Intracellular mechanical fingerprint reveals cell type-specific mechanical differences

Living cells are complex entities that perform various tasks with astonishing robustness. While the direct dependence of biological processes on controlled protein expression is well established, we have only begun to understand how intracellular mechanical characteristics guide and support biological function. This is in stark contrast to the expected functional role that intracellular mechanical properties should have for many core cellular functions such as organization, homeostasis, and transport. From a mechanical point of view, cells are complex viscoelastic materials that are continuously driven out of thermodynamic equilibrium, which makes both a physical measurement and mathematical modeling of their properties difficult. Here, we define a "mechanical fingerprint" that can not only characterize the intracellular mechanical state, but also carve out the mechanical differences between cell types with the potential to relate these to proper cell function. By analyzing the frequency-dependent viscoelastic properties and intracellular activity of cells using microrheology, we distilled the complex active mechanical state into just 6 parameters that comprise the mechanical fingerprint. The systematic investigation of the fingerprint illustrates a parameter tuning that could be related to functional cellular requirements. However, the full potential of the mechanical fingerprint is given by a statistical analysis of its parameters across all investigated cell types, which suggests that cells can modify mechanical parameters in a correlated way to position their intracellular mechanical properties within a well-defined phase-space that is spanned between activity, mechanical resistance, and fluidity. This paves the way for a systematic study of the interdependence of biological function and intracellular active mechanics.