Biofilm density regulates diffusiophoretic colloid penetration

Area of Science:

• Microbiology
• Biophysics
• Materials Science

Background:

• Biofilms, microbial communities in extracellular polymeric substance (EPS) matrices, impede antimicrobial and nanoparticle transport.
• Diffusiophoresis, particle motion along solute gradients, offers potential for enhanced penetration into biofilms.
• The impact of biofilm microstructure and density on diffusiophoretic delivery remains poorly understood.

Purpose of the Study:

• To investigate how biofilm density, quantified by transmitted light intensity index (Ĩ), affects diffusiophoretic particle penetration.
• To explore the influence of biofilm culture time, particle size, and bacterial motility (using Escherichia coli strains) on this process.

Main Methods:

• Systematic variation of biofilm culture time and particle size.
• Comparison of motile and nonmotile Escherichia coli strains.
• Characterization of biofilm density using the transmitted light intensity index (Ĩ).

Main Results:

• Increasing biofilm density (Ĩ) progressively reduces diffusiophoretic mobility, indicating a suppression regime.
• Larger particles demonstrated deeper penetration than smaller particles, overriding geometric factors.
• Observed reverse particle motion at later stages, attributed to weakened penetration and biofilm deformation.

Conclusions:

• Established a quantitative framework for diffusiophoretic delivery into biofilms based on density.
• Identified specific biofilm accumulation states where diffusiophoresis is effective versus suppressed.
• Highlighted the critical role of biofilm density in modulating gradient-enhanced colloidal delivery.