Abstract: Recent experiments on molecular motor driven in vitro F-Actin networks have found anomalously large strain ﬂuctuations at low frequency. In addition, the shear modulus of these active networks becomes as much as one hundred times larger than that of the same system in equilibrium. In this talk I develop a theory of both these phenomena using a two-ﬂuid model of a low-density isotropic semiﬂexible network driven by molecular motors. Relying on only simple assumptions regarding the motor activity in the system, I show that one can quantitatively understand both the low-frequency ﬂuctuation enhancement and the nonequilibrium stiffening of the network. I also show the results of new numerical studies of semiflexible networks driven by molecular motors that explore the effects of high motor density in isotropic networks and the effect of nematic order in the active filament network.
These results have implications for the interpretation of microrheology in such active networks including the cytoskeleton of living cells. In addition, they may form the basis for theoretical studies of biomimetic nonequilibrium gels whose mechanical properties are tunable through the control of their nonequilibrium steady-state.
Bio: Professor Levine received his B.S. in Mathematics and Physics at UCLA and received his Ph.D. at UCLA in 1996. He was a postdoctoral researcher at Exxon Research & Engineering Co. from 1996 to 1998. He then was a postdoctoral fellow at the University of Pennsylvania from 1998 to 2001. After a year as a postdoc at UCSB, he joined the faculty of the Department of Physics at the University of Massachusetts, Amherst. In 2005 he joined the faculty of the Department of Chemistry & Biochemistry at UCLA.
Host: Prof. Megan Valentine