Mean encounter times for cell adhesion in hydrodynamic flow: analytical progress by dimensional reduction

TL;DR

This paper develops an analytical approach to estimate the mean encounter time for cell receptors and ligands in hydrodynamic flow by reducing the dimensionality of the problem, validated through simulations.

Contribution

It introduces a dimensional reduction method that simplifies the calculation of encounter times in a coupled flow and diffusion system, providing a new analytical framework.

Findings

Analytical expressions match simulation results.

Convection and diffusion roles are quantified.

Effective reaction term captures vertical motion effects.

Abstract

For a cell moving in hydrodynamic flow above a wall, translational and rotational degrees of freedom are coupled by the Stokes equation. In addition, there is a close coupling of convection and diffusion due to the position-dependent mobility. These couplings render calculation of the mean encounter time between cell surface receptors and ligands on the substrate very difficult. Here we show for a two-dimensional model system how analytical progress can be achieved by treating motion in the vertical direction by an effective reaction term in the mean first passage time equation for the rotational degree of freedom. The strength of this reaction term can either be estimated from equilibrium considerations or used as a fit parameter. Our analytical results are confirmed by computer simulations and allow to assess the relative roles of convection and diffusion for different scaling regimes of interest.