Patterned collagen layers on polystyrene: direct probing using AFM in the adhesion mapping mode

Patterned collagen layers, showing a net-like structure with nanometer-scale dimensions, were obtained by collagen adsorption onto polystyrene (PS) followed by drying at low rate. These obtained surfaces were characterized and compared, on the one hand, to the PS substratum and, on the other hand, to uniform collagen layers obtained by adsorption onto PS and drying at high rate. In a first approach, atomic force microscope (AFM) images, X-ray photoelectron spectroscopy data and wetting measurements were compared. The results indicated that PS was present at the extreme surface in the holes of the collagen net. A second approach, allowing a direct and spatially-resolved probing of the surface chemistry, was based on the adhesion mapping mode of the AFM. The net-like structure observed on the AFM topographic images was also found in the adhesion map obtained in water: no or very low adhesion was found on collagen threads as observed on a uniform collagen layer; a higher adhesion was recorded in the holes of the net as observed on pure PS. This shows, in a direct manner, that the patterned surface is chemically heterogeneous, with PS domains present at the outermost surface in the holes of the collagen pattern, and that this is preserved under water.