Osteogenic performance of titanium implants modified with bilayer strontium-doped micro/nanostructured functional coating

ABSTRACT Insufficient biological activity of titanium (Ti) implants remains a critical challenge in bone defect repair. Inspired by the hierarchical structure of natural bone (Haversian system), we propose a novel bilayer composite surface modification strategy. A strontium (Sr)-doped micro-arc oxidation (MAO) layer was first fabricated to provide long-term sustained Sr release. Subsequently, a 120-nm pure Ti interlayer was deposited by electron beam evaporation, followed by anodic oxidation (AO) to construct honeycomb-like TiO₂ mesoporous arrays (MPs). This bilayer functionalized micro/nanostructured surface thus enables sustained long-term Sr release. The morphology, composition, and crystallinity of the coatings were systematically characterized by Scanning Electron Microscope (SEM), Atomic Force Microscope (AFM), X-ray Diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS), while their electrochemical and mechanical performances were also evaluated. The results demonstrated that the bilayer coating not only sustained Sr release but also exhibited superior surface roughness, wettability, corrosion resistance, and elastic modulus. In vitro assays confirmed excellent biocompatibility and revealed significantly enhanced proliferation and osteogenic differentiation of MC3T3-E1 cells. Furthermore, in vivo experiments showed that Ti implants modified with the bilayer functionalized coating markedly promoted new bone formation. This surface modification strategy substantially improves the osteogenic capacity of Ti implants and provides a promising reference for the development of next-generation high-performance bone repair materials.