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In this work, we demonstrated a novel approach of corrosion protection based on the fabrication of polyelectrolyte/SiO2 nanoparticles multilayers on magnesium alloys. The original multilayers based merely on electrostatic attraction showed porous morphology and weak anti-corrosion protection for the Mg substrate. However, the heat-treatment process would change the microstructures of the multilayers through the cross-linking between the polyelectrolytes and the capping agents of the nanoparticles, and the barrier effects of the coating could be confirmed by polarization and electrochemical impedance spectroscopy. Thus the heat treatment would be an applicable option for preparing the layer-by-layer assembled anti-corrosive multilayers on biomedical Mg alloys.

The microstructure and chemical compositions of the solid solution-treated Mg-3Nd-1Li-0.2Zn alloy were characterized using optical microscope, scanning electron microscope (SEM), transmission electron microscope (TEM), electron probe micro-analyzer (EPMA) and X-ray photoelectron spectroscopy (XPS). The corrosion behaviour of the alloy was investigated via electrochemical polarization, electrochemical impedance spectroscopy (EIS), hydrogen evolution test and scanning Kelvin probe (SKP). The results showed that the microstructure of the as-extruded Mg-3Nd-1Li-0.2Zn alloy contained α-Mg matrix and nanometric second phase Mg41Nd5. The grain size of the alloy increased significantly with the increase in the heat-treatment duration, whereas the volume fraction of the second phase decreased after the solid solution treatment. The surface film was composed of oxides (Nd2O3, MgO, Li2O and ZnO) and carbonates (MgCO3 and Li2CO3), in addition to Nd. The as-extruded alloy exhibited the best corrosion resistance after an initial soaking of 10 min, whereas the alloy with 4h-solution-treatment possessed the lowest corrosion rate after a longer immersion (1 h). This can be attributed to the formation of Nd-containing oxide film on the alloys and a dense corrosion product layer. The dealloying corrosion of the second phase was related to the anodic Mg41Nd5 with a more negative Volta potential relative to α-Mg phase. The preferential corrosion of Mg41Nd5 is proven by in-situ observation and SEM. The solid solution treatment of Mg-3Nd-1Li-0.2Zn alloy led to a shift in corrosion type from pitting corrosion to uniform corrosion under long-term exposure.

A hydrothermal deposition method was utilized to fabricate Ca-P composite coating induced by the layer-by-layer (LbL) assembled polyvinylpyrrolidone/deoxyribonucleic acid (PVP/DNA)20 multilayer on AZ31 alloy. The surface morphology and compositions were characterized by SEM, EDS, FTIR and XRD. Besides, the corrosion resistance and degradation behavior of the coating were tested via electrochemical polarization, impedance spectroscopy and immersion measurements. Results show that the main components of Ca-P coatings are hydroxyapatite, Ca3(PO4)2 and Mg3(PO4)2·nH2O. The LbL-assembled DNA and PVP promote the adsorption of Ca-P deposits on the sample surface, and structures and functional groups of the polyelectrolyte in the outermost layer are the primary influencing factor for the induction of the Ca-P coating. Carboxyl groups have the best biomineralization effect among all related functional groups. The enhanced corrosion resistance and adhesion highlight a promising use of (PVP/DNA)20-induced Ca-P coatings in the field of biomedical magnesium alloys.

Magnesium (Mg) and its alloys are considered as ideal biodegradable materials due to their excellent mechanical properties and biocompatibility. In order to improve the surface properties to allow better adaptation to the surrounding tissue of the body, surface modification has played a significant role in satisfying multiple clinical requirements such as corrosion resistance, biocompatibility, and antibacterial ability. Here, layer-by-layer (LbL) self-assembly, which can be applied for biodegradable Mg alloys due to its extensive choice of usable units, holds great promise among all the surface techniques. In this review, the mechanisms of the driving force (i.e., electrostatic interaction, hydrogen bonding, charge transfer interaction and covalent bonding), cutting-edge advances in preparation methods (e.g., dipping, spraying, and spinning) and the functional properties (corrosion resistance, antibacterial activity, and biocompatibility) that could be achieved by the LbL coatings are summarized. A reasonable trend of the potential development of LbL for bio-Mg alloys is also proposed at the end of this article.

