The synergistic effect of strontium-substituted hydroxyapatite and microRNA-21 on improving bone remodeling and osseointegration.

Surgical failure, mainly caused by loosening implants, causes great mental and physical trauma to patients. As the population ages, improving the physicochemical properties of implants to achieve favourable osseointegration will continue to be the focus of future research. Herein, we fabricated a titanium (Ti)-based SrHA/miR-21 composite coating that was generated by hydrothermal deposition of SrHA followed by miR-21 nanocapsule immobilisation. Both SrHA nanoparticles with good superhydrophilicity and miR-21 nanocapsules with uniform sizes were distributed evenly on the surface of Ti. In vitro experiments revealed that the composite coating was beneficial for osteoblast proliferation, differentiation and mineralization. In vivo evaluations demonstrated that this coating could not only promote the expression of the angiogenic factor CD31 but also enhance the expression of osteoblastic genes to facilitate angio-osteogenesis. In addition, the composite coating also showed a decreased RANKL expression compared with the miR-21 coating. As a result, the SrHA/miR-21 composite coating promoted new bone formation and mineralization and thus enhanced osseointegration and bone-implant bonding strength. Therefore, this method provides a new strategy for bone repair.