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BP: Fachverband Biologische Physik

BP 33: Active cell and tissue mechanics (focus session) I

BP 33.6: Vortrag

Donnerstag, 3. April 2014, 11:30–11:45, HÜL 386

Living cells: Active at long times but passive at short times — Wylie Ahmed, Matthias Bussonnier, and •Timo Betz — Physical-Chemistry-Curie, Institut Curie, Paris, France

Living cells are per definition out of thermodynamic equilibrium as they consume energy to maintain their organization. This has an important impact on their mechanical properties and on the measurement of these properties. Up to now, the correct description of cell mechanics by using passive techniques such as particle tracking based microrheology inside living cells remains a challenge, since these measurements suffer from incomplete knowledge about the active contribution of cellular dynamics. Active microrheology, where the probe particles are moved by a controlled force, provides a solution to this problem since it offers independent access to the mechanical properties. We combine active and passive microrheology to directly determine the active contribution of intracellular dynamics. These experiments suggest that at short timescales equilibrium thermodynamics hold, while it is violated in long timescales. Using phagocytosed beads and cell organelles we can determine the timescale of this difference which is found to be dependent of the cell type and varies between ≈ 5−100ms. Using this information we exploit the high frequency regime to calibrate the optical forces on cell organelles which gives direct and simple access to the mechanical properties important for organelle transport. This method can be also used in 3D cultures to directly measure the differences in intracellular mechanics for 2D versus 3D cultures. Hence, we can show that at short timescales even a living cell behaves like dead material.