Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net loss	$ (67,636)	$ (32,566)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	192	168
Stock-based compensation	7,238	5,684
Non-cash expense related to warrant modifications	0	1,112
Non-cash lease expense	677	473
Non-cash expense related to equity consideration for a service agreement	494	0
Loss on impairment of intangible assets	45,020	0
Deferred income tax benefit	(9,987)	0
Unrealized loss on foreign exchange rate changes	396	1,142
Changes in assets and liabilities:
Prepaid expenses and other current assets	1,365	1,147
Accounts payable	(468)	(547)
Collaboration and device development payable	0	(1,975)
Accrued expenses	(407)	585
Operating lease liabilities	(548)	(538)
Net cash used in operating activities	(23,664)	(25,315)
Cash flows from investing activities:
Purchase of property and equipment	(279)	(291)
Net cash used in investing activities	(279)	(291)
Cash flows from financing activities:
Proceeds from issuance of common stock and warrants, net of issuance costs	27,390	20,246
Proceeds from ATM Program, net of expenses	4,843	0
Proceeds from research and development funding arrangement	1,000	2,800
Proceeds from exercise of common stock warrants	0	141
Principal payments on loans payable	(3,872)	(3,229)
Proceeds from Paycheck Protection Program loan	0	547
Principal payments on Paycheck Protection Program loan	0	(547)
Net cash provided by financing activities	29,361	19,958
Net increase (decrease) in cash, cash equivalents, and restricted cash	5,418	(5,648)
Cash, cash equivalents, and restricted cash - beginning of year	17,084	22,732
Cash, cash equivalents, and restricted cash - end of year	22,502	17,084
Supplementary disclosure of non-cash activity:
Operating lease liabilities arising from obtaining right-of-use assets	2,141	249
Prepayment of insurance through third-party financing	$ 1,321	$ 1,056