Complex Rheology in Single Cells: compression stiffening but shear softening

Cells need to be able to withstand mechanical deformation. Whether in the human body or any other organism, cells are subject to various physical stresses, such as stretching, compression, and shear forces. This resilience is essential for activities including tissue regeneration, adaptation to changing microenvironment and preventing cell damage or even rupture. Our aim is to understand the response of cells to external mechanical cues. For this purpose, we have developed a novel single cell rheology setup that allows us for the first time to make direct comparisons between a living mammalian cell’s response to compression and shear strain. In this work, I have identified the relative contribution of actin and vimentin intermediate filaments in uniaxial compression experiments on single fibroblasts. Our findings reveal that individual fibroblasts undergo stiffening under physiologically relevant compressive strains, but the removal of vimentin reduces this stiffening effect. Furthermore, we present, to our knowledge, the pioneering example of single-cell shear rheology experiments, where we discovered that cells soften when sheared, in stark contrast to their stiffening behaviour under compression. Finally, we propose a minimal constitutive model to elucidate these phenomena and compare our results to semiflexible polymer models used to explain the mechanics of reconstituted cytoskeletal systems.