Interaction of microswimmers with elastic interfaces

The dynamics of systems constituting active microscopic agents that can propel themselves, such as swimming microorganisms or active colloids is often rich and non-trivial. For instance, dilute suspensions of these motile microswimmers have been known to exhibit viscosity reduction (when weakly sheared), enhanced fluid fluctuations, as well as collective and coherent motion, among others. Typically, however, the microswimmers are often constrained by the presence of an intervening boundary or an interface, that restricts their free-swimming. The detailed dynamics of such systems is then crucially dependent on the nature of the boundary, rigid versus deformable. Simulations and theories have shown that microswimmers subject to confinement between parallel rigid boundaries exhibit an excess accumulation near the boundary; in turn, there is an associated enhancement of the active pressure forces on the wall. Here we relax the rigidity constraint, and consider the motion of finite-sized microswimmers in the vicinity of an elastic interface. In particular, we analyze the character of the hydrodynamic stresses that develop due to the swimmer-interface interaction.