Magnesium has been extensively studied in the past few decades as a potential candidate material for biodegradable metallic implants. Previous studies in our group have demonstrated the electrochemical behaviours of non-aligned pure Mg single crystals (SC). However, SC materials are known for their ability to provide unique properties when precisely aligned with different crystallographic orientations. In this study, a pure Mg single crystal rod was grown and discs from different orientations were cut from it. The discs were then tested both in-vitro and in-vivo to investigate the crystal orientation dependence of Mg SC corrosion behaviour. To our knowledge, this is the first study reporting combined in-vitro and in-vivo study of Mg SCs with different orientations.

In this study, the corrosion behavior of Mg-1Zn and pure Mg wires is investigated in artificial urine solution (AUS). The evolution of local pH and dissolved oxygen near Mg/medium interface in AUS is reported for the first time. The microstructure of the Mg corrosion products in AUS is investigated in details. The obtained results indicate the encrustation risk of Mg ureteral stents.

Coatings and native oxide films on absorbable implants are buffering layers that typically intend to reduce the implant’s biodegradation and enhance its bioactivity. Oxide films that are an integral part of metals and are more stable than metals can be used to manipulate the corrosion rate of metallic implants in biological environments in the early stages of dissolution. In addition, precisely nanoengineered coatings with favorable surface topography can enhance the bioactivity of the implants through modulating favored cell selectivity. Such microporous oxide coatings can also serve as drug carriers. The development of anodic coatings is beneficial as it is cost-efficient and reproducible, where surface chemistry, morphology, and roughness can be precisely controlled. Moreover, the oxide coating is mechanically stiff, chemically stable, and provides excellent biocompatibility. In the present work, we have investigated the formation of anodic coatings on pure Zn. The in-depth coatings characterization highlights our finding that the physical parameters of the anodic films can be easily controlled through the synthesis conditions.

Numerous studies have been dealing with finding the ways to maintain the pH of simulated body fluids (SBF) in a specific range during the degradation of Mg. This is necessary to prevent the degradation behavior of Mg from being affected by the pH out of the targeted range (e.g. 7.35-7.45). As a result, adding pH buffers into SBF turns out a reasonable strategy. However, several synthetic pH buffers (e.g. Tris and HEPES), do alter the degradation behavior of Mg, steering the exploration of Mg biodegradation in the wrong direction. Besides, although the pH buffers regulate the bulk pH of SBF, they do not buffer the local pH near Mg surface that factually dominates the degradation behavior of Mg. Local pH was measured by a glass-type pH microelectrode with a tip diameter of ca. 10 μm (pH-10, Unisense). A Ag/AgCl mini-electrode was adapted as an external reference electrode. The pH microelectrode was positioned at 50 ± 3 μm above the specimen surface, in situ recording the evolution of local pH above Mg alloys (commercial pure Mg (CP-Mg), ultra-high-purity Mg (UHP-Mg), Mg-0.15wt.%Ca (Mg-0.15Ca), Mg-4wt.%Ag (Mg-4Ag) exposed to Hank’s Balanced Salt Solution (HBSS) at either room temperature (RT) or 37 °C under hydrodynamic conditions. Local pH above the surface of Mg alloy was found even lower at 37 °C (7.8±0.3) than that at RT (8.3±0.3) in Ca2+-containing HBSS (pH=7.4) under hydrodynamic conditions. The facilitated formation of Ca-P-containing products layer on the surface of Mg alloys at 37 °C rapidly consumed the hydroxyls generated owing to the cathodic reactions accompanying Mg dissolution, thus stabilizing the local pH and inhibiting the Mg degradation. These findings give powerful support to the slight alkalization and slow degradation of in vivo Mg alloys, and provide valuable guidance for studying in vitro biodegradation of Mg, indicating that no synthetic pH buffers need to be added into the SBF-like mediums under proper conditions (e.g. medium flow and 37 °C). Also, the corrosion rates of Mg alloys were found lower in Ca2+-containing HBSS at 37 °C than that at RT: 15%-30% lower for UHP-Mg, Mg-0.15Ca and Mg-4Ag (0.17-1.20 mm y-1) and almost 5 times lower for CP-Mg (5.22 mm y-1).

An automated pit detection framework was used to examine tensile test specimen by means of microCT scans in terms of the spatial pit formation over the corrosion process. Correlations between several pit features, including those described in ASTM G46-94, and mechanical integrity are shown.

Mg-Ca-Zn alloys have demonstrated the potential to offer well-balanced mechanical strength and corrosion resistance necessary for resorbable medical devices. Improvement to this system requires a full understanding of phase constituents and microstructure due to their role in micro-galvanic corrosion and strengthening of Mg alloys. Through Immersion weight loss measurements and micro-cell potentiodynamic experiments in different phase regimes, the corrosion contribution of individual phases can be probed. Zn-containing phases are shown to accelerate corrosion but are important to the improved strength. A better understanding of the corrosion cost of these phases will aid in alloy development and processing.