Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities
Net loss	$ (12,416)	$ (14,376)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	525	676
Amortization of debt issuance costs and debt discount	65	126
Stock-based compensation	960	1,160
Noncash interest expense and other charges	1,151	1,119
Change in right of use asset	102	129
Provision for excess and obsolete inventories	97	390
Other non-cash charges	3	(52)
Gain on extinguishment of debt	(2,353)	0
Changes in operating assets and liabilities:
Accounts receivable	82	142
Inventories	(733)	(464)
Prepaid expenses and other current assets	(318)	(197)
Other assets	(44)	5
Accounts payable	484	(31)
Accrued compensation	(324)	(327)
Accrued expenses and other current liabilities	122	29
Other long-term liabilities	431	0
Net cash used in operating activities	(12,166)	(11,671)
Cash flows from investing activities
Purchase of property and equipment	(18)	0
Proceeds from sale of property and equipment	0	40
Net cash (used in) provided by investing activities	(18)	40
Cash flows from financing activities
Proceeds from borrowings, net of issuance costs	0	2,330
Proceeds from the issuance of common stock in public offerings, net	13,077	23,648
Proceeds from the issuance of common stock under officers’ and directors’ purchase plan	0	36
Net cash provided by financing activities	13,077	26,014
Net change in cash and cash equivalents	893	14,383
Cash and cash equivalents, beginning of period	22,185	10,943
Cash and cash equivalents, end of period	23,078	25,326
Noncash investing and financing activities:
Accretion of Series A preferred stock dividends	3,132	2,901
Reclassification of right of use asset to prepaid rent	(102)	(129)
Transfers between inventory and property and equipment	$ (7)	$ (7)