Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 11,998	$ 9,125
Short-term investments	9,825	3,898
Accounts receivable	165	1,231
Unbilled revenue	3	4
Inventories — current	181	229
Prepaid expenses and other current assets	704	560
Total current assets	22,876	15,047
Property and equipment, net	395	299
Inventories — noncurrent	746	1,168
Other noncurrent assets	7	56
Total assets	24,024	16,570
Current liabilities:
Accounts payable and accrued expenses	2,645	2,496
Amounts due to related parties	29	29
Unearned revenue — current	96	1,000
Other current liabilities	284
Total current liabilities	3,054	3,525
Unearned revenue — noncurrent		2,038
Common stock warrant liabilities	5,083
Other noncurrent liabilities	3,072	3,000
Total liabilities	11,209	8,563
Stockholders’ equity:
Common stock, $0.001 par value—150,000,000 shares authorized as of December 31, 2018 and December 31, 2017; 4,774,919 and 2,134,154 shares issued and outstanding as of December 31, 2018 and December 31, 2017, respectively.	45	42
Additional paid-in capital	191,136	175,223
Accumulated deficit	(178,366)	(167,257)
Accumulated other comprehensive loss		(1)
Total stockholders’ equity	12,815	8,007
Total liabilities and stockholders’ equity	$ 24,024	$ 16,570