4. Inventories

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Inventories are comprised of unprocessed tissue, work-in-process, Avance Nerve Graft, Axoguard Nerve Connector, Axoguard Nerve Protector, Avive Soft Tissue Membrane, Axoguard Nerve Cap, Acroval Neurosensory and Motor Testing System, Axotouch Two-Point Discriminator and supplies and are valued at the lower of cost (first-in, first-out) or net realizable value and consist of the following:

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For the years ended December 31, 2019, 2018 and 2017, the Company had recorded a provision for inventory write-downs of $1,887, $1,343 and $1,438, respectively, primarily relating to product expiration.