Cell Mechanical Properties Measured with Micron-Scale Constrictions: Influence of Pressure, Strain and Culture Conditions

Abstract

We describe a method for quantifying the mechanical properties of cells in suspension with a microfluidic device consisting of a parallel array of micron-sized constrictions. Using a high-speed CCD camera, we measure the speed, deformation and entry time into microconstrictions of several hundred cells per minute. Cell entry time Δt into microconstrictions decreases with increasing driving pressure Δp and decreasing strain e according to a power-law. From this power-law relationship, cell elasticity E and fluidity can be estimated. Here, we systematically analyze the influence of constriction size and applied pressure on cell mechanical properties. We find that cell stiffness increases with decreasing constriction size and hence increasing strain e according to E ∼ e. Accordingly, cell stiffness shows pronounced pressure stiffening according to E ∼ Δp. Moreover, we investigate the influence of measurement and cell culture procedures on the resulting cell stiffness and fluidity. We find that the stiffness of adherent cells brought into suspension changes markedly over time. Moreover, cells harvested from confluent cultures are softer compared to cells harvested from sub-confluent cultures. Together, these results highlight the importance of well-controlled measurement and cell culture conditions for obtaining reproducible cell mechanical data.