Spatiotemporal control of Mechanical phase transition in 3D active networks

Activity-driven self-assemblies of crosslinked networks of cytoskeletal filaments provide a unique platform to build reconfigurable active materials. However, it remains unclear how cytoskeletal stresses regulate the emergent mechanical properties of living matter. Here, we demonstrate that active networks composed of molecular motors and biopolymers exhibit an activity-controlled phase transition from an active liquid that spontaneously bends in-plane to an active solid that spontaneously buckles out-of-plane. We are mapping the phase space of active and elastic stresses to better understand these two active instabilities. Finally, we establish an optogenetic control over this non-equilibrium phase transition by optically modulating the activity of light-activable motors. Our results elucidate how to spatiotemporal control active and elastic stresses in biomimetic active materials, a fundamental step towards understanding how cytoskeletal stresses control the self-organization of living systems.