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Microbes in motion : from surface interactions to porous media
Swimming microorganisms represent fascinating exemplars of non-equilibrium systems and display a range of unusual physical phenomena. These active agents often operate in complex environments, characterized by confining boundaries and flows, that can strongly modify their swimming dynamics. In this talk, I will first discuss the hydrodynamic interactions of microswimmers with a nearby deformable boundary, like a biological membrane. Using a far-field description for the flows and a perturbation theory for small deformations, we find that elastohydrodynamic couplings can generate behaviors that are fundamentally different to swimming near rigid walls. In the second part, I will discuss the impact of flows on active transport through a disordered, porous channel. While in the absence of flow agents accumulate at boundaries, shear also generates extended trapping phases of microswimmers in areas of the flow backbone, leading to prominent power-law tails in the exit-time distributions. Both examples highlight intricate hydrodynamic couplings in active systems and their potential consequences for the accumulation of microbial communities and the onset of biofilm formation.