The Composite Regenerative Peripheral Nerve Interface (C-RPNI) Facilitates Multimodal Sensory Afferent Signaling and Neuroma Attenuation

The University of Michigan, Ann Arbor, MI, USA

W Adidharma, Huang SL, R Kodali, KD Kozma, R Mauer, RR Jillala, KL Wu, MV Santana-Rivera, PS Cederna

PURPOSE: Modern myoelectric prostheses have sensors that can detect sensory stimuli, offering a promising solution for functional sensory recovery after amputation. However, attempts in re-establishing sensory feedback using available prosthetic-user interfaces (i.e. electrodes that directly contact the nerve) have resulted in unnatural, non-specific, and/or painful sensations. This is in part due to the non-selective simultaneous activation of several different fiber types, resulting in unnatural aggregate neural activity and unnatural sensory perception. Our lab has developed the Composite Regenerative Peripheral Nerve Interface (C-RPNI), a transected mixed peripheral nerve implanted between a muscle graft and dermal graft, as a biologic interface that can facilitate multimodal sensory signaling. Inherent preferential reinnervation properties of regenerating axons encourage cutaneous sensory axons to reinnervate skin, while encouraging motor axons to reinnervate muscle. In a C-RPNI, this would physically separate afferents responsible for cutaneous sensations from other fiber types. Therefore, we hypothesize that the C-RPNI can more naturally facilitate afferent sensory signaling.

METHODS: Male Lewis rats (n=6/group) were randomized to one of the following groups: (1) C-RPNI, (2) transected nerve implanted into muscle graft only (RPNI; Regenerative Peripheral Nerve Interface), and (3) naïve control. The common peroneal (CP) nerve was transected at the distal thigh level in the C-RPNI and RPNI groups, and the proximal nerve segment was implanted into muscle and dermal graft (C-RPNI) or muscle graft alone (RPNI). After 3 months, in situ proximal CP neural afferent activity was recorded during application of sensory stimuli to the constructs or control dorsal hindfoot. The following sensations were tested: fine touch, vibration, heat, and cold.

RESULTS: At three months post-operative, the C-RPNI dermal and muscle grafts were viable and revascularized. There was no graft loss in any animal. Stimulation of the C-RPNI dermal graft with fine touch, vibration, heat, and cold stimuli generates similar neural signal morphology as control intact innervated skin. The same neural activity is not observed when applying the same stimuli to the RPN. Immunohistochemistry reveals selective reinnervation of both dermal and muscle grafts of the C-RPNI.

CONCLUSIONS: The dermal component of the C-RPNI is functionally reinnervated and facilitates multimodal tactile and temperature sensory signaling. This novel biologic interface has the potential to facilitate modality-matched sensory feedback, which would revolutionize the frontier of prosthetic rehabilitation after amputation. Future studies will aim to understand the perceived sensation with C-RPNI stimulation.