Investigating the Effect of Thickener Concentrations on the Corrosion Behavior of Pure Mg

Magnesium (Mg) and its alloys are promising biodegradable implant materials due to their biocompatibility and ease of corrosion in physiological environment. In the tissue, diffusion of ions and gas released by Mg corrosion reaction will be interfered by extracellular matrix and cells, which may retard the corrosion reaction. Therefore, in the present study, we developed the in vitro model tissue with different diffusion rates to understand the effect of diffusion on the Mg corrosion. A thickener called gellan gum was added to the cell culture medium at appropriate concentrations to simulate tissues with different diffusion rates. The immersion study up to 28 days and the electrochemical studies were performed to evaluate the Mg corrosion behavior. The pure Mg specimens without thickener showed the highest corrosion rate in both immersion and electrochemical tests. The highest amount of insoluble salt layer with the lowest Mg and highest O concentrations were deposited on the specimen surface without thickener. The microfocus X-ray computed tomography (μCT) analysis confirmed these findings, showing the lowest remaining volume for specimens without thickener. There is an impediment of ion diffusion in the model tissue with increased thickener concentrations, thereby decreasing the corrosion rate. The corrosion rate for 0.2-0.3 wt. % thickener matched in the range of reported in vivo results. Hence, this model proves to be an effective tool for investigating biodegradation and understanding the mechanisms and controlling factors of this phenomenon.