Title: Nonlinearities of biopolymer gels increase the range of force transmission
Speaker: Dr Xinpeng Xu Department of Materials and Interface, Weizmann Institute of Science, Israel
Time: 2015年9月22日周二下午4:00-5:00
Place：数学楼二楼学术报告厅
Abstract: Many types of cells (e.g., skin, muscle, cartilage) actively adhere to their surrounding extracellular matrix (ECM) and probe its mechanical properties by applying contractile forces. These cellular forces can lead to deformation (strain) and reorganization (fiber alignment) of the matrix, while matrix remodeling feeds back to modulate cell contractility and can thus impact various cellular functions, e.g., migration, differentiation, apoptosis and even gene expression. The ECM is a gel-like assembly of crosslinked, semiflexible, protein filaments, e.g., collagen, fibrin, and elastin. The mechanical properties of such biopolymer gels are quite different from synthetic ones containing flexible filaments, e.g., polyacrylamide gels. Recent experiments and simulations show that cells in fibrous biopolymer gels can sense and respond to mechanical forces over distances (250-1000 μm) much longer than those (20-25 μm) in synthetic gels. Such long-range mechanosensing is essential for cells to function properly. In this talk, I will present our recent theory predicting how cells deform their ECM or more generally, how internal forces are transmitted in fibrous biopolymer gels. We present a simple three-chain model of biopolymer gels that includes their microstructural nonlinearities–stiffening under extension and softening (due to buckling) under compression. We predict the elastic anisotropy induced by both external as well as internal (e.g., due to cell contractility) stresses in biopolymer gels. We show how the stretch-induced anisotropy and the strain-stiffening nonlinearity increase both the amplitude and power-law range of transmission of internal, contractile, cellular forces, and relate this to recent experiments.