Income taxes - Deferred taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Net operating loss carryforwards	$ 19,925	$ 13,693
Research and development credits	2,157	1,560
Share-based compensation	886	82
Accrued bonus	331	201
Amortization	1	2
Gross deferred tax assets	23,300	15,538
Less: valuation allowance	(23,255)	(15,435)
Net deferred tax asset	45	103
Deferred tax liability
Depreciation	(45)	(103)
Total deferred tax liabilities