Transport through crowded and viscoelastic media is governed not only by steric constraints, but also by attractive interactions that reshape local structure, relaxation pathways, and the balance between trapping and motion. Here, I discuss this interplay across three coarse-grained descriptions of passive, active, and externally driven transport in polymeric and fibrous environments. First, Langevin dynamics simulations of tracers in quenched polymer matrices show how crowding and tracer–matrix affinity jointly suppress diffusion. At sufficiently strong affinity, however, increasing tracer concentration produces a nonmonotonic mobility through competition between adsorption, release into the bulk, and self-crowding. Next, models of a self-propelled deformable droplet moving through dense fibrous networks show that adhesion can facilitate cell migration by enhancing traction and deformation, yet excessive adhesion or confinement promotes trapping. Finally, active microrheology simulations reveal how polymer–polymer attraction changes the recoil of a probe after external driving. Increasing cohesion leads to subdiffusion, an earlier breakdown of linear response, and a nonmonotonic recoil whose maximum reflects an optimal balance between elastic stress storage and structural relaxation. Under strong forcing, irreversible rearrangements and local yielding dominate. Taken together, these results show that attractive interactions do more than add friction: they reorganize the surrounding medium and select distinct pathways for stress storage, relaxation, and transport. This perspective connects microscopic interaction rules to slow, history-dependent dynamics and kinetic arrest in complex nonequilibrium media.
Reference
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