Characterization of Motor, Sensory, and Mixed Nerve Regenerative Peripheral Nerve Interfaces (RPNIs) for Prosthetic Control
Scott W. Sabbagh, BSc., Ali L. vanBelkum, BSc., Nathan G. Lawera, BSc., Vincent Thieu, BSc., Paul S. Cederna, M.D., Stephen W. Kemp, Ph.D.
University of Michigan, Ann Arbor, MI, USA.
PURPOSE: Approximately 185,000 Americans suffer devastating limb loss yearly, resulting in substantial functional deficits adversely impacting quality of life. Regenerative Peripheral Nerve Interfaces (RPNIs) present a promising surgical strategy for interfacing human volition with myoelectric prostheses. Rat studies led to proof of RPNI long-term function and high signal to noise ratio with no adverse biological effects. However, characterization of different types of nerve RPNIs has not yet been evaluated.METHODS: RPNIs consisted of a small, autologous partial muscle graft reinnervated by a transected peripheral nerve branch. Animals were randomly assigned to one of five experimental groups: (1) Motor (femoral nerve) RPNI; (2) Sensory (sural nerve) RPNI; (3) Mixed (common peroneal nerve) RPNI; (4) negative control (common peroneal nerve transected and not repaired), and; (5) positive control (surgical na´ve animal). After 3 months of convalescence, terminal EMG measurements were assessed including nerve conduction velocity and compound muscle action potentials (CMAPs). A 5 mm segment proximal to the rpni was harvested and processed for nerve histomorphometry. All RPNI constructs were harvested and processed for Immuno-enabled Three-Dimensional Imaging of Solvent-Cleared Organs (IDISCO) to visualize axonal infiltration into the RPNI.RESULTS: At harvest, all RPNIs were well vascularized and healthy in appearance. Nerve conduction velocities and CMAPs were achieved in all three experimental RPNI groups, with mixed nerve RPNIs displaying the greatest CMAPs and terminal muscle weights. IDISCO revealed the 3-dimensional patterns of extensive axonal reinnervation of each corresponding RPNI (Fig.1).
CONCLUSION: Motor, sensory, and mixed nerve RPNIs displayed robust neural regeneration throughout each construct. Results from this study will provide a framework for further evaluation of electrode-biological interfaces, and help us to develop future prostheses capable of closed loop afferent-efferent signalling.
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