| Dec 31, 2014 | Dec 31, 2015 | Dec 31, 2016 | Dec 31, 2017 | Dec 31, 2018 | Dec 31, 2019 | Dec 31, 2020 | Dec 31, 2021 | Dec 31, 2022 | Dec 31, 2023 |
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| Cash and cash equivalents | 74 | 74 | 73 | 42 | 51 | 11 | 17 | 22 | 10 | 16 |
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| Accounts receivable, net | 0 | 0 | 0 | 0 | 2 | 3 | 5 | 5 | 2 | 1 |
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| Inventories | 0 | 1 | 1 | 1 | 3 | 4 | 4 | 4 | 4 | 5 |
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| Prepaid expenses and other current assets | 1 | 1 | 1 | 1 | 1 | 1 | 3 | 3 | 3 | 3 |
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| Total current assets | 75 | 76 | 75 | 44 | 57 | 19 | 54 | 44 | 19 | 25 |
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| Property and equipment, net | 3 | 11 | 14 | 10 | 7 | 6 | 4 | 5 | 5 | 2 |
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| Operating lease assets | - | - | - | - | - | 3 | 11 | 10 | 9 | 7 |
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| Restricted cash | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 2 | 2 | 1 |
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| Other assets | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
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| Total assets | 79 | 87 | 90 | 55 | 64 | 28 | 79 | 61 | 34 | 35 |
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| Notes payable | - | - | - | - | - | - | - | - | - | 41 |
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| Accounts payable | 1 | 1 | 1 | 1 | 1 | 4 | 2 | 3 | 1 | 2 |
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| Accrued Liabilities, Current | 4 | 4 | 5 | 6 | 6 | 11 | 8 | 8 | 7 | 5 |
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| Accrued final payment fee on Term Loan | - | - | - | - | - | - | - | - | - | 5 |
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| Operating lease liability | - | - | - | - | - | - | - | - | 1 | 2 |
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| Derivative Liability, Current | - | - | - | - | - | - | - | - | - | 2 |
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| Warrant liabilities | - | - | - | - | - | - | - | - | - | 0 |
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| Deferred revenue | - | - | - | - | 1 | 0 | 0 | 1 | 0 | 0 |
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| Total current liabilities | 5 | 12 | 10 | 52 | 52 | 61 | 10 | 12 | 10 | 56 |
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| Notes payable | 21 | 26 | 40 | 1 | - | - | 45 | 48 | 50 | - |
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| Operating Lease, Liability, Noncurrent | - | - | - | - | - | 2 | 11 | 9 | 8 | 7 |
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| Deferred revenue, net of current portion | - | - | - | - | 0 | 0 | 0 | 0 | 0 | 0 |
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| Derivative Liability, Noncurrent | - | - | - | - | - | - | 1 | - | 1 | - |
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| Total liabilities | - | - | - | - | - | - | - | - | 74 | 63 |
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| Common Stock, Value, Issued | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
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| Additional paid-in capital | - | - | 243 | 267 | 329 | 342 | 432 | 459 | 495 | 556 |
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| Accumulated deficit | -104 | -149 | -204 | -266 | -317 | -376 | -423 | -472 | -534 | -584 |
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| Total stockholders' deficit | 53 | 47 | 39 | 1 | 11 | -34 | 9 | -13 | -40 | -28 |
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| Total liabilities and stockholders' deficit | 79 | 87 | 90 | 55 | 64 | 28 | 79 | 61 | 34 | 35 |
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