A finite-element model of inner ear hair bundle micromechanics

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 sterocilia height (6, 8, and 10 microns), diameter (0.25 microns), and rootlet separation (0.5 microns) 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 x 10(-4) to 21 x 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.