Irganox separation in spin coated polyurethane thin films

For medical polymers, their surface condition is an important factor for their biocompatibility in potential applications. The occurrence of antioxidant separation, in form of additive blooming onto the material surface causes changes in the chemical composition, topography, stability and could influence the bioactivity of the medical devices. In this study, the separation of Irganox antioxidant occurring after the spin coating of polyurethane into thin films under 1 mu m thickness was examined. The phenomenon was observed with different polymers from the Pellethane series. The extent of the blooming and its aftereffects were evaluated using scanning electron microscopy (SEM), atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS) and Raman microscopy. The compatibility of Irganox with the polymers was compared on the basis of the Hansen solubility parameter (HSP) concept. Additionally, Raman imaging in combination with basis analysis was established as a viable and fast method for polymer-additive distinction. The surface coverage of the bloomed areas increased with film thickness, and with it, its impact onto the surface chemistry and topography of the thin films. Simple protein coating tests indicated that the bloomed areas slightly impact the ability of fibronectin to form protein netting structures on the surface.