Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating activities:
Net loss	$ (2,969)	$ (4,594)
Adjustments to reconcile net loss to net cash used in operating activities:
Write-off of inventory		3
Depreciation	14	22
Reduction in the carrying amount of right-of-use assets	135	118
Share-based compensation	416	941
Changes in operating assets and liabilities:
Accounts receivable	42	(32)
Inventory		1
Prepaid expenses and other current assets	57	189
Other receivable due from related party	(5)
Accounts payable	99	194
Accrued liabilities and other current liabilities	(23)	293
Deferred revenue	497	(2)
Operating lease liability - current	(146)	20
Operating lease liability - noncurrent		(146)
Net cash used in operating activities	(1,883)	(2,993)
Investing activities:
Purchase of property and equipment	(27)	(5)
Net cash used in investing activities	(27)	(5)
Financing activities:
Proceeds from sales of common stock	2,000
Proceeds from exercise of common stock options	5
Net cash provided by financing activities	2,005
Net change in cash and cash equivalents	95	(2,998)
Cash and cash equivalents at beginning of period	21,407	5,585
Cash and cash equivalents at end of period	21,502	2,587
Supplemental disclosure for noncash investing and financing activities:
Unpaid issuance costs of common stock	$ 66