The performance of biodegradable magnesium alloy requires special attention to rapid degradation and poor biocompatibility, which can cause the implant to fail. Here, a sodium montmorillonite (MMT)/bovine serum albumin (BSA) composite coating was prepared upon magnesium alloy AZ31 via hydrothermal synthesis, followed by dip coating. We evaluated the surface characterization and corrosion behavior in vitro, and the biocompatibility in vitro and in vivo. Biodegradation progress of the MMT-BSA coated Mg pieces was examined through hydrogen evolution, immersion tests, and electrochemical measurements in Hank’s solution. In vitro biocompatibility studies were evaluated via hemolysis tests, dynamic cruor time tests, platelet adhesion, MTT testing and live-dead stain of osteoblast cells (MC3T3-E1). It was found that the MMT-BSA coating had good corrosion resistance and a marked improvement in biocompatibility in comparison to bare Mg alloy AZ31. in vivo studies were carried out in rat model and the degradation was characterized by computed tomography scans. Results revealed that the MMT-BSA coated Mg alloy AZ31 implants maintained their structural integrity and slight degradation after 120 d of post-implantation. A 100% survival rate for the rats was observed with no obvious toxic damages on the organs and tissues. Additionally, we proposed a sound coating formation mechanism. Considering the good corrosion protection and biocompatibility, the MMT-BSA coated Mg alloy AZ31 is a promising candidate material for biomedical implants.

The biocorrosion of magnesium in the external physiological environment is still difficult to accurately evaluate the degradation behavior in vivo, particularly, in the microenvironment of the patients with hyperglycemia or diabetes. Thus, we explored the synergistic effects of glucose and protein on the biodegradation of pure magnesium, so as to have a deeper understanding the mechanism of the degradation in vivo. The surface morphology and corrosion product composition of pure magnesium were investigated using SEM, EDS, FTIR, XRD and XPS. The effect of glucose and albumin on the degradation rate of pure magnesium was investigated via electrochemical and immersion tests. The adsorption of glucose and albumin on the sample surface was observed using fluorescence microscopy. The results showed that the presence of 2 g/L glucose changed the micromorphology of corrosion products on the magnesium surface by reacting with metal cations, thus inhibiting the corrosion of pure magnesium. Protein formed a barrier layer to protect the magnesium at early stage of immersion. The chelation reaction between protein and magnesium surface might accelerate the degradation at later stage. There may be a critical glucose (albumin) content. Biodegradation of pure magnesium was inhibited at low concentrations and promoted at high concentrations. The synergistic effect of glucose and protein restrained the adsorption of aggressive chloride ions to a certain extent, and thus inhibited the degradation of pure magnesium considerably. Moreover, XPS results indicated that glucose promoted the adsorption of protein on the sample surface., Graphical abstract Image 1, Highlights • The absorbed BSA layer delays the corrosion of pure Mg in the initial stage. • BSA promotes the degradation of Mg owing to the chelation effect subsequently. • The glucose curbs the degradation by impeding the attack of Cl− ions. • Glucose promotes the adsorption of protein due to the formation of glycosamine. • The synergistic effects of glucose and BSA reduces the degradation rate of pure Mg.

Biodegradable magnesium (Mg)-based alloys have aroused great concern owing to their promising characteristics as temporary implants for orthopedic application. But their undesirably rapid corrosion rate under physiological conditions has limited the actual clinical application. This study reports the use of a novel biomimetic polyelectrolyte multilayer template, based on polyvinylpyrrolidone (PVP) and polyacrylic acid (PAA) via layer-by-layer (LbL) assembly, to improve the corrosion resistance of the alloy. Surface characterization techniques (field-emission scanning electron microscopy, Fourier transform infrared (FTIR) spectrophotometer and X-ray diffractometer) confirmed the formation of biomineralized Ca–P coating on AZ31 alloy. Both hydrogen evolution and electrochemical corrosion tests demonstrated that the corrosion protection of the polyelectrolyte-induced Ca–P coating on AZ31 alloy. The formation mechanism of biomineralized Ca–P coating was proposed., Graphical abstract Image 1, Highlights • A novel LbL assembled template induces a compact and thick Ca–P coating. • (PVP/PAA)5.5 template improves the binding force of the Ca–P coating. • The templates-induced Ca–P coating exhibits a good corrosion protection for Mg alloy. • Free PAA and PVP may go against the nucleation and growth of the Ca–P crystals. • (PVP/PAA)5.5 template is beneficial to the formation of the crystalline Ca–P coating.

