Osteopontin presentation affects cell adhesion-Influence of underlying surface chemistry and nanopatterning of osteopontin.

Osteopontin is a promising coating material for biomaterials, being important both in remodeling and formation of mineralized tissue and in immunological responses. We have investigated cell attachment to osteopontin adsorbed at different surface chemistries (-NH(2), -COOH, -CH(3), and bare gold) and to osteopontin presented as a nanopattern of 50 nm protein patches separated by a nonadhesive background. MDA-MB-435 cells adhere well to osteopontin presented at the hydrophilic chemistries (-NH2, -COOH, and gold) suggesting that osteopontin is presented in a functional form on these surfaces. On the amine surface, the cell attachment appears partly driven by electrostatic attraction between the positively charged substrate and the negatively charged cell membrane, whereas the spreading of the cells depends on the specific interaction with osteopontin presented at the surface. Significantly, fewer cells adhere to osteopontin presented at the methyl-terminated hydrophobic surface and the cells are less spread. On the nanopatterned osteopontin, only a very low number of cells adhered and those few attached cells showed an elongated morphology with few adhesion points to the surface. This indicates that the adhesive patches are not large enough to support stable focal contacts. The good cell attachment and spreading on the hydrophilic surfaces holds promise for osteopontin as a future coating for biomaterials.