Evaluation of highly carbonated hydroxyapatite bioceramic implant coatings with hierarchical micro-/nanorod topography optimized for osseointegration

Background: Optimal osseointegration has been recognized as a pivotal factor in determining the long-term success of biomedical implants. Materials and methods: In the current study, highly carbonated hydroxyapatite (CHA) with carbonate contents of 8, 12 and 16 wt% and pure hydroxyapatite (HA) were fabricated via a novel hydrothermal method and deposited on the titanium substrates to generate corresponding CHA bioceramic coatings (designated as C8, C12 and C16, respectively) and HA bioceramic coatings (designated as C0). Results: C8, C12 and C16 were endowed with nanoscale, hierarchical hybrid micro-/nanoscale and microscale surface topographies with rod-like superstructures, respectively. Compared with C0, the micro-/nanotextured CHA bioceramic coatings (C8, C12 and C16) possessed excellent surface bioactivity and biocompatibility, as well as better wettability, which mediated improved protein adsorption, giving rise to simultaneous enhancement of a biological cascade of events of rat bone-marrow-derived mesenchymal stem cells including cell adhesion, proliferation, osteogenic differentiation and, notably, the production of the pro-angiogenic growth factor, vascular endothelial growth factor-A. In particular, C12 with biomimetic hierarchical hybrid micro-/nanorod topography exhibited superior fractal property and predominant performance of protein adsorption, cell adhesion, proliferation and osteogenesis concomitant with angiogenesis. Conclusion: All these results suggest that the 12 wt% CHA bioceramic coating with synergistic modification of surface chemistry and topography has great prospect for future use as implant coating to achieve optimum osseointegration for orthopedic and dental applications.