Hydrodynamics of non-homogeneous active gels

We present lattice Boltzmann simulations to study the hydrodynamics of active fluids with spatially inhomogeneous activity. By patterning the system so that there are stripes of active fluids intercalated by passive regions, we show that it is possible to control the shape of the resulting spontaneous flow. Even with one single active stripe, the phenomenology is significantly richer than for uniform systems, and we observe a transition between a shear-like and a Poiseuille like spontaneous flow, corresponding to a switch between apparently free and no slip hydrodynamic boundaries on the edge of the active stripe. With a 2-dimensional patterning, in which activity is confined to spherical patches, we find that extensile gels tend to form rotating vortices which can synchronise, whereas contractile ones show a more complicated behaviour with spontaneous defect nucleation. We discuss possible experimental realisations of the system and geometries we are interested in, via, for instance, cytoskeletal fibers interacting with micropatterned surfaces with immobilised molecular motors, or via microfluidic devices containing bacterial colonies or suspensions.