Hydrodynamic stirring driven by active carpets at fluid interfaces

Biological activity is highly concentrated on surfaces and interfaces, from ciliary arrays to sessile suspension feeders and thin layers, together they form 'active carpets', composed of actuators generating flows near a planar surface, restricted moving parallel to it, exhibit intriguing non-equilibrium characteristics in aquatic environments E.ven if the mean flow generated by the actuators is equal to zero, its variance at any one time is not. Hence, the flows can lead to 'active fluctuations'. While these carpets are known to induce non-Boltzmannian sedimentation profiles, their impact on the environment beyond transport processes remains unclear. Here we investigate the potential of active carpets situated at fluid-fluid interfaces to play a role in aggregation processes and enhance fluid mixing. Our findings shed new light on the non-equilibirium properties of life at interfaces where confinement potentially plays a key role, and offer insights into the development of novel materials with active boundary conditions.. Bibliography [1] Mathijssen, A. J., Guzmán-Lastra, F., Kaiser, A., & Löwen, H. (2018). Nutrient transport driven by microbial active carpets. Physical Review Letters, 121(24), 248101. [2] Guzmán-Lastra, F., Löwen, H., & Mathijssen, A. J. (2021). Active carpets drive non-equilibrium diffusion and enhanced molecular fluxes. Nature Communications, 12(1), 1906.