Quantification of Regenerative Peripheral Nerve Interface Signal Transmission

PURPOSE: Amputees prefer body-powered, cable operated prosthetics over those with advanced technology. Though myoelectric arms offer motorized functions, they use unreliable surface electrode “interfacing” which frustrates patients. Our solution is to surgically construct an interface with residual peripheral nerves for transduction of nerve signals. Our regenerative peripheral nerve interface (RPNI) devices are composed of: a) harvested host muscle freely grafted to the residual stump area, b) residual peripheral nerves for neurotizing the muscle, c) implanted recording electrodes, and d) decellularized small intestine submucosa (SIS) wrap. The purpose of this study is to quantify signal transmission from RPNI devices in the rat.  The hypothesis is: RPNI devices communicate peripheral nerve signaling with capacities approaching Sham devices.

METHODS: F344 rats (n = 29) were randomized into 3 groups.  During Sham device surgeries, the right soleus muscle was exposed (Sham, n=11). For both RPNI not neurotized (RPNI-NN, n=9) and neurotized (RPNI+N, n=9) devices, the right soleus muscle was transferred to the left thigh simulated residual limb area. Additionally within the RPNI+N device, the left peroneal nerve was divided used to neurotize the soleus. SIS was wrapped around all devices. Electrodes were implanted at evaluation. Tests included device nerve conduction, force capacity, and histology after 1 or 3 months of convalescence.

RESULTS: All 29 interface devices were pink and healthy. RPNI compound muscle action potentials (CMAP), muscle mass, and stimulation thresholds indicated ongoing regeneration and recovery between months 1 and 3. At 1 month signals were recorded for Sham and RPNI+N but not for the RPNI-NN. At 3 months, RPNI+N devices transmitted signals of CMAP amplitude, CMAP area, device force, and motor unit number were 50% to 100% Sham device transmissions (Table 1). RPNI-NN values were significantly lower than Sham (p<.05).  Histology showed RPNI+N contained healthy axons demonstrating robust myelination that were organized and integrated with the muscle fibers (Fig 1).

CONCLUSION: Interfacing to peripheral nerves was achieved through RPNI+N device implantation and regeneration. Action potential propagation through peripheral nerves exceeded RPNI tissue excitation thresholds effectively enough that electrodes located in the RPNI forwarded signals to artificial arm  type processors.

Supported by: the DoD Multidisciplinary University Research Initiative (MURI) program (#W911NF0610218), the NIH T32 Training Grant (#GM0008616-11), and the Plastic Surgery Educational Foundation Pilot Research Grant (#174964).