A Zinc-loaded montmorillonite (Zn-MMT) coating was hydrothermally prepared using Zn2+ ion intercalated sodium montmorillonite (Na-MMT) upon magnesium (Mg) alloy AZ31 as bone repairing materials. Biodegradation rate of the Mg-based materials was studied via potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS) and hydrogen evolution tests. Results revealed that both Na-MMT and Zn-MMT coatings exhibited better corrosion resistance in Dulbecco’s modified eagle medium (DMEM) + 10% calf serum (CS) than bare Mg alloy AZ31 counterparts. Hemolysis results demonstrated that hemocompatibility of the Na-MMT and Zn-MMT coatings were 5%, and lower than that of uncoated Mg alloy AZ31 pieces. In vitro MTT tests and live-dead stain of osteoblast cells (MC3T3-E1) indicated a significant improvement in cytocompatibility of both Na-MMT and Zn-MMT coatings. Antibacterial properties of two representative bacterial strains associated with device-related infection, i.e. Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), were employed to explore the antibacterial behavior of the coatings. The measured inhibitory zone and bacterial growth rate confirmed that Zn-MMT coatings exhibited higher suppression toward both E. coli and S. aureus than that of Na-MMT coatings. The investigation on antibacterial mechanism through scanning electron microscopy (SEM) and lactate dehydrogenase (LDH) release assay manifested that Zn-MMT coating led to severe breakage of bacterial membrane of E. coli and S. aureus, which resulted in a release of cytoplasmic materials from the bacterial cells. In addition, the good inhibition of Zn-MMT coatings against E. coli and S. aureus might be attributed to the slow but sustainable release of Zn2+ ions (up to 144 h) from the coatings into the culture media. This study provides a novel coating strategy for manufacturing biodegradable Mg alloys with good corrosion resistance, biocompatibility and antibacterial activity for future orthopedic applications. Statement of Significance The significance of the current work is to develop a corrosion-resistant and antibacterial Zn-MMT coating on magnesium alloy AZ31 through a hydrothermal method. The Zn-MMT coating on magnesium alloy AZ31 shows better corrosion resistance, biocompatibility and excellent antibacterial ability than magnesium alloy AZ31. This study provides a novel coating on Mg alloys for future orthopedic applications.

Magnesium (Mg) alloys have received increasing interest as innovative orthopedic implants, while the extremely rapid degradation rate and the susceptibility to the infection have limited their medical applications. In this study, a novel hydroxyapatite (HAp) coating induced by ciprofloxacin (CIP)-loaded polymeric multilayers was prepared on Mg alloy via the combination of layer-by-layer (LbL) assembly and hydrothermal treatment. The coated substrates were subjected to various characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) techniques. The corrosion resistance was evaluated by electrochemical and immersion tests. The antibacterial activity was investigated via plate-counting method against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Besides, the cytocompatibility was assessed via an indirect extraction test for MC3T3-E1 pre-osteoblasts. The results revealed that the as-prepared HAp coating with a compact topography showed favorable corrosion resistance, antibacterial activity and cell compatibility together with a prolonged release profile of CIP.

One of the major obstacles for the clinical use of biodegradable magnesium (Mg)-based materials is their high corrosion rate. Micro-arc oxidation (MAO) coatings on Mg alloys provide mild corrosion protection owing to their porous structure. Hence, in this study a dense Mg(OH)2 film was fabricated on MAO-coated Mg alloy AZ31 in an alkaline electrolyte containing ethylenediamine tetraacetic acid disodium (EDTA-2Na) to reinforce the protection. Surface morphology, chemical composition and growth process of the MAO/Mg(OH)2 hybrid coating were examined using field-emission scanning electron microscopy, energy dispersive X-ray spectrometer, X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectrophotometer. Corrosion resistance of the coatings was evaluated via potentiodynamic polarization curves and hydrogen evolution tests. Results manifested that the Mg(OH)2 coating possesses a porous nano-sized structure and completely seals the micro-pores and micro-cracks of the MAO coating. The intermetallic compound of AlMn phase in the substrate plays a key role in the growth of Mg(OH)2 film. The current density of Mg(OH)2-MAO composite coating decreases three orders of magnitude in comparison with that of bare substrate, indicating excellent corrosion resistance. The Mg(OH)2-MAO composite coating is beneficial to the formation of calcium phosphate corrosion products on the surface of Mg alloy AZ31, demonstrating a great promise for orthopaedic applications.

