Biodegradable lean Mg-Dy alloy enhances bone repair in senile osteoporotic fractures by modulating macrophage mediated immune microenvironment

Senile osteoporotic fractures pose a major clinical challenge due to age-related immune and skeletal dysfunctions that critically impair bone healing. Advanced biomaterials capable of compensating for impaired osteogenesis and modulating immune responses are therefore urgently needed. In this study, a biodegradable Mg-1Dy alloy was prepared via low-temperature extrusion for potential orthopedic applications. The alloy exhibited an ultimate tensile strength of 275.9$$\pm 1$$ MPa and controlled degradation behavior, which was supported by a Dy-enriched surface product layer. The immunomodulatory effect of this material has been studied, and the results show that within a concentration range of 8 mM, magnesium ions can inhibit the pro-inflammatory M1 phenotype in macrophages and promote their transformation into the anti-inflammatory M2 phenotype, thereby participating in the regulation of the NF-kB pathway. In the mouse model of senile osteoporotic fractures, compared with the control group, the Mg-1Dy alloy enhanced the mineralization and bone integration of osteocytes. These results suggest that the Mg-1Dy alloy can modulate the immune microenvironment to support bone repair, underscoring its potential value in treating fractures in elderly patients with osteoporosis.