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Magnesium alloys have narrow available slip result from close-packed hexagonal structure that limit their processing properties. In the recent work, the Mg-2Zn-0.46Y-0.5Nd, as materials for degradable stents, was applied to produce as-extruded micro-tube with an outer diameter of 3.0 mm and a wall thickness of 0.35 mm by hot extrusion with an extrusion ratio of 105:1 at 653 K and rapid cooling. The fine microstructure of the dynamic recrystallization of as-extruded micro-tube could be preserved by rapid cooling such as water-cooled, resulting in more excellent mechanical properties relative to air-cooled micro-tube. The addition of rare earth elements Y and Nd results in continuous dynamic recrystallization dominated the dynamic recrystallization mechanism. During the hot extrusion process, the activation of the non-basal slip system, especially the pyramidal 〈 c + a 〉 slip, could significantly weaken the texture strength, and the as-extruded micro-tube exhibits weak "RE" texture components 〈 01 1 ¯ 1 〉 ∥ ED and 〈 1 ¯ 2 1 ¯ 1 〉 ∥ ED. Hence, the magnesium alloy micro-tube prepared by the rapid cooling has fine microstructure and weak texture, which is favorable for further process and governance. [ABSTRACT FROM AUTHOR]

Highlights: [•] Microstructure evolution of Ca-def HA coating was systematically investigated. [•] Poor crystalline Ca-def HA has been formed at the deposition time of 5min. [•] Reasons for direct formation of Ca-def HA coating on Mg–Zn–Ca alloy are discussed. [ABSTRACT FROM AUTHOR]

Highlights: [•] It’s effective to fabricate a bio-composite coating on Mg alloy by this method. [•] Most HA got involved in the coating and turned into TCP during the MAO process. [•] HA and the sintering-caused phases changed the cross-section into dense structure. [•] The bioactivity and corrosion resistance of the coating were improved. [ABSTRACT FROM AUTHOR]

• Yttrium-oxygen layer is found under dynamic flow. • Yttrium-oxygen layers decreases the corrosion rate of microtubes under dynamic flow. • A suitable selection of rare earth elements could further improve the corrosion resistance. In the corrosion tests, yttrium (Y) element reacts with oxygen (O) element to form Y-O compound, generating a protective corrosion layer to isolate magnesium (Mg) alloy from further attack of corrosion medium. To better illustrate the protective effects of Y-O compound on corrosion morphology of biodegradable Mg alloys stents, in vitro dynamic corrosion tests were conducted for ZE21B Mg alloy microtubes. Under dynamic flow, Mg-O layer and calcium-phosphate (Ca-P) layer peeled off from microtubes, and the compact and flat Y-O layer started to emerge, protecting ZE21B Mg alloy microtubes against flow induced corrosion. [ABSTRACT FROM AUTHOR]

[Display omitted] • The relation between the features and mechanical behavior of Mg alloys was modeled. • The stacking ensemble model can perform better than single models. • The mechanical properties of biomedical Mg alloys are accurately predicted. In this work, a dataset was constructed by collecting the data of mechanical properties for 365 magnesium (Mg) alloys. Using the composition and process parameters of Mg alloys as input variables, six machine learning (ML) models including ridge regression, support vector machine regression, gradient boosting regression tree, random forest, CatBoost, and Gaussian process regression, were built to predict the ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) of Mg alloys. These single models were then integrated by using model ensemble in order to further improve the prediction accuracy. The results showed that the ensemble model achieved a higher prediction accuracy and better generalization ability for UTS, YS, and EL than that for the single models. The mechanical properties predicted by the optimal model were very close to the experimental values, demonstrating that ML is an effective method for predicting the mechanical properties of biomedical Mg alloys. [ABSTRACT FROM AUTHOR]

Magnesium alloys are considered to be one of the most promising stent materials due to their good biological compatibility and biodegradable properties. However, the poor workability at room temperature restricts the processing of high-precision micro-tubes for the application as stent materials. In this study, Mg–Zn–Y–Nd alloy tube blank was firstly produced through hot extrusion. By multi-pass cold drawing combining with interpass annealing, the extruded tube blank can be processed into high-precision micro-tube with an outer diameter of about 2.0 mm and a wall thickness of about 0.15 mm. The drawn micro-tube after annealing exhibits improved mechanical properties with an ultimate tensile strength of about 298 MPa and a large breaking elongation of up to 20%. Meanwhile, the micro-tube shows good corrosion resistance with a trend of uniform corrosion in simulated body fluid solution. The investigation revealed that a significant improvement in the mechanical properties is mainly attributed to grain refinement and texture weaken, while the good biodegradable properties is related with the low density of crystallographic defects as well as fine and homogeneous microstructure. As a result, the successful processing of magnesium alloy micro-tube provides the precursor for laser engraving stents. [ABSTRACT FROM AUTHOR]

