Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 9,667	$ 9,125
Short-term investments	18,931	3,898
Accounts receivable	180	1,231
Unbilled revenue	106	4
Inventories — current	282	229
Prepaid expenses and other current assets	800	560
Total current assets	29,966	15,047
Property and equipment, net	270	299
Inventories — noncurrent	889	1,168
Other noncurrent assets	7	56
Total assets	31,132	16,570
Current liabilities:
Accounts payable and accrued expenses	2,441	2,496
Amounts due to related parties	12	29
Unearned revenue — current	470	1,000
Total current liabilities	2,923	3,525
Unearned revenue — noncurrent		2,038
Common stock warrant liabilities	17,079
Other noncurrent liabilities	3,000	3,000
Total liabilities	23,002	8,563
Stockholders’ equity:
Common stock, $0.001 par value—150,000,000 shares authorized as of June 30, 2018 and December 31, 2017; 4,774,364 and 2,134,154 shares issued and outstanding as of June 30, 2018 and December 31, 2017	45	42
Additional paid-in capital	190,255	175,223
Accumulated deficit	(182,170)	(167,257)
Accumulated other comprehensive loss		(1)
Total stockholders’ equity	8,130	8,007
Total liabilities and stockholders’ equity	$ 31,132	$ 16,570