Corrosion resistance of Mg-Al-LDH steam coating on AZ80 Mg alloy:Effects of citric acid pretreatment and intermetallic compounds

In this study,the effects of intermetallic compounds(Mg_(17)Al_(12)and Al_(8)Mn_(5))on the Mg-Al layered double hydroxide(LDH)formation mechanism and corrosion behavior of an in-situ LDH/Mg(OH)_(2)steam coatings on AZ80 Mg alloy were investigated.Citric acid(CA)was used to activate the alloy surface during the pretreatment process.The alloy was first pretreated with CA and then subjected to a hydrothermal process using ultrapure water to produce Mg-Al-LDH/Mg(OH)_(2)steam coating.The effect of different time of acid pretreatment on the activation of the intermetallic compounds was investigated.The microstructure and elemental composition of the obtained coatings were analyzed using FE-SEM,EDS,XRD and FT-IR.The corrosion resistance of the coated samples was evaluated using different techniques,i.e.,potentiodynamic polarization(PDP),electrochemical impedance spectrum(EIS)and hydrogen evolution test.The results indicated that the CA pretreatment significantly influenced the activity of the alloy surface by exposing the intermetallic compounds.The surface area fraction of Mg_(17)Al_(12)and Al_(8)Mn_(5)phases on the surface of the alloy was significantly higher after the CA pretreatment,and thus promoted the growth of the subsequent Mg-Al-LDH coatings.The CA pretreatment for 30 s resulted in a denser and thicker LDH coating.Increase in the CA pretreatment time significantly led to the improvement in corrosion resistance of the coated AZ80 alloy.The corrosion current density of the coated alloy was lower by three orders of magnitude as compared to the uncoated alloy.

In vitro corrosion resistance,antibacterial activity and cytocompatibility of a layer-by-layer assembled DNA coating on magnesium alloy

A chitosan/deoxyribonucleic acid(CHI/DNA)_(5)coating was constructed by layer-by-layer(LbL)assembly dip coating method with Mg(OH)_(2)coating as an inner protective layer on AZ31 alloy.X-ray diffractometry,X-ray photoelectron spectrometry,Fourier transform infrared spectroscopy and field-emission scanning electron microscopy were utilized to represent the chemical compositions and surface morphologies of the coatings.Electrochemical tests and hydrogen evolution measurements were implemented to confirm the good corrosion resistance of the composite coating in artificial body fluid.Antimicrobial activity of the composite coatings was tested via the plate-counting method,and the cytotoxicity of the samples was appraised by MTT assay and Live/dead staining.A double action was put into effect for the composite coating,which the inner Mg(OH)2 coating plays the part of physical barrier,and the outer(CHI/DNA)5 coating is employed as an inducer to fabricate a biocompatible Ca-P corrosion product coating during immersion,making up for its thin thickness.Otherwise,the composite coating is also beneficial for the growth of bone,resulting from the biomineralization effect of the outer polyelectrolyte multilayer.The good antibacterial property of the(CHI/DNA)5/Mg(OH)2 coating is ascribed to the contact-killing strength of CHI.Thus,the obtained(CHI/DNA)5/Mg(OH)2 coating has a wide application prospect in the field of Mg-based bone implantation.

镁合金AZ31表面层层组装壳聚糖/聚谷氨酸涂层的体外耐蚀与抗菌性能（英文）

镁合金表面功能化需要获得具有良好耐蚀性和抗菌性的表面。基于壳聚糖与聚谷氨酸之间的静电吸附作用,利用层层组装方法在镁合金AZ31表面获得一种既耐蚀又抗菌的涂层。利用高分辨扫描电子显微镜、傅里叶红外光谱仪以及电化学测试对这种功能涂层进行了表面形貌、化学成分以及耐蚀性能表征。通过平板计数法评定该涂层耐金黄葡萄球菌的性能。结果表明,该涂层具有良好的耐蚀性与抗菌性。

金属间化合物Al-Mn颗粒对AZ31镁合金原位蒸气Mg-Al-LDH涂层的影响

研究金属间合物Al-Mn颗粒对AZ31镁合金原位形成的Mg-Al水滑石(Mg-Al-CO32--LDH)蒸气涂层腐蚀行为的影响。该合金用H3PO4、HCl、HNO3或柠檬酸(CA)进行预处理,然后进行水热处理制备Mg-Al-LDH涂层。研究涂层样品的显微组织、组成和耐腐蚀性。结果表明,经CA预处理后,合金表面暴露的Al-Mn相的表面积分数显著增加,促进Mg-Al-LDH蒸气涂层的生长。此外,经CA预处理后的合金上LDH涂层在所有涂层中表面最致密、涂层厚度最大。与裸合金相比,含有涂层样品的腐蚀电流密度降低3个数量级。

Corrosion resistance of bioinspired DNA-induced Ca-P coating on biodegradable magnesium alloy

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.©2019 Published by Elsevier B.V.on behalf of Chongqing University.

