The effect of charge regulation on cell adhesion to substrates: salt-induced repulsion

The long-range forces controlling cell or bacteria adsorption onto substrates are governed by electrostatic interactions. In this paper we use a simple mean field model (Debye–Huckel) to examine the interactions between cells and surfaces. We model the cell interface as an ion-penetrable, charge-regulating layer, thereby accounting for the finite thickness of the cell's extra-cellular (glycocalyx) layer. We find that charge regulation leads to several non-intuitive trends regarding the repulsion between a cell and similarly charged substrates: (I) instead of increasing monotonically with decreasing cell–substrate separation, the pressure varies non-monotonically, and (II) instead of monotonically decreasing the repulsion (at contact) between the cell and the substrate, there is a regime where adding salt leads to an increase in the repulsion.