A SnO2-doped calcium phosphate (Ca-P-Sn) coating was constructed on Mg-1Li-1Ca alloy by a hydrothermal process. The fabricated functional coatings were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). A triple-layered structure, which is composed of Ca3(PO4)2, (Ca, Mg)3(PO4)2, SnO2, and MgHPO4·3H2O, is evident and leads to the formation of Ca10(PO4)6(OH)2 in Hank’s solution. Electrochemical measurements, hydrogen evolution tests and plating counts reveal that the corrosion resistance and antibacterial activity were improved through the coating treatment. The embedded SnO2 nanoparticles enhanced crystallisation of the coating. The formation and degradation mechanisms of the coating were discussed.

Bioinspired coatings with decreased corrosion rate and enhanced bond strength are at the core of future clinic applications on degradable magnesium (Mg)-based implants. The hybrid of organic and inorganic compounds offers a strategy to fabricate biodegradable, biocompatible and compact coatings on biomedical Mg alloys. Hereby, a comparison with and without DNA addition was made on the corrosion resistance and adhesion strength of Ca–P coatings fabricated on AZ31 alloy via hydrothermal deposition. The morphology, chemical composition, and crystallographic structure of the coatings were investigated by means of SEM, EDS and FTIR as well as XRD before and after corrosion tests. Corrosion resistance was evaluated via potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS) and hydrogen evolution tests in Hank's solution. Results show that the coatings are mainly characterized by tricalcium phosphate (TCP), dicalcium phosphate anhydrous (DCPA) and calcium-deficient hydroxyapatite (CDHA). The presence of DNA leads to the formation of Ca–P coating with improved corrosion resistance and adhesion strength. Additionally, the formation mechanism for DNA-induced Ca–P coating is proposed. The DNA-induced Ca–P coating exhibits a promising future for controlling the corrosion rate of biodegradable Mg alloys. Keywords: DNA, Corrosion resistance, Biodegradability, Magnesium alloys, Coatings

Glucose-induced composite coatings containing crystalline calcium phosphate and Mg(OH)2 interlayer were prepared on pure Mg substrate through hydrothermal deposition from alkaline solution. Surface composition, morphology and corrosion resistance of the coatings were characterized through XRD, FTIR, SEM, XPS, electrochemical and hydrogen evolution measurements. Results reveal that calcium phosphate coatings were composed of dicalcium phosphate anhydrous, calcium-deficient hydroxyapatite and hydroxyapatite. Corrosion resistance of pure Mg specimens was improved by the formation of such a calcium phosphate coating. The findings provide a novel strategy to design calcium phosphate conversion coatings with satisfactory corrosion resistance for biodegradable Mg implants.

A (polyvinylpyrrolidone (PVP)/deoxyribonucleic acid (DNA))n coating was fabricated via layer-by-layer (LbL) assembly dip coating method. The surface morphologies, chemical compositions and corrosion resistances of the coatings were investigated using field-emission scanning electron microscopy, X-ray photoelectron spectrometer, Fourier transform infrared, X-ray diffractometer and electrochemical and hydrogen evolution measurements. The results indicated that the (PVP/DNA)n coating shows a smooth surface with shallow scratches and some corrosion cracks, which possesses a good corrosion resistance in simulated body fluid, especially for n = 20. The (PVP/DNA)n coating can be used as a inducer to construct a biomimetic biocompatible Ca-P coating on Mg alloys. Additionally, we suggest and discuss a corrosion mechanism for the coating.

A Mg-Al-layered double hydroxide (LDH) coating modified with methyltrimethoxysilane (MTMS) and cerium nitrate was prepared on AZ31 magnesium alloy substrate via a hydrothermal process and subsequent the immersion treatment. The surface morphologies and chemical compositions were investigated using FE-SEM, XRD, FT-IR and XPS. These results indicated that the composite coatings were consisted of polymethyltrimethoxysilane (PMTMS) and CeO2. The adherence between the PMTMS/CeO2 coating and the LDH coating was significantly improved with the formation of Si-O-Si and Si-O-Mg chemical bonds. Electrochemical tests and hydrogen evolution illustrated that the optimum corrosion resistance of the composite coating was obtained in presence of 10−3 mol/L cerium nitrate. In addition, experimental data proved that addition of an excess of cerium nitrate was bad for coating formation. Finally, the coating corrosion mechanism was proposed and discussed.

