Hierarchical phases of filamentary active matter

Abstract

Studies of active matter seek to identify the properties of materials made from dense collections of animate objects. Within this effort, one promising direction aims to reconstruct the remarkable properties of living organisms in simplified materials, using well-characterized biochemical building blocks. This thesis describes the generation of dynamic structures from cytoskeletal components: micron-long stiff polar filaments mediated by molecular motors. I show that a filament tip-accumulating motor can drive the hierarchical organization of filaments into dynamic states reminiscent of microphase separation generated by heterogeneous amphiphiles. The formation of a diverse number of states suggests that the form of the active stress is not solely dictated by the properties of individual motors and filaments but is also contingent on the constituent's concentrations and spatial arrangement. I then investigate the dynamic states of dense locally nematic networks mediated by filament-aligning motor proteins. I relate the transitions in dynamics to changes in the microscopic symmetries of particles through a series of photobleaching, second-harmonic generation, and small-angle x-ray scattering experiments. Together, these two systems pose fundamental questions in active matter physics, while also providing a promising experimental platform for creating self-regulating soft materials.