Surface Modification Of Magnesium Alloy Research Articles

Mechanical properties of surface-modified magnesium alloy AZ61 with nanoparticles of aluminum oxide and titanium dioxide by friction stir processing

The present work investigates the mechanical properties of surface-modified magnesium alloy AZ61 reinforced with Al2O3 and TiO2 nanoparticles by using the friction stir processing (FSP) technique. Surface-modified AZ61 alloys were fabricated by the addition of dufferent amount of Al2O3 and TiO2 nanoparticles (5, 10, and 15 vol.%). The developed surface composites were studied regarding microstructure, revealing a uniform dispersion of the added nanoparticles, which resulted in improved mechanical properties of the obtained composites by FSP. The ultimate tensile strength, impact strength, and microhardness improved by 20, 45, and 67 % by reinforcing the alloy with nanoTiO2 particles when compared to the as-cast alloy. The results of this study indicate that the reinforced AZ61 Mg alloy can be a potential material for applications in automobile sectors due to its high strength and lightweight components.

New features of surface modification of magnesium alloys by microarc oxidation (MAO)

New features of surface modification of magnesium alloys by microarc oxidation (MAO)

β-TCP particles additive synergistically improves corrosion resistance and biocompatibility of micro-arc oxide coated magnesium alloy

Optimizing micro-arc oxidation (MAO) coating by introducing functional particles has attracted increasing attention in fields about surface modification of magnesium alloys. However, the incorporation of particles usually destroys the integrity of the coating and resulting in the decreased corrosion resistance. In this work, β-tricalcium phosphate (β-TCP), a degradable calcium phosphate, was introduced in the MAO coating on magnesium surface. The results show that the introduction of β-TCP simultaneously enhances the long-term corrosion resistance and biocompatibility of MAO coating. This work provides a strategy to synergistically improve the corrosion resistance and biocompatibility of magnesium alloy for orthopedic applications.

New Design to Provide Absolute Protection Within a Certain Period for Biodegradable Magnesium Alloys

ObjectivesMagnesium and magnesium alloy materials have excellent potential as biodegradable bone plate implants. However, the practical application of magnesium alloys is limited by their high chemical activity and poor corrosion resistance. Here, we chose a microarc fluorination (MAF) treatment to improve corrosion resistance while enhancing aspects of magnesium alloy properties. The aim of this study was to identify the effect of fixed-point corrosion on the corrosion resistance as well as the mechanical properties of magnesium alloys and to design a new corrosion-oriented model that can provide absolute protection over a period of time. Material and MethodsMAF treatment is used for surface modification of magnesium alloys to improve the corrosion resistance of magnesium alloys. To investigate the effect of the coating and indentation on the corrosion resistance of Mg alloy, electrochemical corrosion experiments were carried out. It is worth mentioning that in this experiment we measured and analyzed the mechanical properties of the samples, especially the tensile strength. ResultsIn the innovative indentation sample test, the coated specimens showed lower tensile strength due to the occurrence of fixed-point corrosion. To avoid the loss of mechanical properties due to fixed-point corrosion, we proposed a new idea (Corrosion-oriented Design). Ultimately, the immersion experiments as well as the mechanical properties analysis concluded that the Corrosion-oriented Design samples could maintain the mechanical properties without detectable loss for a long time. ConclusionThe Corrosion-oriented Design model can avoid the nuisance of fixed-point corrosion and control the centralized orientation of corrosion. This provides a new direction for the clinical application of magnesium alloys, which may offer a completely stable bone-healing condition in trauma treatment and avoid the drawbacks caused by the previous uncontrolled corrosion.

Surface Modification of Biodegradable Mg-Based Scaffolds for Human Mesenchymal Stem Cell Proliferation and Osteogenic Differentiation.