The presence of second phase Mg2Ca has remarkable impacts on the formation and degradation of MAO coating. Microstructure, formation and degradation behaviors of substrate and MAO coating were performed. Results revealed that pitting and filiform corrosion occurred on bare Mg-1Li-1Ca alloy. MAO coating significantly improved the corrosion resistance of alloy. The roles of Mg2Ca on the formation and degradation mechanisms of MAO coating were discussed. Micro-arc oxidation for the Mg-Li-Ca alloy initiated at α-Mg phase with depleted Ca content. The growth rate of coating on α-Mg phase is faster than that of GBs/Mg2Ca. The MAO coating began to degrade from intermetallic compound Mg2Ca, then it underwent the attack from the solution and stress concentration caused by corrosion products.

Mg alloys coated with layer-by-layer assembled multilayers always suffered from rapid degradation. In this research, the cross-linked multilayers consisted of CeO2 nanoparticles on Mg alloys were successfully prepared and glutaraldehyde was selected as the cross-linker. The improved corrosion protection of the resulting coatings assessed by tafel plots, electrochemical impedance spectroscopy and immersion test was attributed to the cross-linkages together with the corrosion inhibition effects of the CeO2 nanoparticles.

Exfoliation on as-extruded Mg-1Li-1Ca magnesium alloy was investigated after an immersion in 3.5 wt% NaCl aqueous solution for 90, 120 and 150 days through optical microscope, digital camera, scanning electron microscope, electrochemical workstation, scanning Kalvin probe, X-ray diffraction and Fourier transform infrared spectroscope. The results demonstrated that exfoliation corrosion occurred on extruded Mg-1Li-1Ca alloy due to elongated microstructure parallel to surface, and delamination of lamellar structure resulted from galvanic effect and wedge effect. Skin layer with fine grains exhibited better corrosion resistance, whereas the interior with coarse grains and the intermetallic compound, Mg2Ca particles existing in a fibrous structure, dispersed along grain boundaries and extrusion direction in a line. Furthermore, galvanic effect between Mg2Ca particles and their neighboring α-Mg matrix facilitated dissolution of Mg2Ca particles and α-Mg matrix; wedge effect was caused by formation of corrosion products. Exfoliation corrosion of extruded Mg-Li-Ca alloys might be a synergic effect of pitting corrosion, filiform corrosion, intergranular corrosion and stress corrosion. Finally, exfoliation corrosion mechanism was proposed.

Regulating degradation rate and moderate pH micro-environment for biodegradable magnesium alloys face huge challenge. The chemical and morphological characteristics of micro-arc oxidation (MAO) and chitosan (CS) composite coatings, fabricated on Mg-4Li-1Ca alloy, are analyzed through field-emission scanning electronic microcopy, energy dispersive X-ray spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. Corrosion resistance of the samples is evaluated via hydrogen evolution, potentiodynamic polarization and electrochemical impedance spectroscopy in Hank's solution. Results indicated that the MAO and CS coating enhances the corrosion resistance and antibacterial growth activity. With increasing immersion time, the degradation of the MAO/CS coatings gives rise to a decrease in pH value and leads to a rapid increase in hydrogen evolution rate after an immersion in Hank's solution after 100 h. The MAO/CS coatings retain the solution pH at a moderate level (less than or equal to 8.25). A novel self-degradation mechanism of the MAO/CS coating on Mg-Li-Ca alloy is proposed due to the fact that MAO/CS coating is cathodic relative to the substrate.

A micro-arc oxidation (MAO)/zinc stearate (ZnSA) composite coating was fabricated via MAO processing and subsequent sealing with electrodeposition of a superhydrophobic ZnSA. The surface morphologies, chemical composition and corrosion resistance of the coatings were investigated using field-emission scanning electron microscopy, Fourier transform infrared, X-ray diffraction and electrochemical and hydrogen evolution measurements. Results indicated that the MAO coating was efficiently sealed by the following superhydrophobic ZnSA coating. The MAO/ZnSA composite coating significantly enhanced the corrosion resistance of Mg alloy Mg-4Li-1Ca due to its superhydrophobic function. Additionally, corrosion mechanism was suggested and discussed for the composite coating.

