Shaking-induced motility in suspensions of soft active particles

We investigate theoretically the collective dynamics of soft active particles living in a viscous fluid. We focus on a minimal model for active but nonmotile particles consisting of N>1 elastic dimers deformed by active stresses and interacting hydrodynamically. We first derive a set of effective equations of motion for the positions of the particles. We then exploit these equations in two experimentally relevant cases: uncorrelated random internal stresses, and uniform monochromatic external shaking. In both cases, we show that small groups of intrinsically nonmotile particles can display nontrivial modes of locomotion resulting from the hydrodynamic correlations between the particle-conformation fluctuations. In addition, we demonstrate that a coherent shaking yields spatial ordering in suspension of soft particles interacting solely through the fluid.