STOCKHOLDERS' EQUITY AND STOCK-BASED COMPENSATION

Non-Vested Restricted Common Stock

The fair value of non-vested restricted common stock awards is generally the market value of the Company’s common stock on the date of grant. The non-vested restricted common stock awards require the employee to fulfill certain obligations, including remaining employed by the Company for one, two or four years (the vesting period) and in certain cases also require meeting either performance criteria or the Company’s stock achieving a certain price. For non-vested restricted common stock awards which solely require the recipient to remain employed with the Company, the stock compensation expense is amortized over the anticipated service period. For non-vested restricted common stock awards which require the achievement of performance criteria, the Company reviews the probability of achieving the performance goals on a periodic basis. If the Company determines that it is probable that the performance criteria will be achieved, the amount of compensation cost derived for the performance goal is amortized over the anticipated service period. If the performance criteria are not met, no compensation cost is recognized and any previously recognized compensation cost is reversed.

Restricted stock activity was as follows:



	Shares		Weighted Average Grant Fair Value
Balance, December 30, 2017	2,629,274		$	3.31
Granted	1,465,000		2.22
Forfeited	(572,025	)	4.12
Vested	(80,000	)	3.64
Balance, June 30, 2018	3,442,249		$	2.71

On December 31, 2017, the Company amended the employment agreement with our CEO, Dr. John Fan, to expire on December 31, 2020 and as part of the amendment issued restricted stock grants. Of the restricted stock grants issued to Dr. Fan, 640,000 shares will vest upon the first 20 consecutive trading day period following the grant date during which the Company's common stock trades at a price equal to or greater than $5.25, 150,000 shares will vest at the end of the first 20 consecutive trading day period following the grant date during which the Company’s common stock trades at a price per share equal to or greater than $6.00, and 150,000 shares will vest at the end of the first 20 consecutive trading day period following the grant date during which the Company’s common stock trades at a price per share equal to or greater than $7.00. All of the grants are subject to certain acceleration events and expire on December 31, 2020. The total fair value of these awards on December 31, 2017 was $1.7 million. The value of restricted stock grants that vest based on market conditions is computed on the date of grant using the Monte Carlo model with the following assumptions:



	For the period ended June 30, 2018
Performance price target	$	5.25		$	6.00		$	7.00
Expected volatility	48.3		%	48.3		%	48.3		%
Interest rate	1.97		%	1.97		%	1.97		%
Expected life (years)	3			3			3
Dividend yield	—		%	—		%	—		%

Stock-Based Compensation

The following table summarizes stock-based compensation expense within each of the categories below as it relates to non-vested restricted common stock awards for the three and six months ended June 30, 2018 and July 1, 2017 (no tax benefits were recognized):



	Three Months Ended				Six Months Ended
	June 30, 2018		July 1, 2017		June 30, 2018		July 1, 2017
Cost of product revenues	$	155,925	$	159,081	$	266,151	$	263,174
Research and development	193,767		194,655		468,083		413,213
Selling, general and administrative	938,682		322,287		1,953,555		1,291,741
Total	$	1,288,374	$	676,023	$	2,687,789	$	1,968,128

Unrecognized compensation expense for non-vested restricted common stock as of June 30, 2018 totaled $6.1 million and is expected to be recognized over a weighted average period of approximately two years.