Optimizing the strontium content to achieve an ideal osseointegration through balancing apatite-forming ability and osteogenic activity

Implant failure caused by unsatisfying osseointegration is still a noteworthy clinical problem. Strontium (Sr) has been confirmed to be a bioactive element that facilitates bone growth. In this study, Sr was surface incorporated in titanium (Ti) implant with different contents. The XRD results demonstrated that Sr existed mainly in the form of SrTiO3. All Srcontained implants showed sustainable Sr2+ release behavior. Meanwhile, the Sr2+ release rate was proportional to the Sr content. The in vitro immersing test showed that the apatite-forming ability on the implant surface was decreased with the increase of Sr content. Conversely, the cell experiments manifested that implants with high content of Sr were more favorable to cell spreading, proliferation, osteogenic differentiation, and extracellular matrix mineralization. The in vivo implant experiment revealed that Sr-incorporation could improve osseointegration, new bone formation and mineralization, and bone-implant bonding strength. In addition, Ti5Sr, which possessed a combined good osteogenic activity and apatite-forming ability, exhibited the best in vivo overall performance. In summary, we first put forward the competitive effect of osteogenic activity and apatite-forming ability on bone-implant osseointegration, which would provide a new strategy for implant design.