Common stock and common stock warrants - Warrants (Details) - Common stock and common stock warrant - $ / shares	Jun. 30, 2022	Dec. 31, 2021
Common stock and common stock warrants
Common stock shares issuable upon exercise of warrant	1,022,303	1,030,944
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	17,194	25,835
Weighted average exercise price (in dollars per share)	$ 292.81	$ 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	10 years
Common stock shares issuable upon exercise of warrant	975,109	975,109
Weighted average exercise price (in dollars per share)	$ 1.46	$ 1.46