Directional cell migration through cell-cell interaction on polyelectrolyte multilayers with swelling gradients

The directional cell migration plays a crucial role in a variety of physiological and pathological processes. It can be controlled by the gradient cues immobilized on the substrate. The poly(sodium 4-styrenesulfonate) (PSS)/poly(diallyldimethylammonium) chloride (PDADMAC) multilayers were post-treated in a gradient NaCl solution with a concentration ranging from 3 m to 5 m, yielding the gradient multilayers with a similar chemistry composition (PSS domination) but gradually changed swelling ratio. The gradient nature and physicochemical properties were characterized by X-ray photoelectron spectroscopy and ellipsometry. Compared to the random migration with a lower rate at a smaller cell-seeding density, the vascular smooth muscle cells migrated directionally to the low hydration side at an appropriate cell-seeding density (1.5 × 104/cm2) under the assistance of cell-cell interactions. The cell migration rates on the gradient surface were significantly larger than those on the corresponding uniform surfaces etched by salt solutions of the same concentrations. Relative cell adherent strength and focal adhesion formation were studied to unveil the intrinsic mechanism of the gradient multilayers on the cell migration. It was found that both the gradient cues and cell-cell contact have major influences on the directional cell migration.