Quarterly report pursuant to Section 13 or 15(d)

7. STOCKHOLDERS' EQUITY (Tables)

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7. STOCKHOLDERS' EQUITY (Tables)
 6 Months Ended
Jun. 30, 2019
STOCKHOLDERS' EQUITY  
Schedule of assumptions
    Six Months Ended June 30,
    2019   2018
         
Expected term     5.8 - 6.3 years       5.8-6.3 years  
Volatility     54.2-62.3%       54-57%  
Dividend yield     0.0       0.0  
Risk-free interest rate     1.80-2.92%       2.40-2.59%  
Schedule of stock option activity
    Shares   Weighted Average Exercise Price
Balance at December 31, 2018     4,342,231     $ 5.16  
Forfeited     (113,667 )   $ 4.04  
Expired     (5,823 )   $ 5.54  
Granted     1,429,100     $ 3.47  
Exercised     (27,238 )   $ 2.76  
Balance at June 30, 2019     5,624,603     $ 4.76  
                 
Options exercisable     2,824,929     $ 5.78  
Stock-based compensation expense
    Three Months Ended June 30,   Six Months Ended June 30,
    2019   2018   2019   2018
                 
Research and development   $ 89,543     $ 83,339     $ 176,066     $ 161,644  
Plasma centers     13,213       7,760       24,753       14,846  
Selling, general and administrative     569,349       406,193       1,067,820       801,050  
Cost of product revenue     54,631       38,099       95,360       72,635  
Total stock-based compensation expense   $ 726,736     $ 535,391     $ 1,363,999     $ 1,050,175