Influence of collagen denaturation on the nanoscale organization of adsorbed layers

Adsorption (at 37 degrees C) of type I collagen, in native and heat-denatured (30 min at 40 and 90 degrees C) forms, on polystyrene was studied using quartz crystal microbalance with energy dissipation monitoring (QCM-D), atomic force microscopy (AFM) in tapping mode and X-ray photoelectron spectroscopy (XPS). The significance of the parameters deduced from QCM-D data was examined by comparing different approaches. The adsorbed layer of native collagen has a complex organization consisting of a thin mat of molecules near the surface, in which fibrils develop depending on concentration and time, and of a thicker overlayer containing protruding molecules or bundles which modify noticeably the local viscosity. As a result of drastic denaturation, the ability of collagen to assemble into fibrils in the adsorbed phase is lost and the protrusion of molecules into the aqueous phase is much less pronounced. The adsorbed layer of denatured collagen appears essentially as a monolayer of flattened coils. At low concentration, this is easily displaced upon drying, leading to particular dewetting figures; at high concentration, aggregates add to the first layer. Moderate denaturation leads to an adsorbed phase which shows properties intermediate between those observed with native and extensively denatured collagen, regarding the ability to form fibrillar structures and the adlayer thickness and viscosity.