Effects of inorganic ions, organic particles, blood cells, and cyclic loading on in vitro corrosion of Mg -Al alloys

Recently, magnesium (Mg) alloys have attracted extensive attention as biodegradable implant materials. However, cyclic loading and the corrosive environment of the body are significant challenges for the practical use of alloys, and there are few studies on this topic. In this study, we conducted a four-point bending fatigue test for 86,400 cycles (12 h) in simulated body fluid (SBF), plasma, and whole blood with an AZ series alloy Mg-9Al-0.5Zn-0.27Mn-0.12Ag, to examine the effects of inorganic ions, organic particles, blood cells, and cyclic loading on Mg alloy corrosion. The Mg2+ concentration and solution pH were measured before and after experimentation, and the sample surfaces were characterized by 3D digital microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS).Our results showed that in the non-loading condition, a porous and weak inorganic product layer (mainly Mg/Ca phosphate and carbonate) formed on the surface of the Mg alloy sample immersed in SBF, which hardly had a protective effect on Mg alloy corrosion. For the samples immersed in plasma, the organic particles promoted the formation of an organic and more compact product layer, which protected the Mg alloy from severe corrosion. For the sample immersed in whole blood, the blood cells affected organic particle deposition on the product layer and thus interfered with the formation of an organic compact product layer, which slightly accelerated the corrosion process. Furthermore, cyclic loading damaged the layer integrity and significantly increased the corrosion rates of all the studied materials compared to the samples not subjected to cyclic loading. Nonetheless, under cyclic loading, blood cells adsorbed on the Mg alloy surfaces, and formed films, which protected the Mg alloy substrate and delayed Mg alloy corrosion.(c) 2021 Chongqing University. Publishing services provided by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )

Automated summary

This study investigates the effects of cyclic loading and corrosive environment on the corrosion of magnesium (Mg) alloys. The results show that a porous and weak inorganic product layer forms on the surface of the Mg alloy in simulated body fluid (SBF), which provides little protection against corrosion. In plasma, organic particles promote the formation of a more compact product layer that protects the Mg alloy. However, blood cells interfere with the formation of the organic product layer in whole blood, slightly accelerating corrosion. Cyclic loading damages the layer integrity and increases corrosion rates, but blood cells adsorbed on the Mg alloy surfaces form films that protect the Mg alloy substrate.