Fixed assets, net, summarized by major category, consist of the following (in thousands):


	September 30,		December 31,
	2022		2021
Machinery and equipment	$	118,233	$	117,264
Leasehold improvements	61,302		59,740
Computer equipment and software	14,449		13,197
Office furniture and equipment	2,420		2,883
Construction in progress	98,770		80,557
Total	295,174		273,641
Less: accumulated depreciation	(101,528)		(85,240)
Fixed assets, net	$	193,646	$	188,401

For the three months ended September 30, 2022 and 2021, depreciation expense was $5.8 million and $3.8 million, respectively. For the three months ended September 30, 2022 and 2021, there was $1.1 million and $0.9 million of capitalized interest on the construction of manufacturing sites, respectively.

For the nine months ended September 30, 2022 and 2021, depreciation expense was $18.0 million and $9.6 million, respectively. For the nine months ended September 30, 2022 and 2021, there was $2.9 million and $3.0 million of capitalized interest on the construction of manufacturing sites, respectively.

At September 30, 2022 and December 31, 2021, total fixed assets, net includes leasehold improvements and manufacturing process equipment located in Europe in the amount of $57.4 million and $65.4 million, respectively.

As of September 30, 2022 and December 31, 2021, the Company had asset retirement obligations of $3.1 million and $2.4 million, respectively, included in accrued expenses and other liabilities on its condensed consolidated balance sheet, for costs associated with returning leased spaces to their original condition upon the termination of certain lease agreements.