title: In vitro degradation of ZM21 magnesium alloy in simulated body fluids.
abstract: In vitro degradation behavior of squeeze cast (CAST) and equal channel angular pressed (ECAP) ZM21 magnesium alloy (2.0wt% Zn-0.98wt% Mn) was studied using immersion tests up to 4w in three different biological environments. Hanks' Balanced Salt Solution (Hanks), Earle's Balanced Salt Solution (Earle) and Eagle minimum essential medium supplemented with 10% (v/v) fetal bovine serum (E-MEM+10% FBS) were used to investigate the effect of carbonate buffer system, organic compounds and material processing on the degradation behavior of the ZM21 alloy samples. Corrosion rate of the samples was evaluated by their Mg(2+) ion release, weight loss and volume loss. In the first 24h, the corrosion rate sequence of the CAST samples was as following: Hanks>E-MEM+10% FBS>Earle. However, in longer immersion periods, the corrosion rate sequence was Earle>E-MEM+10% FBS≥Hanks. Strong buffering effect provided by carbonate buffer system helped to maintain the pH avoiding drastic increase of the corrosion rate of ZM21 in the initial stage of immersion. Organic compounds also contributed to maintain the pH of the fluid. Moreover, they adsorbed on the sample surface and formed an additional barrier on the insoluble salt layer, which was effective to retard the corrosion of CAST samples. In case of ECAP, however, this effect was overcome by the occurrence of strong localized corrosion due to the lower pH of the medium. Corrosion of ECAP samples was much greater than that of CAST, especially in Hanks, due to higher sensitivity of ECAP to localized corrosion and the presence of Cl(-). The present work demonstrates the importance of using an appropriate solution for a reliable estimation of the degradation rate of Mg-base degradable implants in biological environments, and concludes that the most appropriate solution for this purpose is E-MEM+10% FBS, which has the closest chemical composition to human blood plasma.
authors.affiliation: National Institute for Materials Science, Biomaterials Unit, Biometal Group, Tsukuba, Ibaraki 305-0044, Japan; Warsaw University of Technology, Faculty of Materials Science and Engineering, 141 Woloska Street, Warsaw 02-507, Poland.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Witecka
authors.affiliation: Warsaw University of Technology, Faculty of Materials Science and Engineering, 141 Woloska Street, Warsaw 02-507, Poland.
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Bogucka
authors.affiliation: National Institute for Materials Science, Biomaterials Unit, Biometal Group, Tsukuba, Ibaraki 305-0044, Japan. Electronic address: yamamoto.akiko@nims.go.jp.
authors.forename: Akiko
authors.initials: A
authors.lastname: Yamamoto
authors.affiliation: Charles University, Faculty of Mathematics and Physics, Department of Physics of Materials, Ke Karlovu 5,121 16 Praha 2, Czech Republic.
authors.forename: Kristián
authors.initials: K
authors.lastname: Máthis
authors.affiliation: Charles University, Faculty of Mathematics and Physics, Department of Physics of Materials, Ke Karlovu 5,121 16 Praha 2, Czech Republic.
authors.forename: Tomáš
authors.initials: T
authors.lastname: Krajňák
authors.affiliation: Warsaw University of Technology, Faculty of Materials Science and Engineering, 141 Woloska Street, Warsaw 02-507, Poland.
authors.forename: Jakub
authors.initials: J
authors.lastname: Jaroszewicz
authors.affiliation: Warsaw University of Technology, Faculty of Materials Science and Engineering, 141 Woloska Street, Warsaw 02-507, Poland.
authors.forename: Wojciech
authors.initials: W
authors.lastname: Święszkowski
mesh_terms: D000497:Alloys / Q000737:chemistry*; D000818:Animals; D001826:Body Fluids / Q000737:chemistry*; D002417:Cattle; D003343:Corrosion; D003470:Culture Media / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007552:Isotonic Solutions / Q000737:chemistry; D008274:Magnesium / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D013052:Spectrometry, X-Ray Emission; D013499:Surface Properties
chemical_list: D000497:Alloys; D003470:Culture Media; C072670:Hanks Balanced Salt Solution; D007552:Isotonic Solutions; D008274:Magnesium
keywords: ECAP; In vitro degradation; Simulated body fluids; ZM21 magnesium alloy