Stockholders' Equity | 7 . Stockholders’ Equity Authorized, Issued, and Outstanding Common Stock The Company’s authorized common stock has a par value of $0.001 per share and consists of 100,000,000 shares as of September 30, 2021, and December 31, 2020; 23,885,570 and 19,663,698 shares were issued and outstanding at September 30, 2021, and December 31, 2020, respectively. On July 16, 2020, the Company filed a Certificate of Amendment to its Amended and Restated Certificate of Incorporation (the “Amendment”), which became effective on Friday, July 17, 2020, (a) implementing a 1-for- 10 The following table summarizes common stock share activity for the three and nine months ended September 30, 2021 and 2020 (dollars in thousands): Three Months Ended September 30, 2021 Shares of Common Stock Common Stock Additional Paid-in Capital Accumulated Deficit Total Stockholders’ Equity Balance, June 30, 2021 23,147,552 $ 26 $ 361,925 $ (329,631 ) $ 32,320 Net loss — — — (605 ) (605 ) Stock-based compensation expense — — 588 — 588 Common stock issued through employee stock purchase 2,759 — 13 — 13 Common stock issued, net of expenses 733,937 1 5,300 — 5,301 Common stock issued for vested restricted stock units 1,322 — (3 ) — (3 ) Balance, September 30, 2021 23,885,570 $ 27 $ 367,823 $ (330,236 ) $ 37,614 Nine Months September 30, 2021 Shares of Common Stock Common Stock Additional Paid-in Capital Accumulated Deficit Total Stockholders’ Equity Balance, December 31, 2020 19,663,698 $ 20 $ 349,351 $ (326,613 ) $ 22,758 Net loss — — — (3,623 ) (3,623 ) Stock-based compensation expense — — 1,528 — 1,528 Common stock issued through employee stock purchase 4,943 — 22 — 22 Common stock issued, net of expenses 3,250,739 6 8,707 — 8,713 Common stock issued for conversion of April 2020 Notes 959,080 1 7,452 — 7,453 Common stock issued for vested restricted stock units 7,110 — (3 ) — (3 ) Vested Loan Agreement warrants — — 766 — 766 Balance, September 30, 2021 23,885,570 $ 27 $ 367,823 $ (330,236 ) $ 37,614 Three Months Ended September 30, 2020 Shares of Common Stock Common Stock Additional Paid-in Capital Accumulated Deficit Total Stockholders’ Equity Balance, June 30, 2020 10,478,927 $ 10 $ 291,134 $ (284,811 ) $ 6,333 Net loss — — — 909 909 Stock-based compensation expense — — 399 — 399 Common stock issued, net of expenses 315,939 — 1,909 — 1,909 Common stock issued through employee stock purchase plan 2,284 — 9 — 9 Common stock issued for vested restricted stock units 969 — (1 ) — (1 ) Balance, September 30, 2020 10,798,119 $ 10 $ 293,450 $ (283,902 ) $ 9,558 Nine Months Ended September 30, 2020 Shares of Common Stock Common Stock Additional Paid-in Capital Accumulated Deficit Total Stockholders’ Equity Balance, December 31, 2019 9,741,372 $ 10 $ 284,313 $ (271,428 ) $ 12,895 Net loss — — — (12,474 ) (12,474 ) Stock-based compensation expense — — 1,220 — 1,220 Common stock issued through employee stock purchase plan and stock option plans 4,652 — 28 — 28 Common stock issued, net of expenses 647,504 — 4,578 — 4,578 Common stock issued for conversion of April 2020 Notes 316,461 — 2,784 — 2,784 Common stock issued for commitment shares 70,910 — 602 — 602 Common stock issued for vested restricted stock units 17,220 — (75 ) — (75 ) Balance, September 30, 2020 10,798,119 $ 10 $ 293,450 $ (283,902 ) $ 9,558 Shares Reserved for Future Issuance The Company had reserved shares of common stock for future issuance as follows: September 30, 2021 December 31, 2020 Outstanding stock options 1,643,506 830,343 Outstanding restricted stock units 149,134 29,087 Warrants to purchase common stock associated with June 2016 Public Offering — 421,867 Warrants to purchase common stock associated with March 2018 Public Offering – Series 2 798,810 798,810 Warrants to purchase common stock associated with December 2019 Public Offering 4,472,205 4,472,205 Warrants to purchase common stock associated with December 2020 Public Offering - Series 1 6,439,866 6,800,000 Warrants to purchase common stock associated with December 2020 Public Offering - Series 2 6,800,000 6,800,000 Prefunded warrants to purchase common stock associated with December 2020 Public Offering 3,200,000 5,260,000 Warrants to purchase common stock associated with