Kinetically arrested clusters in active filament arrays

TL;DR

This study combines simulations and theory to understand how active elastic filaments self-organize into kinetically arrested clusters, revealing how activity, elasticity, and density influence cluster formation and shape.

Contribution

It introduces a combined simulation and theoretical framework to analyze cluster formation in active filament arrays, highlighting the roles of activity, elasticity, and density.

Findings

Filament arrays form regularly spaced, kinetically arrested clusters.

Cluster size, shape, and spacing depend on activity, elasticity, and density.

Theoretical expressions relate cluster properties to physical parameters.

Abstract

We use Brownian dynamics simulations and theory to study the over-damped spatiotemporal dynamics and pattern formation in a fluid-permeated array of equally spaced, active, elastic filaments that are pinned at one end and free at the other. The filaments are modeled as connected colloidal chains with activity incorporated via compressive follower forces acting along the filament backbone. The length of the chains is smaller than the thermal persistence length. For a range of filament separation and activity values, we find that the filament array eventually self-assembles into a series of regularly spaced, kinetically arrested, compact clusters. Filament activity, geometry, elasticity, and grafting density are each seen to crucially influence the size, shape, and spacing of emergent clusters. Furthermore, cluster shapes for different grafting densities can be rescaled into self-similar forms with activity-dependent scaling exponents. We derive theoretical expressions that relate the number of filaments in a cluster and the spacing between clusters, to filament activity, filament elasticity, and grafting density. Our results provide insight into the physical mechanisms involved in the initiation of clustering and suggest that steric contact forces and friction balance active forces and filament elasticity to stabilize the clusters. Our simulations suggest design principles to realize filament-based clusters and similar self-assembling biomimetic materials using active colloids or synthetic microtubule-motor systems.