Alex Levine, UCLA

Cell Quakes: The mechanics of active polymer networks and microrheology in living cells

Friday February 22, 4pm, Phillips 332
(refreshments served in Phillips 330 starting at 3:30)

Abstract:
The mechanics of the in vivo cytoskeleton is controlled in part by the details of its non-equilibrium steady-state. In this ``active'' material, molecular motors (e.g. myosin) exert transient contractile stresses on the F-actin filament network. Since microrheology traditionally relies of the linear response properties of the soft materials in thermal equilibrium, this departure from equilibrium has profound implications for the interpretation of microrheological data from the interior of living cells and in vitro active networks. In active networks, such as the in vitro systems of Mizuno et al. [Science 315 (5810) pp. 370-373 (2007).] and in living cells, the underlying theoretical foundation of the interpretation of microrheology -- the Fluctuation-Dissipation theorem -- does not apply. New ideas are needed.

In this talk, I review microrheology, and then discuss a new theoretical interpretation of microrheology in active (i.e. molecular motor driven) networks. I also explore how molecular motor activity can reversibly control the elastic properties of these active gels. The cytoskeleton points towards the development of new biomimetic materials whose elastic properties can be tuned by controlling the material's non-equilibrium steady-state.