Magnesium alloys with coatings have the potential to be used for bone substitute alternatives since their mechanical properties are close to those of human bone. However, the surface modification of magnesium alloys to increase the surface biocompatibility and reduce the degradation rate remains a challenge. Here, FHA-Mg scaffolds were made of magnesium alloys and coated with fluorohydroxyapatite (FHA). Human mesenchymal stem cells (hMSCs) were cultured on FHA-Mg scaffolds and cell viability, proliferation, and osteogenic differentiation were investigated. The results showed that FHA-Mg scaffolds display a nano-scaled needle-like structure of aggregated crystallites on their surface. The average Mg2+ concentration in the conditioned media collected from FHA-Mg scaffolds (5.8–7.6 mM) is much lower than those collected from uncoated, Mg(OH)2-coated, and hydroxyapatite (HA)-coated samples (32.1, 17.7, and 21.1 mM, respectively). In addition, compared with hMSCs cultured on a culture dish, cells cultured on FHA-Mg scaffolds demonstrated better proliferation and comparable osteogenic differentiation. To eliminate the effect of osteogenic induction medium, hMSCs were cultured on FHA-Mg scaffolds in culture medium and an approximate 66% increase in osteogenic differentiation was observed three weeks later, indicating a significant effect of the nanostructured surface of FHA-Mg scaffolds on hMSC behaviors. With controllable Mg2+ release and favorable mechanical properties, porous FHA-Mg scaffolds have a great potential in cell-based bone regeneration.

Tunable Microstructure and Morphology of the Self-Assembly Hydroxyapatite Coatings on ZK60 Magnesium Alloy Substrates Using Hydrothermal Methods

Hydroxyapatite coatings have been widely used to improve the corrosion resistance of biodegradable magnesium alloys. In this paper, in order to manufacture the ideal hydroxyapatite (HA) coating on the ZK60 magnesium substrate by hydrothermal method, formation mechanism of enhanced hydroxyapatite (HA) coatings, influence of pH values of the precursor solution on the HA morphology, corrosion resistance and cytotoxicity of HA coatings have been investigated. Results show that the growth pattern of the HA is influenced by the local pH value. HA has a preferential c-axis and higher crystallinity in the alkaline environment developing a nanorod-like structure, while in acid and neutral environments it has a preferential growth along the a(b)-plane with a lower crystallinity, developing a nanosheet-like structure. The different morphology and microstructure lead to different degradation behavior and performance of HA coatings. Immersion and electrochemical tests show that the neutral environment promote formation of HA coatings with high corrosion resistance. The cell culture experiments confirm that the enhanced corrosion resistance assure the biocompatibility of the substrate-coating system. In general, the HA coating prepared in neutral environment shows great potential in surface modification of magnesium alloys.

Magnesium-alloy rods reinforced bioglass bone cement composite scaffolds with cortical bone-matching mechanical properties and excellent osteoconductivity for load-bearing bone in vivo regeneration

Various therapeutic platforms have been developed for repairing bone defects. However, scaffolds possess both cortical bone-matching mechanical properties and excellent osteoconductivity for load-bearing bone defects repair is still challenging in the clinic. In this study, inspired by the structure of the ferroconcrete, a high-strength bifunctional scaffold has been developed by combining surface-modified magnesium alloy as the internal load-bearing skeleton and bioglass-magnesium phosphate bone cement as the osteoconductive matrix. The scaffold combines the high mechanical strength and controllable biodegradability of surface-modified magnesium alloy with the excellent biocompatibility and osteoconductivity of bioglass-magnesium phosphate bone cement, thus providing support for load-bearing bone defects and subsequently bone regeneration. The scaffolds generate hydroxyapatite (HA) during the degrading in simulated body fluid (SBF), with the strength of the scaffold decreasing from 180 to 100 MPa in 6 weeks, which is still sufficient for load-bearing bone. Moreover, the scaffolds showed excellent osteoconductivity in vitro and in vivo. In a New Zealand White Rabbit radius defect model, the scaffolds degrade gradually and are replaced by highly matured new bone tissues, as assessed by image-based analyses (X-ray and Micro-CT) and histological analyses. The bone formation-related proteins such as BMP2, COL1a1 and OCN, all showed increased expression.

Characterization of bioactive ceramic coatings synthesized by plasma electrolyte oxidation on AZ31 magnesium alloy having different Na2SiO3·9H2O concentrations

