topic 606, including when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, the Company assesses the goods or services promised within each contract, determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. For a complete discussion of accounting for product revenue, see Product Revenue, Net (below). ​ Product Revenue, Net ​ The Company recognizes revenue on product sales when the customer obtains control of the Company's product, which occurs at a point in time (upon delivery to the customer). The Company has determined that the delivery of DEXTENZA to its customers constitutes a single performance obligation. There are no other promises to deliver goods or services beyond what is specified in each accepted customer order. The Company has assessed the existence of a significant financing component in the agreements with its customers. The trade payment terms with the Company’s customers do not exceed one year and therefore the Company has elected to apply the practical expedient and no amount of consideration has been allocated as a financing component. Product revenues are recorded net of applicable reserves for variable consideration, including discounts and allowances. ​ Transaction Price, including Variable Consideration ​ The amount of variable consideration which is included in the transaction price may be constrained, and is included in the net sales price, only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized under the contract will not occur in a future period. Actual amounts of consideration ultimately received may differ from the Company’s estimates. If actual results in the future vary from the Company’s original estimates, the Company will adjust these estimates, which would affect net product revenue and earnings in the period such variances become known. ​ Trade Discounts and Allowances ​ Product Returns The Company estimates the amount of its product sales that may be returned by its customers and records this estimate as a reduction of revenue in the period the related product revenue is recognized, as well as within accrued expenses and other current liabilities, in the accompanying consolidated balance sheets. The Company currently estimates product return reserves using available industry data and its own sales information, including its visibility into the inventory remaining in the distribution channel. The Company has received no returns to date and believes the returns of DEXTENZA will be minimal. ​ Government Chargebacks U.S. The 340B Drug Discount Program is a U.S. federal government program created in 1992 that requires drug manufacturers to provide outpatient drugs to eligible health care organizations and covered entities at significantly reduced prices. Customers charge the Company for the difference between what they pay for the product and the statutory selling price to the qualified government entity. These allowances are established in the same period that the related revenue is recognized, resulting in a reduction of product revenue and accounts receivables, net. Chargeback amounts are generally determined at the time of resale to the qualified government healthcare provider by customers, and the Company generally issues credits for such amounts within a few weeks of the Customer’s notification to the Company of the resale. Allowance for chargebacks consist of credits that the Company expects to issue for units that remain in the distribution channel inventories at each reporting period-end that the Company expects will be sold to qualified healthcare providers, and chargebacks that customers have claimed, but for which the Company has not yet issued a credit. ​ Government Rebates ​ Rebates ​ Other Incentives ​ Collaboration Revenue ​ To determine the appropriate amount of revenue to be recognized for arrangements the Company determines are within the scope of Topic 606, the Company performs the following steps: (i) identify the contract(s) with its customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when or as each performance obligation is satisfied. ​ The Company accounts for a contract with a customer that is within the scope of Topic 606 when all of the following criteria are met: (i) the arrangement has been approved by the parties and the parties are committed to perform their respective obligations; (ii) each party’s rights regarding the goods and/or services to be transferred can be identified; (iii) the payment terms for the goods and/or services to be transferred can be identified; (iv) the arrangement has commercial substance; and (v) collection of substantially all of the consideration to which the Company will be entitled in exchange for the goods and/or services that will be transferred to the customer is probable. The Company also determines the term of the contract based on the period in which the Company and its customer have present and enforceable rights and obligations for purposes of identifying the performance obligations and determining the transaction price. ​ The Company evaluates contracts that contain multiple promises to determine which promises are distinct. Promises are considered to be distinct and therefore, accounted for as separate performance obligations, provided that: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer and (ii) the promise to transfer the good or service to the customer is separately identifiable from other promises in the contract. In assessing whether a promise is distinct, the Company considers factors such as whether: (i) the Company provides a significant service of integrating goods and/or services with other goods and/or services promised in the contract; (ii) one or more of the goods and/or services significantly modifies or customizes, or are significantly modified or customized by one or more of the other goods and/or services promised in the contract; and (iii) the goods and/or services are highly interdependent or highly interrelated. Individual goods or services (or bundles of goods and/or services) that meet both criteria for being distinct are accounted for as separate performance obligations. Promises that are not distinct at contract inception are combined and accounted for as a single performance obligation. Options to acquire additional goods and/or services are evaluated to determine if such option provides a material right to the customer that it would not have received without entering into the contract. If so, the option is accounted for as a separate performance obligation. If not, the option is considered a marketing offer which would be accounted for as a separate contract upon the customer’s election. ​ The transaction price is generally comprised of an upfront payment due at contract inception and variable consideration in the form of payments for the Company’s goods and services and materials and milestone payments due upon the achievement of specified events. Other payments the Company could be entitled to include tiered royalties earned when customers recognize net sales of licensed products. The Company considers the existence of any significant financing component within its arrangements and have determined that a significant financing component does not exist in its arrangements as substantive business purposes exist to support the payment structure other than to provide a significant benefit of financing. The Company measures the transaction price based on the amount of consideration to which the Company expects to be entitled in exchange for transferring the promised goods and/or services to the customer. The Company utilizes either the expected value method or the most likely amount method to estimate the amount of variable consideration, depending on which method is expected to better predict the amount of consideration to which the Company will be entitled. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. With respect to arrangements that include payments for a development or regulatory milestone payment, the Company evaluates whether the associated event is considered likely of achievement and estimates the amount to be included in the transaction price using the most likely amount method. Milestone payments that are not within the Company’s control or the licensee, such as those dependent upon receipt of regulatory approval, are not considered to be likely of achievement until the triggering event occurs. At the end of each reporting period, the Company re-evaluates the probability of achievement of each milestone and any related constraint, and if necessary, adjust its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenue and net loss in the period of adjustment. For arrangements that include sales-based royalties, including milestone payments based upon the achievement of a certain level of product sales, wherein the license is deemed to be the sole or predominant item to which the payments relate, the Company recognizes revenue upon the later of: (i) when the related sales occur or (ii) when the performance obligation to which some or all of the payment has been allocated has been satisfied (or partially satisfied). Consideration that would be received for optional goods and/or services is excluded from the transaction price at contract inception. ​ The Company recognizes as an asset the incremental costs of obtaining a contract with a customer if the costs are expected to be recovered. The Company has elected a practical expedient wherein it recognizes the incremental costs of obtaining a contract as an expense when incurred if the amortization period of the asset that it otherwise would have recognized is one year or less. To date, the Company has not incurred any incremental costs of obtaining a contract with a customer.
Inventory	Inventory ​ The Company values its inventories at the lower of cost or estimated net realizable value. The Company determines the cost of its inventories, which includes amounts related to materials and manufacturing overhead, on a first-in, first-out basis. The Company performs an assessment of the recoverability of capitalized inventory during each reporting period, and it writes down any excess and obsolete inventories to their estimated realizable value in the period in which the impairment is first identified. Such impairment charges, should they occur, are recorded within cost of product revenue. The determination of whether inventory costs will be realizable requires estimates by management. If actual market conditions are less favorable than projected by management, additional write-downs of inventory may be required, which would be recorded as a cost of product revenue in the consolidated statements of operations and comprehensive loss. The Company capitalizes inventory costs associated with the Company’s products after regulatory approval when, based on management’s judgment, future commercialization is considered probable and the future economic benefit is expected to be realized. Inventory acquired prior to receipt of marketing approval of a product candidate is expensed as research and development expense as incurred. Inventory that can be used in either the production of clinical or commercial product is expensed as research and development expense when selected for use in a clinical manufacturing campaign. Inventory produced that will be used in promotional marketing campaigns is expensed to selling and marketing expense when it is selected for use in a marketing program. ​ Inventory consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ December 31, ​ ​ 2021 2020 Raw materials ​ $ 388 ​ $ 384 Work-in-process ​ 605 ​ 232 Finished goods ​ ​ 257 ​ ​ 585 ​ ​ $ 1,250 ​ $ 1,201
Restricted Cash	Restricted Cash ​ As of December 31, 2021, 2020 and 2019, the Company held restricted cash of $1,764 , respectively, on its consolidated balance sheet. The Company held restricted cash as security deposits for the lease of its manufacturing space and corporate headquarters. ​ The Company’s statements of cash flows include restricted cash with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on such statements. A reconciliation of the cash, cash equivalents, and restricted cash reported within the balance sheet that sum to the total of the same amounts shown in the statement of cash flows is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ December 31, ​ 2021 2020 2019 Cash and cash equivalents ​ $ 164,164 ​ $ 228,057 ​ $ 54,437 Restricted cash ​ ​ 1,764 ​ ​ 1,764 ​ ​ 1,764 Total cash, cash equivalents and restricted cash as shown on the statements of cash flows ​ $ 165,928 ​ $ 229,821 ​ $ 56,201
Concentration of Credit Risk and of Significant Suppliers and Customers	Concentration of Credit Risk and of Significant Suppliers and Customers ​ Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents and accounts receivable. The Company has all cash and cash equivalents balances at one accredited financial institution, in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. ​ ​ The Company is dependent on a small number of third-party manufacturers to supply products for research and development activities in its preclinical and clinical programs and for sales of its products. The Company’s development programs as well as revenue from future sales of its product sales could be adversely affected by a significant interruption in the supply of any of the components of these products. ​ For the year ended December 31, 2021, three specialty distributor customers accounted for 42%, 26% and 17% of the Company’s total revenue and three specialty distributor customers accounted for 42%, 26% and 21% of the Company’s total accounts receivable. No other customer accounted for more than 10% of total revenue or accounts receivable for the year ended December 31, 2021. ​ For the year ended December 31, 2020, three specialty distributor customers accounted for 42%, 29% and 12% of the Company’s total revenue and three specialty distributor customers accounted for 42%, 33% and 15% of the Company’s total accounts receivable. No other customer accounted for more than 10% of total revenue or accounts receivable for the year ended December 31, 2020.
