8. Warrants to Purchase Common Stock



The following table summarizes non-employee warrant activity under our stock-based plans as of and for the year then ended December 31, 2016, there was no activity for the year ended December 31, 2017:



The following table summarizes investor warrant activity as of and for the years ended December 31, 2017 and 2016:

 

We recorded stock-based compensation expense of $0 and $208,195 in general and administrative expense for the year ended December 31, 2017 and 2016, respectively in connection with the exercise of investor-based warrants.



Warrants Issued to Non-Employees



We issued warrants to purchase 150,835 shares of common stock to non-employees in 2010 and 2011. The valuation assumptions used are consistent with the valuation information for options above. These warrants expired as of December 31, 2016.



Warrants Issued in 2015



In March 2015, we issued warrants to the purchase of 1,259,875 common stock units at $1.20 per share in connection with the equity financing. The grant date fair value of the warrants was $1,171,683 or $0.93 per share. Additionally, we issued to EGE warrants to purchase an aggregate of 234,500 units, exercisable for a period of five years from the closing date, at an exercise price of $1.00 per unit. The grant date fair value of these warrants was $225,120 or $0.96 per share.



As of December 31, 2017, we have warrants to purchase 4,529,164 and 605,185 shares of common stock at $1.20 and $1.00 per share, respectively, which are outstanding. Of this amount, warrants to purchase 2,762,868 shares expire in 2018, warrants to purchase 1,558,356 shares expire in 2019, and warrants to purchase 813,125 shares expire in 2020.



Warrants Exercised in 2016



Between September 29 and October 31, 2016, we conducted an offer to the holders of our outstanding common stock purchase warrants pursuant to which our warrant holders were permitted to exercise their warrants at a reduced exercise price for a period expiring on October 31, 2016. At the commencement of the warrant offer, there were warrants outstanding that entitled their holders to purchase 8,464,339 shares of our common stock at exercise prices of $1.00 and $1.20 per share. As of December 31, 2017, there have been 3,329,990 warrants exercised to purchase 3,329,990 shares of our common stock, resulting in additional capital of $2,330,993. We recorded stock based compensation expense of $208,195 in connection with this transaction. The warrant offer was conducted by our management and there were no commissions paid by us in connection with the solicitation.