Hydrothermal growth of biomimetic calcium phosphate network structure on titanium surface for biomedical application

Calcium phosphate (CaP) coating-modified titanium (Ti) surfaces have been developed to improve the biological activity and osseointegration of Ti-based implants. However, these coatings always lack three-dimensional micro/nanostructures mimicking bone tissue. To fabricate hierarchical CaP coating structures and enhance the bioactivity of Ti implants, this study developed a novel hydrothermal method for preparing biomimetic three-dimensional CaP network structures on alkali-treated Ti surface with the assistance of oleic acid. Moreover, the growth mechanism of the CaP network structure was investigated, and its biocompatibility was evaluated by co-culture with preosteoblasts. The coatings were mainly composed of HA nanowires, which grew vertically along the titanate nanowires and further self-assembled into macropores. Compared to the pristine Ti surface, this hierarchical network structure showed superior hydrophilicity, elevated roughness, and improved cell attachment, proliferation, and osteogenic differentiation. Furthermore, this CaP structure demonstrated significantly higher alkaline phosphatase (ALP) activity and upregulated the expression of osteopontin (OPN) and osteocalcin (OCN) in comparison with similar titanate structures, suggesting improved bioactivity of the hierarchical CaP network structure. These improvements were probably attributed to hierarchical micro/nanostructure and CaP chemistry. The above findings indicate that this method effectively fabricates hierarchical CaP network structures on Ti-based substrates, which construct a favorable microenvironment for inducing osteogenic differentiation.