Fair Value Measurements	Fair Value Measurements ​ Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: ​ ● Level 1—Quoted prices in active markets for identical assets or liabilities. ​ ● Level 2—Observable inputs (other than Level 1 quoted prices) such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. ​ ● Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. ​ The Company’s cash equivalents at December 31, 2021 and 2020 were carried at fair value determined according to the fair value hierarchy described above (Note 3). ​ The carrying value of the Company’s variable interest rate notes payable (Note 9) are recorded at amortized costs, which approximates fair value due to their short-term nature. ​ On March 1, 2019, the Company issued $37,500 aggregate principal amount of unsecured senior subordinated convertible notes (the “2026 Convertible Notes”) (Note 5) which is carried, net of derivative liability, at its amortized cost of $26,435 at December 31, 2021. The estimated fair value of the 2026 Convertible Notes was $52,790 and $129,362 at December 31, 2021 and 2020. The fair value of the 2026 Convertible Notes was estimated utilizing a binomial lattice model which requires the use of Level 3 unobservable inputs. The main input when determining the fair value of the 2026 Convertible Notes is the bond yield that pertains to the host instrument without the conversion option. The significant assumption used in determining the bond yield is the market yield movements of a comparable instrument issued as of the valuation date, which is assessed and updated each period. The main input when determining the fair value for disclosure purposes is the bond yield which is updated each period to reflect the yield of a comparable instrument issued as of the valuation date. The estimated fair value presented is not necessarily indicative of an amount that could be realized in a current market exchange. The use of alternative inputs and estimation methodologies could have a material effect on these estimates of fair value.
Derivative Liability	Derivative Liability ​ The 2026 Convertible Notes allow the holders to convert all or part of the outstanding principal of their 2026 Convertible Notes into shares of the Company’s common stock provided that no conversion results in a holder beneficially owning more than 19.99% of the issued and outstanding common stock of the Company. The entire embedded conversion option is required to be separated from the 2026 Convertible Notes and accounted for as a freestanding derivative instrument subject to derivative accounting. The main input when determining the fair value of the 2026 Convertible Notes is the bond yield that pertains to the host instrument without the conversion option. The significant assumption used in determining the bond yield is the market yield movements of a comparable instrument issued as of the valuation date, which is assessed and updated each period. Therefore, the entire conversion option is bifurcated from the underlying debt instrument and accounted for and valued separately from the host instrument. The Company measures the value of the embedded conversion option at its estimated fair value and recognizes changes in the estimated fair value in other income (expense), net in the consolidated statements of operations and comprehensive loss during the period of change. The embedded conversion is recognized as a derivative liability in the Company’s consolidated balance sheet.
Property and Equipment	Property and Equipment ​ Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over a three
Impairment of Long-Lived Assets and Right of Use Assets	Impairment of Long-Lived Assets and Right of Use Assets ​ Long-lived assets consist of property and equipment and right-of-use assets. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends, and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. The Company has had no impairment triggers of long-lived assets.
Research and Development Costs	Research and Development Costs ​ Research and development costs are expensed as incurred. Included in research and development expenses are salaries, stock-based compensation and benefits of employees and other operational costs related to the Company’s research and development activities, including external costs of outside vendors engaged to conduct preclinical studies and clinical trials, manufacturing costs of the Company’s products prior to regulatory approval, costs related to collaboration agreements and facility-related expenses.
Research Contract Costs and Accruals	Research Contract Costs and Accruals ​ The Company has entered into various research and development contracts with research institutions and other companies both inside and outside of the United States. Certain of these agreements have cancellation clauses, and related payments are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.
Patent Costs	Patent Costs ​ All patent-related costs incurred in connection with filing and prosecuting patent applications are recorded as general and administrative expenses as incurred, as recoverability of such expenditures is uncertain.
Accounting for Stock-Based Compensation	Accounting for Stock-Based Compensation ​ The Company measures all stock options and other stock-based awards granted to employees and directors at the fair value on the date of the grant using the Black-Scholes option-pricing model. The fair value of the awards is recognized as expense, net of estimated forfeitures, over the requisite service period, which is generally the vesting period of the respective award. The straight-line method of expense recognition is applied to all awards with service-only conditions. ​ Following the Company’s adoption of Accounting Standards Update (“ASU”) 2018-07, Compensation—Stock Compensation (Topic 718), Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-07”), on January 1, 2019, for stock-based awards issued to non-employees, the Company no longer revalues non-employee awards at each reporting date and instead calculates the fair value of the awards as of the grant date using the Black-Scholes option-pricing model. Compensation expense for these awards is recognized over the related service period. ​ The Company classifies stock-based compensation expense in its consolidated statement of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified. ​ The Company recognizes compensation expense for only the portion of awards that are expected to vest. In developing a forfeiture rate estimate, the Company has considered its historical experience to estimate pre-vesting forfeitures for service-based awards. The impact of a forfeiture rate adjustment will be recognized in full in the period of adjustment, and if the actual forfeiture rate is materially different from the Company’s estimate, the Company may be required to record adjustments to stock-based compensation expense in future periods.
Income Taxes	Income Taxes ​ The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. ​ The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.
Segment Data	Segment Data ​ The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on advancing its bioresorbable hydrogel product candidates for the programed-release delivery of therapeutic agents, specifically for ophthalmology. All tangible assets are held in the United States. Revenue to date has been generated through product sales, all of which has been earned in the United States.
Comprehensive Loss	Comprehensive Loss ​ Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the years ended December 31, 2021, 2020 and 2019, there were no items that gave rise to other comprehensive loss and therefore, there was no difference between net loss and comprehensive loss.
Net Loss Per Share	Net Loss Per Share ​ Basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net loss attributable to common stockholders is computed by adjusting net loss attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities, including the assumed conversion of the Company’s 2026 Convertible Notes, outstanding stock options and common stock warrants, except where the result would be anti-dilutive. Diluted net loss per share attributable to common stockholders is computed by dividing the diluted net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period, including potential dilutive common shares assuming the dilutive effect of the conversion of the 2026 Convertible Notes, the exercise of outstanding stock options and common stock warrants. In the diluted net loss per share calculation, net loss would also be adjusted for the elimination of interest expense on the 2026 Convertible Notes (which includes amortization of the discount created upon bifurcation of the conversion option from the debt) and, the mark-to-market gain or loss each period to the bifurcated conversion option, if the impact was not anti-dilutive.
Recently Adopted and Issued Accounting Pronouncements	Recently Adopted Accounting Pronouncements ​ In December 2019, the FASB issued ASU No. 2019-12, Income Taxes Topic 740, Simplifying the Accounting for Income Taxes (“ASU 2019-12”). ASU 2019-12 removes certain exceptions for investments, intra-period allocations and interim calculations, and adds guidance to reduce complexity in accounting for income taxes. The guidance is effective for fiscal years beginning after December 15, 2020, including interim periods within those fiscal years. The Company adopted this accounting pronouncement as required effective January 1, 2021 and its adoption did not have a material impact on the consolidated financial statements. ​ In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (‘‘ASU 2016-13’’), which requires the measurement and recognition of expected credit losses for financial assets held at amortized cost. ASU 2016-13 replaces the existing incurred loss impairment model with an expected loss model. It also eliminates the concept of other-than-temporary impairment and requires credit losses related to available-for-sale debt securities to be recorded through an allowance for credit losses rather than as a reduction in the amortized cost basis of the securities. These changes may result in earlier recognition of credit losses. In November 2018, the FASB issued ASU No. 2018-19, Codification Improvements to Topic 326, Financial Instruments—Credit Losses, which narrowed the scope and changed the effective date for non-public entities for ASU 2016-13. The FASB subsequently issued supplemental guidance within ASU No. 2019-05, Financial Instruments—Credit Losses (Topic 326): Targeted Transition Relief (‘‘ASU 2019-05’’). ASU 2019-05 provides an option to irrevocably elect the fair value option for certain financial assets previously measured at amortized cost basis. The Company adopted this accounting pronouncement as required and its adoption did not have a material impact on the consolidated financial statements. ​ Recently Issued Accounting Pronouncements In August 2020, the FASB issued ASU No. 2020-06, Debt – Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40) (“ASU 2020-06”). This standard amends the guidance on convertible instruments and the derivatives scope exception for contracts in an entity’s own equity and improves and amends the related earnings per share guidance for both Subtopics. The amendments in the ASU are effective for public business entities that meet the definition of an SEC filer, excluding entities eligible to be smaller reporting companies as defined by the SEC, for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years. Early adoption is permitted, but no earlier than fiscal years beginning after December 15, 2020, including interim periods within those fiscal years. The FASB also specified that an entity should adopt the guidance as of the beginning of its fiscal year and is not permitted to adopt the guidance in an interim period. The Company is assessing the potential impact of ASU 2020-06 and does not expect it to have a material impact on its consolidated financial statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2021
Summary of Significant Accounting Policies
Components of inventory	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ December 31, ​ ​ 2021 2020 Raw materials ​ $ 388 ​ $ 384 Work-in-process ​ 605 ​ 232 Finished goods ​ ​ 257 ​ ​ 585 ​ ​ $ 1,250 ​ $ 1,201
Reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheet to the total amounts shown in the statement of cash flows	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ December 31, ​ 2021 2020 2019 Cash and cash equivalents ​ $ 164,164 ​ $ 228,057 ​ $ 54,437 Restricted cash ​ ​ 1,764 ​ ​ 1,764 ​ ​ 1,764 Total cash, cash equivalents and restricted cash as shown on the statements of cash flows ​ $ 165,928 ​ $ 229,821 ​ $ 56,201

