Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 14,735	$ 14,463
Marketable securities		40,008
Accounts receivable, net	1,309	865
Inventory, net	3,460
Prepaid expenses and other current assets	2,258	1,449
Total current assets	21,762	56,785
Property and equipment, net	12,911	14,243
Right of use asset	37	138
Other non-current assets	1,972	1,896
Total assets	36,682	73,062
Current liabilities:
Accounts payable	5,632	3,867
Accrued expenses	3,899	3,348
Lease liability, current portion	37	138
Total current liabilities	9,568	7,353
Long-term debt	16,434	16,381
Total liabilities	26,002	23,734
Commitments and contingencies (Note 11)
Stockholders' equity
Common stock, $.0001 par value, 150,000,000 shares authorized, 94,729,385 and 87,563,753 issued and outstanding at September 30, 2021 and December 31, 2020, respectively	9	9
Additional paid-in capital	374,431	361,539
Accumulated other comprehensive income		3
Accumulated deficit	(363,760)	(312,223)
Total stockholders' equity	10,680	49,328
Total liabilities and stockholders' equity	$ 36,682	$ 73,062