Stockholders' Equity (Deficit) (Tables)

12 Months Ended

Dec. 31, 2021

Stockholders' Equity (Deficit)

Schedule of warrants outstanding and exercisable for purchase of common stock

	Number of Shares
	December 31,	December 31,	Weighted-Average
Description	2021	2020	Exercise Price		Expiration Date
Liability-classified Warrants
December 2019 Series B1 warrants (1)	—	2,368,400		$ 1.52	Dec 2026
	—	2,368,400
Equity-classified Warrants
May 2013 warrants	15,437	1,949,754		$ 0.08	None
September 2013 warrants	4,096	514,756		$ 0.08	None
February 2014 warrants	2,171	266,006		$ 0.08	None
April 2020 Private Placement first closing warrants	3,039,514	3,039,514		$ 2.28	Apr 2023
April 2020 Private Placement second closing warrants	1,373,626	1,373,626		$ 2.71	Dec 2023
April 2020 Private Placement second closing warrants	1,143,428	2,677,311		$ 0.01	None
July 2020 Private Placement first closing warrants	389,731	2,014,234		$ 0.01	None
July 2020 Private Placement first closing warrants	2,764,227	2,764,227		$ 2.58	Jul 2023
	8,732,230	14,599,428
Total outstanding	8,732,230	16,967,828

(1) The Series B1 warrants were exercisable for either common stock (exercise price of $1.52) or Series B1 Convertible Preferred Stock (exercise price of $152) at the discretion of the warrant holder. However, as more fully disclosed in Note 7, the December 2019 Series B1 warrants were terminated during the three months ended March 31, 2021 contemporaneously with the termination of the future tranche rights.

Summary of warrant activity

	Number of	Weighted-Average
	Warrants	Exercise Price
Outstanding at December 31, 2020	16,967,828	$	1.28
Issued	—		—
Exercised (1)	(5,867,198)		0.04
Expired	(2,368,400)		1.52
Outstanding at December 31, 2021	8,732,230	$	2.04

(1) During the year ended December 31, 2021, certain related parties were issued warrants as more fully described in Note 15.