In vitro corrosion resistance and antibacterial performance of noveltin dioxide-doped calcium phosphate coating on degradable Mg-1Li-1Ca alloy

A SnO_2-doped calcium phosphate(Ca-P-Sn) coating was constructed on Mg-1 Li-1 Ca 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 Ca_3(PO_4)_2,(Ca, Mg)_3(PO_4)_2, SnO_2, and MgHPO_4·3 H_2O, is evident and leads to the formation of Ca_(10)(PO_4)_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 SnO_2 nanoparticles enhanced crystallisation of the coating.The formation and degradation mechanisms of the coating were discussed.

In vitro corrosion resistance of layer-by-layer assembled polyacrylic acid multilayers induced Ca–P coating on magnesium alloy AZ31

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 layerby-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.

In vitro Degradation of Pure Mg for Esophageal Stent in Artificial Saliva

Magnesium and its alloys as biodegradable implant materials can be potentially used in cardiovascular and orthopedic devices. However, few studies have focused on its application in esophageal stents. In this paper, time-lapse degradation characteristics of pure Mg were analyzed by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, hydrogen evolution, pH and electrochemical measurements after immersion in artificial saliva for different times. Results revealed that a dense degradation product film formed on samples, which mainly consisted of two kinds of layers： one was calcium phosphate compounds with different structures; the other was thin magnesium hydrate layer close to the substrate. Less pH increase and low degradation rate were ob- served in the first 5 days of immersion, which can be ascribed to the formation of a thicker and denser layer on the sample surface with increasing immersion time. And then there was an increase in degradation rate and pH values; the deposition layer remained almost intact after immersion for 6 and 8 days. After 10 days of immersion, the degradation rate and pH value remained stable, and the calcium phosphate layer was delaminated and the inner magnesium hydrate layer was exposed. This study indicated that pure Mg exhibited desirable degradation resistance in artificial saliva, which provided magnesiumbased materials with the potential to be used as esophageal stents.

Corrosion resistance and antibacterial effects of hydroxyapatite coating induced by polyacrylic acid and gentamicin sulfate on magnesium alloy

Magnesium(Mg)alloys have attracted considerable research attention as potential biocompatible implant materials.However,the major barriers to the extended use of such medical devices are the possibility of high corrosion rate and implantassociated infections.To solve them,a novel polyacrylic acid(PAA)/gentamicin sulfate(GS)-hydroxyapatite(HAp)coating was synthesized by a one-step hydrothermal deposition method.Characteristics of functional coatings were investigated by SEM,FTIR and XRD.Corrosion properties of samples were evaluated by electrochemical and hydrogen evolution tests.Antibacterial activities of the coatings against Staphylococcus aureus(S.aureus)were measured by the plate-counting method.Results showed that the as-prepared HAp coating with dense and flawless morphologies could not only enhance the corrosion resistance of Mg alloys,but also improve the adhesion strength between the HAp coating and the substrate.In addition,the induction of the apatite coating during immersion confirmed the excellent mineralization ability of the HAp coating.Moreover,the obtained HAp coati ng possessed antibacterial properties and could prolong the release of GS.Thus,the PAA/GS-HAp coated Mg alloy could serve as a better candidate for biomedical applications with good anti-corrosion and antibacterial properties.

Biocorrosion resistance and biocompatibility of Mg-AI layered double hydroxide/poly(L-lactic acid) hybrid coating on magnesium alloy AZ31

A Mg-AI layered double hydroxide(Mg-AI-LDH)coating was firstly synthesized via an in-situ steam coating growth method on the AZ31 Mg alloy,and then was modified with poly(L-lactic acid)(PLLA)via dipping and vacuum freeze-drying.The microstructure and composition of LDH/PLLA hybrid coating were analyzed by XRD,SEM,EDS and FT-IR.The biocorrosion behavior of hybrid coating was evaluated by potentiodynamic polarization,electrochemical impedance spectroscopy(EIS)and hydrogen evolution test in the Hank's solution.The results showed that LDH/PLLA coatings exhibited a much dense layer compared to the unmodified Mg-AI-LDH coating with unobvious boundary between PLLA and LDH coatings.The corrosion current density of the LDH/PLLA-10 hybrid coating decreased three orders of magnitude in comparison to its substrate.It was proven that the existence of the PLLA coating further prolonged the service life of the Mg-AI-LDH coating.What's more,the MTT assay and livel dead staining showed that the LDH/PLL A-10 coating had good biocompatibility for Mouse NIH3T3 fibroblasts.The formation mechanism and the anti-corrosion mechanism of hybrid coatings were proposed.

