American Society for Peripheral Nerve

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Advanced Regenerative Electrodes Enable Functional Electrical Stimulation of Peripheral Motor and Sensory Axons
Matthew MacEwan, PhD; Paul Gamble, MD; Manu Stephen, MD; Daniel Moran, MD; Wilson Ray, MD
Department of Neurological Surgery, Washington University School of Medicine, St. Louis, MO

Introduction: Neuroprosthetic technologies offer one of the most promising approaches to restoring native sensorimotor function following neurologic injury. Development of electrodes capable of facilitating chronic high-specificity nerve stimulation and recording may enable long-lasting restoration of motor function, hand / arm control, as well as improvements in sensory feedback and proprioception. Regenerative sieve electrodes represent a novel approach to achieving such an advanced interface with peripheral nerve tissue, but have yet to be proven as a singular interface to both motor and sensory nerve fibers. The present study aimed to examine the ability of chronically implanted regenerative sieve electrodes to functionally interface both motor and sensory axons in mammalian mixed nerve.

Materials & Methods: Custom-designed sieve electrodes were fabricated out of polyimide and gold using sacrificial photolithography. Regenerative sieve electrodes were then microsurgically implanted in the sciatic nerve of male Lewis rats using a dorsolateral gluteal muscle splitting incision. Post-operatively, functional nerve regeneration through implanted devices was assessed via nerve conduction studies and evoked muscle force mesaurement. Nerve interfacing was assessed in situ by stimulating regenerated nerve tissue via implanted sieve electrodes while simultaneously recording force production in distal musculature and local field potentials in sensory cortex. Regenerated nerve segments were terminally explanted and fixed for morphological or histomorphometric evaluation.

Results: Micro-surgical implantation of sieve electrodes in the sciatic nerve of healthy male rats for 1, 2, and 3 months demonstrated robust axonal regeneration through implanted devices. Chronically implanted sieve electrodes demonstrated recruitment of integrated nerve tissue at stimulus amplitudes as low as 10-20 ľA, and highly selective activation of distal musculature (99.7% SI for EDL, 99.5% SI for TA, and 99.9% SI for Gastrocnemius) and thereby motor axons. Implanted sieve electrodes additionally demonstrated successful recruitment of sensory nerve fibers and induction of neural activity in somatosensory cortex (S1). Mapping of S1 utilzing silicon microelectrode arrays may further elucidate the selectivity of sensory fiber activation faciliated by chronically-implanted sieve electrodes.

Conclusions: The present study confirms the ability of sieve electrodes to faciliate a selective, stable interface with both motor and sensory nerve fibers. These findings suggest that regenerative sieve electrodes may be able to provide a stable, bi-directional, interface ideal for end translational use in advanced neuroprothetic systems.

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