| Summary of common stock warrants issued |
| | Number of Warrants | | | Weighted-average Exercise Price | | | Weighted-average Remaining Life (Years) | | | Aggregate Intrinsic Value | | | Outstanding, December 31, 2017 | | | 47,437,588 | | | $ | 0.19 | | | | | | | | | Granted | | | 5,431,944 | | | | 0.06 | | | | | | | | | Forfeited or expired | | | (501,645 | ) | | | 0.29 | | | | | | | | | Outstanding, December 31, 2018 | | | 52,367,887 | | | | 0.18 | | | | 1.3 | | | $ | 114,900 | | | Exercisable, December 31, 2018 | | | 52,367,887 | | | | 0.18 | | | | 1.3 | | | $ | 114,900 | | | Granted | | | -- | | | | -- | | | | | | | | | | | Exercised | | | -- | | | | -- | | | | | | | | | | | Forfeited or expired | | | (6,853,719 | ) | | | 0.56 | | | | | | | | | | | Outstanding, December 31, 2019 | | | 45,514,168 | | | | 0.12 | | | | 1.1 | | | | - | | | Exercisable, December 31, 2019 | | | 45,514,168 | | | $ | 0.12 | | | | 1.1 | | | $ | - | | |