#### Seminar 10/5/2011 - Prashant Purohit, University of Pennsylvania: Brownian Motion and Elasticity in Biological Filaments and Networks

Bio: Prashant Purohit got his Ph.D in Applied Mechanics from Caltech in 2002. He is currently an Assistant Professor in Mechanical Engineering and Applied Mechanics at Penn. He is interested in problems at the interface of mechanics, physics and biology. In recent years, he has been working on the entropic elasticity of biomolecules in single molecule experiments, structural transitions in molecules and filament networks and locomotion. Understanding the effects of thermal fluctuations in this context is a major thrust of his research. He is also interested in biological applications of the mechanics of lipid membranes and the mechanics of material interfaces in slender bodies.

Abstract: It is well known that biofilaments at thermodynamic equilibrium under the action of forces and moments fluctuate around their minimum energy configuration due to Brownian motion. This remains true of filaments in networks and gels such as those of actin, spectrin, fibrin or other biopolymers. The thermal motion of these filaments at the microscopic scales manifests itself as entropic elasticity at the macroscopic scales. In this talk we present a theory to efficiently calculate the thermo-mechanical properties of fluctuating heterogeneous filaments and networks. The central problem is to evaluate the partition function and free energy of heterogeneous filaments and networks under the assumption that their energy can be expressed as a quadratic function in the kinematic variables. We analyze the effects of various types of boundary conditions on the fluctuations of filaments and show that our results are in agreement with recent work on homogeneous rods as well as experiments and simulations. We apply similar ideas to filament networks and calculate the area expansion modulus and shear modulus for hexagonal networks.

All seminars are held on Wednesdays from 12:00 noon-1:00 p.m. in the Bowen Hall Auditorium Room 222. A light lunch is provided at 11:30 a.m. in the Bowen Hall Atrium immediately prior to the seminar.

**Location:**
Bowen Hall Atrium

**Date/Time: **10/05/11
at
12:00 pm
- 10/05/11
at
1:00 pm

**Category: **PRISM/PCCM Seminar Series

**Department: **PRISM