Encoding Shape, Structure, Mechanics and Dynamics of a Soft Solid with an Active Fluid

Statistical mechanics describes how one can design targeted macroscale properties of equilibrium assemblages by controlling microscopic interactions. In comparison, our understanding of how large-scale structure and dynamics occur away from equilibrium is less complete. We describe a hierarchical self-organizing process of remarkable complexity. Starting with a uniform mixture of microtubule-based active fluid and passive actin filaments, we observe the emergence of complex structures and dynamical patterns on length scales ranging from nanometers to millimeters. Active fluids sculpt the structure, shape, mechanics, and dynamics of the actin network. Eventually, one observes the formation of macroscopically large actin-based thermalized membranes whose out-of-plane bending rigidity and in-plane oscillatory patterns are driven by the enveloping microtubule-based active fluid. Taken together, these experiments demonstrate a need for developing a theoretical understanding of out-of-equilibrium self-organizing processes.