The degradation behaviors of the novel high-strength AZ31B magnesium alloy wires after surface modification using micro-arc-oxidization (MAO) and subsequently sealing with poly-L-lactic acid (PLLA) in different simulated physiological environments were investigated. The results show the surface MAO micropores could be physically sealed by PLLA, thus forming an effective protection to corrosion resistance for the wires. In simulated gastric fluid (SGF) at a low pH value (1.5 or 2.5), the treated wires have a high degradation rate with a rapid decrease of mass, diameter, mechanical properties and a significant increase of pH value of the immersion fluid. However, surface modification could effectively reduce the degradation rate of the treated wires in SGF with a pH value above 4.0. For the treated wires in simulated intestinal fluid at pH= 8.5, their strength retention ability is higher than that in strong acidic SGF. And the loss rate of mass is faster than that of diameter, while the pH value of the immersion fluid decreases. It should be noted that the modified wires in simulated body environment have the best strength retention ability. The wires show the different degradation behaviors indicating their different degradation mechanisms, which are also proposed in this work.
Content /(g?L-1) of reagent in different simulated fluids
SGF
SIF
SBF
NaCl
2.05
7.8
8.035
NaHCO3
N A
1.37
0.355
KCl
0.37
0.35
0.225
K2HPO4?3H2O
N A
N A
0.231
KH2PO4
0.6
0.32
N A
MgCl2?6H2O
N A
0.02
0.311
CaCl2
0.11
0.37
0.292
Na2SO4
N A
N A
0.072
NH2C(CH2OH)3
*a)
*
6.118
1 mol/L HCl
*
N A
39 b)
Glucose
3.5
1.4
N A
Pepsase
0.0133
N A
N A
Changing period
1 c)
1 c)
2 c)
Tab.1
Fig.1
Fig.2
Fig.3
Fig.4
Fig.5
Fig.6
Fig.7
Fig.8
Fig.9
Fig.10
Fig.11
Immersion time /d
Ca/P ratio
1
0.64
4
0.66
7
0.68
10
1.43
14
0.88
19
0.64
Tab.2
Fig.12
Fig.13
Fig.14
Fig.15
1
Zheng Y F, Gu X N, Witte F. Biodegradable metals. Materials Science and Engineering R: Reports, 2014, 77: 1–34
2
Witte F. The history of biodegradable magnesium implants: a review. Acta Biomaterialia, 2010, 6(5): 1680–1692
3
Staiger M P, Pietak A M, Huadmai J, . Magnesium and its alloys as orthopedic biomaterials: A review. Biomaterials, 2006, 27(9): 1728–1734
4
Reinhart R A. Magnesium metabolism: A review with special reference to the relationship between intracellular content and serum levels. Archives of Internal Medicine, 1988, 148(11): 2415–2420
5
Hort N, Huang Y, Fechner D, . Magnesium alloys as implant materials — Principles of property design for Mg–RE alloys. Acta Biomaterialia, 2010, 6(5): 1714–1725
6
Zong Y, Yuan G Y, Zhang X B, . Comparison of biodegradable behaviors of AZ31 and Mg–Nd–Zn–Zr alloys in Hank's physiological solution. Materials Science and Engineering B, 2012, 177(5): 395–401
7
Witte F, Fischer J, Nellesen J, . In vitro and in vivo corrosion measurements of magnesium alloys. Biomaterials, 2006, 27(7): 1013–1018
8
Gray J E, Luan B. Protective coatings on magnesium and its alloys — a critical review. Journal of Alloys and Compounds, 2002, 336(1–2): 88–113
9
Lorenz C, Brunner J G, Kollmannsberger P, . Effect of surface pre-treatments on biocompatibility of magnesium. Acta Biomaterialia, 2009, 5(7): 2783–2789
10
Xu L P, Pan F, Yu G N, . In vitro and in vivo evaluation of the surface bioactivity of a calcium phosphate coated magnesium alloy. Biomaterials, 2009, 30(8): 1512–1523
11
Zhao L C, Cui C X, Wang Q Z, . Growth characteristics and corrosion resistance of micro-arc oxidation coating on pure magnesium for biomedical applications. Corrosion Science, 2010, 52(7): 2228–2234
12
Zeng R, Dietzel W, Witte F, . Progress and challenge for magnesium alloys as biomaterials. Advanced Engineering Materials, 2008, 10(8): B3–B14
13
Liu G Y, Hu J, Ding Z K, . Bioactive calcium phosphate coating formed on micro-arc oxidized magnesium by chemical deposition. Applied Surface Science, 2011, 257(6): 2051–2057
14
Shang W, Chen B Z, Shi X C, . Electrochemical corrosion behavior of composite MAO/sol–gel coatings on magnesium alloy AZ91D using combined micro-arc oxidation and sol–gel technique. Journal of Alloys and Compounds, 2009, 474(1–2): 541–545
