Correct selection of alloying elements is important for developing novel biodegradable magnesium alloys with superior mechanical and biological performances. In contrast to various reports on ...nutrient elements (Ca, Zn, Sr, etc.) as alloying elements of biomedical magnesium alloys, there is limited information about how to choose the right rare earth elements (REEs) as alloying elements of magnesium. In this work, 16 kinds of REEs were individually added into Mg, including Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Du, Ho, Er, Tm, Yb and Lu, to fabricate binary Mg-RE model alloys with different composition points. Under the same working history, comparative studies were undertaken and the impact of each kind of rare earth element on the microstructure, mechanical property, corrosion behavior and biocompatibility of Mg were investigated. The corresponding influence level for the 16 kinds of REEs were ranked. The results showed that the second phases were detected in some Mg-RE alloys, which were mainly composed of Mg12RE. By adding different REEs into Mg with proper contents, the mechanical properties of resulting Mg-RE binary alloys could be adjusted in wide range. The corrosion resistance of Mg-light REE alloys was generally better than Mg-heavy REE alloys. As for biocompatibility, Mg-RE model alloys showed no cytotoxic effect on MC3T3-E1 cells. The hemolysis rates of all experimental Mg-RE model alloys were lower than 5% except for Mg-Lu alloy model. In general, the addition of different REEs into Mg could improve its performance from different aspects. This work provides a better understanding on suitable REEs as alloying elements for magnesium, and the future R&D direction on biomedical Mg-RE alloys was proposed.
In contrast to various reports on nutrient elements (Ca, Zn, Sr, etc.) as alloying elements of biomedical magnesium alloys, until now there is limited information about how to choose the right rare earth elements (REEs) as alloying elements of magnesium. In this work, comparative studies were undertaken by individually adding 16 kinds of REEs, including Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Du, Ho, Er, Tm, Yb and Lu, into Mg to fabricate binary Mg-RE model alloys, with different composition points, then the impact of each kind of rare earth element on the microstructure, mechanical property, corrosion behavior and biocompatibility of Mg under the same working history were investigated, and the corresponding influence level for the 16 kinds of REEs were ranked. This work provides a better understanding on suitable REEs as alloying elements for magnesium, and the future R&D direction on biomedical Mg-RE alloys was proposed.
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The search for biodegradable metals with mechanical properties equal or higher to those of currently used permanent biomaterials, such as stainless steels, cobalt chromium and ...titanium alloys, desirable in vivo degradation rate and uniform corrosion is still an open challenge. Magnesium (Mg), iron (Fe) and zinc (Zn)-based alloys have been proposed as biodegradable metals for medical applications. Over the last two decades, extensive research has been done on Mg and Fe. Fe-based alloys show appropriate mechanical properties, but their degradation rate is an order of magnitude below the benchmark value. In comparison, alongside the insufficient mechanical performance of most of its alloys, Mg degradation rate has proven to be too high in a physiological environment and corrosion is rarely uniform. During the last few years, Zn alloys have been explored by the biomedical community as potential materials for bioabsorbable vascular stents due to their tolerable corrosion rates and tunable mechanical properties. This review summarizes recent progress made in developing Zn alloys for vascular stenting application. Novel Zn alloys are discussed regarding their microstructural characteristics, mechanical properties, corrosion behavior and in vivo performance.
Numerous studies on magnesium and iron materials have been reported to date, in an effort to formulate bioabsorbable stents with tailorable mechanical characteristics and corrosion behavior. Crucial concerns regarding poor ductility and remarkably rapid corrosion of magnesium, and very slow degradation of iron, seem to be still not desirably fulfilled. Zinc was introduced as a potential implant material in 2013 due to its promising biodegradability and biocompatibility. Since then, extensive investigations have been made toward development of zinc alloys that meet clinical benchmarks for vascular scaffolding. This review critically surveys the zinc alloys developed since 2013 from metallurgical and biodegradation points of view. Microstructural features, mechanical, corrosion and in vivo performances of these new alloys are thoroughly reviewed and evaluated.
//Nbsub.ss and α-Nbsub.5Sisub.3 phases were detected. Meanwhile, Nbsub.2C was observed, and the crystal forms of Nbsub.5Sisub.3 changed in the C-doped composites. Furthermore, micron-sized and ...nano-sized Nbsub.2C particles were found in the Nbsub.ss layer. The orientation relationship of Nbsub.2C phase and the surrounding Nbsub.ss was 001sub.Nbss//010sub.Nb2C, (200) sub.Nbss//(101) sub.Nb2C. Additionally, with the addition of C, the compressive strength of the composites, at 1400 °C, and the fracture toughness increased from 310 MPa and 11.9 MPa·msup.1/2 to 330 MPa and 14.2 MPa·msup.1/2, respectively; the addition of C mainly resulted in solid solution strengthening.
