Shapes and dynamic regimes of a polar active fluid droplet under confinement

Active droplets are artificial microswimmers built from a liquid dispersion by microfluidic tools and showing self-propelled motion. These systems hold particular interest for mimicking biological phenomena, such as some aspects of cell locomotion collective behaviors bacterial colonies, well the design droplet-based biologically inspired materials, engineered tissues. Growing evidence suggests that geometrical confinement crucially affects their morphology motility, but driving physical mechanisms still poorly understood. Here, we study effect activity on droplet containing contractile polar fluid confined within channels various sizes. We find surprising wealth shapes dynamic regimes, whose mechanics is regulated subtle interplay between stress, elasticity, microchannel width. They range worm-like cell-like shaped displaying an oscillating behavior wider to bullet-shaped exhibiting rectilinear motion in narrower slits. Our findings support view can provide viable strategy control predict propulsion direction active droplets. It would be look analogs these motility modes cells or synthetic matter.