Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 9,397	$ 22,245
Marketable securities	9,989	9,996
Accounts receivable	4,361	5,134
Inventories	5,172	3,909
Prepaid expenses and other current assets	4,584	3,110
Total current assets	33,503	44,394
Property and equipment, net	4,778	4,675
Operating lease right-of-use assets	9,472	9,766
Restricted cash	1,131	1,551
Other assets	155	153
Total assets	49,039	60,539
Current liabilities:
Accounts payable	3,385	2,832
Accrued expenses and other current liabilities	8,950	8,338
Deferred revenue	338	518
Total current liabilities	12,673	11,688
Notes payable	48,257	47,790
Operating lease liabilities, net of current portion	9,060	9,359
Deferred revenue, net of current portion	47	28
Other liabilities	4,653	4,577
Commitments and contingencies (see Note 13)
Stockholders’ deficit
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued and outstanding at March 31, 2022 and December 31, 2021
Common stock, $0.001 par value; 400,000,000 shares authorized; 171,412,940 and 166,400,892 shares issued and outstanding at March 31, 2022 and December 31, 2021, respectively	171	166
Additional paid-in capital	462,900	459,151
Accumulated other comprehensive loss	(11)	(4)
Accumulated deficit	(488,711)	(472,216)
Total stockholders’ deficit	(25,651)	(12,903)
Total liabilities and stockholders’ deficit	$ 49,039	$ 60,539