Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Changes in Options Outstanding and Related Exercise Prices for Company's Common Stock Options Issued

The following tables summarize the changes in options outstanding and the related exercise prices for the Company’s common stock options issued:

						Weighted-
						Average
						Remaining
	Number of			Weighted-		Contractual		Aggregate
	Outstanding			Average		Term		Intrinsic Value
	Options			Exercise		(in years)		(in thousands)
Outstanding at December 31, 2020		4,255,371		$	3.41
Granted		1,761,962		$	0.39
Forfeited or canceled		(622,088	)	$	2.14
Expired		(22,042	)	$	284.00
Outstanding at December 31, 2021		5,373,203		$	1.42		7.31	$	146
Vested and expected to vest at December 31, 2021		5,187,332		$	1.46		7.23	$	131
Exercisable at December 31, 2021		3,980,138		$	1.77		6.58	$	34

Fair Value of Stock Options Grants, Weighted Average Assumptions

The weighted-average assumptions used in the Black-Scholes option valuation model to determine the fair value of stock options grants for the years ended December 31, 2021 and 2020 were as follows:

	Years Ended December 31,
	2021		2020
Risk-free interest rate	0.89%		0.37%
Expected stock price volatility	83.90%		88.82%
Expected dividend yield	0%		0%
Expected life of options (in years)		5.67		5.36

Schedule of Total Stock-Based Compensation Expense

Total stock-based compensation expense for the years ended December 31, 2021 and 2020 was comprised of the following (in thousands):

	Years Ended December 31,
	2021		2020
Cost of sales	$	21	$	87
Research and development		46		135
Selling and marketing		32		78
General and administrative		545		979
Total	$	644	$	1,279