Finite Element Modeling of Viscoelastic Cochlear Components Under Acoustic and Blast Wave Transmission

Veterans in the U.S. suffer from tinnitus and hearing loss resulting from acoustic and blast overpressure exposure. Given the difficulty of studying the mechanical behavior of the micron-level hair cells in the organ of Corti (OC) within the fluid-filled inner ear, finite element (FE) modeling has been utilized for investigation. Recently, fully fluid-solid coupled FE models of the OC with linear elastic material properties to simulate the blast wave transmission have been reported. However, the viscoelastic material properties of the components in the OC that could affect the mechanical responses have not been accurately represented in previous studies. A microscale FE model of the OC was developed, consisting of sensory hair cells, membranes, and structural cells. The model represents a cross-sectional slice of the cochlea located 16.75 mm from the base of its basilar membrane (BM). The viscoelastic material models were derived using experimental data of the outer hair cells (OHCs) and tectorial membrane from literature. BM displacements of 2 cases, namely a 90 dB acoustic wave at 800 Hz and a 30 kPa blast overpressure, were applied as input to the microscale OC model. The stress and strain on the OHCs were predicted and compared between a linear elastic OC model. The OC model reported stress and strain on the OHCs in both the acoustic wave and blast simulations. In the acoustic wave transmission, the viscoelastic material properties introduced a phase lag and reduced maximum stresses and strains in the OHCs. In the blast simulation, the viscoelastic model showed its peak stresses and strains at different times than the linear elastic model and also presented a stress relaxation effect because of the viscoelasticity. The FE model with viscoelastic material properties for OC components has improved the accuracy of model prediction for acoustic and blast wave transmissions into cochlear hair cells. The model-derived phase and time lag and changes in maximum strain may affect the likelihood of biomechanical injury to the inner ear. This model is another step toward developing a comprehensive and anatomically accurate multiscale model of the human ear.