Microfluidic aspects of adhesive microbial dynamics: A numerical exploration of flow-cell geometry, Brownian dynamics, and sticky boundaries

Bacterial adhesion and motility are studied at the pore scale by focusing on two interrelated aspects of transport: wall attachment/detachment (reversible sorption) and the role of convection and pore geometry on adhesion. Motility is also examined through use of Brownian dynamics. Bacteria motility and reversible attachment/detachment are incorporated with a numerical laminar flow solver. Since individual bacteria are modeled, the results apply to low concentrations/coverage. Pore geometries consistent with a microflow cell of variable cross sectional area are used. This exploratory modeling work precedes an ongoing microflow cell experimental study and more detailed Lévy particle models. Adsorption reactions occurring over different time scales are modeled as multimodal distributions with power law tails. Computations show the relative magnitude of bacterial motility to advection controls the average number of collisions against solid walls. Variable cross section in pore geometry changes hydrodynamic conditions for deposition (e.g., variable shear stress). In regions of reduced cross sectional area, the ratio of bacteria motility to average velocity is smaller and results in less collisions and reduced retardation. Additionally, reduced cross sectional area increases both wall shear stress and vorticity which should be considered in adhesive models. While the shear forces acting on a particle deposited at the wall work on a spatial scale of the microbe’s size, adhesive forces may be confined to tens of nanometers. Multimodal adhesion causes the first passage time distributions to have long tails.