The majority of available systems for vagus nerve stimulation use helical
stimulation electrodes, which cover the majority of the circumference of the
nerve and produce largely uniform current density within the nerve. Flat
stimulation electrodes that contact only one side of the nerve may provide
advantages, including ease of fabrication. However, it is possible that the flat
configuration will yield inefficient fiber recruitment due to a less uniform
current distribution within the nerve. Here we tested the hypothesis that flat
electrodes will require higher current amplitude to activate all large-diameter
fibers throughout the whole cross-section of a nerve than circumferential
designs. Computational modeling and in vivo experiments were performed to
evaluate fiber recruitment in different nerves and different species using a
variety of electrode designs. Initial results demonstrated similar fiber
recruitment in the rat vagus and sciatic nerves with a standard circumferential
cuff electrode and a cuff electrode modified to approximate a flat
configuration. Follow up experiments comparing true flat electrodes to
circumferential electrodes on the rabbit sciatic nerve confirmed that fiber
recruitment was equivalent between the two designs. These findings demonstrate
that flat electrodes represent a viable design for nerve stimulation that may
provide advantages over the current circumferential designs for applications in
which the goal is uniform activation of all fascicles within the nerve.
Background: The growing use of neuromodulation techniques to treat neurological disorders has motivated efforts to improve on the safety and reliability of implantable nerve stimulators. New Method: The present study describes the ReStore system, a miniature, implantable wireless nerve stimulator system that has no battery or leads and is constructed using commercial components and processes. The implant can be programmed wirelessly to deliver charge-balanced, biphasic current pulses of varying amplitudes, pulse widths, frequencies, and train durations. Here, we describe bench and in vivo testing to evaluate the operational performance and efficacy of nerve recruitment. Additionally, we also provide results from a large-animal chronic active stimulation study assessing the long-term biocompatibility of the device. Results: The results show that the system can reliably deliver accurate stimulation pulses through a range of different loads. Tests of nerve recruitment demonstrate that the implant can effectively activate peripheral nerves, even after accelerated aging and post-chronic implantation. Biocompatibility and hermeticity tests provide an initial indication that the implant will be safe for use in humans. Comparison with Existing Method(s): Most commercially available nerve stimulators include a battery and wire leads which often require subsequent surgeries to address failures in these components. Though miniaturized battery-less stimulators have been prototyped in academic labs, they are often constructed using custom components and processes that hinder clinical translation.
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