Magnesium (Mg) alloys are being actively investigated as potential load-bearing orthopaedic implant materials due to their biodegradability in vivo. With Mg biomaterials at an early stage in their development, the screening of alloy compositions for their biodegradation rate, and hence biocompatibility, is reliant on cost-effective in vitro methods. The use of a buffer to control pH during in vitro biodegradation is recognised as critically important as this seeks to mimic pH control as it occurs naturally in vivo. The two different types of in vitro buffer system available are based on either (i) zwitterionic organic compounds or (ii) carbonate buffers within a partial-CO(2) atmosphere. This study investigated the influence of the buffering system itself on the in vitro corrosion of Mg. It was found that the less realistic zwitterion-based buffer did not form the same corrosion layers as the carbonate buffer, and was potentially affecting the behaviour of the hydrated oxide layer that forms on Mg in all aqueous environments. Consequently it was recommended that Mg in vitro experiments use the more biorealistic carbonate buffering system when possible.

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Biomimetic calcium phosphate coatings have been studied to improve the corrosion resistance of biodegradable magnesium alloys. The corrosion resistance of these coatings is often limited by defects during creation. A method for improving the corrosion response of these coatings is therefore needed if biomimetic coatings are to be used for corrosion protection. In this study, a calcium hydroxide underlayer was applied to improve the properties of these biomimetic coatings. The in vitro corrosion response was studied using hydrogen evolution and electrochemical techniques. It was found that the calcium hydroxide layer increased the corrosion resistance of the coatings. The coatings created had fewer defects than the unmodified biomimetic coatings. Over time, the calcium hydroxide layer also prevented the defects in the coating from growing, leading to longer lasting protection. The results of this study suggest that calcium hydroxide coatings can significantly improve the corrosion protection of a biomimetic coating.

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Introducing coating layers on magnesium substrates for added corrosion protection has been one of the most popular methods to improve the relatively poor corrosion resistance of Mg biomaterials. Investigations on coating systems for Mg biomaterials to date have predominantly focused on smooth, polished surface topographies. Given that the corrosion resistance of biodegradable Mg increases with increasing surface roughness, the potential effectiveness of currently adopted coating methods could also be affected by changes in Mg surface topography. In this study, a biomimetic calcium phosphate (CaP) coating technique was employed to study the corrosion resistance of cast, pure Mg samples with high surface roughness of R a 59?12 mm. The effectiveness of the coating technique on rough samples was tested in vitro and compared with that of the raw polished pure Mg samples. It was found that while the biomimetic coating technique provided excellent corrosion protection to the smooth polished samples, the improvement in corrosion behaviour of rough cast samples was not as significant. With the findings in this study, it is suggested that future studies on Mg coatings should be performed on rough as well as smooth surfaces for a complete evaluation on the effectiveness of the coating system.