Surface modification of magnesium alloys by Plasma Electrolytic Oxidation (PEO) method can be a great help for the development of degradable implants in clinical applications. In this study, the aim was to investigate the effect of changing Na2SiO3·9H2O concentration (5, 10, and 15 g L−1) in a bath containing Ca2H4P2O4, Na3PO4.12H2O, NaF, and KOH compounds at pH = 12 and a conductivity of 20 mS/cm. Coating characterization was performed by Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive X-ray Spectroscopy (EDX), X-ray Diffraction (XRD), nanoindentation, Electrochemical Impedance Spectroscopy (EIS), Fourier Transform-Infrared Spectroscopy (FTIR), and immersion in Simulated Body Fluid (SBF). The formed bioactive ceramic coating contains bioelements from the electrolyte, including Ca, P, Si, F, and Na. And, as Na2SiO3·9H2O concentration increases, it also silicon, sodium, and oxygen values in the coating, and reduces magnesium and phosphor values. Pore density decreases in the coatings by an increase in Na2SiO3·9H2O concentration. The optimum bioactive ceramic coating considering hardness and corrosion resistance contains 10 g L−1 of Na2SiO3·9H2O. The optimized bioactive ceramic coating has the ability to form carbonate hydroxyapatite after immersion in SBF at 37 °C for one and four days.

New approach for improving anticorrosion and biocompatibility of magnesium alloys via polydopamine intermediate layer-induced hydroxyapatite coating

Although magnesium alloys have become a promising candidate for bone implant materials, their rapid degradation has limited their use in medical applications. Surface modification is a feasible strategy for solving the corrosion problem of magnesium alloys. Here, we report a novel hydroxyapatite coating induced by polydopamine obtained using the hydrothermal treatment. The surface morphology and composition of the coating were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. It was found that the dopamine-induced hydroxyapatite coating exhibits a more compact structure than the pure hydroxyapatite coating. Potentiodynamic polarization and simulated body fluid immersion tests demonstrated that the polydopamine-induced hydroxyapatite coating significantly reduced the corrosion rate due to the synergistic effect of the inner polydopamine layer and the outer hydroxyapatite coating. The cytocompatibility tests indicated that the composite coating significantly promoted the proliferation, adhesion and spread of osteoblasts. Thus, this coating may be a promising new approach for the surface modification of magnesium alloys.

Effects of Number of Cyclic Loading in Scanning Cyclic Press on the Surface Modification of Magnesium Alloy

Effects of Number of Cyclic Loading in Scanning Cyclic Press on the Surface Modification of Magnesium Alloy

A pH-sensitive self-healing coating for biodegradable magnesium implants

Self-healing coatings have attracted attention on surface modification of magnesium alloys, as it can recover the barrier ability of the coatings from corrosion attack. Nevertheless, previous works on this aspect are not suitable for biomedical magnesium alloys owing to the lack of biocompatibility. In this study, we fabricated a self-healing coating on biomedical Mg-1Ca alloy by compositing silk fibroin and K3PO4. PO43− ions act as corrosion inhibitor, while K3+ ions help to regulate the secondary structures of silk fibroin. The scratch test, scanning vibrating electrode technique (SVET), and electrochemical impedance spectroscopy (EIS) provide comprehensive results, confirming the pH-sensitive self-healing capacity of the composite coating. Moreover, cells’ (MC3T3-E1) multiple responses including spreading, adhesion, proliferation, and differentiation illustrate the preferable biocompatibility as well as the osteogenic activity of the coating. These primary findings might open new opportunities in the exploration of self-healing coatings on biomedical magnesium alloys. Statement of significanceBiomedical magnesium alloys surface modifications have been studied for years, which however the biomedical self-healing coatings were rarely involved. In this work, silk fibroin and phosphate (K3PO4) were composited to fabricate coating on biomedical magnesium alloys. The coating not only owned the self-healing ability with pH sensitivity, but also endowed the substrate preferable corrosion resistance as well as osteogenic activity. This work gives a new insight into surface modification for biomedical Mg alloys.

Surface modification of AZ61 magnesium alloy with nano-Al<SUB align="right">2O<SUB align="right">3 using laser cladding technique: optimisation of wear properties through hybrid GRA-PCA

The aim of this research is to investigate the wear behaviour of surface modified AZ61 magnesium alloy with nanoceramic reinforcement (Al2O3), done by laser cladding technique. Nano-Al2O3 is added in three different weight proportions, viz., 5%, 10% and 15% on to the surface of AZ61 using Nd:YAG laser. Dry sliding wear behaviour of the surface modified AZ61 material is studied considering various reinforcement of nanoceramic particles, and by varying the speed and axial load in the pin-on-disc apparatus. Experiments were designed using Taguchi's design of experiments and the measured outputs, viz., wear, coefficient of friction and frictional force were analysed using grey relational analysis (GRA), coupled with principal component analysis (PCA) for multivariate optimisation by calculating multi-response performance index (MRPI). Using SEM image, distribution of particles in the magnesium alloy matrix is studied. It is observed that the % reinforcement of nanoceramic particles on the surface of AZ61 alloy is the most critical factor that contributes by 79.30% towards the MRPI, followed by 9.91% contribution by load and speed by 7.94%, as determined from analysis of variance (ANOVA). From confirmation experiment, the optimised condition shows an improved wear resistance obtained from the surface modified magnesium alloy.

