Adhesive-ligand-independent cell-shaping controlled by the lateral deformability of a condensed polymer matrix

Cell adhesion on biomaterial surfaces has been extensively studied from the perspective of the adsorption properties of adhesive ligands, while recent research on mechanobiology has been revealing a critical role of the mechanical properties of the extracellular milieu in the control of cell adhesion, such as the stiffness and viscoelasticity of the matrix. Although the effects of the lateral mobility of an adhesive ligand have been intensively investigated in a model substrate with water-soluble polymer layers, less is known about those in the setting of lateral deformability of hydrophobic condensed polymer layers. In this study, to help clarify this issue, we used PNIPAAm-grafted substrates with a well-controlled degree of graft-polymerization (DGP) as a typical hydrophobic condensed polymer surface at a cell culture temperature of 37 °C. We observed a clear negative correlation between cell spreading and DGP of PNIPAAm regardless of the amount of fibronectin adsorbed on the substrates, which was found to be attributable to the lateral deformability of a condensed PNIPAAm layer based on lateral force microscopic analysis. The surface-lateral-deformation-induced modulation in stability and maturation of focal adhesion of the cells is discussed in relation to the matrix-strain-induced alteration of the density distribution of adsorbed adhesive ligands.