Biodegradability engineering of biodegradable Mg alloys: Tailoring the electrochemical properties and microstructure of constituent phases

Abstract

Crystalline Mg-based alloys with a distinct reduction in hydrogen evolution were prepared through both electrochemical and microstructural engineering of the constituent phases. The addition of Zn to Mg-Ca alloy modified the corrosion potentials of two constituent phases (Mg + Mg2Ca), which prevented the formation of a galvanic circuit and achieved a comparable corrosion rate to high purity Mg. Furthermore, effective grain refinement induced by the extrusion allowed the achievement of much lower corrosion rate than high purity Mg. Animal studies confirmed the large reduction in hydrogen evolution and revealed good tissue compatibility with increased bone deposition around the newly developed Mg alloy implants. Thus, high strength Mg-Ca-Zn alloys with medically acceptable corrosion rate were developed and showed great potential for use in a new generation of biodegradable implants.

Reduction in the Corrosion Rate of Magnesium and Magnesium Alloy Specimens and Implications for Plain Fully Bioresorbable Coronary Artery Stents: A Review

“…For Mg-5Ca alloy specimens in Hank's solution, the rate of hydrogen evolution decreased with increase in Zn content of the alloy (C Zn ); for example, after immersion for 60 h, the rates were ∼92% and ∼98% lower with alloys containing C Zn of 0.5 and 5.0 wt%, respectively, compared to the pure Mg [64]. These results were explained as the selective corrosion of the Mg 2 Ca phase, a consequence of the formation of microgalvanic couples being retarded by the Zn and this retardation effect increasing with increase in C Zn [64].…”

“…First, in some reports, results for the baseline material were not given, an example being the report on the two-step solution treatment method [67]. Second, in other reports, data on important material characteristics that influence corrosion were not given, an example being the report on the relationship between the grain size of the material and its corrosion rate [64]. Third, in some reports, counterpart materials was not given, an example being the report on nanocomposites in which each of the materials had a different composition [87].…”

“…For example, after 75 d in Hank's solution (pH = 7.4), the hydrogen evolution amount of 1) extruded Mg (mean grain size (d M ) = 25 µm) was ∼98% lower than that of as-cast Mg (d M = 1 mm) [64]; and 2) extruded Mg-5Ca-1Zn (d M = 10 µm) was ∼15% lower than that of its as-cast counterpart (d M = 1 mm) [63]. After 20 d, in Hank's solution, hot-rolled AZ31 specimens displayed ∼98% lower corrosion rate than their squeeze-cast counterparts, as a result of lower d M of the former [84].…”

Finite Element Analysis of Surface Integrity in Deep Ball-Burnishing of a Biodegradable AZ31B Mg Alloy

“…The issue is reiterated in an extensive review by Agarwal et al [2], and the challenge now is how to overcome such a problem associated with Mg alloys. One way to tackle this is to adjust the Mg alloys' properties by changing their composition and microstructure [3]. However, alloying by adding rare-earth elements often causes toxicity and lack of biocompatibility, hence making the material unsuitable to be implanted.…”

A Study on How to Improve Magnesium Anodizing Process with High Biocompatibility

“…To solve such problems of fast corrosion and inflammatory responses to bio-degrading magnesium, many studies were conducted with regard to manufacturing Mg alloys and surface treatments for the manufactured Mg alloys. In the magnesium alloy manufacturing, duad elements with high biocompatibility such as Calcium and Zinc (Ca & Zn) were included to produce metal casting alloys to control the corrosion speed and mechanical strength of the magnesium alloys 9) , and the surface treatment studies on highpolymer coatings and ceramic coatings were conducted. Especially, of the surface treatments, the anodizing method has been widely studied since the method enables to control the corrosion rate of magnesium while not changing the properties of magnesium [10][11] .…”