Interfacial adhesion and surface bioactivity of anodized titanium modified with SiON and SiONP surface coatings

Titanium (Ti) surface modification via coating technologies (plasma spraying, electron-beam deposition) has been used to enhance bone-implant bonding by increasing the rate of hydroxyapatite (HA) formation, a property known as bioactivity. Regardless the enhancement in the surface activity, the high fabrication-temperature (> 600 °C) reduces coating-implant adhesion due to thermal expansion mismatch and reduces bioactivity due to increased crystallinity in the coating. Thus, amorphous surface coatings with strong Ti-substrate adhesion that can be fabricated at relatively low temperatures are crucially needed for enhanced osseointegration. Therefore, this study aimed to enhance the Ti surface bioactivity via strongly adherent bioactive thin film coatings deposited by low temperature (< 400 °C) plasma enhanced chemical vapor deposition technique on nanopore anodized-Ti (A-Ti) surface. Two groups of coating (silicon oxynitride (SiON) and silicon oxynitrophosphide (SiONP)) were deposited on anodized Ti and tested for interfacial adhesion and surface bioactivity. TEM and XPS were used to investigate the interfacial composition while interfacial adhesion was tested using nano-indentation tests which indicated a strong interfacial adhesion between the coatings and the A-Ti substrate. Surface bioactivity of the modified Ti was tested by comprehensive surface characterization (i.e., chemical composition, surface energy, morphology, and mechanical properties) and apatite formation on each surface. SiONP coating significantly enhanced the Ti surface bioactivity that presented the highest surface coverage of carbonated hydroxyapatite (HCA, ~ 40%) with a Ca/P ratio (~ 1.65) close to the stoichiometric hydroxyapatite (~ 1.67) found in bone biomineral. The HCA structure and morphology were confirmed by HR-TEM/SAED, XRD, FT-IR, and HR-SEM/EDX. MSCs in-vitro studies indicated preferable cells adhesion and proliferation on the modified surfaces without any cytotoxic effects. This study concluded that the improved surface bioactivity of Ti-SiON and Ti-SiONP coatings suggests their potential use as strongly adherent bioactive surface coatings for Ti implants.