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2021
Fair Value of Financial Assets and Liabilities
Schedule of assets and liabilities measured at fair Value on recurring basis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements as of ​ ​ December 31, 2021 Using: ​ Level 1 Level 2 Level 3 Total Assets: ​ ​ ​ ​ Cash equivalents: ​ ​ ​ ​ Money market funds ​ $ 62,392 ​ $ — ​ $ — ​ $ 62,392 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Liability: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Derivative liability (Note 4) ​ $ — ​ $ — ​ $ 20,192 ​ $ 20,192 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements as of ​ ​ December 31, 2020 Using: ​ Level 1 Level 2 Level 3 Total Assets: ​ ​ ​ ​ Cash equivalents: ​ ​ ​ ​ Money market funds ​ $ 213,372 ​ $ — ​ $ — ​ $ 213,372 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Liability: ​ ​ ​ ​ Derivative liability (Note 4) ​ $ — ​ $ — ​ $ 98,313 ​ $ 98,313

Derivative Liability (Tables)

Derivative Liability (Tables)	12 Months Ended
	Dec. 31, 2021
Derivative Liability
Schedule of main inputs to valuing the 2026 Convertible Notes with the conversion option	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of ​ ​ ​ December 31, ​ December 31, ​ ​ ​ 2021 ​ 2020 ​ Company's stock price ​ $ 6.97 ​ $ 20.70 ​ Expected annual volatility ​ ​ 82.6 % ​ 105.5 % Bond yield ​ ​ 12.6 % ​ 12.0 %
Summary of roll-forward of the derivative liability	​ ​ ​ ​ ​ ​ ​ As of Balance at December 31, 2019 ​ $ 12,124 Change in fair value ​ ​ 86,189 Balance at December 31, 2020 ​ ​ 98,313 Change in fair value ​ ​ (78,121) Balance at December 31, 2021 ​ $ 20,192

Convertible Notes (Tables)

Convertible Notes (Tables)	12 Months Ended
	Dec. 31, 2021
Convertible Notes
Summary of the 2026 Convertible Notes	​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2021 2020 2026 Convertible Notes ​ $ 37,500 ​ $ 37,500 Less: unamortized discount ​ ​ (11,065) ​ ​ (13,193) Total ​ $ 26,435 ​ $ 24,307

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	12 Months Ended
	Dec. 31, 2021
Property and Equipment, net
Schedule of Property and Equipment net	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2021 2020 Equipment ​ $ 10,989 ​ $ 10,186 Leasehold improvements ​ 9,074 ​ 9,074 Furniture and fixtures ​ 1,286 ​ 1,281 Software ​ 236 ​ 220 Construction in progress ​ 578 ​ 120 ​ ​ 22,163 ​ 20,881 Less: Accumulated depreciation and amortization ​ (15,207) ​ (12,786) ​ ​ $ 6,956 ​ $ 8,095