15
Laleh M, Kargar F, Sabour Rouhaghdam A. Improvement in corrosion resistance of micro arc oxidation coating formed on AZ91D magnesium alloy via applying a nano-crystalline sol–gel layer. Journal of Sol–Gel Science and Technology, 2011, 59(2): 297–303
16
Mandelli A, Bestetti M, Forno A D, . A composite coating for corrosion protection of AM60B magnesium alloy. Surface and Coatings Technology, 2011, 205(19): 4459–4465
17
Guo M, Cao L, Lu P, . Anticorrosion and cytocompatibility behavior of MAO/PLLA modified magnesium alloy WE42. Journal of Materials Science: Materials in Medicine, 2011, 22(7): 1735–1740
18
Lu P, Cao L, Liu Y, . Evaluation of magnesium ions release, biocorrosion, and hemocompatibility of MAO/PLLA-modified magnesium alloy WE42. Journal of Biomedical Materials Research Part B: Applied Biomaterials, 2011, 96B(1): 101–109
19
Chu C L, Han X, Bai J, . Fabrication and degradation behavior of micro-arc oxidized biomedical magnesium alloy wires. Surface and Coatings Technology, 2012, 213: 307–312
20
The United States Pharmacopoeia, Inc. Rockville, MD, 2012
21
Song Y W, Shan D Y, Chen R S, . Biodegradable behaviors of AZ31 magnesium alloy in simulated body fluid. Materials Science and Engineering C, 2009, 29(3): 1039–1045
22
Li L C, Gao J C, Wang Y. Evaluation of cyto-toxicity and corrosion behavior of alkali-heat-treated magnesium in simulated body fluid. Surface and Coatings Technology, 2004, 185(1): 92–98
23
Kokubo T. Formation of biologically active bone-like apatite on metals and polymers by a biomimetic process. Thermochimica Acta, 1996, 280–281(0): 479–490
24
Liu H, Yazici H, Ergun C, . An in vitro evaluation of the Ca/P ratio for the cytocompatibility of nano-to-micron particulate calcium phosphates for bone regeneration. Acta Biomaterialia, 2008, 4(5): 1472–1479
25
Weir N A, Buchanan F J, Orr J F, . Processing, annealing and sterilisation of poly-L-lactide. Biomaterials, 2004, 25(18): 3939–3949
26
Chen B K, Shen C H, Chen S C, . Ductile PLA modified with methacryloyloxyalkyl isocyanate improves mechanical properties. Polymer, 2010, 51(21): 4667–4672
27
Verdier S, Boinet M, Maximovitch S, . Formation, structure and composition of anodic films on AM60 magnesium alloy obtained by DC plasma anodising. Corrosion Science, 2005, 47(6): 1429–1444
28
Felfel R M, Ahmed I, Parsons A J, . Investigation of crystallinity, molecular weight change, and mechanical properties of PLA/PBG bioresorbable composites as bone fracture fixation plates. Journal of Biomaterials Applications, 2012, 26(7): 765–789
29
Weir N A, Buchanan F J, Orr J F, . Degradation of poly-L-lactide. Part 2: Increased temperature accelerated degradation. Proceedings of the Institution of Mechanical Engineers – Part H: Journal of Engineering in Medicine, 2004, 218(5): 321–330
30
Shikinami Y, Okuno M. Bioresorbable devices made of forged composites of hydroxyapatite (HA) particles and poly-L-lactide (PLLA): Part I. Basic characteristics. Biomaterials, 1999, 20(9): 859–877
31
Tsuji H, Ikada Y. Properties and morphology of poly(L-lactide). II. Hydrolysis in alkaline solution. Journal of Polymer Science Part A: Polymer Chemistry, 1998, 36(1): 59–66
32
Sharp J S, Forrest J A, Jones R A L. Swelling of poly(DL-lactide) and polylactide-co-glycolide in humid environments. Macromolecules, 2001, 34(25): 8752–8760
33
Matsusue Y, Yamamuro T, Oka M, . In vitro and in vivo studies on bioabsorbable ultra-high-strength poly(L-lactide) rods. Journal of Biomedical Materials Research, 1992, 26(12): 1553–1567
34
Weir N A, Buchanan F J, Orr J F, . Degradation of poly-L-lactide. Part 1: In vitro and in vivo physiological temperature degradation. Proceedings of the Institution of Mechanical Engineers— Part H: Journal of Engineering in Medicine, 2004, 218(5): 307–319
35
Chen Y S, Yanagihara N, Murakami S. Regeneration of facial nerve after hypoglossal facial anastomosis: an animal study. Otolaryngology — Head and Neck Surgery, 1994, 111(6): 710–716
