Optical twisting to monitor the rheology of single cells.

BACKGROUND: Biological cells exhibit complex mechanical properties which determine their responses to applied force.

OBJECTIVE: We developed an optical method to probe the temporal evolution of power-law rheology of single cells.

METHODS: The method consisted in applying optically a constant mechanical torque to a birefringent microparticle bound to the cell membrane, and observing dynamics of the particle's in-plane rotation.

RESULTS: The deformation dynamics of the membrane followed a power law of time, which directly relates to cytoskeletal prestress as reported in the literature. The temporal evolution of this rheological behaviour, over time scales of several minutes, showed strong variations of the exponent on single adherent cells not subject to any specific treatment.

CONCLUSIONS: The consistent observation of variations in the exponent suggests that, in their normal activity, living cells modulate their prestress by up to three orders of magnitude within minutes.