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 November and December of 2009, the Company issued non-qualified stock options to purchase shares of common stock outside the 2006 and 2010 option plans to certain employees and consultants. These options vest over 50 months and expire no later than 10 years from the date of grant. As of September 30, 2019 and 2018, 12,634 and 50,730, options remain outstanding.

Total stock-based compensation expense for the three and nine months ended September 30, 2019 and 2018 was comprised of the following (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Cost of sales	$	29	$	22	$	83	$	37
Research and development		115		176		426		451
Selling and marketing		31		20		88		36
General and administrative		337		283		992		641
	$	512	$	501	$	1,589	$	1,165

Unrecognized compensation expense related to stock options as of September 30, 2019 was $2,365,000, which is expected to be recognized over a weighted average period of approximately 1.65 years.

In accordance with applicable authoritative guidance, the Company is required to establish assumptions and estimates of the fair value of stock options granted, as well as use a valuation model to calculate the fair value of stock-based awards. The Company uses the Black-Scholes option-pricing model to determine the fair-value of stock-based awards. All options are amortized over the requisite service periods.

The fair value of options granted is estimated at the date of grant using the Black-Scholes option-pricing model with the following weighted average assumptions for the nine months ended September 30, 2019 and 2018:


	Nine Months Ended September 30,
	2019			2018
Significant assumptions (weighted average):
Risk-free interest rate at grant date		2.44	%		2.72	%
Expected stock price volatility		84.95	%		92.68	%
Expected dividend payout		0	%		0	%
Expected option life based on management's estimate	5.71 years			5.70 years

Transactions involving stock options issued to employees, directors and consultants under the 2006 Plan, the 2010 Plan and outside the plans 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:

	Number of					Weighted
	Options Issued			Weighted		Average	Aggregate
	Under			Average Exercise		Remaining	Intrinsic
	2006 Plan and			Price Per		Contractual	Value
	2010 Plan			Share		Term	(in thousands)
Outstanding at December 31, 2018		4,354,708		$	3.95
Granted		1,345,964		$	1.44
Exercised		—		$	—
Canceled or expired		(285,749	)	$	2.63
Outstanding at September 30, 2019		5,414,923		$	3.39	8.25 years	$	—
Vested and expected to vest at September 30, 2019		5,176,891		$	3.48	8.21 years	$	—
Exercisable at September 30, 2019		3,042,547		$	4.83	7.74 years	$	—

					Weighted
	Number of		Weighted		Average	Aggregate
	Options Issued		Average Exercise		Remaining	Intrinsic
	Outside		Price Per		Contractual	Value
	the Plan		Share		Term	(in thousands)
Outstanding, vested and exercisable at December 31, 2018		12,634	$	90.23
Granted		—	$	—
Exercised		—	$	—
Canceled or expired		—	$	—
Outstanding, vested and exercisable at September 30, 2019		12,634	$	—	0.16 years	$	—

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.

No restricted stock was awarded for the nine months ended September 30, 2019. For the nine months ended September 30, 2018, there were 9,855 shares of restricted stock awarded and fully vested at a weighted average grant date fair value of $1.55 per share.

The fair value of the restricted stock awards is based on the market value of the common stock on the date of grant. The total grant-date fair value of restricted stock awards vested during the nine months ended September 30, 2019 and 2018, was none and approximately $15,000 respectively. The Company recognized none and approximately $15,000 of stock-based compensation expense related to the restricted stock awards for the nine months ended September 30, 2019 and 2018, respectively. As of September 30, 2019, there was no unrecognized compensation costs related to unvested awards.

Share data related to warrant transactions through September 30, 2019 were as follows:


	Common Stock October 2014 Financing		Common Stock March 2016 Financing		Total Warrants		Exercise Price
Outstanding, December 31, 2018		2,483		3,948,569		3,951,052	$	1.75
Forfeited/Cancelled		—		—		—
Outstanding, September 30, 2019		2,483		3,948,569		3,951,052	$	1.75

Expiration Date	April 14, 2020		March 15, 2021