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Common stock and common stock warrants - Warrants (Details) - Common stock and common stock warrant - $ / shares
Sep. 30, 2021
Dec. 31, 2020
Common stock and common stock warrants    
Common stock shares issuable upon exercise of warrant 1,030,944 55,835
Equity | July 24, 2017    
Common stock and common stock warrants    
Contractual term (in years) 10 years 10 years
Common stock shares issuable upon exercise of warrant 25,835 25,835
Weighted average exercise price (in dollars per share) $ 295.15 $ 295.15
Equity | April 12, 2018    
Common stock and common stock warrants    
Contractual term (in years) 10 years 10 years
Common stock shares issuable upon exercise of warrant 30,000 30,000
Weighted average exercise price (in dollars per share) $ 1.00 $ 1.00
Equity | July 14, 2021    
Common stock and common stock warrants    
Contractual term (in years) 10 years  
Common stock shares issuable upon exercise of warrant 975,109  
Weighted average exercise price (in dollars per share) $ 1.46