Surface modification of AZ61 magnesium alloy with nano-Al<SUB align="right">2O<SUB align="right">3 using laser cladding technique: optimisation of wear properties through hybrid GRA-PCA

The aim of this research is to investigate the wear behaviour of surface modified AZ61 magnesium alloy with nanoceramic reinforcement (Al2O3), done by laser cladding technique. Nano-Al2O3 is added in three different weight proportions, viz., 5%, 10% and 15% on to the surface of AZ61 using Nd:YAG laser. Dry sliding wear behaviour of the surface modified AZ61 material is studied considering various reinforcement of nanoceramic particles, and by varying the speed and axial load in the pin-on-disc apparatus. Experiments were designed using Taguchi's design of experiments and the measured outputs, viz., wear, coefficient of friction and frictional force were analysed using grey relational analysis (GRA), coupled with principal component analysis (PCA) for multivariate optimisation by calculating multi-response performance index (MRPI). Using SEM image, distribution of particles in the magnesium alloy matrix is studied. It is observed that the % reinforcement of nanoceramic particles on the surface of AZ61 alloy is the most critical factor that contributes by 79.30% towards the MRPI, followed by 9.91% contribution by load and speed by 7.94%, as determined from analysis of variance (ANOVA). From confirmation experiment, the optimised condition shows an improved wear resistance obtained from the surface modified magnesium alloy.

Enhancing Corrosion Resistance, Osteoinduction, and Antibacterial Properties by Zn/Sr Additional Surface Modification of Magnesium Alloy.

To control the degradation of magnesium alloy and enhance its osteoinduction activity and antibacterial properties, we proposed the addition of Zn and Sr ions in the process of surface modification of the magnesium alloy (ZK60) by a one-pot hydrothermal process. We found that, after surface modification, the surface of the materials formed a cluster crystal structure coating layer, and the successful incorporation of Zn and Sr ions in the surface coating did not affect the morphology of the microstructure. The corrosion resistance of the surface of the modified magnesium alloy was significantly improved, and cells grew well on the modified material surfaces. Zn and Sr ions released from the coating layer promote cell osteogenic differentiation, and Zn ions also provide a good antibacterial effect. Thus, the combined use of Zn and Sr offers antibacterial effects and promotes osteogenic differentiation of cells. To summarize, we have developed a controllable and degradable magnesium alloy material that offers both osteoinduction and antibacterial effects. The development of this material provides ideas about the preparation of a novel biodegradable magnesium alloy with better bioactivity for clinical application.

Microstructure and Corrosion Resistance of PEO Coatings Formed on KBM10 Mg Alloy Pretreated with Nd(NO₃)₃.

Plasma electrolytic oxidation (PEO) technique is one of the important methods used in the surface modification of magnesium alloys. In this paper, the ceramic coatings on pretreated KBM10 magnesium alloy with Nd(NO3)3 solution were prepared by PEO. The effects of Nd(NO3)3 solution concentration on the microstructure and corrosion resistance of PEO coatings on magnesium alloys were investigated by means of scanning electron microscopy (SEM), X-ray diffractometer (XRD), and electrochemical workstation. It was found that the surface of the coatings was porous after PEO, and element Nd could be deposited on the surface of the coatings by pretreatment and existed in the PEO coatings. The coating formed at Nd(NO3)3 solution concentration of 0.06 mol/L exhibited the best corrosion resistance among all the as-prepared coatings.

