Flat Electrode Contacts for Peripheral Nerve Stimulation

Abstract

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...

A finite element method framework to model extracellular neural stimulation

“…While some applications are not very specific in which neurons are activated, other applications have much higher demands in targeting specific neurons at particular sites with the proper stimulus strength. To meet those requirements, a lot of research goes into the design of electrode systems (Naples et al 1988, Bucksot et al 2019, Flores et al 2019 and the investigation of cell-type specific activation (Meng et al 2018). Especially when extracellular stimulation is used to restore perception, as in cochlear implants (Bai et al 2019, Potrusil et al 2020 or retinal implants (Rattay andResatz 2004, Werginz et al 2015), high spatial and temporal resolutions are necessary.…”