Indirectly extruded biodegradable Zn-0.05wt%Mg alloy with improved strength and ductility: In vitro and in vivo studies

As compared to permanent orthopedic implants for load-bearing applications, biodegradable orthopedic implants have the advantage of no need for removing after healing, but they suffer from the “trilemma” problem of compromising among sufficiently high mechanical properties, good biocompatibility and proper degradation rate conforming to the growth rate of new bones. In the present work, in vitro and in vivo studies of a Zn-0.05wt%Mg alloy (namely, Zn-0.05Mg alloy) were conducted with pure Zn as a control. The Zn-0.05Mg alloy is composed of a small amount of Mg2Zn11 phase embedded in the refined Zn matrix with an average grain size of ∼20 μm. The addition of 0.05 wt% Mg into Zn significantly increases the ultimate tensile strength up to 225 MPa and the elongation to fracture to 26%, but has little influence on the in vitro degradation rate. Both Zn and Zn-0.05Mg alloy exhibit homogeneous in vitro degradation with a rate of about 0.15 mm/year. Based on the cytotoxicity evaluation, Zn and Zn-0.05Mg alloy do not induce toxicity to L-929 cells, indicating that they have little toxicity to the general functions of the animal. An in vivo biocompatibility study of Zn and Zn-0.05Mg alloy samples by placing them in a rabbit model for 4, 12 and 24 weeks, respectively did not show any inflammatory cells, and demonstrated that new bone tissue formed at the bone/implant interface, suggesting that Zn and Zn-0.05Mg alloy promote the formation of new bone tissue. The in vivo degradation of Zn and Zn-0.05Mg alloy does not bring harm to the important organs and their cell structures. More interestingly, Zn and Zn-0.05Mg alloy exhibit strong antibacterial activity against Escherichia coli and Staphylococcus aureus. The above results clearly demonstrate that the Zn-0.05Mg alloy could be a potential biodegradable orthopedic implant material.