The Company adopted the 2006 Equity Participation Plan (as amended the “2006 Plan”), which provides for the grant of stock options, restricted stock and other equity-based awards. Awards for up to 100,000 shares may be granted to employees, directors and consultants under this Plan. The options granted under the 2006 Plan may be either qualified or non-qualified options. Options may be granted with different vesting terms and expire no later than 10 years from the date of grant. The 2006 Plan expired on November 16, 2016. Options and other equity-based awards granted prior to the expiration of the 2006 Plan will continue in effect until the option or award is exercised or terminates pursuant to its terms. No new awards may be granted under the 2006 Plan following its expiration.

In April 2010, the Company adopted the 2010 Equity Participation Plan, as amended (the “2010 Plan”), which provides for the grant of stock options, restricted stock and other equity-based awards. Awards for up to 9,700,000 shares may be granted to employees, directors and consultants under the 2010 Plan. The options granted under the 2010 Plan may be either qualified or non-qualified options. Options may be granted with different vesting terms and expire no later than 10 years from the date of grant. In June 2020, the Company amended the 2010 Plan to extend the term of the 2010 Plan until March 2030. No other material provisions were amended.

Transactions involving stock options issued to employees, directors and consultants under the 2006 Plan and the 2010 Plan are summarized below. Options issued have a maximum life of 10 years. 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

Restricted stock awards are grants that entitle the holder to acquire shares of common stock at zero or a fixed price, which is typically nominal. The Company accounts for the restricted stock awards as issued and outstanding common stock, even though the shares covered by a restricted stock award cannot be sold, pledged, or otherwise disposed of until the award vests and any unvested shares may be reacquired by the Company for the original purchase price following the awardee’s termination of service.

The fair value of restricted stock awards is based on the market value of the common stock on the date of grant. For the years ended December 31, 2021 and 2020, no restricted stock awards were awarded or vested. As of December 31, 2021, there was no unrecognized compensation costs related to unvested awards.

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:

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

Unrecognized compensation expense related to stock options as of December 31, 2021 was $330 thousand, which is expected to be recognized over a weighted-average period of approximately 1.93 years. Unrecognized compensation expense related to stock options as of December 31, 2020 was $604 thousand, which was expected to be recognized over a weighted-average period of less than one year.