Corrosion resistance of a superhydrophobic micro-arc oxidation coating on Mg-4Li-1Ca alloy

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-4 Li-1 Ca due to its superhydrophobic function. Additionally, corrosion mechanism was suggested and discussed for the composite coating.

In vitro degradation,photo-dynamic and thermal antibacterial activities of Cu-bearing chlorophyllin-induced Ca-P coating on magnesium alloy AZ31

Surgical failures,caused by postoperative infections of bone implants,are commonly met,which cannot be treated precisely with intravenous antibiotics.Photothermal therapy(PTT)and photodynamic therapy(PDT)have attracted widespread attention due to their non-invasive antibacterial effects on tissues and no bacterial resistance,which may be an excellent approach to solve infections related to bone implants for biodegradable magnesium alloys.Herein,a sodium copper chlorophyllin(SCC)with a porphyrin ring induced Ca-P coating was prepared on AZ31 magnesium alloy via layer-by-layer(LbL)assembly.The morphology and composition of the samples were characterized through field emission scanning electron microscope(FE-SEM)with affiliated energy dispersive spectrometer(EDS),X-ray diffractometer(XRD),and Fourier infrared spectrometer(FTIR)and X-ray photoelectron spectrometer(XPS)as well.Potentiodynamic polarization,electrochemical impedance spectroscopy(EIS)and hydrogen evolution experiments were employed to evaluate the corrosion behavior of the samples.Atomic absorption spectrophotometer was used to measure Cu elemental content of different immersion periods.Cytocompatibility and antibacterial performance of the coatings were probed using in vitro cytotoxicity tests(MTT assay),live/dead cell staining and plate counting method.The results showed that the obtained(Ca-P/SCC)10 coating exhibited good corrosion resistance,antimicrobial activity(especially under 808 nm irradiation)and biocompatibility.The antibacterial rates for E.coli and S.aureus were 99.9%and 99.8%,respectively;and the photothermal conversion efficiency was as high as 42.1%.Triple antibacterial mechanisms including photodynamic,photothermal reactions and copper-ions release were proposed.This coating exhibited a promising application for biodegradable magnesium alloys.

Corrosion resistance of Ca-P coating induced by layer-by-layer assembled polyvinylpyrrolidone/DNA multilayer on magnesium AZ31 alloy

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,Ca_(3)(PO_(4))_(2) and Mg_(3)(PO_(4))_(2)·nH_(2)O.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.

In vitro degradation and multi-antibacterial mechanisms ofβ-cyclodextrin@curcumin embodied Mg(OH)_(2)/MAO coating on AZ31 magnesium alloy

It is a challenging task to prepare a coating on Mg alloys for desirable corrosion resistance,good antibac-terial ability and biocompatibility.In this research work,an in-situ Mg(OH)_(2)coating incorporated with sodium alginate(SA)andβ-cyclodextrin(β-CD)@curcumin(Cur)was formed on the surface of micro arc oxidation(MAO)coated AZ31 alloy via a low temperature hydrothermal method.Characterization tech-niques such as X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),Fourier transform infrared spectrometer(FT-IR)and scanning electron microscope(SEM)were employed to characterize the chemi-cal composition and surface morphology of the coatings.The corrosion protection ability of the coatings was monitored via electrochemical polarization,hydrogen evolution and immersion tests.Photothermal antibacterial ability and cytocompatibility of the coatings were evaluated by plate counting method under the irradiation of 808 nm-near infrared light,in vitro cytotoxicity tests(MTT)and live/dead cell staining.The results indicate that a chelation of the organic molecules led to the formation of a MAO/(β-CD@Cur)-SA-Mg(OH)_(2)coating with excellent corrosion protection,multi-antibacterial ability and almost no toxic-ity to the cells.Especially,the coating provided photothermal performance through the light absorption of Cur,which was encapsulated byβ-CD to improve its bioavailability.SA enhanced the binding force between the drug and the substrate.This novel coating designated the potential application on bioab-sorbable magnesium alloys.

