Warrants to Acquire Shares of Common Stock

12 Months Ended

Dec. 31, 2021

Warrants and Rights Note Disclosure [Abstract]

Warrants to Acquire Shares of Common Stock

The following is a summary of the Company's warrants to acquire shares of common stock activity for the year ended December 31, 2021 (in thousands, except per share data):


Warrant Issuance	Outstanding, December 31, 2020	Exercised	Outstanding, December 31, 2021	Exercise Price Per Share		Expiration
Warrants classified as equity:
January 2020 Offering	719	(410)	309	$	3.93	July 2025
July 2020 PIPE Offering	445	(420)	25	$	3.30	August 2025
July 2018 Offering	141	(9)	132	$	7.50	July 2023
March 2019 Exercise Agreement	63	(33)	30	$	7.50	March 2024
Other	10	(1)	9	$	306.66	December 2022 - June 2024
	1,378	(873)	505
Warrants classified as liability:	14	—	14	$	729.94	January 2022 - November 2023
	1,392	(873)	519

Warrants to acquire shares of common stock primarily consist of equity-classified warrants. In addition, warrants to acquire shares of common stock that may require the Company to settle in cash are liability-classified warrants.

Warrants Classified as Equity

Equity-classified warrants consist of warrants to acquire common stock issued in connection with previous equity financings. During its evaluation of equity classification for warrants to acquire shares of common stock, the Company considered the conditions as prescribed within ASC 815-40, Derivatives and Hedging, Contracts in an Entity’s own Equity (“ASC 815-40”). The conditions within ASC 815-40 are not subject to a probability assessment. The warrants to acquire shares of common stock do not fall under the liability criteria within ASC 480, Distinguishing Liabilities from Equity, as they are not puttable and do not represent an instrument that has a redeemable underlying security. The warrants to acquire shares of common stock do meet the definition of a derivative instrument under ASC 815, but are eligible for the scope exception as they are indexed to the Company’s own stock and would be classified in permanent equity if freestanding.

Warrants Classified as Liabilities

Liability-classified warrants consist of warrants to acquire common stock issued in connection with previous equity financings. These warrants may be settled in cash and were determined to not be indexed to the Company’s common stock. The liability-classified warrants are grouped within other warrants outstanding in the table above. The estimated fair value of outstanding warrants accounted for as liabilities is determined at each balance sheet date. Any decrease or increase in the estimated fair value of the warrant liability since the most recent balance sheet date is recorded in the consolidated statement of operations as a change in fair value of warrant liability. The fair value of the warrants accounted for as liabilities is estimated using a Black-Scholes pricing model with the following inputs:


	As of December 31,
	2021			2020
Risk free interest rate	0.65		%	0.16		%
Volatility	131.04%			150.38%
Expected term (years)	1.75			2.75
Expected dividend yield	—		%	—		%
Strike price	$	7.50		$	7.50

The changes in fair value of the warrant liability for the year ended December 31, 2021 and 2020 were as follows (in thousands):


	Warrant Liability
Warrant liability, December 31, 2019	$	52

Fair value of warrants exercised	(94)
Change in fair value of warrants	97
Warrant liability, December 31, 2020	55


Change in fair value of warrants	(15)
Warrant liability, December 31, 2021	$	40

Deemed Dividend Arising from Warrant Modifications

On January 2, 2020, the Company amended the March 2019 Exercise Agreement warrants to provide for an exercise price of $7.50 per share (subject to adjustment for stock splits and the like). The reduced exercise price of the 63,000 New Warrants increased the fair value of these warrants by approximately $0.1 million during the year ended December 31, 2020, which was recorded as a deemed dividend increasing the net loss attributable to common stockholders and additional paid-in-capital.The expected volatility assumptions are based on the Company's implied volatility. The expected life assumption is based on the remaining contractual terms of the warrants. The risk-free rate is based on the zero coupon rates in effect at the time of valuation. The dividend yield used in the pricing model is zero, because the Company has no present intention to pay cash dividends on its shares of common stock.