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Stock-Based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2020
Share-based Payment Arrangement [Abstract] |
Stock-based compensation recognized | Stock-based compensation has been recognized in operating results as follows:
| Years ended December 31,
| 2020 |  | 2019 |  |
Research and development expenses | 354,692 |  |  | 399,687 |  |  |
Selling, general and administrative expenses | 1,410,112 |  |  | 485,256 |  |  |
Total stock-based compensation | $ | 1,764,804 |  |  | $ | 884,943 |  |  |
Estimated Fair Value of Stock Options - Assumptions | The estimated fair value of stock option awards was determined on the date of grant using the Black-Scholes option valuation model with the following assumptions during the years indicated below:
| Years ended December 31,
| 2020 |  | 2019 |  |
Risk-free interest rate | 0.39% - 0.93% |  | 1.66% - 2.33% |  |
Dividend yield | 0% |  | 0% |  |
Expected volatility (range) | 102% - 106% |  | 95% - 99% |  |
Expected volatility (weighted-average) | 105% |  | 96% |  |
Expected term (in years) | 5.9 years |  | 5.9 years |  |
Summary of Stock Option Activity | A summary of stock option activity and of changes in stock options outstanding is presented below:
| Number of Options |  | Weighted-Average Exercise Price Per Share |  | Intrinsic Value |  | Weighted-Average Remaining Contractual Life
Balance outstanding, December 31, 2019 | 1,015,418 |  |  | $ | 12.77 |  |  | $ | — |  |  | 9.1 years
Granted | 969,965 |  |  | $ | 2.53 |  |  |  |  |
Exercised | (60,195) |  |  | $ | 2.46 |  |  | $ | 970,145 |  |  |
Forfeited | (48,537) |  |  | $ | 22.91 |  |  |  |  |
Expired | (16,144) |  |  | $ | 21.29 |  |  |  |  |
Balance outstanding, December 31, 2020 | 1,860,507 |  |  | $ | 7.43 |  |  | $ | 27,963,363 |  |  | 8.9 years
Vested and exercisable, December 31, 2020 | 753,206 |  |  | $ | 14.63 |  |  | $ | 10,837,211 |  |  | 8.5 years
Vested and expected to vest, December 31, 2020 | 1,777,407 |  |  | $ | 7.65 |  |  | $ | 26,682,849 |  |  | 8.9 years
Summary of Restricted Stock Unit Activity | A summary of the RSU's activity is presented below:
| Number of Shares |  | Weighted Average Grant Date Fair Value Per Share |  | Intrinsic Value
Non-vested RSU's outstanding, December 31, 2018 | 30,132 |  |  | $ | 14.36 |  |  | $ | 95,005 |
Granted | 9,167 |  |  | $ | 1.61 |  |  |
Vested | (22,057) |  |  | $ | 8.68 |  |  |
Forfeited | (5,941) |  |  | $ | 13.82 |  |  |
Non-vested RSU's outstanding, December 31, 2019 | 11,301 |  |  | $ | 15.38 |  |  | $ | 14,013 |
Vested | (10,810) |  |  | $ | 9.37 |  |  |
Non-vested RSU's outstanding, December 31, 2020 | 491 |  |  | $ | 147.60 |  |  | $ | 7,641 |

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- Definition Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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