Research on an Mg-Zn alloy as a degradable biomaterial.

In this study a binary Mg-Zn magnesium alloy was researched as a degradable biomedical material. An Mg-Zn alloy fabricated with high-purity raw materials and using a clean melting process had very low levels of impurities. After solid solution treatment and hot working the grain size of the Mg-Zn alloy was finer and a uniform single phase was gained. The mechanical properties of this Mg-Zn alloy were suitable for implant applications, i.e. the tensile strength and elongation achieved were approximately 279.5MPa and 18.8%, respectively. The results of in vitro degradation experiments including electrochemical measurements and immersion tests revealed that the zinc could elevate the corrosion potential of Mg in simulated body fluid (SBF) and reduce the degradation rate. The corrosion products on the surface of Mg-Zn were hydroxyapatite (HA) and other Mg/Ca phosphates in SBF. In addition, the influence caused by in vitro degradation on mechanical properties was studied, and the results showed that the bending strength of Mg-Zn alloy dropped sharply in the earlier stage of degradation, while smoothly during the later period. The in vitro cytotoxicity of Mg-Zn was examined. The result 0-1 grade revealed that the Mg-Zn alloy was harmless to L-929 cells. For in vivo experiments, Mg-Zn rods were implanted into the femoral shaft of rabbits. The radiographs illustrated that the magnesium alloy could be gradually absorbed in vivo at about 2.32mm/yr degradation rate obtained by weight loss method. Hematoxylin and eosin (HE) stained section around Mg-Zn rods suggested that there were newly formed bone surrounding the implant. HE stained tissue (containing heart, liver, kidney and spleen tissues) and the biochemical measurements, including serum magnesium, serum creatinine (CREA), blood urea nitrogen (BUN), glutamic-pyruvic transaminase (GPT) and creatine kinase (CK) proved that the in vivo degradation of Mg-Zn did not harm the important organs. Moreover, no adverse effects of hydrogen generated by degradation had been observed and also no negative effects caused by the release of zinc were detected. These results suggested that the novel Mg-Zn binary alloy had good biocompatibility in vivo.