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2021
Accrued Expenses
Schedule of accrued expenses	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2021 2020 Accrued payroll and related expenses ​ $ 6,597 ​ $ 5,853 Accrued rebates and programs ​ ​ 3,615 ​ ​ 1,438 Accrued professional fees ​ 1,227 ​ 868 Accrued research and development expenses ​ 1,102 ​ 1,013 Accrued interest payable on 2026 convertible notes ​ 6,475 ​ 4,194 Accrued other ​ 1,105 ​ 941 ​ ​ $ 20,121 ​ $ 14,307

Notes Payable (Tables)

Notes Payable (Tables)	12 Months Ended
	Dec. 31, 2021
Notes Payable
Schedule of borrowings outstanding	​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ 2021 2020 Borrowings outstanding ​ $ 25,000 ​ $ 25,000 Accrued exit fee ​ ​ 110 ​ ​ 355 Unamortized discount ​ ​ (110) ​ ​ (129) ​ ​ ​ 25,000 ​ ​ 25,226 Less: current portion ​ ​ — ​ ​ (8,290) Long-term notes payable ​ $ 25,000 ​ $ 16,936
Schedule of Annual Repayment Requirements for Credit Facility	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ending December 31, Principal Final Payment Total 2022 ​ ​ — ​ ​ — ​ ​ — 2023 ​ ​ — ​ ​ — ​ ​ — 2024 ​ ​ 8,333 ​ ​ — ​ ​ 8,333 2025 ​ ​ 16,667 ​ ​ 875 ​ ​ 17,542 ​ ​ $ 25,000 ​ $ 875 ​ $ 25,875

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	12 Months Ended
	Dec. 31, 2021
Stock-Based Awards
Schedule of Assumptions Used to Determine Fair Value of Stock Options Granted to Employees and Directors Presented on Weighted Average Basis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ 2021 2020 2019 Risk-free interest rate 0.80 % 1.12 % 2.25 % Expected term (in years) 6 6 6 ​ Expected volatility 87.65 % 86.00 % 87 % Expected dividend yield — % — % — %
Schedule of Stock Option Activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ Weighted ​ Average ​ ​ ​ ​ ​ ​ ​ Average ​ Remaining ​ Aggregate ​ ​ Shares Issuable ​ Exercise ​ Contractual ​ Intrinsic ​ Under Options Price Term Value ​ ​ ​ ​ ​ ​ ​ (In years) ​ ​ ​ Outstanding as of December 31, 2020 9,114,735 ​ $ 6.66 7.4 ​ $ 16,075 Granted 3,339,974 ​ 17.22 ​ ​ ​ ​ ​ Exercised (598,924) ​ 4.32 ​ ​ ​ ​ ​ Forfeited (920,957) ​ 11.48 ​ ​ ​ ​ ​ Outstanding as of December 31, 2021 10,934,828 ​ $ 9.60 ​ 7.1 ​ ​ 13,283 Options vested and expected to vest as of December 31, 2021 9,504,572 ​ $ 8.93 ​ 6.8 ​ ​ 12,381 Options exercisable as of December 31, 2021 6,570,556 ​ $ 8.22 ​ 6.1 ​ ​ 9,002
Schedule of stock-based compensation expense related to stock options	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2021 2020 2019 Research and development ​ $ 3,750 ​ $ 1,514 ​ $ 2,312 ​ Selling and marketing ​ 4,014 ​ 1,719 ​ 1,013 ​ General and administrative ​ 7,214 ​ 4,298 ​ 5,434 ​ ​ ​ $ 14,978 ​ $ 7,531 ​ $ 8,759 ​

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2021
Net Loss Per Share
Schedule of basic and diluted net loss per share attributable to common stockholders	​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2020 ​ 2019 Numerator: ​ ​ ​ ​ Net loss $ (155,636) ​ $ (86,372) Denominator: ​ ​ Weighted average common shares outstanding, basic and diluted 60,752,225 ​ 45,273,231 Net loss per share - basic and diluted $ (2.56) ​ $ (1.91) ​ ​ ​ ​ ​ ​
Schedule of antidilutive securities, excluded from computation of diluted net loss per share	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2021 2020 2019 Options to purchase common stock 10,934,828 9,114,735 7,920,417 Shares issuable upon conversion of 2026 Convertible Notes, if converted — 5,769,232 5,769,232 Warrants for the purchase of common stock — 18,939 18,939 ​ 10,934,828 14,902,906 13,708,588

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2021
Leases
Summary of lease cost	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the ​ For the ​ For the ​ ​ Year Ended ​ Year Ended ​ Year Ended ​ ​ December 31, ​ December 31, ​ December 31, ​ ​ 2021 ​ 2020 ​ 2019 Operating lease costs ​ $ 2,482 ​ $ 2,418 ​ $ 2,070 Variable lease costs ​ ​ 629 ​ ​ 677 ​ ​ 538 Total lease costs ​ $ 3,111 ​ $ 3,095 ​ $ 2,608
Summary of the presentation in the Company's consolidated balance sheet of its operating leases	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ Balance sheet location 2021 ​ 2020 Assets: ​ ​ ​ ​ ​ ​ ​ ​ Operating lease assets ​ Operating lease assets ​ $ 4,867 ​ $ 5,844 ​ ​ ​ ​ ​ ​ ​ ​ ​ Liability: ​ ​ ​ ​ ​ ​ ​ ​ Current operating lease liabilities ​ Operating lease liabilities ​ $ 1,624 ​ $ 1,358 Non-current operating lease liabilities ​ Operating lease liabilities, net of current portion ​ ​ 5,924 ​ ​ 7,548 Total Operating lease liabilities: ​ ​ ​ $ 7,548 ​ $ 8,906
Schedule of minimum lease payments	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, Year Ending December 31, ​ ​ 2021 2022 ​ ​ ​ ​ 2,549 2023 ​ ​ ​ ​ 2,355 2024 ​ ​ ​ ​ 1,569 2025 ​ ​ ​ ​ 1,447 2026 ​ ​ ​ ​ 1,482 Thereafter ​ ​ ​ ​ 884 Total lease payments ​ ​ ​ $ 10,286 Less: interest ​ ​ ​ ​ 2,738 Present value of operating lease liabilities ​ ​ ​ $ 7,548
Schedule of weighted average remaining lease term and the average incremental borrowing rate	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ December 31, ​ 2021 ​ ​ 2020 Weighted average remaining lease term in years ​ ​ 4.8 ​ ​ 5.6 ​ Weighted average discount rate ​ ​ 13.55 % ​ 13.55 %
Supplemental disclosure of cash flow information related to our operating leases included in cash flows provided by operating activities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the ​ ​ For the ​ For the ​ ​ Year Ended ​ ​ Year Ended ​ Year Ended ​ ​ December 31, ​ ​ December 31, ​ December 31, ​ 2021 ​ ​ 2020 ​ 2019 Cash paid for amounts included in the measurement of lease liabilities ​ $ 2,482 ​ $ 2,418 ​ $ 2,215

