Soft Condensed Matter and Biological Physics
In addition, since the dynamics of soft matters are diffusive in nature, with characteristic time of t = kT/x 3 , where x is the characteristic length scale of the system, on the order of 1 second, giving the material a unique mechanical properties that can be both viscous and elastic. For example, a lunch Jell-O cube can bounce if drop on the plate and yet, given enough time, it can also conform to the shape of its container. Although the nature of the interactions in the soft condensed matter is relatively simple, the soft matters can reveal themselves in the fasinating structures, from the basic bcc and fcc crystal structures in charged latex suspensions to bi-continuous structures of block-copolymers. To understand the underlying physics of these systems, we use both experimental and theoretical approaches to study the structure, the dynamics and the statistical mechanics of the phase transitions of the soft condense matter in both non-bio and biological systems. The experimental techniques we use include x-ray scattering, light scattering, electron microscopy, fluorescence and confocal optical microscopy, optical tweezers, rheological measurements, as well as the surface forces apparatus. The theoretical studies are based on stochastic modeling, molecular dynamics, and a range of many-body, field theoretical approaches.
One research group studies the nucleation and growth of crystals of globular proteins from an initially homogeneous protein solution. Globular proteins are crucial to the function of living cells and biological processes. Thus biologists are trying to determine the structure of these proteins. The function of proteins depends in large part on their structure. As a consequence, scientists are currently trying to determine their molecular structure using X-ray crystallography. This in turn requires growing high quality crystals from aqueous solutions of proteins, which is very difficult to do. Crystal nucleation is the crucial bottleneck in this process and is known to depend sensitively on the initial conditions of the solution. Current research uses theory and simulation to understand the optimal conditions for crystal nucleation. This requires determining the phase diagrams and nucleation rates for various models of globular proteins in solution, including both continuum phase field models and microscopic models of systems with short range attractive forces.
Endothelial cells form the inner lining of a blood vessel's wall. Under constant flow-induced stress, these cells respond both chemically and mechanically. Understanding the mechanotransduction pathway, by which these responses occurs within a single cell and are communicated between neighboring cells, is important for establishing strategies for atherosclerosis control and treatments. The goal of our research is to establish a quantitative description at cell level on how the cytoskeleton structure responds to a controlled mechanical force on a single cell. Currently our research work is focused on establishing a reliable method to simultaneously determine the intracellular viscoelasticity and the structures of the cytoskeleton network in living cells. An oscillating optical tweezers-based 3D confocal imaging cytorheometer is being developed for conducting this study.
