Semester

Summer

Date of Graduation

2025

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Chemical and Biomedical Engineering

Committee Chair

Stephen Cain

Committee Member

Loren Rieth

Committee Member

Xueyan Song

Abstract

Auditory Nerve Interface (ANI) devices, currently in developmental stages, represent an emerging neuroprosthetic approach to restore hearing in severe sensorineural loss patients by directly stimulating the auditory nerve via the Utah Slanted Electrode Array (USEA). Conventional implant leads are comprised of multiple wires made from materials such as platinum-iridium and MP35N stainless steel that are overmolded in an insulative material. These materials are not possible to bond with to electrode array used in the ANI device, necessitating the evaluation of a new material like Au-Pd to ensure its functionality and durability under cyclic stresses. This gap necessitates characterization of alternative leads for ANI durability under cyclic stresses, aligned with standards such as ANSI/AAMI CI86 for cochlear implants. This research evaluates a helical gold-palladium (99% Au,1% Pd) alloy leads encapsulated in NuSil 4211 medical-grade silicone. Uniaxial tensile testing was conducted to examine the silicone's nonlinear elastomeric properties through a Neo-Hookean model, which was imported into ANSYS finite element analysis of the stresses present in a 15˚bend. Finite element analysis revealed peak von mises stresses of 137 MPa in straight wires along the tensile portion, exceeding gold's yield strength, versus 20-24 MPa in helical designs. Comparison with literature predictions of fatigue lifetimes of helical Au-Pd leads estimates 1,000,000 cycles through improved stress distribution. Optical imaging was compared to finite element analysis, with silicone strains aligning with simulated strains. In vitro cyclic fatigue tests in compliance with the CI86 standard issues 100,000 cycles of a 15˚bend at 2 Hz. Measurements of both prototype leads and ANI devices were monitored via electrical impedance below thresholds (120 Ω and 70 kΩ), with the ANI device was quantified via voltage matrices. No channel failures occurred despite pre-existing handling damage, confirming helical geometry's resistance of fatigue and compliance with CI86 requirements. This characterization certifies Au-Pd helical wires as an effective lead for developmental ANI devices, potentially establishing a model for design improvement as well as validating safety toward clinical trials.

Download

Share

COinS