Loan Agreement 170,410 — Warrants to purchase common stock associated with Solar loan agreement — 12,243 For possible future issuance for the conversion of the March 2019 Notes 1,138,200 1,138,200 For possible future issuance for the conversion of the April 2020 Notes — 1,299,790 For possible future issuance under 2014 Plan (Note 8) 184,497 146,488 For possible future issuance under Employee Stock Purchase Plan 3,893 5,895 For possible future issuance under 2015 Plan (Note 8) 231,450 14,050 Total common shares reserved for future issuance 25,231,971 28,028,978 Common Stock Purchase Agreement and Sales Agreement On April 10, 2020, the Company entered into the Common Stock Purchase Agreement with Aspire Capital pursuant to which the Company has the right to sell to Aspire Capital from time to time in its sole discretion up to $20.0 million in shares of the Company’s common stock over the next 30 months, subject to certain limitations and conditions set forth in the Common Stock Purchase Agreement. The aggregate number of shares that we can sell to Aspire Capital under the Common Stock Purchase Agreement may in no case exceed 1,956,547 shares of the Company’s common stock (which is equal to approximately 19.99% of the common stock outstanding on the date of the Common Stock Purchase Agreement), including the 70,910 commitment shares (the Exchange Cap), unless either (a) shareholder approval is obtained to issue more, in which case the Exchange Cap will not apply, or (b) the average purchase price of all shares sold under the Common Stock Purchase Agreement exceeds $8.461; provided that at no time shall Aspire Capital (together with its affiliates) beneficially own more than 19.99% of the Company’s common stock. During the nine months ended September 30, 2021 and 2020, the Company sold 400,000 and 125,000 shares, respectively, of its common stock under the Common Stock Purchase Agreement for gross proceeds of $2.6 million and $0.6 million, respectively. During the nine months ended September 30, 2021, we sold 430,605 shares of our common stock and received net proceeds of $2.5 million under the Controlled Equity Offering SM Sales Agreement Cantor Fitzgerald & Co. Ladenburg Thalmann & Co. Inc. Warrants Associated with the March 2018, December 2019, and December 2020 Public Offerings The outstanding warrants associated with the March 2018, December 2019, and December 2020 public offerings contain a provision where the warrant holder has the option to receive cash, equal to the Black-Scholes fair value of the remaining unexercised portion of the warrant, as cash settlement in the event that there is a fundamental transaction (contractually defined to include various merger, acquisition or stock transfer activities). Due to this provision, ASC 480, Distinguishing Liabilities from Equity, respectively. During the three months ended September 30 , 2021 and 2020 , the Company rec ognized gain s of $18.8 million and $7.8 million . During the nine months ended September 30, 2021 and 2020, the Company recognized gains of $35.4 million and $16.1 million , respectively , in the warrant liabilities fair value adjustment . As of September 30 , 2021 and December 31, 2020 , the fair value of the warrant liabilities was $15.3 million and $ 51.2 million , respectively . Warrants Associated with Loan Agreement In connection with the entry into the Loan Agreement, the Company issued to each of Hercules and SVB a warrant (collectively, the “Warrants”) to purchase shares of the Company’s common stock, par value $0.001 per share (the “Shares”). The amount of shares that may be purchased for the Warrants, collectively between Hercules and SVB, will not exceed 0.04 multiplied by the aggregate amount of the term loan advances, divided by the exercise price of the Warrants. At the closing of the Loan Agreement, the Company issued 113,607 warrants to purchase shares of the Company’s common stock and recognized the initial warrants at their relative fair value in shareholder's equity. In accordance with ASC 815-40, the remaining warrants to purchase shares of the Company’s common stock at closing were recognized at their fair value as warrant liabilities given the variable settlement amount of the warrant shares. |