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Magnesium (Mg) and its alloys have become a research frontier in biodegradable materials owing to their superior biocompatibility and excellent biomechanical compatibility. However, ...their high degradation rate in the physiological environment should be well tackled prior to clinical applications. This review summarizes the latest progress in the development of polymeric coatings on biodegradable Mg alloys over the last decade, regarding preparation strategies for polylactic acid (PLA), poly (latic-co-glycolic) acid (PLGA), polycaprolactone (PCL), polydopamine (PDA), chitosan (CS), collagen (Col) and their composite, and their performance in terms of corrosion resistance and biocompatibility. Feasible perspectives and developing directions of next generation of polymeric coatings with respect to biomedical Mg alloys are briefly discussed.
Magnesium (Mg) and its alloys have become a research frontier in biodegradable materials owing to their superior biocompatibility and suitable biomechanical compatibility. However, the principal drawback of Mg-based implants is their poor corrosion resistance in physiological environments. Hence, it is vital to mitigate the degradation/corrosion behavior of Mg alloys for safe biomedical deployments. This review summarizes the latest progress in development of polymeric coatings on biomedical Mg alloys regarding preparation strategy, corrosion resistance and biocompatibility, including polylactic acid (PLA), poly (latic-co-glycolic) acid (PLGA), polycaprolactone (PCL), chitosan (CS), polydopamine (PDA), collagen (Col) and their composite. In addition, functionalized polymer coatings with Mg alloys exhibits a promising prospect owing to their ability of degradation along with biocompatibility, self-healing, drug-delivery and osteoinduction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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.
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•The change in open circuit potentials leads to alternating degradation mechanisms.•Degradation mechanisms include chemical and electrochemical corrosion.•Chemical corrosion of the coatings may be related to the non-through pores.•Electrochemical corrosion is due to through-pores and micro-cracks of the coating.•Through-pores in the microarc oxidation coating designate a galvanic effect.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•The microstructure is characterised by the α-Mg matrix and the Mg2Ca phase.•Fe and Si coexist with the Mg2Ca particles.•Ca plays a dual role in the corrosion of the Mg–Ca alloys.•The Mg–0.79Ca alloy ...has the highest hardness, strength and corrosion resistance.
Microstructure, composition and the corrosion resistance of Mg–Ca alloys were analysed using SEM, EDS, XPS, EPMA, XRD, electrochemical and immersion tests. The results revealed that Ca played a dual role, decreasing the corrosion rate due to the refinement of grain size and accelerating corrosion due to the formation of the Mg2Ca phase. The Mg2Ca particles coexisted with Fe and Si led to pitting corrosion. The Mg–0.79Ca alloy had the highest hardness, ultimate tensile/yielding strength and corrosion resistance in comparison with the Mg–0.54Ca and Mg–1.35Ca alloys, representing the promising candidate for degradable biomaterials.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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•The MAO/PMTMS coating has a compact morphology with some spherical particles.•The MAO/PMTMS coating (thickness=13.65μm) possesses a good corrosion resistance.•The PMTMS film acts as ...a physical and blocking barrier.•The self-healing of PMTMS film plays an important role in its long-term protection.•The PMTMS film peels off due to its swelling and the stress of corrosion products.
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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Mg–Al-layered double hydroxide (LDH) coatings were fabricated by a combined co-precipitation method and hydrothermal process on an AZ31 alloy substrate. The characteristics of the coatings were ...investigated using SEM, XRD, FT-IR and EDS. The corrosion resistance of the LDH coatings was studied using potentiodynamic polarization and electrochemical impedance spectrum. The results demonstrated that the LDH coatings, characterized by nanoplates stacked vertically to the substrate surface and ion-exchange ability, possess excellent corrosion resistance.
•The microstructure of the LDH coatings was composed of the nanoplates.•The LDH-coated alloys possess excellent anticorrosion property.•The LDH coatings possess the ion-exchangeability.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A molybdate intercalated hydrotalcite (HT-MoO 4 2− ) coating with a nanosized lamellar structure was synthesized on AZ31 Mg alloy by a combination of the co-precipitation and hydrothermal processes. ...The characteristics of the coatings were investigated by SEM, EPMA, XRD, EDS and FT-IR. The corrosion resistance of the coatings was assessed by potentiodynamic polarization, electrochemical impedance spectrum, and hydrogen evolution. The results indicated that the HT-MoO 4 2− coating, characterized by interlocking plate-like nanostructures, ion-exchange and self-healing ability, has a potential to be a “smart” coating capable of responding to stimuli from the environment.
