Diffusion of Tracer Particles in Early Growing Biofilms. A Computer Simulation Study

TL;DR

This study uses computer simulations to analyze how tracer particles diffuse in early-stage bacterial biofilms, revealing diffusion behaviors influenced by colony growth and structure, and measuring the biofilm's viscoelastic properties.

Contribution

It introduces an agent-based simulation approach to study tracer diffusion in biofilms and quantifies the biofilm's viscoelastic moduli during growth.

Findings

Short-time diffusion is standard and affected by colony age.

Long-time diffusion is dominated by colony growth and structure.

Viscoelastic properties of biofilms are quantified during development.

Abstract

The diffusion of particles in complex media has gained significant interest due to its dual relevance: probing the viscoelastic properties of materials via microrheology and assessing the extent of particle displacement over time. In this work, we explore the early-stage diffusion of a tracer particle within a developing bacterial biofilm using implicit-solvent Brownian dynamics simulations. At these initial stages, bacterial colonies form two-dimensional structures that expand through cell growth and division. Employing an agent-based computational model (IbM), we analyse the passive diffusion of a spherical tracer within colonies of varying compaction levels. Our findings reveal that, at very short timescales, tracer diffusion follows a standard diffusive regime, modulated by colony ageing. However, at longer times, the dominant factor governing tracer motion is colony growth, which effectively confines the tracer within the expanding structure, except in cases where the microcolony is highly unstructured or the tracer is sufficiently small. Additionally, through MR techniques, we quantify the elastic and viscous moduli of the growing microcolony, offering insight into its evolving viscoelastic behavior.