In vitro biodegradation behavior of magnesium and magnesium alloy

Abstract

Magnesium has the potential to be used as degradable metallic biomaterial. For magnesium and its alloys to be used as biodegradable implant materials, their degradation rates should be consistent with the rate of healing of the affected tissue, and the release of the degradation products should be within the body's acceptable absorption levels. Conventional magnesium degrades rapidly, which is undesirable. In this study, biodegradation behaviors of high purity magnesium and commercial purity magnesium alloy AZ31 in both static and dynamic Hank's solution are systematically investigated. The in vitro test results show that magnesium purification and selective alloying are effective approaches to reduce the degradation rate of magnesium. In the static condition, the corrosion products accumulate on the materials surface as a protective layer, which results in a lower degradation rate than the dynamic condition. Anodized coating can significantly further reduce the degradation rate of magnesium. This study strongly indicates that magnesium can be used as degradable implant material as long as the degradation is controlled at a low rate. Magnesium purification, selective alloying, and anodized coating are three effective approaches to reduce the rate of degradation. © 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2011.

Mg and Mg alloys: How comparable are in vitro and in vivo corrosion rates? A review

“…This result may be due to the formation of a protective layer [95]. In dynamic fluid tests, the corrosion rate does not tend to decrease with time because the protective layer cannot be formed [93]. In addition, with the aim of better simulating in vivo conditions, Schinhammer et al used gaseous CO2 in SBF to keep the pH constant, avoiding the need of a buffer.…”

“…Most of the studies considered corrosion rates as a constant; however, a more detailed time-dependent study can show that the corrosion rate is not linear over time due to, for example, the formation of a protective corrosion layer on the material surface [93,94]. Furthermore, alloying elements can increase the complexity of the time-dependent corrosion behaviour.…”

“…To illustrate the high variability of corrosion rates depending on the immersion time as an example, in two studies, the corrosion rate of AZ31 (high purity; commercial) was observed over 20 days (data shown in Table 3). The authors determined the corrosion rate after 1, 2, 5, 10, 15 and 20 days [96] or after 5 and 20 days [93]. In both publications, the corrosion rate decreased from day 5 to day 20 by approximately 0.3 mm/year.…”

In vitro study of polycaprolactone/bioactive glass composite coatings on corrosion and bioactivity of pure Mg

“…Mg is an essential element of the human body, and also the second most important cation in cells. It assumes many particular physiological functions, like activating different kinds of enzymes, restraining abnormal hectic in nerves, keeping the structure stable for nucleic acid and participating in protein synthesis, muscle contraction and temperature adjustment [18] [19].…”

Chemical Immersion Coatings to Improve Biological Degradability of Magnesium Substrates for Potential Orthopaedic Applications

“…During the recovery period, initial mechanical strength would be maintained until the effects of corrosion start to occur. This would be followed by a gradual decrease in strength over the period of tissue recovery and finally the implant would be absorbed leaving the recovered tissues to carry the full load [50]. Other corrosion related factors that need to be considered is the increase in local pH and hydrogen evolution, both of which could have significant effects on tissues surrounding the implant.…”