Significance of thermal fluctuations and hydrodynamic interactions in receptor-ligand mediated adhesive dynamics of a spherical particle in wall bound shear flow

TL;DR

This study reveals that thermal fluctuations and hydrodynamic interactions significantly influence the adhesion dynamics of spherical particles in shear flow, especially at low receptor densities and Péclet numbers, challenging conventional assumptions.

Contribution

The paper demonstrates the importance of thermal fluctuations and wall hydrodynamic interactions in receptor-ligand adhesion dynamics, providing new insights into their roles at different Péclet numbers.

Findings

Thermal fluctuations enhance bond formation at low receptor densities.

Wall hydrodynamic interactions significantly affect particle velocity near the wall.

Coupling of translational and rotational motions has minimal impact on binding dynamics.

Abstract

The dynamics of adhesion of a spherical micro-particle to a ligand-coated wall, in shear flow, is studied using a Langevin equation that accounts for thermal fluctuations, hydrodynamic interactions and adhesive interactions. Contrary to the conventional assumption that thermal fluctuations play a negligible role at high P$\acute{e}$clet numbers, we find that for particles with low surface densities of receptors, rotational diffusion caused by fluctuations about the flow and gradient directions aids in bond formation, leading to significantly greater adhesion on average, compared to simulations where thermal fluctuations are completely ignored. The role of wall hydrodynamic interactions on the steady state motion of a particle, when the particle is close to the wall, has also been explored. At high P$\acute{e}$clet numbers, the shear induced force that arises due to the stresslet part of the Stokes dipole, plays a dominant role, reducing the particle velocity significantly, and affecting the states of motion of the particle. The coupling between the translational and rotational degrees of freedom of the particle, brought about by the presence of hydrodynamic interactions, is found to have no influence on the binding dynamics. On the other hand, the drag coefficient, which depends on the distance of the particle from the wall, plays a crucial role at low rates of bond formation. A significant difference in the effect of both the shear force and the position dependent drag force, on the states of motion of the particle, is observed when the P$\acute{e}$let number is small.