A finite-element model of inner ear hair bundle micromechanics

Abstract

Understanding hair-cell micromechanics is central to the discussion of mechanotransduction in these cells. This paper presents a finite-element model that characterizes the stiffness and deflection properties of an inner-ear hair bundle. Average morphological dimensions were used for stereocilia height (6, 8, and 10 μm), diameter (0.25 μm), and rootlet separation (0.5 μm) for a single bundle column containing three rows. Stereocilia material properties were described as isotropic, homogeneous, linearly elastic, and nearly incompressible. Young's modulus for the stereocilia ranged from a maximum of actin and down. The column of stereocilia were coupled by linear elastic material modeling tip and lateral links. When the hairs were deflected by a static force applied to the tip of the tallest cilium, the hair-bundle model yielded a stiffness of 9.5 × 10 −4 to 21 × 10 −4 N/m, which was in the range of typical experimental values but approximately a factor of 4–10 times the average of all experimental values. Model parameters such as bundle size, shape, and material properties were systematically varied to determine each component's contribution to bundle stiffness. Additionally, tip-link tensions were determined for a range of deflections in a five cilium model and were shown to be proportionally graded in magnitude along the bundle staircase.