Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement [Abstract]

Stock-based compensation recognized

Stock-based compensation has been recognized in operating results as follows:

	Years ended December 31,
	2019		2018
Cost of revenue	$	—	$	30,488
Research and development expenses	399,687		752,127
Selling, general and administrative expenses	485,256		1,392,012
Total stock-based compensation	$	884,943	$	2,174,627

Estimated Fair Value of Stock Options - Assumptions

The estimated fair value of stock option awards was determined on the date of grant using the Black-Scholes option valuation model with the following assumptions during the years indicated below:

	Years ended December 31,
	2019	2018
Risk-free interest rate	1.66% - 2.33%	2.42% - 2.93%
Dividend yield	0%	0%
Expected volatility (range)	95% - 99%	89% - 98%
Expected volatility (weighted-average)	96%	91%
Expected term (in years)	5.9 years	5.2 years

Summary of Stock Option Activity

A summary of stock option activity and of changes in stock options outstanding is presented below:

	Number of Options		Weighted-Average Exercise Price Per Share		Intrinsic Value		Weighted-Average Remaining Contractual Life
Balance outstanding, December 31, 2017	62,376		$	291.10	$	—	7.1 years
Granted	52,791		$	18.69
Forfeited	(31,590	)	$	219.03
Expired	(232	)	$	216.00
Balance outstanding, December 31, 2018	83,345		$	146.09	$	—	7.3 years
Granted	971,313		$	2.49
Forfeited	(36,148	)	$	26.55
Expired	(3,092	)	$	220.27
Balance outstanding, December 31, 2019	1,015,418		$	12.77	$	—	9.1 years
Vested and exercisable, December 31, 2019	71,518		$	147.46	$	—	4.8 years

Summary of Restricted Stock Unit Activity

A summary of the RSU's activity is presented below:

	Number of Shares		Weighted Average Grant Date Fair Value Per Share		Intrinsic Value
Non-vested RSU's outstanding, December 31, 2017	17,700		$	103.32	$	391,878
Granted	34,125		$	4.64
Vested	(18,609	)	$	59.06
Forfeited	(3,084	)	$	147.60
Non-vested RSU's outstanding, December 31, 2018	30,132		$	14.36	$	95,005
Granted	9,167		$	1.61
Vested	(22,057	)	$	8.68
Forfeited	(5,941	)	$	13.82
Non-vested RSU's outstanding, December 31, 2019	11,301		$	15.38	$	14,013