Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 22,245	$ 16,793
Marketable securities	9,996	25,396
Accounts receivable	5,134	5,099
Inventories	3,909	3,636
Prepaid expenses and other current assets	3,110	2,660
Total current assets	44,394	53,584
Property and equipment, net	4,675	3,771
Operating lease right-of-use assets	9,766	11,034
Restricted cash	1,551	551
Marketable securities		10,002
Other assets	153	136
Total assets	60,539	79,078
Current liabilities:
Accounts payable	2,832	2,058
Accrued expenses and other current liabilities	8,338	7,512
Deferred revenue	518	230
Total current liabilities	11,688	9,800
Notes payable	47,790	45,235
Operating lease liabilities, net of current portion	9,359	10,533
Deferred revenue, net of current portion	28	424
Derivative liability		1,010
Other liabilities	4,577	3,350
Commitments and contingencies (see Note 13)
Stockholders’ (deficit) equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.001 par value; 400,000,000 shares authorized; 166,400,892 and 148,078,974 shares issued and outstanding at December 31, 2021 and December 31, 2020, respectively	166	148
Additional paid-in capital	459,151	431,544
Accumulated other comprehensive (loss) income	(4)	9
Accumulated deficit	(472,216)	(422,975)
Total stockholders’ (deficit) equity	(12,903)	8,726
Total liabilities and stockholders’ (deficit) equity	$ 60,539	$ 79,078