A SnO2-doped dicalcium phosphate coating was prepared on AZ31 alloy by means of hydrothermal deposition. The results showed that the coating possessed a globular morphology with a long lamellar crystalline structure and a thickness of approximately 40 μm. The surface of the coating became smooth with an increase additive amount of the SnO2 nanoparticles. The corrosion current density and hydrogen evolution rate of the coating prepared in presence of SnO2 were reduced compared to the coating without SnO2 and the bare AZ31 substrate, indicating an improvement in the corrosion resistance of the SnO2-doped coating., Graphical abstract Image 1, Highlights • A thick and dense SnO2-doped DCPA coating forms via hydrothermal deposition. • The DCPA coating doped with 10 g L−1 SnO2 exhibits the best corrosion resistance. • SnO2 provided heterogeneous nucleation sites for the deposition of Ca2+ and HPO42−.

A crosslinked ciprofloxacin (CIP) and polymethyltrimethoxysilane (PMTMS) with an inner micro-arc oxidation (MAO) coating was designed to improve the corrosion resistance and antibacterial property of magnesium alloy AZ31. Surface morphology and roughness of the obtained coating were characterized through scanning electron microscopy (SEM) and three-dimensional surface profilometry. Structural components and chemical compositions of the composite coatings were detected via Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectrometry (EDS). Corrosion resistance of the coatings was investigated by means of electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves and hydrogen evolution measurements. Cytocompatibility and antibacterial performance of the coatings were probed using in vitro cytotoxicity tests (MTT), live/dead cell staining and plate counting method. Results indicate that the MAO/CIP-PMTMS coating possesses enhanced corrosion resistance, antibacterial ability and cytocompatibility. It provides a way to effectively curb the sudden release and short release period of drugs, due to the reversible esterification reaction between -COOH in CIP and Si-OH in PMTMS during the coating formation and degradation process. And it holds a great potential in the applications of medical devices and bone implant materials.

In vitro degradation is an important approach to screening appropriate biomedical magnesium (Mg) alloys at low cost. However, corrosion products deposited on Mg alloys exert a critical impact on corrosion resistance. There are no acceptable criteria on the evaluation on degradation rate of Mg alloys. Understanding the degradation behavior of Mg alloys in presence of Tris buffer is necessary. An investigation was made to compare the influence of Tris-HCl and Tris on the corrosion behavior of Mg alloy AZ31 in the presence of various anions of simulated body fluids via hydrogen evolution, pH value and electrochemical tests. The results demonstrated that the Tris-HCl buffer resulted in general corrosion due to the inhibition of the formation of corrosion products and thus increased the corrosion rate of the AZ31 alloy. Whereas Tris gave rise to pitting corrosion or general corrosion due to the fact that the hydrolysis of the amino-group of Tris led to an increase in solution pH value, and promoted the formation of corrosion products and thus a significant reduction in corrosion rate. In addition, the corrosion mechanisms in the presence of Tris-HCl and Tris were proposed. Tris-HCl as a buffer prevented the formation of precipitates of HCO3−, SO42−, HPO42− and H2PO4− ions during the corrosion of the AZ31 alloy due to its lower buffering pH value (x.x). Thus, both the hydrogen evolution rate and corrosion current density of the alloy were approximately one order of magnitude higher in presence of Tris-HCl than Tris and Tris-free saline solutions.

Influence of glucose on corrosion of biomedical Mg-1.35Ca alloy was made using hydrogen evolution, pH and electrochemical polarization in isotonic saline solution. The corrosion morphologies, compositions and structures were probed by virtue of SEM, EDS, FTIR, XRD and XPS. Results indicate that the glucose accelerated the corrosion of the alloy. The elemental Ca has no visible effect on the corrosion mechanism of glucose for the Mg-1.35Ca alloy in comparison with pure Mg. In addition, the presence of CO2 has beneficial effect against corrosion due to the formation of a layer of carbonatecontaining products.

