Preparation and characterization of chemical gradient surfaces and their application for the study of cellular interaction phenomena

Chemical gradient surfaces are surfaces with a gradually changing chemistry along their length which is responsible for a position bound variation in physical properties, most notably, the wettability. In this review, methods to prepare (palladium deposition, diffusion technique, density gradient method, gas diffusion technique, radio frequency plasma and corona discharge, poly(vinylene carbonate) hydrolysis) and characterize gradient surfaces are summarized. The number of techniques available to characterize gradient surfaces is effectively limited to the Wilhelmy plate method for wettability characterization, because the spatial resolution of more chemically oriented techniques, like infrared spectroscopy or X-ray photoelectron spectroscopy is still too limited, apart from their poor surface sensitivity as compared to contact angles. Gradient surfaces are especially useful to study biological interactions along their lengths, as the influence of the entire wettability spectrum upon protein adsorption or cellular interactions can be obtained in one single experiment, therewith minimizing biological variations. In general, proteins adsorb more extensively on the hydrophobic ends of gradient surfaces, which is accompanied by a lesser spreading and adhesion of tissue cells than on the hydrophilic ends of gradient surfaces. An influence of the specific chemistry constituting the gradient, upon protein adsorption as well as on cellular interactions always remains, indicating that biological interactions at an interface are not solely governed by wettability.