9. OTHER BALANCE SHEET COMPONENTS

Property and equipment

Property and equipment consist of the following (in thousands):

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Total depreciation and amortization expense was $0.9 million, $1.2 million and $0.7 million for the years ended December 31, 2022, 2021 and 2020, respectively. During the year ended December 31, 2022, we wrote down certain property and equipment amounting to $0.7 million associated with our leased facility which expired in January 2023, and recognized such amount within selling, general and administrative expense.

Intangible asset

Intangible asset pertain to amortized cost of capitalized milestone payment obligations to Forma, incurred upon and after regulatory approval of an acquired product. See “Note 4 - Sponsored Research and License Agreements and Government Contract” for related discussions. Such costs are being amortized on a straight-line basis over the estimated useful life of approximately 14 years. For the year ended December 31, 2022, we recorded amortization expense of approximately $0.1 million, which was included within cost of sales in the statements of operations.

The following table presents the estimated future amortization expense of intangible asset (in thousands):

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Other accrued liabilities

Other accrued liabilities consist of the following (in thousands):

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