CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities
Net loss	$ (7,936)	$ (8,304)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	432	437
Loss on extinguishment of debt		1,942
Amortization of operating lease right-of-use-assets	191	56
Expense on modification of warrants	85
Stock-based compensation	760	427
Amortization of debt issuance costs and debt discount	14	178
Change in fair value of warrants, conversion option and derivative liability	(1)	46
Changes in assets and liabilities
Accounts receivable	609	81
Other receivable	(1)	4
Inventory	(575)	382
Prepaid expenses and other current assets	189	150
Other non-current assets	27	27
Operating lease liabilities	(119)	(93)
Accounts payable	191	1,150
Accrued expenses	191	52
Total cash used in operating activities	(4,296)	(3,465)
Cash flows from investing activities
Purchase of equipment	(7)
Total cash used in investing activities	(7)
Cash flows from financing activities
Proceeds from issuance of notes payable, net of issuance costs and debt discount	350	800
Repayment of notes payable	(50)	(100)
Proceeds from issuance of common stock		2,769
Total cash provided by financing activities	2,023	3,469
Net increase in cash and restricted cash	(2,280)	4
Cash and restricted cash at beginning of period	3,883	2,568
Cash and restricted cash at end of period	1,603	2,572
Supplemental schedule of cash flow information
Cash paid for interest	6
Supplemental schedule of non-cash financing and investing activities
Accretion to redemption value of Series A redeemable convertible preferred stock	(480)
Private Investment in Public Entities
Cash flows from financing activities
Proceeds from the issuance of convertible preferred stock	698
2019 Bridge Note Warrants
Cash flows from financing activities
Proceeds from issuance of common stock	173
Notes payable
Supplemental schedule of non-cash financing and investing activities
Common stock issued as redemption of notes payable and related interest		4,821
Issuance of warrants		893
Accounts payable and accrued expenses
Supplemental schedule of non-cash financing and investing activities
Offering costs included in accounts payable and accrued expenses	240
Series 2 warrants
Cash flows from financing activities
Proceeds from issuance of common stock	708
Series 1 warrants
Cash flows from financing activities
Proceeds from issuance of common stock	144
March 2019 letter of credit warrant
Supplemental schedule of non-cash financing and investing activities
Issuance of warrants		$ 116
Series B convertible preferred stock
Adjustments to reconcile net loss to net cash used in operating activities:
Series B convertible preferred stock inducement expense	1,647
Series A convertible preferred stock
Supplemental schedule of non-cash financing and investing activities
Accretion to redemption value of Series A redeemable convertible preferred stock	480
Series B-2 convertible preferred stock
Supplemental schedule of non-cash financing and investing activities
Conversion of Series B-2 convertible preferred stock into common stock	$ 320