this theory can describe the observed change in the reversible cellular adhesion due to changing ionic strength, e.g., Ca2+/Mg2' concentrations, and substratum interfacial physics. According to
this theory, three situations are possible between the cell and the substratum: (1) a weak, reversible attraction when cells are located a certain distance from the substratum (secondary minimum); (2) a repulsion when electrostatic interactions dominate; and (3) a strong irreversible
attraction when van der Waals forces are dominating (primary minimum)