Finite Element Analysis of the Effect of Actuator Coupling Conditions on Round Window Stimulation

Abstract

The finite element (FE) method was used to analyze the effect of coupling conditions between the actuator and the round window membrane (RWM) on the performance of round window (RW) stimulation. A FE model of the human ear consisting of the external ear canal, middle ear and cochlea was firstly developed, and then validation of this model was accomplished through comparison between analytical results and experimental data in the literature. Intracochlear pressure were derived from the model under normal forward sound stimulation and reverse RW stimulation. The equivalent sound pressure of RW stimulation was then calculated via comparing the differential intracochlear pressure produced by the actuator and normal ear canal sound stimulus. The actuator was simulated as a floating mass and placed onto the middle ear cavity side of RWM. Two aspects about the actuator coupling conditions were considered in this study: (1) the cross-section area of the actuator relative to the RWM; (2) the coupling layer between the actuator and the RWM. The results show that smaller actuator size can improve the implant performance of RW stimulation, and size requirements of the actuator can also be reduced by introducing a coupling layer between the actuator and RWM, which will benefit the manufacture of the actuator.

Evaluation of Round Window Stimulation Performance in Otosclerosis Using Finite Element Modeling

“…The material properties defined for the cochlea were elastic modulus, density, and Poisson's ratio. Similarly, the material properties of the cochlear components were initially assumed according to published literatures [ 13 , 22 ]. Then, these parameters were checked and some of them modified in the validation process.…”

“…Its vibration cannot reflect the inner dynamical properties of the cochlea accurately. As the intracochlear differential pressure across the cochlear partition at the base of the cochlea is proved to be a sensitive measure of the cochlear input [ 29 ] and the vibration of the basilar membrane can be deduced by the intracochlear pressure [ 30 , 31 ], the intracochlear pressure was measured by many researchers to uncover the mechanism of cochlear mechanics [ 29 , 32 , 33 ] and evaluate the middle ear implant's performance [ 13 , 34 , 35 ]. Thus, in this paper, we also used the intracochlear pressure to assess the round window stimulation's performance.…”

“…Thus, in this paper, we also used the intracochlear pressure to assess the round window stimulation's performance. Specifically, we used the equivalent sound pressure (ESP), which is expressed as [ 13 ] where P SV F , P ST F are the fluid pressures in the cochlear scala vestibule and scala tympani under forward sound stimulation (90 dB SPL applied onto the eardrum) and P SV R , P ST R are the fluid pressures in the scala vestibule and scala tympani under reverse RW stimulation (50 μ N driving force applied onto the round window membrane [ 12 , 13 ]). The detailed derivation of ( 1 ) can be found in [ 13 ].…”

“…Experiments included variations such as different orientation, intervening materials between the RW and the actuator, overlaying materials, and pretension force applied on the actuator. In addition to the experimental measurements on temporal bones, the finite element models of the human ear were also used by Zhang and Gan [ 12 ] and Tian et al [ 13 ] to investigate the effect of the actuator size and the coupling conditions, respectively. However, all of the variables are device-loading variables.…”

Influence of ossicular chain malformation on the performance of round-window stimulation: A finite element approach

“…In addition to experimental studies, finite element (FE) analyses were also conducted to study the influence of the actuator’s mass, cross-sectional area, and coupling condition on the RW stimulation. 17–19 Whereas, all these reports mainly focus on the impact of the actuator’s loading parameters; the influence of patients’ ossicular chain lesions was not studied.…”