Impact of flow on ligand-mediated bacterial flocculation

Abstract

To understand the adhesion-fragmentation dynamics of bacterial aggregates (i.e., flocs), we model the aggregates as two ligand-covered rigid spheres. We develop and investigate a model for the attachment/detachment dynamics in a fluid subject to a homogeneous planar shear-flow. The binding ligands on the surface of the flocs experience attractive and repulsive surface forces in an ionic medium and exhibit finite resistance to rotation (via bond tilting). For certain range of material and fluid parameters, our results predict a nonlinear or hysteretic relationship between the binding/unbinding of the floc surface and the net floc velocity (translational plus rotational velocity). We show that the surface adhesion is promoted by increased fluid flow until a critical value, beyond which the bonds starts to yield. Moreover, adhesion is not promoted in a medium with low ionic strength, or flocs with bigger size or higher binder stiffness. The numerical simulations of floc-aggregate number density studies support these findings.

Sticky surface: sphere–sphere adhesion dynamics

“…Due to stagnant fluid conditions, we neglect the shearing effect of the fluid flow on the mean rest length of the binders and the spatial inhomogeneities in the material parameters. This assumption allows us to study the attachment/detachment of the binders normal to the adhering surface (thereby ignoring the tangential displacement of the spheres) [28]. Further, the binder kinetics is assumed to be independent of the salt concentration (i.e.…”

“…We explore how this adhesion ( collision as termed in the colloid science literature) mechanism for rigid, micron-size, spherical flocs is governed by various geometric and fluid parameters as well as how the surface forces and binding kinetics of the ligands impact the eventual size of these flocs. Unlike results from our earlier paper [28], this work focuses on how to model the aggregation kernel, K A , influenced by two microscopic effects (e.g., binding kinetics and surface charges). Further, this modeling methodology gives an idea on how to extend other similar effects in future.…”

Shape effects in biological adhesion of ellipsoidal cells

“…collagen fibers, von Willebrand factor and membrane receptors of other cells) [1,[5][6][7]. The ligand-receptor bonds thus represent elastic bridges that emerge and dissociate with different kinetics, depending on the mechanical actuation and the molecular interactions of the involved proteins [8,9]. A number of experimental techniques has been used to study the adhesive forces between platelets, most of which rely on mechanical separation of the adhering surfaces [10][11][12].…”

Ligand-mediated adhesive mechanics of two static, deformed spheres

“…These results are in aggrement with the published experimental findings.Biological adhesion is couched in a very different vocabulary from the mechanical adhesion theory, although there is a tremendous overlap of applications [42]. Examples include binding of bacterial clusters to medical implants or host cell surfaces during infection [44], cancer cell metastasis [27], coalescence of medical gels with functionalized particles or micro-bubbles for targeted drug delivery [32] and more recent applications in Micro-Electro-Mechanical Systems (MEMS) and nanotechnology [43]. Molecular bioadhesion is commonly mediated by specific ligand interactions, e.g., the ligand-mediated surface adhesion is an important case in the experimental studies of the P-selectin/PSGL-1 catch bond interactions of leukocytes (a roughly spherical particle) with and without fluid flow [26].…”

“…1 Introduction range interactions [32]. Consequently, many detailed kinetic models have successfully, yet independently, described these physical features imperative in the adhesion-fragmentation processes.…”