The stiffness of tissues in which cells are embedded has effects on cell structure and function that can act independently of or override chemical stimuli. Most measurements of tissue stiffness, including those made by diagnostic devices, report elastic moduli measured at a single frequency and at a low strain. Such measurements are valuable for comparing different tissues or changes resulting from pathology, but are inadequate to define the mechanical environment to which cells respond in vivo. Tissues and the cells within them are subjected to a range of strains in vivo depending on their elastic modulus and the forces applied to them. These strains often exceed the range of linear viscoelasticity that is reflected in measurements at small strains. Rheologic measurements of liver, brain, and adipose tissues over a range of shear, compressive, and elongational strains show that the viscoelastic response of these tissues differs from that of synthetic hydrogels or blood clots that have similar elastic moduli when measured in the linear range. The shear moduli of soft tissues generally decrease with increasing shear or elongational strain, but they strongly increase under uniaxial compression at stresses in the range of those produced by interstitial pressures in disease states such as cancer and fibrosis. The mechanisms leading to the unusual strain-dependent rheology of soft tissues do not appear to be explained by current models of polymer mechanics.
About the Speaker
Paul Janmey is Professor of Physiology, Physics, and Bioengineering at the Institute of Medicine and Engineering at the University of Pennsylvania. He received his Ph.D. in physical chemistry from the University of Wisconsin and completed his postdoc at the Hematology-Oncology Unit at Massachusetts General Hospital. Dr. Janmey’s research interests include the interaction between cytoskeletal and extracellular matrix stiffness, effects of substrate mechanics on cell structure and function, phosphoinositide signaling for actin assembly, fibrin-based materials for wound healing, and intermediate filament assembly and mechanics.
Hosts: Professors Taher Saif and Amy Wagoner Johnson
* Check http://mechanical.illinois.edu for updated information. This seminar counts toward the requirements for ME 591 BIG.