Therotical Study On Outer Hair Cell Electromotility Based On Flexoelectric Effect

The flexoelectric effect is an electromechanical coupling.For the plasma membrane deflection,the coupling relationship between polarization and curvature is flexoelectricity.The electromechanical coupling response of cochlear outer hair cells under the electrical stimulation is an important basis for the active mechanism of cochlear enlargement.Due to the special structure of outer hair cells,the flexoelectric effect plays a very important role.Based on the special membrane structure of outer hair cell sidewall,the relationship between membrane curvature,axial stretching and transmembrane potential difference was deduced.The effective flexoelectric-piezoelectric linear model of outer hair cells was established,and the effective piezoelectric coefficient was obtained.Combined with momentum conservation and charge conservation,the dynamic governing equation and dynamic electrical equation of the axial vibration under the external electrical stimulation were established.To solve the governing equations in the frequency domain,the isometric condition and zero force condition are considered.Due to the linear small deformation of the flexoelectric model,these two boundary conditions can be superimposed to simulate different loading conditions.The electro-excitation is applied at the end of the cell,and two different electrical boundary conditions,voltage clamp and microchamber voltage,are considered.Under the microchamber voltage condition,the influence of material parameters,excitation current and fluid resistance on electromotility mechanisms of outer hair cells was analyzed and discussed in the frequency domain.The calculation results show that the fluid resistance would restrict the output mechanical power with increasing the stimulus frequency in the high frequency zone.The output mechanical power and peak frequency are related to the cell length,flexoelectric coefficient and electrical impedance at the end of cells,The longer the cells,the larger the flexoelectric coefficients and the larger electrical impedances would lead to the larger the output mechanical power,and the smaller the peak frequency.External excitation current is beneficial to output mechanical power,but it will not affect the efficiency of electro-mechanical conversion.In this paper,the effects of membrane thickness,axial resistance and fluid viscosity on the axial vibration velocity and mechanical work under the voltage clamp boundary conditions were further studied.The end axial velocity,output mechanical power and electro-mechanical conversion in the low frequency domain decreased with increasing membrane thickness,and increased with increasing axial resistance.The fluid viscosity would restrict the end axial velocity and output mechanical power in the high frequency zone.Comparing two electrical boundary conditions,the results show that under the microchamber voltage condition,the output mechanical work decreases with increasing cell base voltage.And the output mechanical power under the microchamber voltage condition is greater than that under the voltage clamp conditionThe work in this paper is helpful to understand the mechanism of the outer hair cells electromotility,and to provide an effective theoretical reference for the sound amplification mechanism in the cochlea.