Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net loss	$ (6,537)	$ (4,512)
Adjustments to reconcile net loss to net cash used in operating activities:
Recognition of deferred revenue	(40)	(204)
Depreciation	50	41
Amortization of operating lease right-of-use assets	192
Amortization of debt discount	55
Stock-based compensation	1,530	418
Realized gain on investments	(11)
Changes in:
Prepaid expenses and other current assets	5	293
Accounts payable	(2,003)	1,635
Collaboration and device development payable	(692)	49
Accrued expenses	(1,118)	(266)
Operating lease liabilities	(214)
Other liabilities	24
Net cash used in operating activities	(8,759)	(2,546)
Cash flows from investing activities:
Purchase of property and equipment	(74)
Proceeds from sale of marketable securities	499
Net cash provided by investing activities	425
Cash flows from financing activities:
Proceeds from loan payable, net of expenses		2,500
Principle payments on loan payable	(447)
Payment for taxes related to net share settlements of restricted stock units	(151)
Net cash (used in) / provided by financing activities	(598)	2,500
Effect of exchange rate changes on cash and cash equivalents	(202)
Net decrease in cash and cash equivalents	(9,134)	(46)
Cash, cash equivalents and restricted cash - beginning of year	11,358	2,040
Cash, cash equivalents and restricted cash - end of year	$ 2,224	$ 1,994