Effects of different electrodes used in bone-guided extracochlear implants on electrical stimulation of auditory nerves in guinea pigs

Chien-Hao Liu; Yung-Shan Lu; Po-Chun Chen; Chia-Fone Lee

doi:10.4103/tcmj.tcmj_46_20

Effects of different electrodes used in bone-guided extracochlear implants on electrical stimulation of auditory nerves in guinea pigs

Tzu Chi Med J. 2020 Jul 13;33(1):42-48. doi: 10.4103/tcmj.tcmj_46_20. eCollection 2021 Jan-Mar.

Authors

Chien-Hao Liu¹, Yung-Shan Lu¹, Po-Chun Chen², Chia-Fone Lee^{3

4}

Affiliations

¹ Department of Mechanical Engineering, National Taiwan University, Taipei, Taiwan.
² Department of Materials and Mineral Resource Engineering, Institute of Materials Science and Engineering, National Taipei University of Technology, Taipei, Taiwan.
³ Department of Otolaryngology, Hualian Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Hualien, Taiwan.
⁴ Department of Otolaryngology Head and Neck Surgery, School of Medicine, Tzu Chi University, Hualien, Taiwan.

Abstract

Objective: Conventional cochlear implants provide patients who are deaf with hearing via electrical intracochlear stimulations. Stimulation electrodes are inserted into the cochlea through a cochleostomy or round window membrane (RWM) approach. However, these methods might induce cochlear ossificans and loss of residual hearing by damaging inner ear structures. To avoid an invasive electrode insertion, we developed a novel bone-guided extracochlear implant that stimulated the auditory nerves between the cochlear bones and the RWM to prevent cochlea damage. Power consumption plays an important role in wireless implantable electronic devices. Therefore, we aimed to investigate the effects of different electrodes on the stimulating threshold currents of the auditory nerve and the power consumption of bone-guided extracochlear implants using a commercial stimulator.

Materials and methods: Inert aurum (Au) electrodes were compared with biocompatible platinum (Pt) and iridium oxide (IrO_x) electrodes in practical implantable applications. IrO_x electrodes were used for their high-charge storage capacity, low impedance, and biocompatibility. The electrodes were fabricated via sputtering and were experimentally characterized with cyclic voltammetry and then examined using in vivo tests.

Results: Based on electrical auditory brainstem responses, IrO_x electrodes yielded lower acoustic nerve-stimulating threshold currents (132 μA) compared with Au electrodes (204 μA). IrO_x electrodes also had a lower acoustic nerve stimulating threshold current (132 μA) compared with Pt electrodes (168 μA).

Conclusion: As expected, IrO_x electrodes were beneficial in the development of multielectrode bone-guided extracochlear implants, with the lowest acoustic nerve-stimulating threshold and current consumptions compared with Au and Pt electrodes.

Keywords: Current consumption; Cyclic voltammetry; Implantable electronics; Iridium oxide electrode; Stimulation threshold.