Plastic Surgery Research Council
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PSRC 60th Annual Meeting
Program and Abstracts

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Dermal-Based Peripheral Nerve Interface for Transduction of Sensory Feedback from Upper Extremity Prostheses
Ian C. Sando, MD1, Gregory J. Gerling, PhD2, Daniel C. Ursu, MS1, Kristoffer B. Sugg, MD1, Yaxi Hu, BS1, Steven C. Haase, MD1, Nicholas B. Langhals, PhD1, Paul S. Cederna, MD1, Melanie G. Urbanchek, PhD1.
1University of Michigan, Ann Arbor, MI, USA, 2University of Virginia, Charlottesville, VA, USA.

PURPOSE: We developed a Dermal-based Sensory Regenerative Peripheral Nerve Interface (DSRPNI) with the long-range goal of providing high fidelity somatosensory feedback from prosthetic limbs. DSRPNI units consist of small de-epithelialized skin grafts placed subcutaneously that are reinnervated by residual sensory peripheral nerves. Patterned electrical stimuli applied to the DSRPNI may excite native mechanoreceptors within the DSRPNI sending action potentials along the residual nerve to the somatosensory cortex for tactile perception. Our purpose is to verify native mechanoreceptors reinnervation in DSRPNI units and establish electrical stimulation thresholds.
METHODS: Using a rat model, DSRPNIs were fabricated by harvesting de-epithelialized glabrous skin grafts from donor rats. Grafts were secured around the distal end of the transected sural nerve in a submuscular pocket. After two months (Fig 1), we compared electrophysiological signals recorded at the proximal sural nerve of both DSRPNI units (n=4) and native full-thickness skin (n=8) in response to: a) mechanical; or b) electrical stimulation. Mechanoreceptor signals were evoked using a custom indenter to depths of 1, 2, and 3mm. Secondly, electrical stimulations were applied to DSRPNI units and full thickness skin. Stimulation pulse amplitudes were varied between 0.05 and 1.5 mV. Peak-to-peak voltage in the proximal sural nerve was measured.
RESULTS: Mechanical indentation of native full-thickness skin elicited compound sensory nerve action potentials (CSNAPs), which were similar to the DSRPNI units. CSNAP firing rates increased in a similar linear fashion for DSRPNI units (1.9 ± 1.3, 14.8 ± 19.1, and 26.6 ± 36.8 spikes/second) and full-thickness skin (6.1 ± 1.8, 17.7 ± 8.3, and 22.7 ± 8.3 spikes/second) with increased depths of displacement (1, 2, and 3 mm, respectively). Stimulation of DSRPNI units produced firing patterns characteristic of normal skin during ramp and hold phases (Fig 2). Transcutaneous electrical stimulation evoked afferent sural nerve signals in both DSRPNI units (threshold: 500 μA) and native skin (threshold: 600 μA). Increased stimulation current applied to DSRPNI units correlated strongly (r2 = 0.97) with increased peak-to-peak CSNAP voltage (Fig 3). Histomorphometric analysis of DSRPNI tissue revealed healthy dermis with minimal inflammation and no evidence of neuroma.
CONCLUSIONS: Varying the amount of mechanical indention on DSRPNI units produced differential CSNAP firing rates characteristic of native skin with similar firing patterns during mechanical stimulation. Pulsed electrical stimulation applied to DSRPNI units also produced graded afferent nerve signals. These findings suggest reinnervation of mechanoreceptors within DSRPNI units and that patterned electrical stimuli applied to the units can produce graded somatosensory feedback.
Acknowledgement: American Foundation for Surgery of the Hand 2014 Basic Science Grant and DARPA MTO Contract No. N66001-11-C-4190.



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