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Dermal Sensory Regenerative Peripheral Nerve Interface (DS-RPNI) For Multimodal Sensory Feedback
Jennifer C. Lee, BSE, MSE, Widya Adidharma, MD, Amir Dehdashtian, MD, MPh, Paul S. Cederna, MD, Stephen WP Kemp, PhD.
University of Michigan, Ann Arbor, MI, USA.

PURPOSE - Sensory tactile feedback is crucial in our everyday lives as it helps us characterize held objects, modulate motor actions, and understand our limbís position in space. Though sensors for exteroceptive stimuli detection have been developed for advanced prostheses, persons with upper extremity amputation often never regain physiologically relevant, natural sensory feedback largely in part due to lack of an appropriate user-prosthetic interface.  Current neural interfaces lack stable long-term transmission of sensory information from the environment, natural sensory perception, and modality- and somatotopic-matched sensory feedback. To address the critical need for a high fidelity, stable interface that can facilitate natural sensory feedback, our lab has created the Dermal Sensory Regenerative Peripheral Nerve Interface (DS-RPNI), which involves securing a de-epithelialized dermal graft around a transected sensory nerve. The DS-RPNI provides the ideal end organ targets for physiologic reinnervation by regenerating sensory axons, attenuates neuroma formation, and allows for stability and longevity of neural signaling that is not painful to the user. Natural reinnervation also has the potential for providing a full range of modality-matched sensation. We have previously shown that DS-RPNIs are successfully revascularized and neurotized with minimal scar tissue formation, and that they facilitate graded neural signaling to both mechanical and electrical stimuli. Expanding on this previous work, the purpose of this study was to assess the range of sensory modalities (i.e., pressure, vibration, heat, cold, nociception) that can successfully elicit compound sensory nerve action potentials following application of stimuli to DS-RPNI.
METHODS - Twenty rats underwent transection of the sural sensory nerve with subsequent securement of the transected nerve end in either acellular dermal matrix (negative control group) or de-epithelialized dermal graft from the hindpaw of a donor rat (DS-RPNI group). Compound sensory nerve action potentials (CSNAPs) were evaluated after a 3-month maturation period and elicited after exposure to pressure, vibration, heating, cooling, and nociceptive modality testing for each rat. Only one sensory modality was tested at a time, and an intertrial interval of 5 minutes was waited between testing trials for each modality testing.  Statistical analyses were performed to compare the DS-RPNI group to negative control group.
RESULTS - We found that the DS-RPNI can effectively respond to different sensory modalities and that the elicited CSNAP were greater than those of the negative control group that lack the end organ targets for reinnervation. Increased DS-RPNI response compared to the negative control suggests that DS-RPNI response is most likely due to functional reinnervation rather than direct nerve end stimulation.
CONCLUSIONS - The results of this study demonstrate the potential of the DS-RPNI as a multi-modality sensory peripheral nerve interface, potentially revolutionizing the frontier of prosthetic innovations. Future directions will focus on understanding the immunohistological composition of the DS-RPNI that contributes to its success as a neural interface. 


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