A rough morphology of the adsorbed fibronectin layer favors adhesion of neuronal cells

A range of substrates made of polystyrene (PS) and poly(methyl methacrylate)-poly(methacrylic acid) copolymer (PMMA-PMAA) containing 98 and 80% PMMA (PA98, PA80) and presenting a homogeneous or a patterned surface were used to study fibronectin adsorption and neuronal cell behavior. Fibronectin adsorption showed weak differences regarding the adsorbed amount (evaluated by XPS), but large differences in adsorbed layer morphology as observed by AFM. A fine granular morphology, with dimensions up to 8 nm height and 50-150 nm width, was observed on top of a thin adsorbed layer in the case of PS, PA98, and of a surface made of nanoscale inclusions of the latter in PS. In contrast, the layer adsorbed on PA80, which carries more ionizable groups, showed a higher roughness on the PA80 zones with differences in height up to 30 nm and characteristic lateral dimensions of 400 nm. On substrates of the former category, the cells formed large clusters, revealing poor interactions with the substrate. On PA80, the cells formed large networks with only a few small clusters. The adsorbed layer roughness, resulting from aggregation of fibronectin upon adsorption and from the substrate surface chemical composition, is responsible for neuronal cell spreading and growth. Its effect is not prevented by the presence of inclusions (< 30% of the surface) responsible for smoother areas of adsorbed fibronectin and for protrusions below 40 nm.