Initial Electrochemical Activity of Magnesium Alloy AZ31 Surface Exposed to Simulated Body Fluid by Scanning Electrochemical Microscopy
Journal Title: Biomedical Journal of Scientific & Technical Research (BJSTR) - Year 2019, Vol 13, Issue 2
Abstract
This study applies scanning electrochemical microscopy (SECM) in feedback mode to monitor the initial activity of AZ31 magnesium alloy surface, exposed to simulated body fluid (SBF). The alloy surface suffers a degradation process since the very first moments of immersion, considered as intense uniform activity and later a localized attack was detected. The additional information provided by SEM-EDS helped to characterize the composition of sites of interest observed on the AZ31 surface. The corrosion layer contains O, C, P and Ca coming from the SBF solution, as well as the basic elements of the alloy Mg, Al, Zn and Mn. The results allowed concluding that the locally formed pits nucleated around Al-Mn intermetallic particles in contact with the Mg alloy matrix, as a consequence of chloride ions attack.Over the last years, magnesium alloys have been demonstrated to be the most promising biodegradable and resorbable materials for medical implants applications. They present physical and mechanical properties close to those of natural bone, thus avoiding the effects of stress shielding [1-6]. In addition, the released Mg-ions during the implant degradation bind strongly to phosphates, which are part of physiological human solution, thus promoting bone cell attachment and tissue growth on the implants [7-11]. Many previous studies have been performed on Mg alloys, employing conventional electrochemical techniques, which only reflect the average electrochemical behavior of the entire surface. Therefore, it is necessary to assess the activity of these materials through other methods, in order to gain more information about local changes occurring at alloys surface [12,13]. Local probe techniques are a suitable option for characterizing these materials in physiological environments. Among them, the scanning electrochemical microscopy (SECM) is an advantageous tool, which allows detection of electrochemical processes in situ with high spatial and electrochemical resolution [14]. SECM in Feedback Mode: The feedback mode of SECM is the most widely used one. In this mode, a current flow through a microelectrode situated close to a substrate and immersed in an electrolytic solution having a redox mediator. Typically, the micro-disk electrode is set at a potential that allows to attain a steady state diffusion-controlled current iT,∞, resulting from the electrochemical reaction of the mediator redox pair (O + ne- ↔ R), where iT,∞ becomes a function of the concentration of reactant species and its diffusion coefficient, as shown by the following equation.where, n is the number of electrons transferred in the redox reaction, F - the Faraday constant, D - the diffusion coefficient, c - the concentration, and a is the microelectrode radius. Figure 1 illustrates the principle of operation of the feedback mode of SECM. The capabilities of SECM in this operation mode allow to monitor different systems in situ. However, only a few studies on Mg alloys have been conducted with SECM [15-24], of which not all focus on biomedical applications. The goal of this study is to detect through SECM the initial stages of electrochemical activity on AZ31 Mg alloy surface during its exposure to buffered simulated body fluid (SBF).
Authors and Affiliations
Emmanuel Mena Morcillo, Lucien Veleva, David O Wipf
Keywords
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- EP ID EP594420
- DOI 10.26717/BJSTR.2019.13.002374
- Views 123
- Downloads 0
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