Active diffusion of self-propelled particles in flexible polymer networks

TL;DR

This study uses computational simulations to analyze how self-propelled particles diffuse through biopolymer networks, revealing size-dependent diffusion mechanisms and the influence of activity levels on long-term mobility.

Contribution

It provides a detailed computational model of active diffusion in biopolymer networks, highlighting size-dependent behaviors and the impact of activity on diffusivity.

Findings

Small particles move freely with decreased mobility based on density and Pe.

Particles comparable to mesh size explore via trapped-and-hopping mechanisms.

Long-time diffusivity exhibits a nontrivial power-law dependence on Pe.

Abstract

Biopolymer networks having a meshwork topology, e.g., extracellular matrix and mucus gels, are ubiquitous. It is an open question to understand how self-propelled agents such as Janus colloidal particles diffuse through such a biopolymer network. Here, we computationally explore this issue in-depth by explicitly modeling three-dimensional biopolymer networks and performing Langevin dynamics simulations of active diffusion of the self-propelled tracers therein. We show that the active tracer performs distinct diffusion dynamics depending on the mesh-to-particle size and P\'eclet number (Pe). When the particle is smaller than the mesh size, it moves as if in free space with a decreased mobility depending on the polymer occupation density and Pe. However, when the particle size is increased to be comparable to the mesh size, the active particles explore the polymer network using the trapped-and-hopping mechanism. We study the trapped time distribution, flight length distribution, the mean-squared displacement, and the long-time diffusivity at varying Pe. If the particle is larger than the mesh, it captures the collective viscoelastic dynamics from the polymer network at short times and the simple diffusion of the total system at large times. Finally, we discuss the scaling behavior of the long-time diffusivity with Pe, where we find a range of Pe that yields a nontrivial power law. The latter turns out to arise from a large fluctuation of trapped, activated tracers in conjugation with responsive polymer networks.