Development of a bioactive hydroxyapatite concentration gradient double hydroxyapatite/titanium dioxide coating on TiO<sub>2</sub> core block bone

There is an increasing demand for bone graft procedures to create sufficient bone volume for implant fixture placement. Among various techniques, block bone grafting is considered a favorable option for both horizontal and vertical augmentation. To meet the required physical and biological characteristics, a novel hydroxyapatite (HA)-coated titanium dioxide (TiO₂) core block bone was developed in this study. The coating layer was designed with an HA concentration gradient to achieve superior compressive strength and wear resistance. The concentration gradient was confirmed by scanning electron microscopy/energy-dispersed X-ray spectroscopy, and coating stability was demonstrated through scratch testing. Furthermore, alizarin red S staining revealed that the HA gradient layer retained bone formation compared to a single-layer HA coating. Taken together, the developed doubled-layered HA gradient TiO₂ block bone shows strong potential as a substitute for conventional block bone grafts.