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income Taxes
Reconciliation of Federal Income Tax Rate	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2021 2020 2019 Federal statutory income tax rate 21.0 % 21.0 % 21.0 % Research and development tax credits 35.9 ​ 1.0 2.1 ​ State taxes, net of federal benefit 19.3 ​ 1.0 2.7 ​ Stock-based compensation (7.8) ​ — (1.3) ​ Derivative liability ​ 244.7 ​ (11.5) ​ ​ ​ Other (12.2) ​ — (0.5) ​ Change in the valuation allowance (300.9) ​ (11.5) (24.0) ​ Effective income tax rate — % — % — %
Net Deferred Tax Assets	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2021 2020 Deferred tax assets: ​ ​ ​ ​ ​ ​ Net operating loss carryforwards ​ $ 106,265 ​ $ 90,797 Tax credit carryforwards ​ 15,853 ​ 13,514 Capitalized start-up costs ​ 373 ​ 514 Capitalized research and development expenses, net ​ 7,828 ​ 10,657 Operating lease liabilities ​ ​ 1,705 ​ ​ 2,066 Derivative liability ​ ​ 2,499 ​ ​ 3,061 Accrued expenses and other ​ 11,712 ​ 6,828 Total deferred tax assets ​ 146,235 ​ 127,437 Valuation allowance ​ (142,637) ​ (123,020) Net deferred tax assets ​ ​ 3,598 ​ ​ 4,417 ​ ​ ​ ​ ​ ​ ​ Deferred tax liabilities: ​ ​ ​ ​ ​ ​ Operating lease right of use assets ​ ​ (1,099) ​ ​ (1,356) 2026 Convertible Notes ​ ​ (2,499) ​ ​ (3,061) Total deferred tax liabilities ​ ​ (3,598) ​ ​ (4,417) Net deferred tax assets ​ $ — ​ $ —
Changes in Valuation Allowance for Deferred Tax Assets	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2021 2020 2019 Valuation allowance as of beginning of year ​ $ 123,020 ​ $ 105,062 ​ $ 84,343 Increases recorded to income tax provision ​ 19,617 ​ 17,958 ​ 20,719 Valuation allowance as of end of year ​ $ 142,637 ​ $ 123,020 ​ $ 105,062

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Nature of Business (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Nature of the Business and Basis of Presentation
Accumulated deficit	$ 545,804	$ 539,251
Cash and cash equivalents	$ 164,164	$ 228,057	$ 54,437

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Inventory Valuation (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Inventory
Raw materials	$ 388	$ 384
Work-in-process	605	232
Finished goods	257	585
Total inventory	$ 1,250	$ 1,201

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of the cash, cash equivalents, and restricted cash reported within the balance sheet that sum to the total of the same amounts shown in the statement of cash flows:
Cash and cash equivalents	$ 164,164	$ 228,057	$ 54,437
Restricted cash	1,764	1,764	1,764
Total cash, cash equivalents and restricted cash as shown on the statements of cash flows	$ 165,928	$ 229,821	$ 56,201	$ 60,676

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Concentration of Credit Risk (Details) - Customer - customer	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Total revenue
Concentration risk
Number of major customers	3	3
Total revenue | Customer one
Concentration risk
Concentration risk	42.00%	42.00%
Total revenue | Customer two
Concentration risk
Concentration risk	26.00%	29.00%
Total revenue | Customer three
Concentration risk
Concentration risk	17.00%	12.00%
Accounts receivable
Concentration risk
Number of major customers	3	3
Accounts receivable | Customer one
Concentration risk
Concentration risk	42.00%	42.00%
Accounts receivable | Customer two
Concentration risk
Concentration risk	26.00%	33.00%
Accounts receivable | Customer three
Concentration risk
Concentration risk	21.00%	15.00%

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Fair Value Measurements (Details) - 2026 Convertible Notes - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Mar. 01, 2019
Summary of Significant Accounting Policies
Convertible notes issued	$ 37,500	$ 37,500	$ 37,500
Convertible notes at amortized cost	26,435	24,307
Estimated fair value	$ 52,790	$ 129,362

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Derivative Liability (Details)	Mar. 01, 2019
2026 Convertible Notes
Summary of Significant Accounting Policies
Maximum beneficial ownership percent	19.99%

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2021
Summary Of Significant Accounting Policies
Income tax examination, likelihood of settlement, description	The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement.
Minimum
Summary Of Significant Accounting Policies
Property and equipment, estimated useful life	3 years
Income tax examination, likelihood of settlement, percentage	50.00%
Maximum
Summary Of Significant Accounting Policies
Property and equipment, estimated useful life	5 years

Fair Value of Financial Asset_3

Fair Value of Financial Assets and Liabilities - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Liability:
Derivative liability	$ 20,192	$ 98,313	$ 12,124
Recurring Basis
Liability:
Derivative liability	20,192	98,313
Money Market Funds | Recurring Basis
Assets:
Cash equivalents	62,392	213,372
Level 1 | Money Market Funds | Recurring Basis
Assets:
Cash equivalents	62,392	213,372
Level 3 | Recurring Basis
Liability:
Derivative liability	$ 20,192	$ 98,313

Fair Value of Financial Asset_4

Fair Value of Financial Assets and Liabilities - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Fair Value of Financial Assets and Liabilities
Transfers between fair value measurement levels	$ 0	$ 0

Derivative Liability - Main Inp

Derivative Liability - Main Inputs to Valuing Convertible Notes with Conversion Option (Details) - 2026 Convertible Notes	Dec. 31, 2021	Dec. 31, 2020
Company's stock price
Derivative Liability
Debt instrument, measurement input	6.97	20.70
Expected annual volatility
Derivative Liability
Debt instrument, measurement input	0.826	1.055
Bond yield
Derivative Liability
Debt instrument, measurement input	0.126	0.120

Derivative Liability - Roll for

Derivative Liability - Roll forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Roll forward of the derivative liability
Balance at beginning of period	$ 98,313	$ 12,124
Change in fair value	(78,121)	86,189
Balance at end of period	$ 20,192	$ 98,313

Convertible Notes - Other (Deta

Convertible Notes - Other (Details) $ / shares in Units, $ in Thousands	Mar. 01, 2019USD ($)D$ / shares	Dec. 31, 2021USD ($)$ / shares	Dec. 31, 2020USD ($)$ / shares
Senior Convertible Notes
Common stock, par value | $ / shares		$ 0.0001	$ 0.0001
2026 Convertible Notes
Senior Convertible Notes
Convertible notes issued | $	$ 37,500	$ 37,500	$ 37,500
Interest rate (as a percent)	6.00%
Effective annual interest rate (as a percent)		14.80%
Common stock, par value | $ / shares	$ 0.0001
Maximum beneficial ownership percent	19.99%
Conversion rate	153.8462
Principal amount of debt that is used in conversion calculations | $	$ 1,000
Initial conversion price | $ / shares	$ 6.50
Debt repurchase price percent	100.00%
Consecutive trading days | D	20
Percentage of product of conversion rate and daily VWAP	5.00%
Percentage of outstanding principal amount	100.00%
2026 Convertible Notes | On or after March 1, 2022
Senior Convertible Notes
Debt repurchase price percent	100.00%
Consecutive trading days | D	30
Minimum percentage of common stock for conversion of debt	130.00%
Consecutive proceeding trading days for conversion of purchase price | D	20

Convertible Notes - Summary (De

Convertible Notes - Summary (Details) - 2026 Convertible Notes - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Mar. 01, 2019
Senior Convertible Notes
Convertible notes	$ 37,500	$ 37,500	$ 37,500
Less: unamortized discount	(11,065)	(13,193)
Total	$ 26,435	$ 24,307

