Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2018

Summary of Estimated Fair Value of Stock Option Award

The estimated fair value of each stock option award granted was determined on the date of grant using the Black Scholes option-pricing valuation model with the following weighted-average assumptions for option grants during the three months ended March 31, 2018 and 2017:

	Three Months Ended March 31,
	2018	2017
Common Stock Options
Risk free interest rate	2.66%	2.16%
Expected option term	6.0 years	6.0 years
Expected volatility of common stock	90.15%	94.05%
Expected dividend yield	0.0%	0.0%

Summary of Estimated Fair Value of Employee Stock Purchase Plan Award

The estimated fair value of each ESPP award was determined on the date of grant using the Black Scholes option-pricing valuation model with the following weighted-average assumptions for option grants during the three months ended March 31, 2018 and 2017:

	Three Months Ended March 31,
	2018	2017
Employee Stock Purchase Plan
Risk free interest rate	1.85%	0.79%
Expected term	6.0 months	6.0 months
Expected volatility of common stock	58.76%	99.23%
Expected dividend yield	0.0%	0.0%

Summary of Recognized Non-Cash Stock-Based Compensation Expense

The Company recognized non-cash stock-based compensation expense to employees and directors in its research and development and its general and administrative functions as follows:

	Three Months Ended March 31,
	2018		2017
Research and development	$	188,777	$	206,858
General and administrative		204,998		257,300
Total stock-based compensation expense	$	393,775	$	464,158