[Display omitted] • Corrosion of the substrate was effectively inhibited by the presence of MgSO 4 during coating preparation. • MgSO 4 results in the transformation of the middle calcite from cubic to spindle-shaped crystals. • Mg2+ and SO 4 2− promote the precipitation of metastable aragonite and vaterite in the outer layer. • The corrosion resistance of CaCO 3 coating for Mg substrate can be adjusted by MgSO 4 concentration. • CaCO 3 could be transformed into Ca-P products during immersion. Too fast corrosion of magnesium(Mg)-based materials is one of main concerns prior to their applications as biodegradable biomaterials. In present study, a CaCO 3 coating on Mg alloy is developed via hydrothermal method to control the corrosion of Mg2Zn0.2Ca alloy. The morphology and anti-corrosion property of the CaCO 3 protective coating are adjusted by the concentration of MgSO 4 in coating preparation electrolyte. The results reveal that the presence of MgSO 4 stabilizes the precipitation of metastable CaCO 3 crystalline (aragonite and vaterite) and affects the structure and growth rate of the middle calcite layer on Mg alloy surface, which leads to the transformation of cubic calcite into small rhombohedral aggregates in the middle layer as the concentration of MgSO 4 increases. Consequently, the corrosion protection property of the coating is significantly enhanced due to the increased compactness of the coating as the concentration of MgSO 4 increases from 0 mM to 20 mM. Whereas, with further increase of MgSO 4 concentration, the spindle-shaped calcite crystalline formed in the middle layer provides more penetrable boundaries, leading to a lower resistance for Mg substrate. Long-term immersion tests indicate the transformation of CaCO 3 into calcium phosphate, which exhibits a great prospect for Mg alloys as orthopedic implants. [ABSTRACT FROM AUTHOR]

To reduce the degradation of magnesium alloy, improve its antibacterial activity, and fulfil specific requirements for bone implant material applications, a chitosan (CS)/boron nitride nanosheet (BNNS) composite coating was constructed on the surface of Mg–Zn–Y–Nd–Zr alloy via electrodeposition. The results show that BNNS was uniformly embedded and significantly changed the morphology and roughness of the CS coating. Electrochemical and immersion tests suggest that the CS–BNNS composite coating can effectively provide a long-term protection to the substrate. The antibacterial activity results show that BNNS significantly improved the antibacterial activity of the CS coating against E. coli and S. aureus , and verified the sterilisation mechanism of BNNS in contact with bacterial membranes. Meanwhile, cytocompatibility tests showed that the CS–BNNS coating has no adverse effect on the adhesion and proliferation of mouse osteoblasts cells. Thus, the fabricated CS–BNNS composite coating could be a promising application in surface modification for Mg-based bone implants. In this study, a chitosan (CS)/boron nitride nanosheet (BNNS) composite coating was constructed on a magnesium (Mg) alloy via electrodeposition. The CS–BNNS coating improves the antibacterial activity and reduces the degradation rate of the Mg alloy. BNNS was uniformly embedded into the chitosan coating, which significantly improved the bactericidal activity of the CS coating. Meanwhile, cytocompatibility tests showed that the CS–BNNS coating has no adverse effect on the adhesion and proliferation of mouse osteoblasts cells. [Display omitted] • CS–BNNS coatings were synthesised on a Mg alloy via electrodeposition. • CS-BNNS coating reduces the degradation rate of Mg alloy. • CS-BNNS coating improves the antibacterial activity of Mg alloy. [ABSTRACT FROM AUTHOR]

Abstract: In present paper, an in vivo study was carried out on uncoated and calcium-deficient hydroxyapatite (Ca-def HA) coated Mg–Zn–Ca alloy to investigate the effect of Ca-def HA coating on the degradation behavior and bone response of magnesium substrate. Magnesium alloy rods were implanted into rabbit femora and evaluated during 24 weeks implantation. The characterization of both implants indicates that in vivo degradation of the Ca-def HA coating and magnesium substrate occurs almost simultaneously, and in vivo valid life of the coating is about 8 weeks, after that the degradation rate of the coated implants increases obviously. The main reasons for the Ca-def HA coating degradation can be attributed to its reaction with body fluid and the substitution of Mg2+ ions in Ca-def HA. Histopathological examinations show that the Ca-def HA coating has good osteoconductivity and is in favor of the formation of more new bone on the surface of magnesium alloy. So the Ca-def HA coating could not only slow down in vivo degradation of magnesium alloy but also improve its bone response. [Copyright &y& Elsevier]

Severe and non-uniform degradation of magnesium (Mg) alloys limits their general application in the field of vascular stents. Polymer coatings, which have been widely used in biodegradable materials, can simultaneously reduce degradation and improve the biocompatibility of Mg alloys. In this study, polycaprolactone (PCL) coating was prepared on Mg–Zn–Y–Nd alloy by electrografting. The microstructure of the prepared coating is significantly influenced by current density and monomer concentration, according to scanning electron microscope/energy dispersive spectroscopy results. The electrografted PCL coating has two molecular weights, 15.5 × 103 g·mol−1 and 1.08 × 103 g·mol−1, according to gel permeation chromatography results. Electrochemical and immersion tests show that the electrografted PCL coating has better anti-corrosion properties than the PCL coating prepared using the traditional dipping method. Meanwhile, human umbilical vein endothelial cells and smooth muscle cells culture results show that electrografted PCL coating improves the magnesium alloy's ability to maintain cell viability. Furthermore, arginine-glycine-aspartic acid was fixed on the surface of the PCL coating to confirm the possibility of functionalisation of the electrografted PCL coating. The results show that the composite coating promotes cell adhesion. In this study, polycaprolactone (PCL) coating was prepared by the ring-opening polymerization of ε-caprolactone by electrografting. The micro-morphology of PCL coating changed from cauliflower-like porous structure to smooth surface after heat treatment. The cytocompatibility of the PCL coating is further improved by loading arginine-glycine-aspartic acid, which is expected to be used as a multi-functional coating for cardiovascular stents. [Display omitted] [ABSTRACT FROM AUTHOR]