The following table summarizes information with respect to outstanding warrants to purchase common stock of the Company, all of which were vested and exercisable, at December 31, 2014: 

 

Exercise			Number			Expiration
Price			Outstanding			Date
$	4.25			920,979		August 2018
$	12.00			456,009		December 2017 to February 2018
$	20.00			14,538		January 2015
$	25.00			354,229		January 2017 to February 2019
				1,745,755

 

On January 1, 2013, the Company issued warrants to non-employees to purchase  10,800 shares of the Company's common stock at an exercise price of $12.00 per share expiring five years from the date of issuance vesting ratably over twelve months beginning January 1, 2013 in connection with services.

 

In connection with the August 2013 Financing, the Company issued to investors Warrants to purchase  2,680,000 shares of the Company's common stock. The Warrants are exercisable at $4.25 per share, expire five years from the date of issuance, and may be exercised on a cashless basis under certain circumstances. In addition, the Company issued to the First Underwriters warrants to purchase 509,200 shares of the Company's common stock. The warrants are exercisable at $4.25 per share, expire five years from the date of issuance, and may be exercised on a cashless basis.

 

The Company measures the fair value of the vested portion of the issued warrants based on a Binomial option pricing model using certain assumptions discussed in the following paragraph, and the closing market price of the Company's common stock on the date of the fair value determination.

 

The assumptions used in the valuation of warrants, which vested during the year ended December 31, 2013, were as follows:

 

Risk-free interest rate			0.77 to 1.75	%
Life of warrant			4.75 to 4.01 years
Expected stock price volatility			91.31% to 102.46	%
Expected dividend yield		$	0.0

 

The risk-free interest rate is based on the yield of Daily U.S. Treasury Yield Curve Rates with terms equal to the life of the warrants as of the grant date. The expected stock price volatility is based on comparable companies’ historical stock price volatility since the Company does not have sufficient historical volatility data because its equity shares have been publicly traded for only a limited period of time.

 

Compensation of $51,114 related to vested warrants was recognized for the year ended December 31, 2013.

 

In April 2013, the Company issued an aggregate of  38,334 shares of its common stock upon the exercise of warrants at $8.00 per share. 

 

In December 2013, the Company issued an aggregate of  884,885 and  70,031 shares of its common stock upon the exercise of warrants at $4.25 and $8.00 per share, respectively.

 

In December 2013, the Company issued  1,672 shares of its common stock upon the exercise of  3,185 warrants exercisable at $4.25 per share on a cashless basis.

 

In January 2014, 750 warrants with an exercise price of $20.00 expired.

 

In August 2014, the Company issued 33,678 shares of its common stock upon the exercise of 48,240 warrants exercisable at $4.25 per share on a cashless basis.

 

During the year ended December 31, 2014, the Company issued an aggregate of 1,331,911 shares of its common stock upon the exercise of warrants at $4.25 per share.