A network of mutually propelled rods: theory and experiment

Cellular components such as cytoskeletal filaments and motors are the essential constituents of a new class of materials: so called active fluids. We present experiments and theory on a system of stabilized microtubules driven by the molecular motor protein XCTK2. Through photobleaching experiments, we demonstrate that in this system microtubules are aligned along the long direction of the system and travel through the gel at a velocity independent of the local average polarity. We show that this result is most naturally understood in the frameworks of an active gel theory that goes beyond pairwise microtubule interactions and treats the gel as highly cross-linked. Our theory bridges the length scales from the microscopic mechanical behavior of motor-filament interactions to the large scale behavior of the active gel and generalizes to describe different kinds of cytoskeletal assemblies.