Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 16,464	$ 14,463
Marketable securities	23,647	40,008
Accounts receivable, net	322	865
Inventory	1,590
Prepaid expenses and other current assets	1,651	1,449
Total current assets	43,674	56,785
Property and equipment, net	13,801	14,243
Right of use asset	106	138
Other non-current assets	1,896	1,896
Total assets	59,477	73,062
Current liabilities:
Accounts payable	5,944	3,867
Accrued expenses	2,737	3,348
Lease liability, current portion	106	138
Total current liabilities	8,787	7,353
Long-term debt	15,636	16,381
Total liabilities	24,423	23,734
Commitments and contingencies (Note 12)
Stockholders' equity
Common stock, $.0001 par value, 150,000,000 shares authorized, 88,263,741 and 87,563,753 issued and outstanding at March 31, 2021 and December 31, 2020, respectively	9	9
Additional paid-in capital	364,396	361,539
Accumulated other comprehensive income		3
Accumulated deficit	(329,351)	(312,223)
Total stockholders’ equity	35,054	49,328
Total liabilities and stockholders’ equity	$ 59,477	$ 73,062