Property and Equipment, net - S

Property and Equipment, net - Schedule of Property and Equipment, net (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property and Equipment, net
Property and equipment, gross	$ 22,163	$ 20,881
Less: Accumulated depreciation and amortization	(15,207)	(12,786)
Property and equipment, net	6,956	8,095
Equipment
Property and Equipment, net
Property and equipment, gross	10,989	10,186
Leasehold improvements
Property and Equipment, net
Property and equipment, gross	9,074	9,074
Furniture and fixtures
Property and Equipment, net
Property and equipment, gross	1,286	1,281
Software
Property and Equipment, net
Property and equipment, gross	236	220
Construction in progress
Property and Equipment, net
Property and equipment, gross	$ 578	$ 120

Property and Equipment, net - A

Property and Equipment, net - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property and Equipment, net
Depreciation and amortization expense	$ 2,421	$ 2,773	$ 2,530

Accrued Expenses - Summary (Det

Accrued Expenses - Summary (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Accrued Expenses
Accrued payroll and related expenses	$ 6,597	$ 5,853
Accrued rebates and programs	3,615	1,438
Accrued professional fees	1,227	868
Accrued research and development expenses	1,102	1,013
Accrued interest payable on 2026 convertible notes	6,475	4,194
Accrued other	1,105	941
Total	$ 20,121	$ 14,307

Collaboration Agreements - Addi

Collaboration Agreements - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2020
License Agreement | AffaMed
Collaboration Agreement
Amount of non-refundable upfront payments received			$ 12,000
Additional payments to be received upon the achievement of certain development and commercial milestones		$ 90,000
Payment received on milestone achievement	$ 1,000
Transaction price	13,000	13,000
Potential regulatory, development and commercial milestone payments excluded from transaction price	$ 90,000	$ 90,000
License Agreement | AffaMed | Minimum
Collaboration Agreement
Revenue expected to be recognized period	7 years	7 years
License Agreement | AffaMed | Maximum
Collaboration Agreement
Revenue expected to be recognized period	8 years	8 years
Collaboration, Option and License Agreement | Regeneron Pharmaceuticals, Inc
Collaboration Agreement
Collaboration Agreement termination, reimbursement of certain development costs no longer required, amount	$ 30,000	$ 30,000
Amount of cost recorded, to date, for work performed for preclinical development activities in connection with the revised work plan		768	1,256
Costs associated with preclinical development activities included in prepaid expenses and other current assets	$ 0	$ 0	$ 1,256

Notes Payable - Additional Info

Notes Payable - Additional Information (Details)	1 Months Ended		12 Months Ended
	Jun. 30, 2021USD ($)	Dec. 31, 2018USD ($)installment	Dec. 31, 2021USD ($)	Dec. 31, 2018USD ($)	May 31, 2021	Dec. 31, 2020USD ($)
Credit Facility.
Notes Payable
Borrowing capacity under the agreement			$ 25,000,000
Borrowings outstanding			25,000,000			$ 25,000,000
Credit Agreement, 2018
Notes Payable
Outstanding borrowings under credit facility, net of unamortized discount		$ 25,000,000		$ 25,000,000
Debt Instrument, Percentage of Exit Fee				3.50%
Accrued amount paid				$ 429,000
Credit Agreement, 2018 | Period commencing January 2021
Notes Payable
Number of equal monthly installments | installment		36
Required monthly principal payment		$ 694,000
Credit Agreement, 2018 | LIBOR
Notes Payable
Interest rate (as a percent)					9.25%
Interest rate floor (as a percent)		2.00%		2.00%
Basis spread (as a percent)		7.25%
2021 Amended Credit Facility
Notes Payable
Borrowings outstanding	$ 25,000,000
Indebtedness with existing lenders in which terms of credit facility were amended, amount	20,833,000
Incremental borrowing, amount	4,167,000
Final payment due at maturity	$ 5,208,000
Effective annual interest rate (as a percent)	8.80%
Exit fee (as a percent)	3.50%
Exit fee, amount	$ 875,000		875,000
Additional final payment			$ 875,000
2021 Amended Credit Facility | Period commencing May 2024
Notes Payable
Number of equal monthly installments	19
Required monthly principal payment	$ 1,042,000
2021 Amended Credit Facility | Achievement of certain milestones
Notes Payable
Number of equal monthly installments	5
Required monthly principal payment	$ 1,042,000
2021 Amended Credit Facility | LIBOR
Notes Payable
Interest rate floor (as a percent)	1.00%
Basis spread (as a percent)	6.75%

Notes Payable - Borrowings Outs

Notes Payable - Borrowings Outstanding (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Notes Payable
Less: current portion		$ (8,290)
Long-term notes payable	$ 25,000	16,936
Credit Facility.
Notes Payable
Borrowings outstanding	25,000	25,000
Accrued exit fee	110	355
Unamortized discount	(110)	(129)
Borrowings	25,000	25,226
Less: current portion		(8,290)
Long-term notes payable	$ 25,000	$ 16,936

Notes Payable - Schedule of Ann

Notes Payable - Schedule of Annual Repayment Requirements for Credit Facility (Details) - 2021 Amended Credit Facility - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2021
Annual repayment requirements
Credit Facility, Principal		$ 25,000
Credit Facility, Final Payment	$ 875	875
Total		25,875
2024
Annual repayment requirements
Credit Facility, Principal		8,333
Total		8,333
2025
Annual repayment requirements
Credit Facility, Principal		16,667
Credit Facility, Final Payment		875
Total		$ 17,542

Warrants - Additional Informati

Warrants - Additional Information (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Jan. 29, 2021	Dec. 31, 2020	Jul. 31, 2014	Apr. 30, 2014
Series D-1 Redeemable Convertible Preferred Stock Warrants | Silicon Valley Bank and MidCap Financial SBIC, LP
Warrants
Number of shares callable by warrants					100,000
Weighted average exercise price to purchase common stock					$ 3
Warrants for Common Stock
Warrants
Number of shares callable by warrants		18,939
Weighted average exercise price to purchase common stock		$ 7.92
Warrants outstanding	0
Warrants for Common Stock | Silicon Valley Bank and MidCap Financial SBIC, LP
Warrants
Number of shares callable by warrants				37,878
Weighted average exercise price to purchase common stock				$ 7.92
Warrants for Common Stock | Silicon Valley Bank
Warrants
Number of shares callable by warrants				18,939
Warrants for Common Stock | MidCap Financial, SBIC, LP
Warrants
Number of shares callable by warrants			18,939	18,939
Warrants for Common Stock | MidCap Financial, SBIC, LP | Weighted Average
Warrants
Weighted average exercise price to purchase common stock			$ 7.92
Common Stock
Warrants
Common stock issued upon exercise of warrants	11,737

Preferred Stock (Details)

Preferred Stock (Details) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
Preferred Stock
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Common Stock (Details)

