Biophysics

We use our expertise and our experimental tools to investigate the properties of biological materials and to study the behavior of cells. Much of our focus is on developing an understanding of the mechanical properties of biopolymer networks, formed by reconstituting proteins into gelled networks. These include networks of actin, microtubules, intermediate filaments, fibrin and collagen. We combine visualization of the network structure with probes of their mechanical properties to understand the nature of these properties. We also add molecular motors to the networks to investigate the properties of active gels. In addition, we extend our investigations to study the mechanical properties of cells and collections of cells. We also have an effort in understanding the growth and physical properties of biofilms.

Mechanical properties of composite cytoskeleton networks: Cytoskeleton is composed of three components: actin, microtubule and intermediate filament. To study cytoskeleton mechanics, the method of reconstituting it in salt buffer has been employed for a long history. Though mechanics of single component, or any two components of composite network has been known well, the system of triple components of cytoskeleton networks is rarely known: what kind of mechanical role does one sort of filament play in the background of the other two? How do these three components work in concert, from the perspective of physics? My work is to reconstitute cytoskeleton filament network of all of the three different components in salt buffer, be able to have a precise control of morphology of each filament, and rely on the methods of bulk and micro rheology to study mechanical properties of this composite biopolymer networks. Yinan Shen 

Microrheology in cells and networks: Cells are mechanical objects, with mechanics largely determined by their biopolymer cytoskeleton. We characterize local mechanics in cells and reconstituted biopolymer networks using active optical tweezer microrheology. We aim to determine the mechanical role of the biopolymers, as well as the effects of molecular motors and enzymes on the mechanics of the networks. Helen Wu, Mikkel Jensen, Ming Guo

Mechanics of vimentin intermediate filament networks: Intermediate filaments (IF) make up a component of the cytoskeleton that has received much less attention than actin and microtubules. I am studying the mechanics of vimentin, a Type III IF, using bulk and microrheological techniques as well as traction force microscopy on single cells. I am interested in its contribution to cell stiffness and its role in cell mechanosensitivity. Helen Wu