Autonomous microfluidics and active flow networks in active nematics*

Active systems are particularly promising in the design of autonomous machines because they are highly responsive to their environment and exhibit spontaneous flows. Developing techniques to control active flows is a current challenge. Here, we study experimentally how lateral confinement can control the dynamics of a 2-dimensional active nematic, made of microtubule bundles sheared by kinesin dimers. In long, straight microfluidic channels, we observe directional flows along one direction, selected by spontaneous symmetry breaking. Interestingly, in certain cases, the system can reverse the flow direction and transiently undergo an episode of shear flow. We show that the flow amplitude and switching frequency can be controlled through geometry. For instance, we are able to effectively enforce either shear or directed flow state by shaping the confining wall with a ratchet pattern. Geometrical patterning induces spatial and orientational ordering of motile topological defects. Finally, we build an active flow network by connecting straight and ratchet channels together. We show that, with the appropriate design, the circuit performs the AND and OR logical operations.