Quantitative features of osteo-bioactive Ti surfaces at the atomic/molecular level

The osteo-bioactive potential of biomaterials can be modulated by altering material properties such as chemical composition, surface topography, and geometry. The correlation between the physicochemical properties of biomaterials and their osteo-bioactivity is highly complex. As a material widely used in bone repair, the structure-activity/dose-effect relationship between titanium (Ti) surface features and osteo-bioactivity remains unclear. To quantitatively enhance the osteogenic activity of Ti, we employed femtosecond laser (FSL) technology to create Ti surfaces with gradient changes in bioactive (nucleation) sites. Based on the apatite deposition ability on the etched surfaces, the quantitative relationship between the osteo-bioactivity of Ti surfaces and their characteristic parameters was systematically explored. Concurrently, classical molecular dynamics (MD) simulations were utilized to investigate the aggregation behavior of calcium and phosphate ions on the Ti surfaces with different sites. The findings from mineralization experiments revealed that the type and density of bioactive sites could influence the deposition of apatite. It was further identified that TiO₂ and Ti-OH are the crucial bioactive sites, with basic Ti-OH exhibiting superior efficacy as a bioactive site compared to its acidic counterpart. Moreover, the bioactive (nucleation) site densities should be maintained at a minimum of 2.33 ± 0.55 nm^-2 for TiO₂ and 2.50 ± 0.59 nm^-2 for -OH, ensuring satisfactory osteo-bioactivity on the Ti surface. The results provide the atomic/molecular features of Ti surfaces that effectively foster apatite deposition and bioactivity, promoting the rapid progression of titanium-based bone repair materials.