Degradation Behavior Of Magnesium Research Articles

Investigation of correlation of oxide layer surface morphology and magnesium degradation using a gas atmosphere dependent nanosecond laser processed model

In biomedical applications, degradation behavior of Magnesium (Mg) and its alloys is crucial for its outcomes. Various methods have been adopted to regulate Mg metals degradation, in which oxide layer generation has been considered to be a reliable strategy. However, correlation of magnesium oxide layer surface morphology and magnesium degradation is difficult to clarify due to interruption of oxide layer thickness and co-effect of other surface characteristics. In this work, Mg samples with two distinctive oxide layer morphology were prepared by nanosecond laser processing under N2 and CO2 atmospheres, coupled with essential surface and cross-section characterizations using SEM, AFM, TEM, XPS, XRD, and contact angle instrument. Furthermore, oxide layer morphology dependent Mg degradation behavior was investigated by electrochemical experimental, hydrogen precipitation, and pH tests. Results indicated that by changing laser treatment processing gas atmosphere, magnesium oxide morphology generated on sample surface could be tailored while maintaining consistency in thickness and composition. Larger particle size, surface roughness and wettability of magnesium oxide can decrease degradation rate.

Research on the degradation behaviors of biomedical Mg-2 wt.% Zn alloy under a biliary environment in vitro and in vivo

Magnesium and its alloys have been initially applied to biliary tract surgery. Currently, few reports on the degradation behavior of magnesium in the bile environment were investigated. Thus, in-depth research on the degradation behavior of Mg and its alloys in bile is beneficial to the further application of Mg in biliary tract surgery. In this study, the degradation behavior of HP-Mg (HPM) and Mg-2 wt.%Zn (MZ2) alloys in human bile and Hanks balanced salt solution (HBSS) was systematically investigated. The MZ2 alloy biliary stent was implanted into the porcine common bile duct to study the degradation behavior of MZ2 alloy in vivo, and to verify the biosafety of MZ2 alloys degradation in the bile duct. It was found that the degradation product layer formed by MZ2 alloys in bile consisted of three layers, including organic matter (fatty acid, etc.), calcium and magnesium phosphate, and Mg(OH)2/MgO, respectively from the outside to the inside. The multi-layered degradation product layer slowed down the corrosion of the Mg matrix. During the 21 days of stent implantation, the degradation rate of the MZ2 stent was about 0.83 mm/y, there was no blockage and stenosis of the tube diameter, and the bile drainage function was normal.

Predicting the inhibition efficiencies of magnesium dissolution modulators using sparse machine learning models

The degradation behaviour of magnesium and its alloys can be tuned by small organic molecules. However, an automatic identification of effective organic additives within the vast chemical space of potential compounds needs sophisticated tools. Herein, we propose two systematic approaches of sparse feature selection for identifying molecular descriptors that are most relevant for the corrosion inhibition efficiency of chemical compounds. One is based on the classical statistical tool of analysis of variance, the other one based on random forests. We demonstrate how both can—when combined with deep neural networks—help to predict the corrosion inhibition efficiencies of chemical compounds for the magnesium alloy ZE41. In particular, we demonstrate that this framework outperforms predictions relying on a random selection of molecular descriptors. Finally, we point out how autoencoders could be used in the future to enable even more accurate automated predictions of corrosion inhibition efficiencies.

Hydrogen Embrittlement of Biodegradable Magnesium

Magnesium alloys are increasingly used in biomedical applications as temporary implants in the human body. The degradation behaviour of magnesium in physiological environments, in combination with the tendency of the corrosion products to be harmlessly dissolved and excreted with the urine, make magnesium very attractive for temporary implant applications. One of these applications is the use of the material for making coronary stents. Such applications are, on the other hand, critically dependent on the mechanical integrity of the implant during service. A number of recent studies have evaluated the in-vivo and in-vitro corrosion behaviour of magnesium and its alloys, and the ongoing research seeks to provide a fundamental understanding of the factors that influence their bio-degradation and environmental failure and to expand this understanding through experimental evidence. In this paper, the propensity of the magnesium alloys AM30 and WE43 to hydrogen embrittlement and to corrosion fatigue was studied using constant extension rate tensile tests on fatigue pre-cracked compact specimens and corrosion fatigue tests on tubes which are typically used for the production of stents and which were tested in simulated body fluid.

Influence of HEPES buffer on the local pH and formation of surface layer during in vitro degradation tests of magnesium in DMEM

The human body is a buffered environment where pH is effectively maintained. HEPES is a biological buffer often used to mimic the buffering activity of the body in in vitro studies on the degradation behavior of magnesium. However, the influence of HEPES on the degradation behavior of magnesium in the DMEM pseudo-physiological solution has not yet been determined. The research aimed at elucidating the degradation mechanisms of magnesium in DMEM with and without HEPES. The morphologies and compositions of surface layers formed during in vitro degradation tests for 15–3600s were characterized. The effect of HEPES on the electrochemical behavior and corrosion tendency was determined by performing electrochemical tests. HEPES indeed retained the local pH, leading to intense intergranular/interparticle corrosion of magnesium made from powder and an increased degradation rate. This was attributed to an interconnected network of cracks formed at the original powder particle boundaries and grain boundaries in the surface layer, which provided pathways for the corrosive medium to interact continuously with the internal surfaces and promoted further dissolution. Surface analysis revealed significantly reduced amounts of precipitated calcium phosphates due to the buffering activity of HEPES so that magnesium became less well protected in the buffered environment.