Stock-based compensation (Tables)

3 Months Ended

Mar. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Stock-Based Compensation Expense

Total stock-based compensation expense was recorded to operating expenses based upon the functional responsibilities of the individuals holding the respective options as follows:

	Three months ended March 31,
	2017		2016
Research and development	$	166,611	$	126,441
General and administrative		585,581		241,942
Total stock-based compensation	$	752,193	$	368,383

Schedule of Fair Value Assumptions

The weighted-average fair value of the options granted was $1.31 and $1.00 for the three months ended March 31, 2017 and 2016, respectively. The calculation was based on the following assumptions:

	Three months ended March 31,
	2017	2016
Risk free interest rate	2.04%-2.16%	1.35%-1.61%
Expected term	5.0 – 5.7 years	5.0 – 5.7 years
Dividend yield	—	—
Expected volatility	75.09%-75.13%	75.53%-76.00%