Biocompatible Wireless Device for Stimulation and Repair of Peripheral Nerves Without Electrodes

Peripheral nerve repair is a challenging problem because axon regeneration is often inadequate and only 50% of patients regain some function after surgery. Existing stimulators can improve nerve regeneration and functionality but have significant limitations not yet addressed. A major disadvantage is their inability to function concurrently as wireless non-invasive stimulators and conduits for nerve grafting. Other important disadvantages include device bulkiness, migration and breakdown of electrodes, complex electronics, and invasive tissue implantation with sutures that hinder positive clinical outcomes. In this study, we present a wireless stimulator that functions as a scaffold for nerve repair, which does not include electronic circuits or electrodes.<br/>After cutting a 10 mm section of a rat sciatic nerve, the surgeon applied the autograft to bridge the gap using a biocompatible scaffold. The latter is a thin chitosan film (area ~5x5 mm, thickness ~15 µm) that incorporates a gold loop antenna (diameter ~1.3 mm, thickness ~70 nm), which is powered by a transdermal magnetic stimulator (TMS). The film is wrapped around the nerve and bonded to tissue by a laser and without sutures, thereby exploiting the photo-adhesive properties of the chitosan scaffold. We called our device “graft-antenna” to indicate the double role in restoring nerve functionality. In separate experiments, the graft-antenna was applied to unoperated nerves to test the wireless stimulation capability and stability. The graft-antenna steadily triggered compound muscle action potentials (CMAP) for 12 weeks (CMAP~1.3 mV) in unoperated nerves, while no CMAP was elicited by the TMS when the device was not implanted on nerves. In the grafted-nerve groups, better axon regeneration occurred in sciatic nerves with implanted graft-antennas following a stimulation regime of 1 hour, once a week (magnetic field magnitude~0.72 T, pulse duration ~350 μs, repetition rate=1 pulse/sec). Eight weeks post-operatively, myelinated axon count, CMAP and nerve conduction velocity were statistically higher in the graft-antenna group (n=5) than in nerves grafted with the chitosan scaffold without the antenna. The graft-antennas did not migrate throughout the entire experimental periods. Our study showed that the graft-antenna wirelessly stimulates nerves and facilitates axon regeneration without circuitry components or separate electrodes as it relies on a new stimulation mechanism.