Nanostructuring polyetheretherketone for medical implants

Abstract

Surface roughness is a vital factor for medical implants since the cells of the surrounding tissue interact with the underlying substrate on the micro- and nanometer scales. In order to improve the surface morphology of implants, appropriate large-area micro- and nanostructuring techniques have to be identified being applicable to irregularly shaped structures. We demonstrate that plasma treatments of polyetheretherketone (PEEK) thin films produce nanostructured surfaces in a reproducible manner. They are easily tailored by varying plasma intensity using oxygen and ammonia as process gases. It was observed that roughness and nanostructure density linearly depend on plasma intensity. Oxygen plasma turned out to exhibit a stronger effect compared to ammonia plasma at the same processing conditions. For cell interaction studies, the mean size of the nanostructures was intentionally varied between 10 nm and 100 nm. In vitro experiments revealed that human mesenchymal stem cells (hMSC) adhere inhomogenously on untreated PEEK films, but the plasma treatment with oxygen or ammonia allows the hMSC to adhere and proliferate. Fluorescence microscopy of the cells on the PEEK films turned out to be difficult because of the strong auto-fluorescence of the PEEK substrate. Stains including the whole cell vital stain Calcein-AM allowed cell morphology studies on plasma-treated PEEK films. In the case of the analysis of cell compartments such as the actin cytoskeleton, confocal laser scanning microscopy (CLSM) was successfully applied.