Inter-particle adhesion regulates the surface roughness of growing dense three-dimensional active particle aggregates

TL;DR

This study investigates how inter-particle adhesion influences the surface roughness of dense 3D active particle aggregates expanding in viscous media, revealing that higher adhesion increases roughness and affects particle displacement dynamics.

Contribution

The paper introduces a particle-based simulation framework that links adhesion strength to surface roughness and displacement asymmetry in active matter aggregates.

Findings

Surface roughness increases with adhesion strength.

Asymmetry in particle displacement suppresses roughness at low adhesion.

Particle movement towards the core drives surface roughness at high adhesion.

Abstract

Activity and self-generated motion are fundamental features observed in many living and non-living systems. Given that inter-particle adhesive forces are known to regulate particle dynamics, we investigate how adhesion strength controls the boundary growth and roughness in an active particle aggregate. Using particle based simulations incorporating both activity (birth, death and growth) and systematic physical interactions (elasticity and adhesion), we establish that inter-particle adhesion strength ($f^{ad}$) controls the surface roughness of a densely packed three-dimensional(3D) active particle aggregate expanding into a highly viscous medium. We discover that the surface roughness of a 3D active particle aggregate increases in proportion to the inter-particle adhesion strength, $f^{ad}$. We show that asymmetry in the radial and tangential active particle mean squared displacement (MSD) suppresses 3D surface roughness at lower adhesion strengths. By analyzing the statistical properties of particle displacements at the aggregate periphery, we determine that the 3D surface roughness is driven by the movement of active particle towards the core at high inter-particle adhesion strengths. Our results elucidate the physics controlling the expansion of adhesive 3D active particle collectives into a highly viscous medium, with implications into understanding stochastic interface growth in active matter systems characterized by self generated particle flux.