Finite element analysis of micropipette aspiration considering finite size and compressibility of cells

Abstract

Micropipette aspiration (MA) is widely applied in cell mechanics, however, at small deformations a common model corresponding to the MA is the half-space model wherein the finite cell size and cell compressibility are neglected. This study extends the half-space model by accounting for the influence of cell geometry and compressibility (sphere model). Using a finite element analysis of cell aspiration into a micropipette, an elastic approximation formula of the aspirated length was derived for the sphere model. The approximation formula includes the geometry parameter ξ of the sphere model (ξ= R/a, R is the radius of the cell, and a is the inner radius of the micropipette) and the Poisson’s ratio v of the cell. The results indicate that the parameter ξ and Poisson’s ratio v markedly affect the aspirated length, particularly for smallξ and v. Whenξ→∞ and v→0.5, the approximation formula tends to the analytical solution for the half-space model. In the incompressible case (v = 0.5), within the general experimental range (ξ varying from 2 to 4), the difference between the analytical solution and the approximate one is significant, and is up to 29% of the approximation solution whenξ = 2. Additionally, parametere was introduced to evaluate the error of elastic moduli between the half-space model and sphere model. Based on the approximation formula, theξ thresholds, beyond which e becomes larger than 10% and 20%, were derived.