Implant removal after fracture healing is often indicated but requires a second surgery. Biodegradable implants might therefore be an attractive alternative to standard steel or titanium implants. We therefore developed an intramedullary nail made of a novel biodegradable magnesium-silver-alloy (Mg2Ag, 2.5% Ag) and tested its in vivo degradation, biocompatibility, and effect on fracture repair using a long-bone fracture model in mice. Briefly, Mg2Ag intramedullary nails of 0.8 mm diameter were introduced into the right femur of 8-weeks old C57Bl/6 male mice. Compared to steel nails and no implant controls, Mg2Ag implants degraded over time with remnants being still visible 100 days after implantation as determined by radiographs. Fracture healing was investigated using the same model after introducing open femoral midshaft fractures. Mice were overall healthy and no differences in body weight or any histological abnormalities in kidney, liver, muscle, or spleen were found. Radiographs, μCT, and bone histomorphometry revealed that compared with steel implants, fractures supported by Mg2Ag nails demonstrated a significant increase in callus size with a higher bone formation rate, number of osteoblasts and osteoid volume, while the number of osteoclasts, osteoclast surface, and the eroded surface were decreased. These findings indicate that intramedullary Mg2Ag nails may augment bone formation while reducing bone resorption, leading to a larger callus size. However, degradation of Mg2Ag implants causes hydrogen production. Indeed, gas bubbles were found in the soft tissue surrounding the fracture zone and within the femora, leading to misshaped bones. Our findings therefore suggest that Mg2Ag implants degrade in mouse long bones over time without systemic adverse effects and support callus formation while causing hydrogen production. Thus, additional investigations are needed to further determine the applicability of Mg2Ag alloys for fracture healing.
Disclosure: The authors declared no competing interests. This work was supported as part of the Helmholtz Virtual Institute MetBioMat by the Helmholtz Zentrum (grant number VH-VI-523).