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Multichannel Carbon Fiber Electrode Arrays For Selective Stimulation And Recording Of Sensory-motor Signals In Peripheral Nerve Interfaces
Amir Dehdashtian, MD, Dan Ursu, PhD, Paras G. Patel, PhD, Elissa Welle, Cynthia A. Chestek, PhD, Paul S. Cederna, MD, Stephen WP Kemp, PhD.
University of Michigan, Ann Arbor, MI, USA.

PURPOSE:Advanced motorized prosthetic limbs are capable of fine multiple joint manipulations and possess the potential to emulate the intricate functions of the native extremity. Equipped with force or pressure sensors, these devices are also able to provide tactile information to the user. However, increasing a prosthetic’s manipulative degrees of freedom requires additional controlled inputs from the amputee. The development of a reliable interface between amputee and prosthetic device is therefore crucial for closing the motor-sensory feedback loop between human and machine. The Regenerative Peripheral Nerve Interface (RPNI) and Composite-RPNI (C-RPNI) are biologic nerve interfaces designed for stable integration of a prosthetic device with transected peripheral nerves in a residual limb. The former employs a free muscle graft as a neural signal transducer, while the latter incorporates a skin graft combined with the muscle graft to simultaneously transduce efferent nerve signals via muscle, and afferent sensory cues back to the brain. Both RPNIs and C-RPNIs may benefit from electrode arrays able to simultaneously record multiple motor units in order to enhance the degrees of freedom for prosthetic control. In addition, electrode arrays placed on the dermal component of the C-RPNI may be able to individually stimulate dermal sensory organelles, thereby providing a range of sensory modalities to the user. The present work utilized ultrafine carbon fiber electrode arrays to stimulate and record single unit motor and sensory information from skin, muscle and nerve. METHODS:12 rats were randomly assigned to either an RPNI (n=6) or C-RPNI (n=6) surgical group. After a three month convalescent period, animals were anesthetized and Carbon Fiber Micro-electrode Arrays (CFMA) of eighteen 500 μm long electrodes were implanted into the peroneal nerve and muscle graft of the RPNI group, as well as the skin graft for the C-RPNI cohort, for acute single fiber stimulation and recordings. Both RPNIs and CRPNIs were electrophysiologically evaluated ex-vivo by electrically stimulating single carbon fibers with biphasic pulse trains of up to 3 mA within: 1) nerve, 2) muscle, and for the latter, 3) skin, while simultaneously recording signals from: a) muscle, b) nerve, and in the case of CRPNIs c) nerve and skin, or muscle and skin, respectively.
RESULTS:Single CFMA electrode stimulation of nerve generated signals in the muscle grafts of RPNIs and CRPNIs of 5.1±1.7 mV amplitude. Alternating EMG signals were noted as the stimulating electrode was varied. Muscle graft stimulation in RPNIs and CRPNIs yielded compound neural signals of 28±10 µVPeak-Peak. Selective skin graft stimulation in CRPNI constructs generated alternating compound neural signals of 65±22 µVPeak-Peak, some of which displayed a shift in conduction velocity. CONCLUSION:CFMAs incorporated into RPNI and CRPNI constructs are capable of recording from subsets of reinnervated myocytes, and selectively stimulating different skin regions of CRPNI dermal grafts. Results from this study have potential broad implications for the realization of an intuitive, selective, and novel prosthetic interface.


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