Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2019

Stockholders' Equity

Schedule of warrants outstanding and exercisable for purchase of common stock

	Number of Shares
	December 31,	December 31,	Weighted-Average
Description	2019	2018	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	1,949,754	1,977,041		$ 0.08	None (2)
September 2013 warrants	514,756	521,997		$ 0.08	None (2)
February 2014 warrants	266,006	269,844		$ 0.08	None (2)
	2,730,516	2,768,882
Total outstanding	5,098,916	2,768,882

(1) The Series B1 warrants are 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.

(2) In connection with December 2019 Private Placement, the expiration date on these warrants was amended to be indefinite.

Summary of warrant activity

	Number of	Weighted-Average
	Warrants	Exercise Price
Outstanding at December 31, 2018	2,768,882	$	0.08
Issued (1)	2,368,400		1.52
Exercised	(38,366)		0.08
Expired	—		—
Outstanding at December 31, 2019	5,098,916	$	0.75

(1) During the year ended December 31, 2019, certain related parties were issued warrants as more fully described in Note 16.