Surface-level Regenerative Peripheral Nerve Interfaces (RPNIs) for a Novel Control Method of Advanced Prosthetic Devices
Shelby Svientek, MD1, Amir Dehdashtian, MD, MPH2, Jarred Bratley, BS2, Paul S Cederna, MD3 and Stephen WP Kemp, PhD2, (1)The University of Michigan, Ann Arbor, MI, (2)University of Michigan, Ann Arbor, MI, (3)Plastic Surgery, University of Michigan, Ann Arbor, MI
Although intuitive control of advanced prosthetics is quickly becoming reality, criticisms often focus on their prohibitive cost, lack of sensory feedback, and requirement for indwelling electrodes. The Regenerative Peripheral Nerve Interface (RPNI) was developed as a biologic nerve interface to provide intuitive control of these devices and consists of a transected peripheral nerve implanted in a segment of autologous muscle graft. As RPNI afferent sensory transmission is limited, the RPNI was integrated with a dermal graft, termed the Composite-RPNI (C-RPNI). The RPNI and C-RPNI are located deep within the extremity, necessitating electrode insertion which can be associated with foreign body reaction or even infection from the transcutaneous wires. The purpose of this study was to investigate superficial placement of RPNIs and C-RPNIs as a method to improve afferent sensory feedback and avoid surgical placement of indwelling electrodes.
Six rats were assigned to either superficial-RPNI or C-RPNI groups. The RPNI was fabricated by securing autologous muscle graft to the transected common peroneal (CP) nerve. This was then secured to dermis that had been debrided of underlying subcutaneous tissues. The C-RPNI was constructed similarly, but overlying skin was cut to form a pedicled skin flap. Endpoint evaluations were performed at three months. Electrical stimulus was applied to the proximal CP nerve with recordings obtained from the muscle component using superficial and insertional EMG electrodes. A variety of stimuli was applied to the dermal portion with recordings obtained from the CP nerve.
All RPNI and C-RPNI constructs demonstrated regeneration, revascularization, and reinnervation on histology. Muscle EMG signals (CMAPs) generated were robust and easily obtained via superficial electrodes (0.31+/-0.05mV). All constructs demonstrated visible contraction that was readily apparent when observing overlying skin. To characterize afferent sensory transduction, a variety of physical and thermal stimuli was applied to the dermal portion of the C-RPNI with distinct, reproducible signal patterns generated at the proximal nerve (Figure 1).
Superficial fabrication of the RPNI is a viable methodology and could potentially negate the need for indwelling electrodes for control of advanced prosthetic devices. Additionally, the superficial C-RPNI appears to generate unique afferent signal patterns dependent on the applied stimulus, raising the possibility that it can be manipulated to provide dermatomal sensory feedback similar to that of the native limb.
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