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Fluid Dynamics Seminar

Thursday, Jan. 31, 2013, 4:00 PM
Cullimore, Room 611
New Jersey Institute of Technology

Rheology of cytoskeleton: from mesoscopic mechanics to macroscopic instabilities

Len Pismen

Department of Chemical Engineering - Technion, Israel Institute of Technology

Abstract

Cytoskeleton is the principal structural element of eukaryotic cells responsible for their integrity, reshaping, proliferation and motion. Its main building blocks are actin filaments - semiflexible polymer chains cross-linked into a network and prestressed by molecular motors. Cytoskeleton is a highly complex polar medium characterized by nonlinear viscoelastic response that may be modified by external forces or chemical signals. It is an active medium driven out of equilibrium by ATP hydrolysis, needed both for continuous polymerization (treadmilling) and for generating stress induced by myosin motors.

The talk concentrates upon specific rheological properties of cytoskeleton caused by the presence of motors, which result both in generation of active forces and in flexible anisotropic response to external forcing, that may lead to opposite effects of fluidization or reinforcement. A mesoscopic description of cytoskeleton is aimed at deducing its macroscopic response based on microstructural characteristics, including chemo-mechanical interactions related to motor activity and assembly or disintegration of acto-myosin stress cables.

On the macroscopic level, the challenging problem of cytoskeleton mechanics lies in strong interactions among the three interconnected fields - network polarization, elastic deformation, and motor activity causing prestress and agitation of the network. We explore nonlinear dynamics of an active polarizable layer based on generic continuum model with neo-Hookean elasticity and chemo-mechanical interactions. The model exhibits two kinds of instabilities: a stationary long wavelength instability can be observed if the medium is activated by expansion, while an oscillatory short wavelength instability can occur in the case of compressive activation. The former instability may lead to the spontaneous polarization effect, and the latter, to patchiness and oscillations in tissue reshaping.