Evaluation of gold helical microwire structure electrode for long-term rodent nerve stimulation

Objective.The development of electrodes for chronic peripheral nerve stimulation faces several challenges, including complex compositions, intricate manufacturing processes, and high costs associated with the availability and fabrication of suitable materials. These limitations hinder the accessibility and feasibility of producing effective devices for chronic preclinical studies. This study evaluated the feasibility of a simple-to-manufacture gold helical microwire structure electrode (Au-HMSE) for peripheral nerve stimulation, electromyography (EMG) recording, and preliminary tissue response on the rat sciatic nerve.Approach.Manufactured electrodes were used for up to 8 weeks in rats for nerve stimulation and EMG recordings, with electrode-tissue impedances and motor thresholds measured to assessin vivostability and feasibility. Evoked motor responses were measured via gastrocnemius muscle activity and ankle torque. Terminal histology was performed at 12 weeks to assess chronic tissue response to the implanted electrodes.Main results.Implanted electrodes with impedances <10 kΩ effectively evoked motor responses in monopolar and bipolar configurations and successfully recorded EMG activity. Gastrocnemius activation overlapped with off-target motor responses, likely due to the electrode's size relative to rat nerve anatomy and the absence of anchoring, which may have allowed migration. High impedance failure appeared related to interconnects between electrodes and tunneled leads and at solder joints in the stimulating and recording setup. Histology showed typical fibrotic encapsulation, with the helical design promoting tissue in-growth around the microwires, creating a high surface area electrode-tissue interface.Significance.This study evaluated the early feasibility of Au-HMSE for chronically implanted rodent nerve stimulation and EMG recordings. While gold electrodes are non-standard for chronic stimulation, the construction of these devices may be appropriate for the evaluation of chronic peripheral nerve stimulation in the preclinical setting due to their simple composition, manufacturing, and availability of gold microwire as a raw material. The findings provide valuable insights for developing future implantable leads used for peripheral nerve stimulation.