Common Stock (Details) $ / shares in Units, $ in Thousands	Aug. 09, 2021USD ($)	Dec. 14, 2020USD ($)$ / sharesshares	Oct. 13, 2020USD ($)$ / sharesshares	Apr. 05, 2019USD ($)	May 31, 2020USD ($)$ / sharesshares	Dec. 31, 2021Voteshares	Dec. 31, 2020USD ($)shares	Dec. 31, 2019USD ($)shares	Mar. 01, 2021USD ($)shares	Feb. 27, 2022shares	Jun. 30, 2021shares
Common Stock
Common Stock, Shares Authorized						200,000,000	100,000,000				200,000,000
Number of votes per share | Vote						1
Voting right description						Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders.
Net proceeds from issuance of common stock | $		$ 86,390	$ 75,406		$ 48,327		$ 224,682	$ 37,537
Common Stock
Common Stock
Number of shares issued							24,934,222	8,655,940
Number of shares of common stock reserved for issuance						10,934,828
Common Stock | 2019 Sales Agreement
Common Stock
Maximum aggregate proceeds from offering | $				$ 50,000
Net proceeds from issuance of common stock | $							$ 14,359		$ 46,985
Number of shares issued							2,984,381		10,321,840
Common Stock | 2021 Sales Agreement
Common Stock
Maximum aggregate proceeds from offering | $	$ 100,000
Number of shares issued										0
Common Stock | Follow-on Offering
Common Stock
Number of shares issued		3,725,000	7,180,000		8,181,819
Common stock, price per share | $ / shares		$ 21.50	$ 9.75		$ 5.50
Common Stock | Over-allotment Option
Common Stock
Number of shares issued		558,750	1,077,000		1,227,272
Common stock, price per share | $ / shares		$ 20.21	$ 9.17		$ 5.17

Stock-Based Awards - Stock Ince

Stock-Based Awards - Stock Incentive Plan (Details) - shares	Jan. 01, 2021	Jan. 01, 2015	Dec. 31, 2021	Dec. 31, 2014
Common Stock
Stock-Based Awards
Number of shares of common stock reserved for issuance			10,934,828
2014 and 2006 Stock Incentive Plan
Stock-Based Awards
Number of shares of common stock available for issuance			9,766,336
2014 Stock Incentive Plan
Stock-Based Awards
Number of shares of common stock available for issuance			456,334
2014 Stock Incentive Plan | Common Stock
Stock-Based Awards
Number of shares of common stock reserved for issuance		2,126,907		1,336,907
Additional shares of common stock that may be issued under the plane		1,659,218
Additional number of shares of common stock , percentage		4.00%
Additional number of shares authorized for issuance	1,659,218
2021 Incentive Plan
Stock-Based Awards
Number of shares of common stock reserved for issuance			6,000,000
Number of shares of common stock available for issuance			6,263,365

Stock-Based Awards - Inducement

Stock-Based Awards - Inducement Stock Option Awards (Detail) - $ / shares	Feb. 01, 2021	Dec. 10, 2020	Jul. 09, 2019	Jun. 20, 2017	Dec. 31, 2021
Stock-Based Awards
Shares Issuable Under Options, Granted					3,339,974
Exercise price (in dollars per share)					$ 17.22
Non-statutory Stock Option | Management
Stock-Based Awards
Shares Issuable Under Options, Granted			60,000	590,000
Exercise price (in dollars per share)			$ 5.13	$ 10.94
Vesting period			4 years	4 years
Percentage of shares underlying the option award vesting on first anniversary			25.00%	25.00%
Percentage of shares underlying the option award vesting monthly after the first anniversary			75.00%	75.00%
2019 Inducement Plan
Stock-Based Awards
Number of shares of common stock authorized for issuance		1,054,000
Number of shares of common stock available for issuance					510,252
Additional number of shares authorized for issuance		554,000
2019 Inducement Plan | Non-Statutory Stock Option Vesting Based on Time | Senior Vice President, Clinical Development
Stock-Based Awards
Shares Issuable Under Options, Granted	100,000
Exercise price (in dollars per share)	$ 18.70
Vesting period	4 years
Percentage of shares underlying the option award vesting on first anniversary	25.00%
2019 Inducement Plan | Non-Statutory Stock Option Vesting Based on Performance | Senior Vice President, Clinical Development
Stock-Based Awards
Shares Issuable Under Options, Granted	5,000,000
Exercise price (in dollars per share)	$ 18.70
Percentage of shares underlying the option award vesting monthly after the first anniversary	75.00%

Stock-Based Awards - ESPP (Deta

Stock-Based Awards - ESPP (Details) - Common Stock - shares	Jan. 01, 2020	Jan. 01, 2015	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2014
Stock-Based Awards
Number of shares of common stock reserved for issuance			10,934,828
2014 Employee Stock Purchase Plan
Stock-Based Awards
Number of shares of common stock reserved for issuance		232,402			207,402
Additional number of shares authorized for issuance	207,402
Additional shares of common stock that may be issued under the plane		207,402
Additional number of shares of common stock , percentage		0.50%
Number of shares of common stock available for issuance				607,048

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Details)	Dec. 31, 2021shares
Stock-Based Awards
Unvested service-based stock options held by nonemployees	27,903

Stock-Based Awards - Fair Value

Stock-Based Awards - Fair Value Assumptions (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Assumptions Used to Determine Fair Value of Stock Options Granted to Employees and Directors Presented on a Weighted Average Basis
Risk-free interest rate	0.80%	1.12%	2.25%
Expected term (in years)	6 years	6 years	6 years
Expected volatility	87.65%	86.00%	87.00%

Stock-Based Awards - Schedule o

Stock-Based Awards - Schedule of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Shares Issuable Under Options
Shares Issuable Under Options, Beginning balance	9,114,735
Shares Issuable Under Options, Granted	3,339,974
Shares Issuable Under Options, Exercised	(598,924)
Shares Issuable Under Options, Forfeited	(920,957)
Shares Issuable Under Options, Ending balance	10,934,828	9,114,735
Shares Issuable Under Options, Vested and expected to vest	9,504,572
Shares Issuable Under Options, Exercisable	6,570,556
Weighted Average Exercise Price
Weighted Average Exercise Price, Beginning balance	$ 6.66
Weighted Average Exercise Price, Granted	17.22
Weighted Average Exercise Price, Exercised	4.32
Weighted Average Exercise Price, Forfeited	11.48
Weighted Average Exercise Price, Ending balance	9.60	$ 6.66
Weighted Average Exercise Price, Vested and expected to vest	8.93
Weighted Average Exercise Price, Exercisable	$ 8.22
Weighted Average Remaining Contractual Term	7 years 1 month 6 days	7 years 4 months 24 days
Weighted Average Remaining Contractual Term, Vested and Expected to vest	6 years 9 months 18 days
Weighted Average Remaining Contractual Term, Exercisable	6 years 1 month 6 days
Other disclosures
Aggregate Intrinsic Value	$ 13,283	$ 16,075
Aggregate Intrinsic Value, Vested and Expected to vest	12,381
Aggregate Intrinsic Value, Exercisable	9,002
Aggregate intrinsic value of stock options exercised	$ 6,779	$ 4,307	$ 54
Weighted average fair value of stock option granted	$ 12.48

Stock-Based Awards - Stock-Base

Stock-Based Awards - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock-based Compensation
Stock-based compensation expense	$ 14,978	$ 7,531	$ 8,759
Unrecognized stock-based compensation cost	$ 20,382
Weighted average period of unrecognized stock-based compensation cost expected to be recognized	2 years 9 months 18 days
Research and Development Expense
Stock-based Compensation
Stock-based compensation expense	$ 3,750	1,514	2,312
Selling and Marketing Expense
Stock-based Compensation
Stock-based compensation expense	4,014	1,719	1,013
General and Administrative Expense
Stock-based Compensation
Stock-based compensation expense	$ 7,214	$ 4,298	$ 5,434

Net Loss Per Share - Basic and

Net Loss Per Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Basic net loss per share attributable to common stockholders:
Net loss	$ (6,553)	$ (155,636)	$ (86,372)
Weighted Average Number of Shares Outstanding, Basic	76,392,870	60,752,225	45,273,231
Net loss per share, basic and diluted		$ (2.56)	$ (1.91)

