Active particles (APs) extract energy from their surroundings to sustain motion while simultaneously modifying the chemical and hydrodynamic fields in which they swim [1, 2]. These changes can feed back onto particle dynamics and collective organization, giving rise to emergent transport behavior and effective material properties [3, 4]. A central challenge is therefore to determine when the environment can be treated as a prescribed background and when it must instead be considered as a dynamical field coupled to the particles. I will first consider catalytic AP suspensions using a multiscale model coupling particle dynamics, substrate consumption and transport, and hydrodynamic interactions (HI). By consuming the substrate, the particles reshape the local chemical field and the gradients driving diffusiophoretic motion. Coupling this evolving field with HI generates particle–environment feedback that affects aggregation, transport, long-range correlations, and dissipation [5, 6, 7]. Collective organization can therefore emerge not only from direct particle interactions, but also from interactions mediated by the surrounding fields [6]. I will then discuss how AP–environment coupling can be used to control transport. An effective one-dimensional model of catalytic APs under confinement shows that periodic chemical forcing can enhance particle displacement while reducing substrate consumption through a stochastic-resonance mechanism [8, 9]. Finally, I turn from chemically controlled transport to mechanically driven active suspensions. In my current work, I consider confined rod-like APs driven by an imposed pressure gradient [10]. Using a mean-field model, I examine how swimmer-generated active stresses modify the mean flow and effective rheological response, and consequently the transport obtained for a given external forcing. These effects could be relevant to active transport through porous media, with applications ranging from drug delivery to in-situ bioremediation. References [1] Gerhard Gompper, Roland G Winkler, Thomas Speck, Alexandre Solon, Cesare Nardini, Fernando Peruani, Hartmut L¨owen, Ramin Golestanian, U Benjamin Kaupp, Luis Alvarez, et al. J. Phys. Condens. Matter, 32(19):193001, 2020. [2] Michael E. Cates and Julien Tailleur. .Annu. Rev. Condens. Matter Phys., 6(Volume 6, 2015):219–244, 2015. [3] Juan P Hern´andez-Ortiz, Juan J de Pablo, and Michael D Graham. Phys. Rev. Lett., 98(14):140602, 2007. [4] Akash Ganesh, Carine Douarche, and Harold Auradou. Phys. Rev. Lett., 134:128301, Mar 2025. [5] JD Torrenegra-Rico, A Arango-Restrepo, and JM Rub´ı. J. Chem. Phys., 157(10):104103, 2022. [6] J. D. Torrenegra-Rico, A. Arango-Restrepo, and J. M. Rub´ı. J. Chem. Phys., 161(22):224101, 12 2024. [7] A. Arango-Restrepo, J. D. Torrenegra-Rico, and J. M. Rubi. J. Chem. Phys., 162(21):214905, 2025. [8] J. D. Torrenegra-Rico, A. Arango-Restrepo, and J. M. Rub´ı. Phys. Rev. E, 108:014134, Jul 2023. [9] Juan David Torrenegra-Rico, A Arango-Restrepo, and JM Rub´ı. J. Chem. Phys., 156(5):054118, 2022. [10] Maxime Theillard, Roberto Alonso-Matilla, and David Saintillan. Soft Matter, 13:363–375, 2017.
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