Exploring key ionic interactions for magnesium degradation in simulated body fluid – A data-driven approach

Berit Zeller-Plumhoff,Melissa Gile,Melissa Priebe,Hanna Slominska,Benjamin Boll,Björn Wiese,Tim Würger,Regine Willumeit-Römer,Robert Horst Meißner

doi:10.1016/j.corsci.2021.109272

Berit Zeller-Plumhoff, Melissa Gile + Show 7 more

Open Access

https://doi.org/10.1016/j.corsci.2021.109272

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Abstract

We have studied the degradation of pure magnesium wire in simulated body fluid and its subsets under physiological conditions to enable the prediction of the degradation rate based on the medium's ionic composition. To this end, micro-computed tomography and scanning electron microscopy with energy-dispersive X-ray spectroscopy were used, followed by a tree regression analysis. A non-linear relationship was found between degradation rate and the precipitation of calcium salts. The mean absolute error for predicting the degradation rate was 1.35 mm/yr. This comparatively high value indicates that ionic interactions were exceedingly complex or that an unknown parameter determining the degradation may exist.

Highlights

Magnesium (Mg) is studied increasingly for its potential as a tem porary non-load-bearing bone implant due to its biodegradability, suitable mechanical properties and non-toxicity [1,2]
We have investigated the degradation of pure Mg wire in simulated body fluid (SBF) and pH-adjusted subsets thereof under physiological conditions (37 ◦C, 5% CO2) using laboratory μCT and scanning electron microscopy (SEM)+ energy-dispersive X-ray spectroscopy (EDX) and a subsequent analysis using randomised decision trees in order to: (i) Understand the interaction of the individual ionic components of SBF and their influence on Mg degradation under physiological conditions. (ii) Understand the interplay of the ionic components and Mg degradation for the formation of hydroxyapatite within the degradation layer. (iii) Evaluate the ac curacy of thermodynamic predictions of precipitate formation by comparing them to experimental results. (iv) Predict Mg degradation based on experimental conditions and ionic media composition
By studying the degradation of pure Mg in simulated body fluid and its subsets using μCT and SEM+EDX imaging in combination with a subsequent tree regression analysis, we have determined interactions of individual ionic components, namely HCO−3, HPO24− and Ca2+, in driving the degradation of Mg and the formation of precipitates as a protective layer

Summary

Introduction

Magnesium (Mg) is studied increasingly for its potential as a tem porary non-load-bearing bone implant due to its biodegradability, suitable mechanical properties and non-toxicity [1,2]. Different immersion media are used; some of them con taining only ionic components, such as simulated body fluid (SBF) or Hank’s balanced salt solutions (HBSS), while others include glucose and can be enriched with proteins, which is the case for most cell culture media, such as Dulbecco’s modified Eagle’s medium. SBF in particular is used due to its simplicity and ease of preparation – different for mulations exist as the initial formulation by Kokubo [4] was updated to account for the binding of multiple components to proteins [5] with further simplification and refinements in terms of pH equilibration [6]. The formation of hydroxyapatite (Ca5(PO4)3OH) in particular is desired, which in its carbonated form is the mineral phase of bone [8,9]

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