Neural Signal Transduction with the Muscle Cuff Regenerative Peripheral Nerve Interface
Carrie A. Kubiak, M.D., Daniel C. Ursu, Ph.D., Jana D. Moon, B.S., Theodore A. Kung, M.D., Paul S. Cederna, M.D., Stephen W. P. Kemp, Ph.D..
University of Michigan, Ann Arbor, MI, USA.
Purpose: In the past three decades, robotic exoskeletons have emerged as promising tools for the restoration of functional independence for patients with intact peripheral nerves but poor motor control or strength. An ideal exoskeleton assists in the execution of specific actions through the detection of a user's intended motions. However, current motor-intent detection technologies remain suboptimal and are overall unsatisfactory to the user. The Muscle Cuff Regenerative Peripheral Nerve Interface (MC-RPNI) is a novel biologic interface that may allow for more accurate detection of the user's motor intention for the control of functional assistive devices. The MC-RPNI construct is composed of a free autologous muscle graft implanted circumferentially around an intact peripheral nerve. The muscle graft becomes reinnervated by the collateral sprouting of axons so that peripheral nerve action potentials can be amplified and recorded from intact peripheral nerves. The purpose of this study was to investigate the in vivo stability of MC-RPNIs, as well as signal transduction capability of this novel interface.
Methods: A total of twenty F344 rats were randomly assigned to one of four experimental groups: (A) 8mm MC-RPNI with epineurial window; (B) 8mm MC-RPNI without epineurial window; (C) 13mm MC-RPNI with epineurial window, and (D) 13mm MC-RPNI without epineurial window. MC-RPNIs were surgically created by wrapping free skeletal muscle grafts circumferentially around the intact right common peroneal nerve. At three months, electrophysiologic evaluation was performed. The proximal peroneal nerve was stimulated while efferent signals (CMAPs) were measured from (1) the Muscle Cuff-RPNI, and; (2) the distal target muscle (EDL). The muscle cuff-RPNI was then stimulated while (3) efferent signals (CMAPs) were recorded from the EDL, and; (4) afferent signals (CSNAPs) were recorded from the proximal peroneal nerve. Ipsilateral extensor digitorum longus (EDL) muscle force testing was also performed with stimulation of the proximal common peroneal nerve.
Results: MC-RPNI constructs remained viable over the three-month period and demonstrated robust regeneration, revascularization, and reinnervation. Results of electrophysiologic testing is presented in Table 1. Large CMAP signals were generated from the MC-RPNIs, regardless of cuff length or presence of epineurial window. MC-RPNIs do not disrupt the innervation to the distal target muscle (EDL) nor is it detrimental to the force generation capacity of the EDL (Table 2).
Conclusion: The MC-RPNI is capable of amplifying neuronal signals from intact peripheral nerves to larger, recordable EMG signals and also facilitates afferent signal transduction along the proximal nerve. This signal transduction occurs without adversely impacting the function of the common peroneal nerve or the distal EDL muscle. The MC-RPNI offers a way to detect volitional motor commands and deliver exogenous sensory feedback without sacrificing peripheral nerve or end-organ function.
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