Editorial: Active matter in complex environments

Editorial on the Research Topic Active matter in complex environmentsUnlike inert materials in equilibrium, active matter is intrinsically out of equilibrium.Whether as individual or a collective of many self-propelled objects, active matter is often surrounded by physically, chemically, and/or biologically complex environments.Articles of this issue described how such complexities change the behavior of active matter in fascinating and often unexpected ways.At the level of individuals, theoretical and numerical models are providing new insights into the fundamental physics of motility.For example, Barriuso-Gutierrez et al. developed a numerical algorithm based on dissipative particle hydrodynamics, which properly accounts for hydrodynamic interactions and thermal fluctuations.This approach allowed them to investigate active particles of different swimming mechanisms and shapes in bulk fluids and under confinement.They showed that geometric confinement could substantially vary the translational and orientational dynamics of active spherical colloids and modify the morphology of active polymers.In a related work, Faúndez et al. used simulations to investigate how adhesive active Brownian particles interact with a cylindrical obstacle under an imposed fluid flow.When the flow is strong, particles encounter and adhere to the entire obstacle surface, leading to the formation of multi-layered deposits.Conversely, when the flow is weak, particles directly intercept and adhere to the obstacle in a single-layered deposit.The crossover of these two regimes then defines an optimal flow velocity at which the number of deposited particles is maximized, which provides a useful guide for applications seeking to e.g., filter and retain microswimmers.Fluid flow also plays an important role in influencing the transport of biological swimmers, such as bacteria.As an example, Savorana et al. experimentally explored how the shear rate and the rheological behavior of polymer solutions affect the motility of Pseudomonas aeruginosa in a Poiseuille flow.They found that in the flow of Newtonian fluids, the bacteria are more concentrated towards the center of the microchannel where the shear rate is minimum.By contrast, in the flow of a shear-thinning fluid, the concentration profile of bacteria is not much different from that in the low-viscosity, Newtonian buffer, despite the

Abstract licence: CC BY

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