Mg-Li based alloys hold much attention as potential biomedical materials due to their excellent ductility. A reduced mechanical strength and concern for biocompatibility are exhibited for Mg-Li binary alloys due to the presence of Li element. Addition of the Ca element into Mg-Li alloys leads to an improvement in mechanical strength and biocompatibility. In the present work, the microstructure, mechanical property and corrosion behaviors of three kinds ( α , α + β , β ) of as-extruded Mg-Li (1, 9 and 15 wt.%)-1Ca alloys were investigated using optical microscope, X-ray diffraction (XRD), tensile, immersion and electrochemical polarization measurements. In vitro biocompatibility was evaluated by cytotoxicity assays, hemolysis and four coagluation tests. The results indicated that the Mg-1Li-1Ca and Mg-15Li-1Ca alloys were characterized by α -Mg and β -Li phases besides Mg2Ca particles, respectively; while the Mg-9Li-1Ca by dual ( α -Mg+ β -Li) phase together with Mg2Ca phase. The Mg-1Li-1Ca alloy had the highest ultimate tensile strength (UTS) and yield strength (YS) and the lowest elongation (EL) to failure (10.1±1.24%) as well. The EL for the Mg-9Li-1Ca alloy was the highest (52.2±0.01%). The long-term immersion tests revealed a decrease in corrosion resistance with increasing Li content. The results of cytotoxicity assays clearly showed that the Mg-Li-Ca alloys demonstrated no toxicity to L-929 cells in 10% concentration of extracts. The Mg-1Li-1Ca alloy also exhibited an acceptable hemolysis ratio. The results of four coagulation tests designated no sign of thrombogenicity for the Mg-Li-Ca alloys except for the Mg-15Li-1Ca alloy.

A polymethyltrimethoxysilane (PMTMS)/hydroxyapatite (HA) hybrid coating was successfully fabricated on a magnesium alloy by hydrothermal treatment and immersion method. The microstructure and composition of the coating were characterized by using X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. The physical properties were investigated using scratch testing. At the same time, the corrosion resistance was evaluated via electrochemical and immersion tests. The results demonstrated that the corrosion resistance of the silane hybrid coating was significantly enhanced compared with the naked magnesium alloy. Especially, the corrosion current density of the PMTMS/HA magnesium alloy was three orders of magnitude lower than that of the bare material.

Surface functionalization of magnesium (Mg) alloys is desired to obtain the surfaces with both improved corrosion resistance and antibacterial property. A corrosion-resistant and antimicrobial coating was prepared on Mg alloy surface by layer-by-layer (LbL) assembly of chitosan (CHI) and poly-L-glutamic acid (PGA) by electrostatic attraction. The functionalized surfaces of the Mg alloys were characterized by field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy and electrochemical tests. The bactericidal activity of the samples against Staphylococcus aureus was assessed by the zone of plate-counting method. The obtained coating on the Mg alloy substrates exhibits good corrosion resistance and antibacterial performance.

A micro-arc oxidation (MAO)/polymethyltrimethoxysilane (PMTMS) hybrid coating was fabricated via MAO processing and subsequent sealing with alkaline treatment and PMTMS. The surface morphologies, chemical compositions and corrosion resistances of the coatings were investigated using FE-SEM, FTIR, XRD and electrochemical and hydrogen evolution measurements. The results indicated that the alkaline treatment was beneficial to the silane treatment and that the MAO coating was efficiently sealed by the PMTMS film. The MAO/PMTMS coating significantly enhanced the corrosion resistance of the AZ31 alloy due to its self-healing function. Additionally, we suggest and discuss a corrosion mechanism for the coating.

The morphology, porosity and corrosion resistance of MAO coatings on as-extruded Mg-Ca alloys were analysed using SEM, XRD, EDS and electrochemical tests. The roles of non-through and through-pores in the MAO coating were identified. The results demonstrated that the corrosion resistance of the MAO-coated Mg-Ca alloys is related to the corrosion resistance of the substrates, the porosity of the MAO coating and the galvanic effect. Chemical and electrochemical corrosion alternately occurred on the MAO coatings. The alternating chemical and electrochemical corrosion mechanisms for the MAO coating are discussed.

A layer-by-layer (LbL)-assembled composite coating containing SiO2 and a biocompatible polyvinylpyrrolidone (PVP) and polyacrylic acid (PAA) multi-layer, designated as SiO2/(PVP/PAA)5, was prepared on AZ31 Mg alloy via dip-coating. The surface morphology, microstructure and chemical composition of the coating were investigated using FE-SEM, FT-IR, XRD and XPS. The physical properties of the coating were characterized by scratch testing. The results demonstrated that the coating was amorphous and remarkably soft. PVP and PAA promoted the formation of Ca–P precipitates, and the amorphous silica film further enhanced corrosion resistance. The SiO2/(PVP/PAA)5 coating may be a promising surface modification for degradable Mg cardiovascular stents.

A superhydrophobic surface was successfully constructed to modify the layered double hydroxide (LDH) coatings on aluminum alloy using stearic acid. The characteristics of the coatings were investigated using SEM, XRD, FT-IR and XPS. The corrosion resistance of the prepared coatings was studied using potentiodynamic polarization and electrochemical impedance spectrum. The results revealed that the superhydrophobic surface considerably improved the corrosion-resistant performance of the LDH coatings on the aluminum alloy substrate. The formation mechanism of the superhydrophobic surface was proposed.

