(686g) Self-Organization and Division in Active Biopolymer Droplets

Biomolecules self-assemble into a myriad of soft materials that work in concert to support physiological processes. One critical soft material is the actin cytoskeleton, a viscoelastic material composed of cross-linked actin filaments. We recently demonstrated a predominately viscous phase of cross-linked actin, in which cross-linker condenses dilute short actin filaments into spindle shaped droplets, or tactoids. The cross-linker, which acts an attractive interaction analogous to a molecular cohesion, controls the tactoid shape and dynamics. Using a continuum model of an anisotropic liquid, we relate the shape and dynamics to an interfacial tension and viscosity. Cellular actin assemblies are driven from equilibrium by molecular motors, biopolymer particles that bind to actin filaments and exert forces capable of translocating filaments. We find that these active particles self-organize within tactoids, cluster, and divide tactoids. We investigate the influence of activity on particle self-organization and tactoid division and present a simple model of an adhesive particle in an anisotropic liquid droplet. Our results demonstrate self-organization in anisotropic biopolymer assemblies and provide insight into design principles for complex, macromolecular liquid phases.