Plastic Surgery Research Council
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Presenter: Nicholas B Langhals, PhD
Co-Authors: Larson JV; Urbanchek MG; Cederna PS; Kung TA
University of Michigan

Background: The regenerative peripheral nerve interface (RPNI) consists of a unit of free muscle that has been reinnervated by a peripheral nerve. Electrophysiologic nerve signals may be transduced via an electrode from the muscle component of the RPNI. Thin-film polyimide electrode arrays exhibit superior flexibility compared to other available electrodes and as such may yield a better long term biocompatibility. The purpose of this study is to demonstrate in vivo recording of bioelectric signals from polyimide arrays applied to intact muscle.

Methods: Novel multi-channel polyimide electrode arrays were developed for this study (NeuroNexus Technologies, Ann Arbor, MI). Each array contains 32 microelectrodes within a polyimide substrate (15 ?m thick). In 9 rats, the left common peroneal nerve and extensor digitorum longus (EDL) muscle were exposed. A polyimide array was sutured to the epimysium of the EDL muscle. Proximally, a stimulating hook electrode was placed around the common peroneal nerve. Electrophysiological tests were performed to evaluate signal transduction through the polyimide array.

Results: Compound muscle action potentials (CMAPs) were recorded from 97% of the microelectrodes (Figure 1). The average electrical stimulation threshold for eliciting a CMAP was 96.72 uA (range, 35-225; SD, 50.52), which resulted in an average CMAP peak-to-peak amplitude of 16.99 mV (range, 0.75-24.81; SD 7.70) at an average latency of 3.57 ms (range, 2.53-5.48; SD 1.03) (Table 1). These findings are descriptively comparable to results using a standard needle electrode inserted into intact EDL muscle.

Conclusion: Flexible thin-film polyimide electrode arrays can successfully record bioelectric signals from skeletal muscle with high fidelity. These findings support the use of polyimide arrays in conjunction with RPNIs for the purpose of achieving control of an effective closed-loop neuroprosthetic limb. Future efforts will investigate the recording potential of polyimide arrays when applied to implanted RPNIs.

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