An electrically conductive coating was prepared on micro-arc oxidized (MAO) Mg alloy AZ31 via antimony tin oxide (ATO) particles doping in methyltrimethoxysilane (MTMS) coating. A sandwich structure was observed as the ATO particles agglomerated at the top and bottom layers in the MTMS coating via field-emission scanning electron microscopy (FE-SEM). Electrochemical and hydrogen evolution tests revealed high corrosion resistance of the composite coating. Although the ATO-doped MAO/MTMS coating showed a low electrical conductivity, a conductive path was formed on the coating surface layer, enhancing the transfer of static charges. The formation and corrosion mechanisms of the composite coatings are proposed.

Complications related to corrosion and infection of magnesium (Mg) implants are encountered by physical barrier and local drug delivery system. In this work, the multilayer films composed of ciprofloxacin (CIP) and SiO2 nanoparticles were fabricated on Mg alloys by the spin-spray layer-by-layer assembly method. The resultant films were characterized via FT-IR, XPS, SEM and EDS techniques. The corrosion behaviors of the multilayer films were investigated via electrochemical tests and hydrogen evolution experiment. The obtained films showed corrosion resistance, self-healing ability, antibacterial efficacy and a prolonged release profile. The results also suggested that the loading dosage and the release rate of CIP could be controlled by the assembly parameters. Moreover, the in vitro release kinetics of CIP from the multilayer films could be fitted with the pseudo-second-order model.

Influences of proteins on degradation of magnesium alloys are of great significance but not well understood. In particular the roles of amino acids, the basic unit of proteins in regulating the progress of biodegradation of magnesium based materials remain unclear. This study aims to investigate the impacts of alanine, glutamic acid and lysine on degradation of pure magnesium in phosphate buffer solution through SEM, XPS, FTIR, potentiodynamic polarisation curves, electrochemical impedance spectroscopy and immersion tests. The changed contents of amino acids in solutions were detected by UV-vis spectrophotometer. Results demonstrate that the charges of the selected amino acids imposed significant contribution to suppressing the degradation of pure magnesium in phosphate buffer solution. The presence of amino acids led to the formation of phosphate-based corrosion products, increasing free corrosion potential, and reduction in corrosion current density and solution pH depending on their isoelectric points and molecular structures. A plausible corrosion mechanism organised by amino acids on pure magnesium was proposed.

Manipulating the degradation rate of biomedical magnesium alloys poses a challenge. The characteristics of a microarc oxidation (MAO), prepared in phytic acid, and poly(L-lactic acid) (PLLA) composite coating, fabricated on a novel Mg-1Li-1Ca alloy, were studied through field emission scanning electron microscopy (FE-SEM), electron probe X-ray microanalysis (EPMA), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The corrosion behaviors of the samples were evaluated via hydrogen evolution, potentiodynamic polarization and electrochemical impedance spectroscopy in Hanks' solution. The results indicated that the MAO/PLLA composite coatings significantly enhanced the corrosion resistance of the Mg-1Li-1Ca alloy. MTT and ALP assays using MC3T3 osteoblasts indicated that the MAO/PLLA coatings greatly improved the cytocompatibility, and the morphology of the cells cultured on different samples exhibited good adhesion. Hemolysis tests showed that the composite coatings endowed the Mg-1Li-1Ca alloys with a low hemolysis ratio. The increased solution pH resulting from the corrosion of magnesium could be tailored by the degradation of PLLA. The degradation mechanism of the composite coatings was discussed. The MAO/PLLA composite coating may be appropriate for applications on degradable Mg-based orthopedic implants.

The influences of glucose and amino acid (L-cysteine) on the degradation of pure magnesium have been investigated using SEM, XRD, Fourier transformed infrared (FTIR), X-ray photoelectron spectroscopy (XPS), polarization and electrochemical impedance spectroscopy and immersion tests. The results demonstrate that both amino acid and glucose inhibit the corrosion of pure magnesium in saline solution, whereas the presence of both amino acid and glucose accelerates the corrosion rate of pure magnesium. This may be due to the formation of -C=N- bonding (a functional group of Schiff bases) between amino acid and glucose, which restricts the formation of the protective Mg(OH)2 precipitates.