Effects of composition of hydroxyapatite/gray titania coating fabricated by suspension plasma spraying on mechanical and antibacterial properties

While several metallic implants with bioactive coatings have been developed thus far for treating bone deformations or deterioration, a multifunctional coating with the desired mechanical and antibacterial properties has not been demonstrated. This study aimed to reveal the effect of the composition of hydroxyapatite (HAp)/gray titania coatings on the mechanical and antibacterial properties for biomedical applications. Suspension plasma spray (SPS) aided successful deposition of HAp/gray titania coatings on the surface of titanium substrates. The microstructure of coatings with different compositions was then characterized using scanning electron microscopy, X-ray diffraction, and Raman spectroscopy to identify the crystal structure. All results consistently demonstrated that SPS could transform Ti2O3 into TiO2 with mixed Magneli phases, such as Ti4O7 and Ti3O5, which could typically demonstrate photocatalytic activity. Hardness, Young's modulus, and interfacial strength of composite coatings commonly increased with an increase in the weight percentage of TiO2. A multi-modal damage assessment combining acoustic emission (AE), infrared ray camera (IR), and digital-image-correlation (DIC) was performed to monitor the damage process of HAp composite coating, which successfully revealed initiations of microcracks and nonlinear deformation at interface until fracture. Antibacterial test performed for examining the cytotoxic effects against E. coli under LED light irradiation conditions revealed that SPS HAp/gray titania coating could significantly enhance the antibacterial properties. Enhanced antibacterial properties can be attributed to an increase in the number of Magneli phases and better bacterial adhesion was attributed to hydrophilic properties conferred by submicron-sized particles. Hence, SPS can help fabricate visible light-responsive antibacterial coating, which can be used for medical devices.