Fractal microelectrodes for more energy-efficient cervical vagus nerve stimulation.

Vagus nerve stimulation (VNS) has the potential to treat various peripheral dysfunctions, but the traditional cuff electrodes for VNS are susceptible to off-target effects. Microelectrodes may enable highly selective VNS that can mitigate off-target effects, but they suffer from increased impedance. Recent studies on microelectrodes with non-Euclidean geometries have reported higher energy-efficiency in neural stimulation applications. These previous studies used electrodes with mm/cm-scale dimensions, mostly targeted for myelinated fibers. Our study evaluated fractal microelectrodes for VNS in a rodent model (N = 3). We fabricated a thin-film device with fractal and circle microelectrodes to compare their neural stimulation performance on the same radial coordinate of the nerve. Our results show that fractal microelectrodes can activate C-fibers with up to 52% less energy (p = 0.012) compared to circle microelectrodes. To the best of our knowledge, our work is the first to demonstrate a geometric advantage of fractal microelectrodes for VNS in vivo. This article is protected by copyright. All rights reserved.