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 unclear.

Purpose of the Study:

• To investigate how biofilm density, quantified by transmitted light intensity (Ĩ), affects diffusiophoretic particle penetration.
• To determine the influence of particle size and bacterial motility on diffusiophoretic delivery into biofilms.
• To identify conditions under which diffusiophoresis is effective for biofilm penetration.

Main Methods:

• Systematically varied biofilm culture time and particle size.
• Compared diffusiophoretic penetration using motile and nonmotile Escherichia coli (E. coli) strains.
• Quantified biofilm density using the transmitted light intensity index (Ĩ).

Main Results:

• Increasing biofilm density (Ĩ) progressively reduced early-time diffusiophoretic mobility.
• Larger particles exhibited deeper penetration than smaller particles, overriding size-based geometric advantages.
• 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 biofilm accumulation states.
• Identified a critical biofilm density threshold beyond which gradient-enhanced delivery is significantly suppressed.
• Highlighted the interplay between particle size, biofilm density, and diffusiophoresis in modulating transport.