CPM Seminar

Diffusion and deformation in biopolymer networks

Jeffrey Urbach

Department of Physics
Georgetown University

I will describe our efforts to use fast confocal imaging to study the dynamics of biopolymer networks. One application is an extension of fluorescence correlation spectroscopy (FCS) that allows us to spatially map diffusion coefficients or flow velocities at thousands of independent locations simultaneously. We have applied this technique to microspheres diffusing in Type 1 collagen, and find complex spatially-varying diffusion caused by hydrodynamic and steric interactions with the collagen matrix. These results show evidence for anomalous diffusion, stochastic transport where the mean squared displacement does not grow linearly with time. I will discuss different techniques for analyzing this behavior, and compare results from different types of networks.

I will also describe our recent measurements of the distortions of biopolymer matrices induced by microspheres in an oscillating optical trap. We find that networks of unbundled actin filaments show only very short range deformation. Networks of stiffer polymers, such as collagen or bundled actin, exhibit distortions over much larger distances, but the strain field is very inhomogeneous. These results, consistent with recent theoretical studies, suggest that the mechanical properties of cells and tissues cannot be accurately modeled as continuum viscoelastic media.