Controlling assembly and oscillations of elastic membranes with an active fluid

We use the chaotic flows generated by a microtubule-based active fluid to assemble self-binding actin filaments into a thin elastic sheets. Starting from a uniformly dispersed state, active flows drive the motion of actin filaments, inducing their bundling and formation of bundle-bundle connections that ultimately generate an elastic network. The emerging network separates from the active fluid to form a thin elastic sheets suspended at the sample midplane. At intermediate times, the active fluid drives large in-plane and out-of-plane deformations of the elastic sheet which are driven by low-energy bending modes. Self-organized sheets eventually exhibit centimeter-sized global spontaneous oscillations and traveling waves, despite being isotropically driven on micron lengths by the active fluid. The active assembly generates diverse network structures which are not easily realizable with conventional paradigms of equilibrium self-assembly and materials processing. Self-organized mechanical sheets pose a challenge for understanding of how a hierarchy of structure, mechanics, and dynamics emerges from a largely structureless initial suspension of active and passive microscopic components.