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Acta Metall Sin  2017, Vol. 53 Issue (10): 1207-1214    DOI: 10.11900/0412.1961.2017.00266
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Recent Advances on Biodegradable MgYREZrMagnesium Alloy
Lili TAN1(), Junxiu CHEN1,2, Xiaoming YU1, Ke YANG1
1 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
2 School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
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In recent years, magnesium and its alloys as biodegradable materials have attracted much attention. Biodegradable MgYREZr, mainly WE43 alloy, with good integrated properties has been studied in favor. In this paper, the microstructure, mechanical properties, biodegradable property and biocompatibility of biodegradable MgYREZr alloy were reviewed, as well as the clinical results of the bone fixation screws developed in Germany using the alloy with similar composition to WE43. MgYREZr alloy presents uniform microstructure and higher mechanical properties after large plastic deformation with the grain size of less than 1 μm. The RE elements can be dissolved and stabilize the corrosion layer, which can decrease the degradation rate of the alloy accompanying with optimized heat treatment. The animal tests showed biocompatibility and good bioactivity. Clinical tests showed the MgYREZr alloy screws presented equivalent to titanium screws for the treatment of mild hallux valgus deformities, however resorption cysts was revealed by X-rays when the acute scaphoid fractures were treated with a double-threaded screw made of MgYREZr, and it was only after 6 months that the fractures were consolidated enough to allow physical work. So for different clinical cases, the degradation and biological behaviors of MgYREZr alloys need to be further studied in vitro and in vivo. To control the degradation rates to meet the different clinical requirements is still a major obstacle for biodegradable MgYREZr alloys to enlarge their clinical application.

Key words:  MgYREZr alloy      microstructure      mechanical property      biodegradable property      biocompatibility     
Received:  03 July 2017     
ZTFLH:  R318.08  
Fund: Supported by National Natural Science Foundation of China (Nos.81401773 and 31500777)

Cite this article: 

Lili TAN, Junxiu CHEN, Xiaoming YU, Ke YANG. Recent Advances on Biodegradable MgYREZrMagnesium Alloy. Acta Metall Sin, 2017, 53(10): 1207-1214.

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Alloy Y Nd RE Zr Cu Fe Li Mn Ni Si Zn Others Mg
WE43A 3.7~4.3 2.0~2.5 1.9a 0.4~1.0 0.03 0.01 0.2 0.15 0.005 0.01 0.2 0.20 Bal.
WE43B 3.7~4.3 2.0~2.5 1.9a 0.4~1.0 0.03 0.01 0.2 0.03 0.005 - <0.2b 0.01 Bal.
Table 1  Chemical compositions of WE43A and WE43B in ASTM B80.21866 (mass fraction / %)
Fig.1  Cast WE43 shows a white contrast phase with eutectic lamellar structure (a) and extruded WE43 shows fine distributed white contrast structures without lamellar appearance (b) (The white contrast is a second phase)[19]
Fig.2  Maximum load to failure in Newton (N) (Significant difference parameter p<0.05)[23]
Fig.3  Picture of MgYREZr interference screws (MAGNEZIX?) with different thread design. All screws have a length of 23 mm and diameters of 8 mm[23]
(a) thread design 1 has an asymmetric pitch of 2.5 mm and a depth of 0.8 mm
(b) design 2 has a slightly shorter asymmetric pitch of 2.25 mm and a wider root with a depth of 0.8 mm
(c) pitch of design 3 is significantly shorter at 1.5 mm with a reduced depth of 0.5 mm and a symmetric shape
Material Ultimate tensile Yield strength Elongation
strength / MPa MPa %
Cortical bone 35~283 - 1.07~2.10
WE43A-T6 250 162 2
WE43B 220 - 2
WE43 extruded 277 198 17
WE43 tube 260 170 25
Table 2  Mechanical properties of WE43 and cortical bone[20]
Fig.4  Corrosion rates of pure Mg and WE43 alloy immersed in Hank's solution in static, stirring and flowing conditions calculated by weight loss[26]
Fig.5  Schematic diagrams of Zr distribution in the Mg-Y-RE-Zr alloy after different ageing for 3 h (a) and 8 h (b)[27]
Fig.6  Schematic summary of the localized corrosion processes of WE43 at static exposure to SBF[13]
Fig.7  Mineralized area (Md.Ar) of bone specimen after 6 and 18 weeks implantation of magnesium alloys (AZ31, AZ91, WE43, LAE442) and a degradable polymer (SR-PLA96) measured on Masson-Goldner stained uncalcified sections of guinea pig femur. The rate of mineral apposition per week was measured as the distance between two fluorescence labels. p<0.001[28]
Fig.8  Micro-computer tomography images of the interference screw and the surrounding tissue at 4, 12 and 24 weeks of implantation time[31]
(a) at 4 weeks after being implanted, the Mg group of screws showed extensive gas formation (white star) in themedullary cavity
(c) some gas cavities were still visible at 12 weeks
(e) at 24 weeks after implantation, bone attachment to the Mg implant (white arrows) was observed
(b, d, f) μCT images of the titanium screw in panels showed the typical metallic artifacts on the edges of the implants. All titanium interference screws became well integrated into the bone structure
Fig.9  Results of ICP-MS analysis of the alloying elements zirconium (a) and yttrium (b) in blood samples at 4, 12, and 24 weeks after implantation (n=6 per implantation time)[31]
(a) elevated levels of zirconium were observed in the 4-week group. At 12 and 24 weeks, all values were within the reference range
(b) median levels of yttrium were within the reference range at all examination times
Fig.10  The two cannulated screws with the same design[15]
(a) titanium screw (Fracture compressing screw, K?nigsee Implantate GmbH, Am Sand 4, 07426 Allendorf, Germany)
(b) MAGNEZIXW compression screw (Syntellix AG Schiffgraben 11, 30159 Hannover, Germany)
Fig.11  Preoperative radiographs (posterior-anterior) of a mild hallux valgus deformity. The correction is achieved by a chevron osteotomy. The postoperative radiographs show a bony healing in both groups[15]
Fig.12  At one-year follow-up, the patient showed an excellent clinical result. The contour of the MAGNEZIX CS implant is still clearly visible[33]
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