Effect of Immersion Time in Simulated Body Fluid on Adhesion Strength of Hydrothermally Treated Hydroxyapatite-Titanium Nitride Films on Polyetheretherketones

Abstract This study sought to investigate the effect of immersion time in simulated body fluid (SBF) on the adhesion strength of hydrothermally treated hydroxyapatite-titanium nitride (HA-TiN) films on polyetheretherketone (PEEK) substrates. The HA-TiN films were deposited on PEEK substrates via magnetron sputtering and annealed with hydrothermal treatment. The crystalline phase and element compositions on the deposited films were confirmed by X-ray diffractometry (XRD), and X-ray photoelectron spectrometry (XPS). The samples were then immersed in SBF at 37°C for 7 to 56 days, where the surface characterization and chemical composition of the films were analyzed using scanning electron microscopy (SEM), atomic force microscopy (AFM), and XPS. After the in vitro degradation in SBF, the adhesion strength between HA-TiN films and PEEK substrates were measured by a universal testing machine and further investigated the failure mode using a stereomicroscope and SEM. The results demonstrated the improvement of crystallinity on HA-TiN sputtered films after hydrothermal treatment. After immersion in SBF, the coating surface revealed some nucleation without any detachment and exhibited an increase of surface roughness. The hydroxyapatite and titanium dioxide were revealed on the surface throughout the 56 days, while the Ca/P ratio decreased and remained constant during immersion. The adhesion strength did not significantly differ in all groups. These findings concluded that hydrothermally treated HA-TiN sputtered films on PEEK substrates showed the stability of adhesion strength throughout 56 days in simulated physiological conditions. The dissolution and precipitation during immersion represented the favorable characteristics of the films in the orthopedic or dental application. Keywords: Adhesion, Degradation, Thin films, Hydroxyapatite, Titanium dioxide