Enhanced diffusion of a tracer particle in a lattice model of a crowded active system

TL;DR

This paper investigates how active particles in crowded systems enhance the diffusion of passive tracers using a lattice model, revealing regimes of motility, effects of clustering, and the influence of active particle fraction.

Contribution

It introduces a minimal lattice model to quantify passive tracer diffusion in active crowded environments, highlighting the effects of density, activity, and clustering.

Findings

Enhanced diffusion depends on crowder density and activity levels.

Clustering of active particles can suppress tracer diffusion.

A small fraction of active particles can significantly enhance diffusion.

Abstract

Living systems at the sub-cellular, cellular, and multi-cellular level are often crowded systems that contain active particles. The active motion of these particles can also propel passive particles, which typically results in enhanced effective diffusion of the passive particles. Here we study the diffusion of a passive tracer particle in such a dense system of active crowders using a minimal lattice model incorporating particles pushing each other. We show that the model exhibits several regimes of motility and quantify the enhanced diffusion as a function of density and activity of the active crowders. Moreover, we demonstrate an interplay of tracer diffusion and clustering of active particles, which suppresses the enhanced diffusion. Simulations of mixtures of passive and active crowders show that a rather small fraction of active particles is sufficient for the observation of enhanced diffusion.