The dominant role of cell surface tension in cytoplasmic fluid mechanics

Mechanical properties of cells are important in various physiological functions. Here we present experiments and theory regarding cell deformation and cytoplasmic fluid dynamics. Our results suggest that cell membrane and cortex tension play a dominant role in the cytoplasmic fluid dynamics. In particular, we see large scale rapid fluid movement (<50ms timescale) along with a small component that equilibrates slowly. A key implication of this finding is that the modeling of cell stiffness measurements should take into account cell surface tension and volume conservation effects, as their contribution to cell stiffness appears to dominate over the deformation of the cytoskeleton. Overall, the results suggest a much more dynamic cell mechanical behavior than viscoelastic and poroelastic models portray.