Stock Based Compensation (Tables)

3 Months Ended

Mar. 31, 2016

Stock Based Compensation [Abstract]

Schedule of total stock-based compensation expense from stock options and warrants

The following table sets forth the total stock-based compensation expense resulting from stock options and warrants included in our unaudited interim statements of operations:

	Three Months Ended March 31,
	2016		2015
Research and development — employee	$	480,811	$	335,938
General and administrative — employee		657,050		955,404
Total employee stock-based compensation	$	1,137,861	$	1,291,342
Research and development — non-employee	$	—	$	—
General and administrative — non-employee		187,956		93,551
Total non-employee stock-based compensation	$	187,956	$	93,551

Schedule of share-based payment award, fair value of the stock options granted , assumptions

The fair value of the stock options and warrants was estimated using the Black-Scholes option-pricing model, based on the following assumptions:

	Three months Ended March 31, 2016			Three Months Ended March 31, 2015
Risk-free interest rate		1.47	%		2.20	%
Expected volatility		76.3	%		84.3	%
Expected lives (years)		5 - 10			10
Expected dividend yield		0.00	%		0.00	%

Schedule of share-based compensation, stock options, activity

Presented below is our stock option activity:

	Three months Ended March 31, 2016
	Number of Options (Employees)			Number of Options (Non-Employees)		Total Number of Options			Weighted-Average Exercise Price
Outstanding at January 1, 2016		13,573,862			635,714		14,209,576		$	3.10
Granted		425,000			—		425,000		$	2.22
Exercised, forfeited or expired		(312,571	)		—		(312,571	)	$	4.10
Outstanding at March 31, 2016		13,686,291			635,714		14,322,005		$	3.05
Exercisable at March 31, 2016		8,307,207			635,714		8,942,921		$	3.36

Schedule of share-based compensation, summarizes significant ranges of outstanding stock options

The following table summarizes significant ranges of outstanding stock options under our plans at March 31, 2016:

Range of Exercise Prices		Number of Options		Weighted-Average Remaining Contractual Life (years)		Weighted-Average Exercise Price		Number of Options Exercisable		Weighted-Average Remaining Contractual Life (years)		Weighted-Average Exercise Price
$	1.75 - $2.00		1,274,500		6.70	$	1.83		1,274,500		6.70	$	1.83
$	2.01 – $2.50		8,565,558		8.92	$	2.32		3,734,284		8.38	$	2.30
$	2.51 – $4.00		1,058,407		7.97	$	2.86		917,574		7.78	$	2.86
$	4.01 – $32.55		3,423,540		6.76	$	5.39		3,016,563		6.63	$	5.47
			14,322,005		8.14	$	3.05		8,942,921		7.49	$	3.36