Mg-Zn-Y-Nd coated with citric acid and dopamine by layer-by-layer self-assembly to improve surface biocompatibility

Magnesium alloy has been generally accepted as an important biodegradable material on cardiovascular stent development for a long time. However, its limited biocompatibility, especially delayed endothelialization process restricts its further application. In this contribution, we modified the Mg-Zn-Y-Nd alloy surface with citric acid and dopamine via a layer-by-layer self-assembly assay, aiming at improving the biocompatibility of the magnesium alloy. The citric acid/dopamine (CA/PDA) layer exhibited a remarkable suppression of platelet activation/aggregation and thrombosis under 15 dyn/cm2 blood flowing. Inhibition on vascular smooth muscle cells growth and macrophages attachment/activation were also observed on this layer. In particular, the CA/PDA layer presented a promoted property for the vascular endothelial cells growth and spreading compared with the bare magnesium alloy, suggesting the pro-endotelialized function. In conclusion, this research may support potential application on surface modification of magnesium alloy based cardiovascular stents for better biocompatibility.

Surface Modification of Magnesium alloy by Shot Lining

Surface Modification of Magnesium alloy by Shot Lining

Loading 5-Fluorouracil into calcined Mg/Al layered double hydroxide on AZ31 via memory effect

The clinic application of magnesium is mainly impeded by its poor corrosion resistance and implants with localized drug delivery attract tremendous interest. Here, Mg/Al layered double hydroxide (Mg-Al LDH) film was in situ prepared on AZ31 alloy by a hydrothermal process, and further calcined to form metastable mixed oxides, also named Mg/Al layered double oxide (LDO). Finally, immersing in 5-Fluorouracil (5-FU) solution, Mg/Al LDO would revert to Mg/Al LDH via a memory effect, and be loaded with 5-FU (#LDO-5FU). Comparing to AZ31 alloy, the corrosion resistance of the as-prepared #LDO-5FU sample was enhanced. The amount of released 5-FU from #LDO-5FU sample was ∼993 ng/cm2. The proliferation of human cholangiocarcinoma cell (RBE) was effectively inhibited on the surface of #LDO-5FU sample owing to the release of 5-FU. This work broadens the application of calcined LDH and provides a new strategy in the field of surface modification of magnesium alloy.

Biofunctionalisation of magnesium alloys by successive immobilisation of poly(ethylene glycol), fibronectin and heparin

In the present study, with the aim of improving their corrosion resistance, anticoagulation and cytocompatibility with endothelial cells, a magnesium alloy (AZ31B) was modified by the alkali heat treatment followed by the immobilisation of the dopamine layer. Subsequently, molecules of poly(ethylene glycol) (PEG) and fibronectin or fibronectin–heparin complexes were successively immobilised on the dopamine-modified surface. After the surface modification, the hydrophilicity of magnesium alloy was obviously improved. The corrosion resistance of the magnesium alloy was improved through alkali heat treatment, and the immobilisation of dopamine and PEG can further reduce the corrosion rate. However, the corrosion resistance of the magnesium alloy was slightly reduced by the grafting of fibronectin or fibronectin–heparin complex. Furthermore, the modified samples showed improved hemocompatibility and good cytocompatibility with the endothelial cells on the fibronectin or fibronectin–heparin-modified surfaces. Therefore, the corrosion resistance, anticoagulation and cytocompatibility of the magnesium alloy can be enhanced by alkali heat treatment and subsequent immobilisation of biomolecules. The method of this study can be used for surface modification of magnesium alloys to impart these with better corrosion resistance, blood compatibility and cytocompatibility with endothelial cells simultaneously.

Multifunctional polymer-containing coatings on magnesium alloys

The results of surface modification of magnesium alloys by plasma electrolytic oxidation (PEO) and post-treatment in suspension of tetrafluoroethylene (TFE) telomeric solution or superdispersed polytetrafluoroethylene (SPTFE) dispersion have been presented. Electrochemical, tribological properties and wetting ability of obtained protective composite coatings were investigated. The fabricated coatings decrease both the corrosion current density (1.7×10 -9 –5.4×10 -11 A/cm 2 ) and wear (9.8×10 -6 –7.6×10 -7 mm 3 /(N m)) by orders of magnitude as compared to bare magnesium alloy (5.3×10 -5 A/cm 2 and 3.8×10 -3 mm 3 /(N m)) and base PEO-coating (2.4×10 -7 A/cm 2 and 1.7×1 -3 mm 3 /(N m)). Moreover, coatings obtained by means of PEO and polymer dispersion dipping possess hydrophobic and superhydrophobic properties. Such multifunctional coatings have high corrosion resistance and good friction coefficient under dry wear conditions that extends the application field of magnesium alloys.