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Intangible Assets
9 Months Ended
Sep. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]  
Intangible Assets Intangible Assets
Intangible assets consisted of the following:
(in thousands)September 30, 2021December 31, 2020
Patents$431 $430 
Less accumulated amortization(206)(172)
$225 $258 
The weighted average useful life of the intangible assets was 9.87 years. For the three months ended September 30, 2021 and 2020, amortization expense was $0.0 million and $0.0 million, respectively.