A Magnesium Phosphate-Based Platform Alleviates Bone–Fat Imbalance for the Repair of Age-Related Osteoporotic Bone Defects

Background/Objectives: Osteoporosis poses significant obstacles as it causes an imbalance between osteoblasts and adipocytes, which results in the disruption of bone homeostasis. Although various magnesium-based scaffolds have been deployed for the treatment of osteoporotic bone defects, whether this can be achieved by alleviating bone–fat imbalance still requires further elucidation. Methods: We designed magnesium phosphate-based platforms (GMPCs), based on magnesium photopolymerized methacrylated gelatin (GelMA) and phosphate (K-struvite, MPC), and used them to deliver magnesium ions (Mg2+) for alleviating bone–fat imbalance locally. Results: The in vivo results demonstrated that the GMPCs not only improved osteogenic behavior at the implanted site, but also reduced the proportion of adipose tissues in a femoral defect model in 18-month-old SD rats. Moreover, by promoting the differentiation of bone marrow mesenchymal stem cells (BMSCs) into osteoblasts in a concentration-dependent manner, GMPCs significantly reduced adipogenic differentiation in vitro. Also, 5GMPC demonstrated the best comprehensive biologic properties compared to other platforms. Conclusions: GMPCs have great potential in the treatment of age-related osteoporosis via the effective delivery of Mg2+.