Net Loss Per Share - Diluted Ne

Net Loss Per Share - Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reconciliation of net loss attributable to common stockholders for basic and diluted net loss per share
Net loss attributable to common stockholders, basic	$ (6,553)
Interest expense on 2026 Convertible Note	4,409
Change in fair value of derivative liability	(78,121)
Net loss attributable to common stockholders, diluted	$ (80,265)
Weighted average common shares outstanding, basic	76,392,870	60,752,225	45,273,231
Shares issuable upon conversion of 2026 Convertible Note, as if converted	5,769,232
Weighted average common shares outstanding, diluted	82,162,102	60,752,225	45,273,231
Net loss per share attributable to common stockholders, basic	$ (0.09)	$ (2.56)	$ (1.91)
Net loss per share attributable to common stockholders, diluted	$ (0.98)	$ (2.56)	$ (1.91)

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Antidilutive Securities, Excluded from Computation of Diluted Net Loss per Share (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share
Total common stock equivalents	10,934,828	14,902,906	13,708,588
Options to Purchase Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Total common stock equivalents	10,934,828	9,114,735	7,920,417
2026 Convertible Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share
Total common stock equivalents		5,769,232	5,769,232
Warrant | Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Total common stock equivalents		18,939	18,939

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Incept
Commitments and Contingencies
Royalties paid from inception	$ 1,908

Leases - Other (Details)

Leases - Other (Details)	Apr. 18, 2019ft²	Jun. 30, 2016ft²period	Dec. 31, 2021period
Leases
Options to renew			true
Minimum
Leases
Lease term			1 year
Renewal terms			1 year
Additional periods for renewal | period			1
Maximum
Leases
Lease term			8 years
Renewal terms			6 years
Office space lease, Bedford, Massachusetts
Leases
Lease term	5 years
Options to renew	false
Area covered under lease | ft²	30,036
Lease Agreement, June 2016, Bedford, Massachusetts
Leases
Renewal terms		5 years
Additional periods for renewal | period		2
Area covered under lease | ft²		70,712
Lease Agreement, June 2016, Bedford, Massachusetts | Minimum
Leases
Written notice period to extend the lease		12 months
Lease Agreement, June 2016, Bedford, Massachusetts | Maximum
Leases
Written notice period to extend the lease		15 months

Leases - Costs (Details)

Leases - Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Lease Costs
Operating lease costs	$ 2,482	$ 2,418	$ 2,070
Variable lease costs	629	677	538
Total lease costs	$ 3,111	$ 3,095	$ 2,608

Leases - Balance sheet presenta

Leases - Balance sheet presentation (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Assets
Operating lease assets	$ 4,867	$ 5,844
Liabilities
Current operating lease liabilities	1,624	1,358
Noncurrent operating lease liabilities	5,924	7,548
Total operating lease liabilities	$ 7,548	$ 8,906

Leases - Future minimum payment

Leases - Future minimum payments (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Minimum lease payments
2022	$ 2,549
2023	2,355
2024	1,569
2025	1,447
2026	1,482
Thereafter	884
Total lease payments	10,286
Less: interest	2,738
Present value of operating lease liabilities	$ 7,548	$ 8,906

Leases - Terms and discount rat

Leases - Terms and discount rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Leases
Weighted average remaining lease term in years	4 years 9 months 18 days	5 years 7 months 6 days
Weighted average discount rate	13.55%	13.55%
Supplemental disclosure of cash flow information related to operating leases
Cash paid for amounts included in the measurement of lease liabilities	$ 2,482	$ 2,418	$ 2,215

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Federal Income Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Taxes
Income tax benefit	$ 0	$ 0	$ 0
Reconciliation of the U.S. federal statutory income tax rate to the Company's effective income tax rate
Federal statutory income tax rate	21.00%	21.00%	21.00%
Research and development tax credits	35.90%	1.00%	2.10%
State taxes, net of federal benefit	19.30%	1.00%	2.70%
Stock-based compensation	(7.80%)		(1.30%)
Derivative liability	244.70%	(11.50%)
Other	(12.20%)		(0.50%)
Change in valuation allowance	(300.90%)	(11.50%)	(24.00%)
Effective income tax rate

Income Taxes - Net Deferred Tax

Income Taxes - Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforwards	$ 106,265	$ 90,797
Tax credit carryforwards	15,853	13,514
Capitalized start-up costs	373	514
Capitalized research and development expenses, net	7,828	10,657
Operating lease liabilities	1,705	2,066
Derivative liability	2,499	3,061
Accrued expenses and other	11,712	6,828
Total gross deferred tax assets	146,235	127,437
Valuation allowance	(142,637)	(123,020)	$ (105,062)	$ (84,343)
Net deferred tax assets	3,598	4,417
Operating lease right of use assets	(1,099)	(1,356)
2026 Convertible Notes	(2,499)	(3,061)
Total deferred tax liabilities	(3,598)	(4,417)
Net deferred tax assets

Income Taxes - Changes in Valua

Income Taxes - Changes in Valuation Allowance for Deferred Tax Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Taxes
Valuation allowance as of beginning of year	$ 123,020	$ 105,062	$ 84,343
Increases recorded to income tax provision	19,617	17,958	20,719
Valuation allowance as of end of year	$ 142,637	$ 123,020	$ 105,062

Income Taxes - Net Operating Lo

Income Taxes - Net Operating Loss Carryforwards (Details) $ in Thousands	Dec. 31, 2021USD ($)
Federal
Net operating loss carryforwards
Net operating loss carryforwards	$ 423,628
Net operating loss carryforward that can be carried forward indefinitely	297,823
State
Net operating loss carryforwards
Net operating loss carryforwards	$ 296,998

Income Taxes - Tax Credit Carry

Income Taxes - Tax Credit Carryforwards (Details) - Research and Development $ in Thousands	Dec. 31, 2021USD ($)
Federal
Tax credit carryforwards
Tax credit carryforwards	$ 10,898
State
Tax credit carryforwards
Tax credit carryforwards	$ 6,142

Income Taxes - Other (Details)

Income Taxes - Other (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Taxes
Unrecognized tax benefits		$ 0	$ 0
Accrued interest or penalties related to uncertain tax positions	$ 0	0
Interest expense or penalties related to uncertain tax positions	$ 0	$ 0

401(k) Savings Plan - Additiona

401(k) Savings Plan - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)
401(k) Savings Plan
Contributions to savings plan	$ 493

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Specialty Pharma
Related Party Transactions
Expenses incurred	$ 155
Accounts payable		$ 47
Accrued expenses		0
McCarter | Legal Fees.
Related Party Transactions
Expenses incurred		766	$ 1,119
Accounts payable		47
Accrued expenses	0
WilmerHale | Chief Business Officer
Related Party Transactions
Accounts payable	119	114
Accrued expenses	68	239
WilmerHale | Legal Fees. | Chief Business Officer
Related Party Transactions
Expenses incurred	$ 1,396	$ 1,772

Subsequent Events (Details)

Subsequent Events (Details) - Common Stock - 2014 Employee Stock Purchase Plan - shares	Jan. 01, 2022	Jan. 01, 2020	Jan. 01, 2015
Subsequent Events
Additional shares of common stock that may be issued under the plane			207,402
Additional number of shares of common stock , percentage			0.50%
Additional number of shares authorized for issuance		207,402
Subsequent Event
Subsequent Events
Additional number of shares authorized for issuance	207,402