Alloying design of biodegradable zinc as promising bone implants for load-bearing applications

TLDR

Magnesium‑based biodegradable metals offer superior mechanical properties to polymers but typically have strengths below 350 MPa. The study aims to screen binary Zn alloys containing Mg, Ca, Sr, Li, Mn, Fe, Cu, and Ag for bone implant applications. The alloys were systematically evaluated through in vitro and in vivo studies. Li addition provides the strongest strengthening effect in Zn, followed by Mg, while alloying accelerates degradation yet still delivers mechanical integrity suitable for bone fracture healing; cytocompatibility, osteogenesis, and osseointegration improve with Mg, Ca, Sr, and Li, and optimized ternary Zn‑0.8Li‑0.4Mg and Zn‑0.8Li‑0.8Mn alloys achieve ultimate tensile strengths of ~647 MPa and elongations of ~103 %, respectively, positioning biocompatible Zn‑based BMs with Ti‑like strength as promising load‑bearing orthopedic implants.

Abstract

Abstract Magnesium-based biodegradable metals (BMs) as bone implants have better mechanical properties than biodegradable polymers, yet their strength is roughly less than 350 MPa. In this work, binary Zn alloys with alloying elements Mg, Ca, Sr, Li, Mn, Fe, Cu, and Ag respectively, are screened systemically by in vitro and in vivo studies. Li exhibits the most effective strengthening role in Zn, followed by Mg. Alloying leads to accelerated degradation, but adequate mechanical integrity can be expected for Zn alloys when considering bone fracture healing. Adding elements Mg, Ca, Sr and Li into Zn can improve the cytocompatibility, osteogenesis, and osseointegration. Further optimization of the ternary Zn-Li alloy system results in Zn-0.8Li-0.4Mg alloy with the ultimate tensile strength 646.69 ± 12.79 MPa and Zn-0.8Li-0.8Mn alloy with elongation 103.27 ± 20%. In summary, biocompatible Zn-based BMs with strength close to pure Ti are promising candidates in orthopedics for load-bearing applications.