Corrosion resistance of in-situ growth of nano-sized Mg（OH）2 on micro-arc oxidized magnesium alloy AZ31—Influence of EDTA

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-2 Na) 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.

New insights into the effect of Tris-HCl and Tris on corrosion of magnesium alloy in presence of bicarbonate,sulfate,hydrogen phosphate and dihydrogen phosphate ions

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, p H 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 p H 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 HCO;, SO;,HPO;and H;PO;ions during the corrosion of the AZ31 alloy due to its lower buffering p H 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.

Advance in Antibacterial Magnesium Alloys and Surface Coatings on Magnesium Alloys:A Review

Magnesium(Mg)alloys as a bioabsorbable light metal have shown great clinical potential as bone replacement implants.In this review,the categories,progress in cutting-edge preparation technologies and antibacterial mechanisms of Mg alloys and considerable numbers of corrosion-resistant and functional coatings are summarized.The relationship among the microstructure(grain size,intermetallic compounds),biocorrosion resistance and biocompatibility for antibacterial Mg alloys is discussed.The challenge and outlooks of biomedical Mg alloys and coatings are proposed from an antibacterial perspective.

Corrosion resistance of Zn-AI layered double hydroxide/ poly（lactic acid） composite coating on magnesium alloy AZ31

A Zn-AI layered double hydroxide （ZnAI-LDH） coating consisted of uniform hexagonal nano-plates was firstly synthesized by co-precipitation and hydrothermal treatment on the AZ31 alloy, and then a poly（lactic acid） （PLA） coating was sealed on the top layer of the ZnAI-LDH coating using vacuum freeze-drying. The characteristics of the ZnAI-LDH/PLA composite coatings were investigated by means of XRD, SEM, FTIR and EDS. The corrosion resistance of the coatings was assessed by potentiodynamic polarization and electrochemical impedance spectroscopy （EIS）. The results showed that the ZnAI-LDH coating contained a compact inner layer and a porous outer layer, and the PLA coating with a strong adhesion to the porous outer layer can prolong the service life of the ZnAI-LDH coating. The excellent corrosion resistance of this composite coating can be attributable to its barrier function, ion-exchange and self-healing ability.

Corrosion resistance of an amino acid-bioinspired calcium phosphate coating on magnesium alloy AZ31

An L-cysteine-bioinspired calcium phosphate(Ca-P)coating is prepared upon magnesium alloy AZ31 in a water bath at 60℃.FE–SEM,FTIR,XRD,electrochemical characterization,hydrogen evolution tests and XPS were used to evaluate the microstructure,chemistry and corrosion performance of the samples.Results indicate that L-cysteine promotes the nucleation process of the coating and significantly increases its thickness.This can be attributed to the complexation of the carboxyl group and mercapto group of L-cysteine with calcium ions.Indeed,the obtained Ca-P coating possesses higher corrosion resistance than that prepared in L-cysteine-free bath.

Corrosion resistance of biodegradable polymeric layer-by-layer coatings on magnesium alloy AZ31

Biocompatible polyelectrolyte multilayers （PEMs） and polysiloxane hybrid coatings were prepared to improve the corrosion resistance of biodegradable Mg alloy AZ31. The PEMs, which contained alternating poly（sodium 4-styrenesulfonate） （PSS） and poly（allylamine hydrochloride） （PAH）, were first self-assembled on the surface of the AZ31 alloy substrate via electrostatic interactions, designated as （PAH/PSS）s/AZ31. Then, the （PAH/PSS）5/AZ31 samples were dipped into a methyltrimethoxysilane （MTMS） solution to fabricate the PMTMS films, designated as PMTMS/（PAH/PSS）5/AZ31. The surface morphologies, microstructures and chemical compositions of the films were investigated by FE-SEM, FTIR, XRD and XPS. Potentiodynamic polarization, electro- chemical impedance spectroscopy and hydrogen evolution measurements demonstrated that the PMTMS/（PAH/PSS）s/AZ31 composite film significantly enhanced the corrosion resistance of the AZ31 alloy in Hank＇s balanced salt solution （HBSS）. The PAH and PSS films effectively improved the deposition of Ca-P compounds including Ca3（PO4）2 and hydroxyapatite （HA）. Moreover, the corrosion mechanism of the composite coating was discussed. These coatings could be an alternative candidate coating for biodegradable Mg alloys.