Microalloying Design of Biodegradable Mg-2Zn-0.05Ca Promises Improved Bone-Implant Applications

Mg and its alloys have been comprehensively studied and show huge potential for clinical orthopedic applications. However, balancing the mechanical strength and corrosion resistance of alloys is still a challenge. In light of this, micro-level contents of Zn and Ca were added to pure Mg to fabricate a Mg-2Zn-0.05Ca microalloy to expectedly enhance the mechanical strength and concurrently improve the corrosion resistance. The characteristics of the rolled Mg-2Zn-0.05Ca microalloy were explored using optical microscopy, X-ray diffraction, and tensile tests. The corrosion behavior and mechanical strength loss were explored using electrochemical and immersion tests. The effects of the microalloy extract on the proliferation, adhesion, and osteogenic differentiation of MC3T3-E1 cells were systematically studied. Moreover, implantations were done in femoral condyles of rabbits to study the degradation properties, osteogenic effect, mechanical strength loss, and biosafety of the microalloy. The ultimate tensile strength and yield strength of the rolled microalloy were found to be significantly elevated to 257 ± 2.74 and 237.6 ± 8.29 MPa, respectively. The microalloy showed a stable and gradual strength loss during degradation, both in vivo and in vitro. Concurrently, the microalloy exhibited improved corrosion resistance ability and especially, in vivo, the rolled microalloy exhibited a comparable degradation rate to that of rolled pure Mg within the initial 12 weeks of implantation. Additionally, the microalloy promoted osteogenesis, both in vitro and in vivo, and no short- and long-term toxicities of the microalloy were observed in rabbits. This study suggested that the rolled Mg-2Zn-0.05Ca microalloy effectively balanced the mechanical strength and corrosion resistance and showed potential application as bone implants.