Structure function properties of cytoskeletal and extracellular networks: Mechanics and crack propagation*

Living cells and tissues are highly mechanically sensitive and active. Mechanical stimuli influence the shape, motility, and functions of cells, modulate the behavior of tissues, and play a key role in several diseases. In this talk I will discuss the structure function properties of biopolymer networks in cells and tissues that arise due to the interplay of their mechanical and statistical mechanical properties. I will start with articular cartilage (AC), a soft tissue mainly made of network like extra-cellular matrix. AC covers the ends of long mammalian bones, serving to minimize friction and distribute mechanical loads in joints. It is a remarkable tissue: it can support loads exceeding ten times our body weight and bear 60+ years of daily mechanical loading despite having minimal regenerative capacity. I will discuss the physical principles underlying this exceptional mechanical response and crack resistance in AC, and compare our theoretical predictions with experimental results. The second focus of my talk consists of the dynamic mechanical response of actin networks. Actin is a key component of the cytoskeleton essential to cell growth, division, shape change, and motility. To enable this wide range of mechanical processes and properties, networks of actin filaments continuously disassemble and reassemble via active de/re-polymerization. I will discuss how de/re-polymerization kinetics of individual actin filaments translate to experimentally observed time-varying mechanical properties of dis/re-assembling networks. Understanding the mechanical structure function properties of these systems will provide insights into the dynamic response, toughness, and failure of biopolymer neworks in cells and tissues, tissue repair therapies, and design principles for soft robotics.