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.
11The majority of available systems for nerve stimulation use circumferential stimulation electrodes inside 12 an insulating cuff, which produce largely uniform current density within the nerve. Flat stimulation 13 electrodes that contact only one side of the nerve may provide advantages including simpler 14 implantation, ease of production, and more resistance to mechanical failure. However, it is possible that 15 the flat configuration will yield inefficient fiber recruitment due to a less uniform current distribution 16 within the nerve. Here we tested the hypothesis that flat electrodes will require higher current amplitude 17 to achieve effective stimulation than circumferential designs. Computational modeling and in vivo 18 experiments were performed to evaluate fiber recruitment in different nerves and different species using 19 a variety of electrode designs. Initial results demonstrated similar fiber recruitment in the rat vagus and 20 sciatic nerves with a standard circumferential cuff electrode and a cuff electrode modified to 21 approximate a flat configuration. Follow up experiments comparing true flat electrodes to 22 circumferential electrodes on the rabbit sciatic nerve confirmed that fiber recruitment was equivalent 23 between the two designs. These findings demonstrate that flat electrodes represent a viable design for 24 nerve stimulation that may provide advantages over the current circumferential designs for applications 25 in which the goal is uniform activation of the nerve. 26 3 27 4 49 greater resistance to mechanical failure, and reduce cost of production. However, this electrode 50 geometry provides contact with only a portion of the circumference of the nerve, which is likely to 51 produce non-uniform stimulation. This would yield increased activation of axons near the contacts and 52 reduced activation of distant axons. The resulting polarity would lead to a lower threshold and higher 53 point of saturation and thus a less steep recruitment curve. Whether the magnitude of this effect would 54 substantially influence efficacy is not known. A direct comparison of flat and circumferential cuff 55 electrodes is needed to determine if flat contacts represent a practical alternative for nerve stimulation.56 57 5 58 Materials and Methods 59 Computational Model 60 A 3D model was created in Comsol (COMSOL Multiphysics® Version 5.3) consisting of a nerve with a 61single fascicle, perineurium, epineurium, two platinum contacts, an insulating cuff, and ambient 62 medium, similar to previous studies (14,15). In a subset of models, a multi-fascicle nerve containing five 63 fascicles was used ( Fig. 9). The nerve had a diameter of either 0.9 mm for the rat sciatic, 0.4 mm for the 64 rat vagus, or 3 mm for the rabbit sciatic (16-18). Perineurium thickness was set to 3% of the fascicle 65 diameter (19). Epineurium thickness was set to 0.13 mm for the rat sciatic, 0.1 mm for the rat vagus, and 66 0.43 mm for the rabbit sciatic (20-22). To investigate the effect of nerve size, the rabbit sciatic mode...
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