Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating activities
Net loss	$ (27,808)	$ (15,730)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization expense	459	467
Gain on PPP Loan forgiveness	(662)	0
Stock-based compensation	2,923	2,614
Other	46	154
Change in operating assets and liabilities:
Contracts and other receivables	503	638
Prepaid materials	304	610
Prepaid expenses and other assets	(221)	(605)
Accounts payable	(250)	(786)
Accrued liabilities	240	(188)
Accrued research and development expenses	(287)	949
Accrued compensation	273	66
Operating lease right-of-use assets and liabilities, net	279	(150)
Contract liabilities	0	(6)
Other liabilities	73	(569)
Net cash used in operating activities	(24,128)	(12,536)
Investing activities
Purchases of property and equipment	(251)	0
Acquisition of intangibles	0	(11)
Net cash used in investing activities	(251)	(11)
Financing activities
Proceeds from issuance of securities through private placement, net of issuance costs	32,360	18,166
Proceeds from issuance of common stock, net	21,431	957
Proceeds from borrowing under Paycheck Protection Program	0	662
Proceeds from exercise of common stock options	26	5
Payments on financing leases	(80)	(277)
Principal payments on term loan	0	(10,000)
Net cash provided by financing activities	53,737	9,513
Net increase (decrease) in cash, cash equivalents and restricted cash	29,358	(3,034)
Cash, cash equivalents and restricted cash at beginning of period	31,087	34,121
Cash, cash equivalents and restricted cash at end of period	60,445	31,087
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents	60,383	31,087
Restricted cash	62	0
Total cash, cash equivalents and restricted cash	60,445	31,087
Supplemental disclosure of cash flow information
Interest paid	(729)	(1,356)
Income taxes paid	(1)	(1)
Supplemental disclosure of non-cash investing and financing activities
Paycheck Protection Program loan forgiveness	662	0
Unsettled sales of common stock through ATM	$ 0	$ 392