RESUMO
BACKGROUND: Although several studies on the Mg-Zn-Ca system have focused on alloy compositions that are restricted to solid solutions, the influence of the solid solution component of Ca on Mg-Zn alloys is unknown. Therefore, to broaden its utility in orthopedic applications, studies on the influence of the addition of Ca on the microstructural, mechanical, and corrosion properties of Mg-Zn alloys should be conducted. In this study, an in-depth investigation of the effect of Ca on the mechanical and bio-corrosion characteristics of the Mg-Zn alloy was performed for the optimization of a clinically approved Mg alloy system comprising Ca and Zn. METHODS: The Mg alloy was fabricated by gravitational melting of high purity Mg, Ca, and Zn metal grains under an Ar gas environment. The surface and cross-section were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to analyze their crystallographic structures. Electrochemical and immersion tests in Hank's balanced salt solution were used to analyze their corrosion resistance. Tensile testing was performed with universal testing equipment to investigate the impact of Ca addition. The examination of cytotoxicity for biometric determination was in line with the ISO10993 standard. RESULTS: In this study, the 0.1% Ca alloy had significantly retarded grain growth due to the formation of the tiny and well-dispersed Ca2Mg6Zn3 phase. In addition, the yield strength and elongation of the 0.1% Ca alloy were more than 50% greater than the 2% Zn alloy. The limited cell viability of the 0.3% Ca alloy could be attributed to its high corrosion rate, whereas the 0.1% Ca alloy demonstrated cell viability of greater than 80% during the entire experimental period. CONCLUSION: The effect of the addition of Ca on the microstructure, mechanical, and corrosion characteristics of Mg-Zn alloys was analyzed in this work. The findings imply that the Mg-Zn alloy system could be optimized by adding a small amount of Ca, improving mechanical properties while maintaining corrosion rate, thus opening the door to a wide range of applications in orthopedic surgery.
RESUMO
BACKGROUND: Magnesium alloys have been receiving much attention for use in biodegradable metal implants because of their excellent mechanical properties and biocompatibility. However, their rapid breakdown and low bioactivity can cause the implant to lose mechanical integrity before the bone is completely healed. Moreover, hydrogen gas released during degradation can significantly delay the tissue regeneration process. To solve the instability of magnesium alloys, Zn and Ca can be added to improve the mechanical properties and biocompatibility. One other way to improve the mechanical properties of Mg is plasma electrolytic oxidation (PEO), which provides a dense, thick ceramic-like coating on the Mg surface. In this study, high-purity Mg was selected as the control, and Mg-1wt%Zn-0.1wt%Ca alloy and PEO-treated Mg-1wt%Zn-0.1wt%Ca alloy were selected as the test materials; the results of radiographic and histological analyses of their biocompatibility are reported herein. MATERIALS AND METHOD: Nineteen New Zealand white rabbits were used in the study. Rod-bars (Ø2.7 × 13.6 mm) were placed on both paravertebral muscles, and cannulated screws (Ø2.7x10mm) were placed on both femur condyle notches. Each animal was implanted in all four sites. X-rays were taken at 0, 2, 4, 8, and 12 weeks, micro-CT, and live-CT were taken at 4, 8, and 12 weeks. At weeks 4, 8, and 12, individuals representing each group were selected and sacrificed to prepare specimens for histopathological examination. RESULT: The results confirm that in vivo, Mg-1wt%Zn-0.1wt%Ca alloy had higher corrosion resistance than high-purity Mg and safely degraded over time without causing possible side effects (foreign body or inflammatory reactions, etc.). In addition, PEO treatment of Mg-1wt%Zn-0.1wt%Ca alloy had a positive effect on fracture recovery by increasing the bonding area with bone. CONCLUSION: Our results suggest that PEO treatment of Mg-1wt%Zn-0.1wt%Ca alloy can be a promising biomaterials in the field of various clinical situations such as orthopedic and maxillofacial surgerys.