Osteo-angiogenic activity of a micro/nano hierarchical SrSi-codoped hydroxyapatite coating on zirconium alloy

Abstract

Numerous studies highlight the significance of biomimetic metallic implant surfaces for enhancing osseointegration through synergistic regulation of osteogenesis-angiogenesis. However, achieving clinical demands through singular structural or compositional biomimicry poses challenges. Therefore, the integration of both structural and compositional biomimicry, to closely emulate the host bone surface, is crucial for maximizing the biological activity of metallic implants. We synthesized a micro/nano hierarchical SrSi-codoped hydroxyapatite coating on Zr16Nb12Ti alloy through a simple microarc oxidation-hydrothermal reaction. Results revealed that Si doping enhances hydroxyapatite (HA) growth along the c-axis, forming large-sized nanorods. However, co-doping of Sr and Si inhibits grain growth by reducing crystal growth freedom, yielding a finer HA nanowire coating (MH-SrSi). MH-SrSi exhibits outstanding hydrophilicity attributed to the finer HA nanowires on the coating surface, promoting the adhesion of proteins and cells. Additionally, the released Sr and Si from MH-SrSi stimulate the secretion of osteogenesis-related proteins in osteoblasts and angiogenesis-related factors in endothelial cells, exhibiting a synergistic effect on promoting osteogenesis and angiogenesis. In vivo evaluation mirrors these results and shows that the micro/nano hierarchical structures of MH-SrSi elicited inward bone growth. Overall, MH-SrSi, combining structural biomimicry and compositional biomimicry, exhibits excellent osseointegration capability, making it a promising candidate for implant materials.