In vivo degradation and bone formation behaviors of hydroxyapatite-coated Mg alloys in rat femur.

Various coatings have been developed for biodegradable Mg alloys to control the degradation speed and to improve the bone conductivity. In this study, hydroxyapatite (HAp) coatings were formed on pure Mg, Mg-0.8mass% Ca (MgCa), Mg-4mass% Y-3mass% rare earth (RE) (WE43), Mg-3mass% RE-1mass% Y (EW31) and Mg-4mass% RE (RE4) alloy rods with a chemical solution deposition method. The HAp-coated and uncoated Mg/Mg alloy rods were implanted in the femurs of rats for 3-6 months, and the corrosion suppression and bone formation abilities of the HAp coating were examined using a scanning electron microscope. The corrosion rate of WE43 was suppressed by 1/3 with the HAp coating for 6 months, and the corrosion product showed very slow dissolution. The effect of the HAp coating for pure Mg and MgCa disappeared in 1-2 months with the thinning of the rods accompanying with the obvious dissolution of the corrosion products. The effect of the HAp coating for EW31 and RE4 was not stable due to the expansion and collapse of the corrosion products. The bone formation was enhanced on the HAp layers. Eventually, the HAp coating basically suppressed the corrosion initiation and corrosion progress of Mg substrates. The magnitude of the suppression effect depended mainly on the chemical and physical stability of the corrosion products.

Biodegradable Surgical Staple Composed of Magnesium Alloy.

Currently, surgical staples are composed of non-biodegradable titanium (Ti) that can cause allergic reactions and interfere with imaging. This paper proposes a novel biodegradable magnesium (Mg) alloy staple and discusses analyses conducted to evaluate its safety and feasibility. Specifically, finite element analysis revealed that the proposed staple has a suitable stress distribution while stapling and maintaining closure. Further, an immersion test using artificial intestinal juice produced satisfactory biodegradable behavior, mechanical durability, and biocompatibility in vitro. Hydrogen resulting from rapid corrosion of Mg was observed in small quantities only in the first week of immersion, and most staples maintained their shapes until at least the fourth week. Further, the tensile force was maintained for more than a week and was reduced to approximately one-half by the fourth week. In addition, the Mg concentration of the intestinal artificial juice was at a low cytotoxic level. In porcine intestinal anastomoses, the Mg alloy staples caused neither technical failure nor such complications as anastomotic leakage, hematoma, or adhesion. No necrosis or serious inflammation reaction was histopathologically recognized. Thus, the proposed Mg alloy staple offers a promising alternative to Ti alloy staples.

Fabrication of Mg alloy tubes for biodegradable stent application.

Though Mg alloys are promising candidates for biodegradable stents, it is very difficult to fabricate stent tubes with high dimensional accuracy using Mg alloys because of their low deformability. This study aimed to develop thin-walled, high-quality Mg alloy tubes with good performance in stent applications. Cold drawing with a fixed mandrel was carried out for extruded Mg-0.8%Ca and AZ61 alloy tubes using optimized drawing parameters and lubrication, and stent tubes with 1.5-1.8mm outer diameter and 150 µm thickness were fabricated. A dimensional evaluation showed that the tube dimensional errors were within 0.02-2.5%. Also, an immersion test of pure Mg with different crystal orientations showed that the crystal orientation affected the corrosion properties, results that are the same with other Mg alloys. The crystal orientation of the stent tube could be controlled by changing the deformation amount and direction in the drawing, showing that it is possible to further improve the biodegradability of stents by approaching their fabrication from a processing aspect.