Modeling composite cytoskeletal networks using effective medium theory*

The mechanical response of most eukaryotic cells is due to their cytoskeleton, a polymeric scaffold made up of two major types of biopolymers, actin filaments (F-actin) and microtubules, which have very different mechanical properties. The cytoskeleton is responsible for a number of cellular functions including maintaining cell shape, rigidity, and facilitating movement. Here we seek to investigate, understand, and predict the structure-function properties of engineered cytoskeletal scaffolds with tunable mechanics. We study composite networks of F-actin and microtubules using an effective medium theory, and characterize their mechanical response using rigidity percolation theory. We obtain the shear rigidity of these networks as a function of the concentrations of F-actin and microtubules, the type of crosslinking, and the concentration of the crosslinkers. Our results may help to elucidate the design principles of smart biopolymer composites with adaptive mechanical properties.