Abstract
Controlling degradation of magnesium or its alloys in physiological saline solutions is essential for their potential applications in clinically viable implants. Rapid degradation of magnesium-based materials reduces the mechanical properties of implants prematurely and severely increases alkalinity of the local environment. Therefore, the objective of this study is to investigate the effects of three interactive factors on magnesium degradation, specifically, the addition of yttrium to form a magnesium-yttrium alloy versus pure magnesium, the metallic versus oxide surfaces, and the presence versus absence of physiological salt ions in the immersion solution. In the immersion solution of phosphate buffered saline (PBS), the magnesium-yttrium alloy with metallic surface degraded the slowest, followed by pure magnesium with metallic or oxide surfaces, and the magnesium-yttrium alloy with oxide surface degraded the fastest. However, in deionized (DI) water, the degradation rate showed a different trend. Specifically, pure magnesium with metallic or oxide surfaces degraded the slowest, followed by the magnesium-yttrium alloy with oxide surface, and the magnesium-yttrium alloy with metallic surface degraded the fastest. Interestingly, only magnesium-yttrium alloy with metallic surface degraded slower in PBS than in DI water, while all the other samples degraded faster in PBS than in DI water. Clearly, the results showed that the alloy composition, presence or absence of surface oxide layer, and presence or absence of physiological salt ions in the immersion solution all influenced the degradation rate and mode. Moreover, these three factors showed statistically significant interactions. This study revealed the complex interrelationships among these factors and their respective contributions to degradation for the first time. The results of this study not only improved our understanding of magnesium degradation in physiological environment, but also presented the key factors to consider in order to satisfy the degradation requirements for next-generation biodegradable implants and devices.
Highlights
Magnesium alloys possess many advantageous properties over current materials used for biomedical implants
The mechanical strength and elastic modulus of magnesium alloys are similar to cortical bone, and magnesium alloys can be used for load-bearing implants with minimal stress shielding [2]
This study demonstrated that the presence or absence of yttrium in magnesium alloys, the presence or absence of surface oxides, and the presence or absence of physiological ions in the immersion fluid collectively contributed to magnesium degradation, and interacted with one another on influencing magnesium degradation rate and mode
Summary
Magnesium alloys possess many advantageous properties over current materials used for biomedical implants. Despite the many desirable properties of magnesium for medical implant and device applications, the rapid degradation of magnesium in vivo remains a critical challenge [5]. One method of controlling magnesium degradation is to add certain alloying elements into the magnesium and Yttrium (Y) is often added to magnesium alloys to increase material strength [6,7], ductility [8], and degradation (or corrosion) resistance [9,10,11,12,13]. Certain alloy compositions and surface properties that improve corrosion resistance in one environment may accelerate degradation in another environment. It is important to elucidate the interactions among the factors influencing magnesium alloy degradation in order to tailor magnesium alloys more effectively for their intended applications at various anatomical locations in vivo, achieving desirable life span for magnesiumbased biodegradable implants
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