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 (≤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.
The degradation of micro-arc oxidation coating (MAO)/chitosan (CS) coating decreases solution pH value at lower level (≤8.25) in comparison to MAO coating. A self-degradation mechanism of CS-based materials is proposed. And the degradation process experiences three stages: (1) initial water diffusion, absorption and hydration of CS coatings; (2) gradual decrease in molecular weight; and (3) scission and dissolution of oligomers and monomers. Thus, the degraded CS releases -NH3+ ions, which react with MgO of MAO coating and lead to the formation of Mg2+ ions and water along with the micro-cracks and pores of the MAO coating. Display omitted
•MAO/CS coating improves corrosion resistance and antibacterial effect of the alloy.•Degradation of MAO/CS coating retains a lower pH of ≤8.25 during long immersion.•MAO/CS coating is negative and cathodic relative to its substrate.•Self-degradation mechanism of MAO/CS coating on Mg-4Li-1Ca alloy is proposed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Mo-Dependent perchlorate reductase (PcrAB), responsible for the ending step of anaerobic respiration of perchlorate reducing bacteria, catalyzes the conversion of perchlorate to chlorate and ...subsequently chlorite and is also able to deoxidate bromate, iodate, and nitrate. Herein, the reaction mechanisms for the PcrAB-catalyzed decomposition of these oxyanions have been investigated using density functional calculations and a chemical model constructed from the X-ray crystal structure. It is revealed that the reactions of halogen oxyanions proceed through a very fast O-X (X = Cl, Br, and I) heterolytic cleavage activated by the MoIV center, followed by a rate-limiting reduction of the resulting MoVIdouble bond, length as m-dashO back to MoIV dominated by the slow proton-coupled electron transfer (PCET). However, the O-N bond heterolysis in the nitrate decomposition has a barrier (16.2 kcal mol-1) comparable to the PCET-dominating reduction of MoVIdouble bond, length as m-dashO. This heralds an exciting future where a proper mutation of electron/proton transfer passage of perchlorate reducing bacteria may lead to a decomposition preference for halogen oxyanions rather than non-toxic nitrate, providing a friendly bioremediation method. Other open mechanistic questions are also addressed, where in particular an O-O rebound mechanism without PCET has been ruled out.
Compared to inorganic electrodes, organic materials are regarded as promising electrodes for lithium-ion batteries (LIBs) due to the attractive advantages of light elements, molecular-level ...structural design, fast electron/ion transferring, favorable environmental impacts, and flexible feature, etc. Not only specific capacities but also working potentials of organic electrodes are reasonably tuned by polymerization, electron-donating/withdrawing groups, and multifunctional groups as well as conductive additives, which have attracted intensive attention. However, organic LIBs (OLIBs) are also facing challenges on capacity loss, side reactions, electrode dissolution, low electronic conductivity, and short cycle life, etc. Many strategies have been applied to tackle those challenges, and many inspiring results have been achieved in the last few decades. In this review, we have introduced the basic concepts of LIBs and OLIBs, followed by the typical cathode and anode materials with various physicochemical properties, redox reaction mechanisms, and evolutions of functional groups. Typical charge–discharge behaviors and molecular structures of organic electrodes are displayed. Moreover, effective strategies on addressing problems of organic electrodes are summarized to give some guidance on the synthesis of optimized organic electrodes for practical applications of OLIBs.
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IJS, KILJ, NUK, PNG, UL, UM
Silica “nanorattles” are fabricated by means of selective etching of ingeniously designed organic–inorganic hybrid silica spheres with a three‐layer “sandwich” structure. The size (95–645 nm), shell ...thickness, and core diameter of the monodisperse nanorattles can be precisely controlled, even in gram‐scale production. This method is also shown to be promising for development as a general method for synthesis of rattle‐type functional nanomaterials.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
