Synergistic effects of elastic modulus and surface topology of Ti-based implants on early osseointegration

Early osseointegration plays a crucial role in determining the therapeutic efficacy of orthopedic implants. Some factors responsible for early osseointegration, such as inherent mechanical properties and surface topology of implants, are well-characterized. However, the synergistic effects of elastic modulus and surface topology of implants on the osteogenic differentiation of stem cells and early osseointegration have not been thoroughly investigated. In this study, the titanium (Ti) and β-titanium alloy Ti–24Nb–4Zr–8Sn (TNZS) were used to evaluate the synergistic effects of elastic modulus and surface topology on the biological performance of these materials in vitro and in vivo. Scanning electron microscopy imaging confirmed the presence of a micro-scale porous oxide layer on the Ti and TNZS surfaces upon treatment with microarc oxidation (MAO), which resulted in increased surface roughness, enhanced surface wettability and favourable mechanical properties. As compared with Ti-MAO, the TNZS-MAO samples with lower elastic modulus displayed increased cell attachment, alkaline phosphatase activity, collagen secretion, osteogenic marker expression, and mineralization of rat bone marrow mesenchymal stem cells. Upon implantation in rat femoral condylar defects, an inherently low elastic modulus could cooperatively accelerate early osseointegration and maturation of trabecular bone after 4 weeks implantation with the MAO modified surface. These results demonstrated that elastic modulus and the surface micro-scale topographical structure of Ti alloy implants have a synergistic effect on their osseointegration.