9. Stock Based Compensation

The Company has a stock-based compensation plan which is described below. Total stock-based compensation expense of $1.9 million, $3.2 million and $3.5 million was recognized for the years ended December 31, 2015, 2014 and 2013, respectively. Total stock-based compensation expense was allocated to research and development, manufacturing and production and general and administrative expense as follows (in thousands):

	Year Ended December 31,
	2015		2014		2013
Research and development	$	392	$	785	$	908
Manufacturing and production		159		229		258
General and administrative		1,351		2,145		2,300
Total stock-based compensation expense	$	1,902	$	3,159	$	3,466
Cash received from RSU grants and options exercised	$	3	$	2	$	816

Stock Incentive Plan

The Company has a stock incentive plan, under which 19,700,000 shares of common stock, subject to adjustment as provided in the plan, are reserved for issuance to employees, non-employee directors and consultants of the Company. As of December 31, 2015 there were 16,448,052 shares reserved for future issuance under the plan. The plan provides for the grant of incentive and nonstatutory stock options and the direct award or sale of shares, including restricted stock. The exercise price of stock options must equal at least the fair market value of the underlying common stock on the date of grant. The maximum term of options granted under the plan is ten years. Except for annual grants to non-employee directors which vest at the next annual meeting, options generally vest 25% on the first anniversary of the date of grant, with the balance vesting quarterly over the remaining three years. The plan also limits the number of options that may be granted to any plan participant in a single calendar year to 1,300,000 shares.

The Company has granted RSUs to executive officers, other executives, and employees under the stock incentive plan. In 2015, 2014, and 2013 the Company granted RSUs covering an aggregate of 788,429, 828,000, and 409,189 shares of common stock, respectively. These RSUs generally vest 25% on the first anniversary date of the grant, with the remaining rights vesting quarterly over the remaining three years and, once vested, allow the participants to acquire the underlying shares of common stock at par value. The participants are not entitled to sell or transfer any unvested RSUs and are not entitled to vote or receive dividends on any shares of common stock covered by the RSUs prior to the acquisition of such shares. Granted but unvested RSUs are forfeited at termination of employment. Compensation expense related to the RSUs for the years ended December 31, 2015, 2014, and 2013 was approximately $0.8 million, $1.1 million and $1.0 million, respectively.

The following table summarizes stock option transactions under the Company’s stock incentive plans for the years ended December 31, 2015, 2014 and 2013:

	Shares			Weighted Average Exercise Price
Outstanding December 31, 2012		7,996,569		$	3.36
Granted		2,876,382		$	2.56
Exercised		(347,450	)	$	2.34
Forfeited		(2,121,313	)	$	3.27
Outstanding December 31, 2013		8,404,188		$	3.15
Granted		1,889,614		$	1.40
Exercised		—		$	—
Forfeited		(1,699,370	)	$	3.69
Outstanding December 31, 2014		8,594,432		$	2.66
Granted		2,356,750		$	1.01
Exercised		—		$	—
Forfeited		(1,495,344	)	$	2.15
Outstanding December 31, 2015		9,455,838		$	2.33
Vested and unvested options expected to vest as of December 31, 2015		9,235,450		$	2.35

The number of underlying shares and weighted average exercise price of options exercisable at December 31, 2015, 2014 and 2013, were 6,884,679 shares at $2.68, 6,037,169 shares at $2.89, and 5,212,897 shares at $3.49, respectively. The weighted average remaining contractual term of options outstanding and options exercisable at December 31, 2015, was 6.3 years and 5.5 years, respectively. The weighted average remaining contractual term of vested and unvested options expected to vest at December 31, 2015, was 6.3 years. The aggregate intrinsic value of options outstanding and options exercisable at December 31, 2015, was $0.0 million and $0.0 million, respectively. As of December 31, 2015, the total unrecognized compensation cost related to unvested options was $0.8 million, which is expected to be recognized over a weighted-average period of 1.34 years.

The weighted average grant-date fair value of options granted during the years ended December 31, 2015, 2014 and 2013, was $0.51, $0.73 and $1.31 per share, respectively. There were no options exercised during the years ended December 31, 2015 or 2014. The total intrinsic value of options exercised during the year ended December 31, 2013 was $0.5 million. At December 31, 2015, there were 5,421,917 shares available for grant under the Company’s stock incentive plans.

A summary of the outstanding RSUs as of December 31, 2015, and changes during the year then ended is presented below:

	Shares			Weighted Average Grant-Date Fair Value per Share
Unvested at December 31, 2014		960,066		$	1.70
Granted		788,429		$	1.04
Vested		(579,677	)	$	1.68
Cancelled		(128,076	)	$	1.37
Unvested at December 31, 2015		1,040,742		$	1.26

The aggregate grant-date fair value of RSUs granted during the years ended December 31, 2015, 2014 and 2013, was $0.8 million, $1.2 million and $1.0 million, respectively. As of December 31, 2015, the total unrecognized compensation cost related to unvested RSUs was $0.5 million, which is expected to be recognized over a weighted average period of 1.35 years. The aggregate grant-date fair value of shares subject to RSUs vested during the years ended December 31, 2015, 2014 and 2013, was $1.0 million, $0.8 million and $1.0 million, respectively. As of December 31, 2015, there were 529,555 shares of common stock underlying RSUs that were fully vested but the issuance of such shares has been deferred.