Active Composites of Actin and Kinesin-driven Microtubules

Two major structural proteins, actin and microtubules, form multiple co-existing and interpenetrating filamentous protein networks within the cell cytoplasm. The out-of-equilibrium active reorganization of these structures by molecular motors is necessary for basic physiological processes such as cell division, cell motility, and environmental sensing. While the passive structure and mechanics of such materials have been well documented, the effects of their steady-state out-of-equilibrium reorganization is a site of current research. To demonstrate some of the mechanics governing the active reorganization of these materials, we have built a polymer blend of kinesin-driven microtubule networks which reorganize a passive entangled actin network. We find both the mechanics of the actin network as well as its initial structure can have dramatic effects on the steady-state behavior of the system. To capture the range of behaviors, we build a state diagram which captures the non-equilibrium phenomena we observe.