Nanorheology and Nanoindentation Revealed a Softeningand an Increased Viscous Fluidity of Adherent Mammalian Cells upon Increasing the Frequency

Abstract

[EN] The nanomechanical response of a cell depends on the frequency at which thecell is probed. The components of the cell that contribute to this property andtheir interplay are not well understood. Here, two force microscopy methodsare integrated to characterize the frequency and/or the velocity-dependentproperties of living cells. It is shown on HeLa and fibroblasts, that cells softenand fluidize upon increasing the frequency or the velocity of the deformation.This property was independent of the type and values (25 or 1000 nm) of thedeformation. At low frequencies (2-10 Hz) or velocities (1–10μms−1), theresponse is dominated by the mechanical properties of the cell surface. Athigher frequencies (>10 Hz) or velocities (>10μms−1), the response isdominated by the hydrodynamic drag of the cytosol. Softening andfluidization does not seem to involve any structural remodeling. It reflects aredistribution of the applied stress between the solid and liquid-like elementsof the cell as the frequency or the velocity is changed. The data indicates thatthe quasistatic mechanical properties of a cell featuring a cytoskeletonpathology might be mimicked by the response of a non-pathological cellwhich is probed at a high frequency.