Strontium content and collagen‐I coating of Magnesium–Zirconia–Strontium implants influence osteogenesis and bone resorption

Objective Our objective was to study the role of Collagen type-I (Col-I) coating on Magnesium–Zirconia (Mg–Zr) alloys, containing different quantities of Strontium (Sr), in enhancing the in vitro bioactivity and in vivo bone-forming and mineralisation properties of the implants. Materials and methods MC3T3-E1 osteoblast cell line was used to analyse the in vitro properties of Col-I coated and uncoated alloys. Cell viability analysis was performed by MTT assay; cell attachment on alloy surfaces was studied by scanning electron microscopy (SEM); and gene profiling of bone-specific markers in cells plated on uncoated alloys was performed by Quantitative RT-PCR. In vivo studies were performed by implanting 2-mm-sized cylindrical pins of uncoated and coated alloys in male New Zealand white rabbits (n = 33). Bone formation and mineralisation was studied by Dual Energy X-ray Absorptiometry (DXA) and histological analysis at one and three months post-implantation. Results Our results clearly showed that Sr content and Col-I coating of Mg–Zr–Sr alloys significantly improved their bone inducing activity in vitro and in vivo. Osteoblasts on coated alloys showed better viability and surface binding than those on uncoated alloys. Sr inclusion in the alloys enhanced their bone-specific gene expression. The in vivo activity of implants with higher Sr and Col-I coating was superior to uncoated and other coated alloys as they showed faster bone induction and higher mineral content in the newly formed bone. Conclusion Our results indicate that bone-forming and mineralising activity of Mg–Zr–Sr implants can be significantly improved by controlling their Sr content and coating their surface with Col-I.