In this article, the experimental measurements of the absorption/desorption P–C–T isotherms of hydrogen in the LaNisub.4.4Fesub.0.3Alsub.0.3 alloy at different temperatures and constant hydrogen ...pressure have been studied using a numerical model. The mathematics equations of this model contain parameters, such as the two terms, nsub.α and nsub.β, representing the numbers of hydrogen atoms per site; Nsub.mα and Nsub.mβ are the receptor sites’ densities, and the energetic parameters are Psub.α and Psub.β. All these parameters are derived by numerically adjusting the experimental data. The profiles of these parameters during the absorption/desorption process are studied as a function of temperature. Thereafter, we examined the evolution of the internal energy versus temperature, which typically ranges between 138 and 181 kJmolsup.−1 for the absorption process and between 140 and 179 kJmolsup.−1 for the desorption process. The evolution of thermodynamic functions with pressure, for example, entropy, Gibbs free energy (G), and internal energy, are determined from the experimental data of the hydrogen absorption and desorption isotherms of the LaNisub.4.4Asub.l0.3Fsub.e0.3 alloy.
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Novel Mg-(3.5, 6.5wt%)Li-(0.5, 2, 4wt%)Zn ternary alloys were developed as new kinds of biodegradable metallic materials with potential for stent application. Their mechanical ...properties, degradation behavior, cytocompatibility and hemocompatibility were studied. These potential biomaterials showed higher ultimate tensile strength than previously reported binary Mg-Li alloys and ternary Mg-Li-X (X=Al, Y, Ce, Sc, Mn and Ag) alloys. Among the alloys studied, the Mg-3.5Li-2Zn and Mg-6.5Li-2Zn alloys exhibited comparable corrosion resistance in Hank’s solution to pure magnesium and better corrosion resistance in a cell culture medium than pure magnesium. Corrosion products observed on the corroded surface were composed of Mg(OH)2, MgCO3 and Ca-free Mg/P inorganics and Ca/P inorganics. In vitro cytotoxicity assay revealed different behaviors of Human Umbilical Vein Endothelial Cells (HUVECs) and Human Aorta Vascular Smooth Muscle Cells (VSMCs) to material extracts. HUVECs showed increasing nitric oxide (NO) release and tolerable toxicity, whereas VSMCs exhibited limited decreasing viability with time. Platelet adhesion, hemolysis and coagulation tests of these Mg-Li-Zn alloys showed different degrees of activation behavior, in which the hemolysis of the Mg-3.5Li-2Zn alloy was lower than 5%. These results indicated the potential of the Mg-Li-Zn alloys as good candidate materials for cardiovascular stent applications.
Mg-Li alloys are promising as absorbable metallic biomaterials, which however have not received significant attention since the low strength, controversial corrosion performance and the doubts in Li toxicity. The Mg-Li-Zn alloy in the present study revealed much improved mechanical properties higher than most reported binary Mg-Li and ternary Mg-Li-X alloys, with superior corrosion resistance in cell culture media. Surprisingly, the addition of Li and Zn showed increased nitric oxide release. The present study indicates good potential of Mg-Li-Zn alloy as absorbable cardiovascular stent material.
In this study, we have investigated the electrochemical corrosion behavior of boron carbide (Bsub.4C) ceramic-reinforced Al-Mg-Si matrix composites in various aqueous environments (NaOH, NaCl, HCl, ...and Hsub.2SOsub.4). The samples were produced by the powder metallurgy (P/M) route and the corrosion investigations were conducted by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) methods. The morphology of the as-prepared and corroded samples was examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) studies. The investigations revealed that the corrosion resistance of Al-Mg-Si composites is highest in NaCl medium due to a less negative corrosion potential, higher charge transfer (Rsub.ct) resistance, and lower double-layer capacitance (Csub.dl) as compared to other media. The SEM morphology suggests that Bsub.4C ceramics enhance corrosion resistance by forming a protective barrier layer of OH- and Cl- deposits in the composite and unreinforced alloy, respectively.
Closed-cell metal syntactic foam is a new material consisting of hollow spheres embedded in metal matrix syntactic foams. These foams have good physical and mechanical properties and are increasingly ...used worldwide in industrial and high-tech fields. Magnesium matrix syntactic foams containing hollow Alsub.2Osub.3 spheres ((Alsub.2Osub.3hs)/AZ91D) were successfully fabricated by hot press sintering at different temperatures. The fabrication of Alsub.2Osub.3hs/AZ91D and the effect of sintering temperature on the microstructure and properties are reported in this paper. Additionally, sandwiched magnesium matrix syntactic foams were prepared by placing magnesium plates on both sides of the syntactic foam. Some Alsub.2Osub.3hs particles became filled with matrix particles during preparation. Thus, the actual density was greater than the theoretically calculated value and increases with increasing sintering temperature. Above 723 K, a brittle phase MgAlsub.2Osub.4 formed in Alsub.2Osub.3hs/AZ91D. The quasistatic and dynamic compressive strengths of Alsub.2Osub.3hs/AZ91D first increased and then decreased with increasing sintering temperature, and the maximums were 162 MPa and 167.87 MPa, respectively. Thus, this paper reports a new strategy for the controlled preparation of metal matrix syntactic foams with predetermined porosity. The results show that this strategy improved the performance of lightweight and high-strength syntactic foam materials and shows potential for further research.
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