# A Physical Approach to Simulate the Corrosion of Ceramic-Coated Magnesium Implants
## 4 Conclusions  
The diffusion-based physical model of the uniform galvanic corrosion in HP-Mg is calibrated in this study. Saturation tests were conducted to find the saturation limit of the magnesium ions in simulated body fluid under physiological conditions. The magnesium ions diffusion coefficient was calibrated for the first time against mass loss data under controlled pH and physiological conditions. Furthermore, the impact of the added porous coating layer on the effective diffusion coefficient in the coating region was measured. The calibrated model was validated by using the repeated immersion test of near-standard orthopedic screws. The calibrated diffusion-based model predictions are limited to long-term corrosion which is approximately after the first two weeks of corrosion. The model by itself cannot predict the geometry change directly; yet, it offers an estimation for the mass-loss rate for the geometry under question. This rate can be easily converted to the corrosion front speed under the assumption of uniform corrosion to monitor the geometry change at the sections of concern. Further investigation utilizing ALE or the level set method and the developed parameters in this work is needed to provide both accurate qualitative and quantitative simulations for the corrosion in magnesium-based implants. Geometric change due to corrosion is crucial to the mechanical analysis of the implant structure and fatigue studies. Parallel experimental assessment of the mechanical properties of the corroded samples is of great importance to the development of empirical equations for the mechanical properties as functions in time.  
Figure 16: The calibrated model results for the screw geometry vs. the experimental mass loss data for 3 and 4 weeks duration for (**a**) the bare; (**b**) the MAO-coated HP-Mg screws.  
Figure 15: Mg ions concentration (Kg/m\({}^{3}\)) contour plots at t = 28 days for (**a**) bare and (**b**) MAO-coated HP-Mg. The bare screw model shows wider spread in the contour plot of the concentration near the screw surface than for the coated screw model.  
**Author Contributions:** Writing--original draft preparation, M.A.; writing--review and editing, M.A. and H.I.; visualization, H.I.; supervision, H.I.; funding acquisition, H.I. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.  
**Acknowledgments:** The authors acknowledge the support of the University of Tennessee at Chattanooga. Research reported in this publication was supported by the FY2021 & FY2022 Center of Excellence for Applied Computational Science competition.  
**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.  
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