Time-domain finite element models of electrochemistry in intracochlear electrodes

Abstract

Most neural prostheses feature metallic electrodes to act as an interface between the device and the physiological tissue. When charge is injected through these electrodes, potentially harmful reactions may result. Others have developed finite element models to evaluate the performance of stimulating electrodes in vivo. Few however, model an electrode-electrolyte interface, and many do not address electrode corrosion and safety concerns with respect to irreversible reactions. In this work, we successfully develop a time domain finite element model of cochlear implant electrodes that incorporate oxygen reduction and platinum oxidation reactions. We find that when electrodes are stimulated with current pulses (0.5 mA, 25 µs), faradaic reactions may cause an increase in the peripheral enhancement of the current density.

Modeling the effects of electrode recessing on electrochemical safety in cochlear implant electrodes

“…Greater detail of the modeling used in this paper has been previously documented [12]. The methodology is briefly outlined here, with changes relevant to the current study.…”

“…Tissue damage may also occur by "mass action" inducing excitotoxicity in the excitable tissues if the charge delivered is beyond safe limits [4], [8], [9]. Previous works have shown that current concentrates at high curvature regions of electrode geometries, such as the crests of high perimeter electrodes [10], tips of needle electrodes [11], and the vertices of CI-like half-band electrodes [12]. Early models suggested recessing the electrode to eliminate the non-uniform current distribution on the electrode surface [5], [6], based on studies of planar disc electrodes.…”

“…These models have ignored or provided relatively simple representations of the electrodeelectrolyte interface. Recent studies have effectively utilized the finite element (FE) method to model the current density distributions at the electrode-tissue interface in the broader context of electrode safety [11], [12], [17], but with simplified electrode geometries. This study aims to use the FE method to model half-band CI electrodes at various recess depths, and analyze their effect on the levels of irreversible faradaic reactions.…”

Finite element modelling of cochlear electrical coupling

“…Some conductivities are from Briaire and Frijns (2000), who refer to Finley et al (1990) and Suesserman (1992). Sue et al (2013) cite Cantrell et al (2008) as giving perilymph properties of conductance r ¼ 1420 mS/m and relative permittivity e r ¼ 78. It has been assumed that inter-species variation in these properties is insignificant.…”

“…This ability has, for example, permitted accurate modelling of cochlear micro-mechanics (Ni et al, 2016). Electrical FEMs have been used to study the behaviour of cochlear implants (Briaire and Frijns, 2000;Choi and Wang, 2014;Saba, 2012;Sue et al, 2013;Tran et al, 2011;Tran et al, 2013). Harland et al (2015) present a very detailed model of OHC membranes.…”