Plastic Surgery Research Council
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Presenter: Theodore A Kung, Resident
Co-Authors: Langhals NB; Moon JD; Qu J; Martin DC; Cederna PS; Urbanchek MG
University of Michigan

Background: The regenerative peripheral nerve interface (RPNI) consists of a unit of free muscle that has been neurotized by a peripheral nerve. In conjunction with a biocompatible electrode on the muscle surface, the RPNI facilitates signal transduction from a residual peripheral nerve to a neuroprosthetic limb. Electrodes can be coated with conductive polymer to enhance conductivity. We study the augmentation of signal strength and fidelity from the RPNI when conductive polymer is applied to implanted stainless steel electrodes.

Methods: Ten rats underwent RPNI fabrication whereby the left extensor digitorum longus (EDL) muscle was removed as a nonvascualrized free tissue transfer and reinnervated by the divided common peroneal nerve (Fig. 1). The RPNI was interfaced to either an implanted stainless steel pad electrode (RPNISS group, n = 5) or a pad electrode coated with conductive polymer (RPNICP group, n = 5). The contralateral intact EDL muscle of each rat was used as control (ControlSS and ControlCP, n = 5 each). Electrodiagnostic testing was performed 1 month postoperatively using percutaneous needle stimulation.

Results: Compound muscle action potentials (CMAP) were obtained from the implanted electrode in all 10 RPNIs. Both RPNISS and RPNICP groups showed significantly lower mean maximum CMAP amplitudes compared to respective controls (ControlCP = 10.00 mV, ControlSS = 11.74 mV). The addition of conductive polymer to the electrode yields a 60% increase in mean maximum CMAP amplitude (RPNICP = 7.52 mV, RPNISS = 4.72 mV) (Fig. 2). The RPNICP group showed a trend towards increased mean CMAP area compared to the RPNISS group (Tab. 1).

Conclusions: Implanted electrodes with and without conductive polymer can be utilized with the RPNI to transduce electrophysiological signals from a transected nerve. At 1 month after RPNI fabrication, the indwelling electrode displays stability and permits reliable CMAP recordings. Conductive polymer coating results in increased CMAP amplitude and area. Serial testing of the RPNI will determine the long-term effects of continued reinnervation and scarring on signal quality.

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