Degradation and biocompatibility of one-step electrodeposited magnesium thioctic acid/magnesium hydroxide hybrid coatings on ZE21B alloys for cardiovascular stents

Constructing a functional hybrid coating appears to be a promising strategy for addressing the poor corrosion resistance and insufficient endothelialization of Mg-based stents.Nevertheless,the steps for preparing composite coatings are usually complicated and time-consuming.Herein,a novel composite coating,composed of bioactive magnesium thioctic acid(MTA)layer formed by deposition and corrosion-resistant magnesium hydroxide(Mg(OH)_(2))layer grown in situ,is simply fabricated on ZE21B alloys via one-step electrodeposition.Scanning electron microscopy(SEM)shows that the electrodeposited coating has a compact and uniform structure.And the high adhesion of the MTA/Mg(OH)_(2)hybrid coating is also confirmed by the micro-scratch test.Electrochemical test,scanning kelvin probe(SKP),and hydrogen evolution measurement indicate that the hybrid coating effectively reduces the degradation rate of Mg substrates.Haemocompatibility experiment and cell culture trial detect that the composite coating is of fine biocompatibility.Finally,the preparation mechanism of MTA/Mg(OH)_(2)hybrid coatings is discussed and proposed.This coating shows a great potential application for cardiovascular stents.

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.

Corrosion resistance and mechanisms of smart micro-arc oxidation/epoxy resin coatings on AZ31 Mg alloy: Strategic positioning of nanocontainers

Smart micro-arc oxidation(MAO)/epoxy resin(EP) composite coatings were formed on AZ31 magnesium(Mg) alloy. Mesoporous silica nanocontainers(MSN) encapsulated with sodium benzoate(SB) corrosion inhibitors were strategically incorporated in the MAO micropores and in the top EP layer. The influence of the strategic positioning of the nanocontainers on the corrosion protective performance of coating was investigated. The experimental results and analysis indicated that the superior corrosion resistance of the hybrid coating is ascribed to the protection mechanisms of the nanocontainers. This involves two phenomena:(1) the presence of the nanocontainers in the MAO micropores decreased the distance between MSN@SB and the substrate, demonstrating a low admittance value(^5.18 × 10^(-8)Ω^(-1)), and thus exhibiting significant corrosion inhibition and self-healing function;and(2) the addition of nanocontainers in the top EP layer densified the coating via sealing of the inherent defects, and hence the coating maintained higher resistance even after 90 days of immersion(1.13 × 10^(10)Ω cm^(2)).However, the possibility of corrosion inhibitors located away from the substrate transport to the substrate is reduced, reducing its effective utilization rate. This work demonstrates the importance of the positioning of nanocontainers in the coating for enhanced corrosion resistance,and thereby providing a novel perspective for the design of smart protective coatings through regulating the distribution of nanocontainers in the coatings.

Advances in Mg-Al-layered double hydroxide steam coatings on Mg alloys:A review

Layered double hydroxide(LDH)coatings on magnesium(Mg)alloys shine brightly in the field of corrosion protection because of their special ion-exchange function.State-of-the-art steam coating as a type of LDH film preparation technique has emerged in recent years because only pure water is required as the steam source and its environmentally friendly LDH coating fits the current need for green development.Moreover,this coating can effectively inhibit the corrosion of the Mg alloy substrate due to the chemical bonding between the coating and the Mg alloy substrate.This review systematically explains cutting-edge advancements in the growth mechanism and corrosion behavior of LDH steam coatings,and analyzes the advantages and limitations of the steam-coating method.The influencing factors including pressure,CO_(2)/CO_(3)^(2-),aluminum content of the substrate alloy,solution type,and acid-pickling pretreatment,as well as the post-treatment of steam-coating defects,are comprehensively elucidated,providing new insights into the development of the in situ steam-coating technique.Finally,existing issues and future prospects are discussed to further accelerate the widespread application of Mg alloys.

In vitro corrosion resistance and antibacterial properties of layer-by-layer assembled chitosan/poly-L-glutamic acid coating on AZ31 magnesium alloys

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.

Advances in coatings on biodegradable magnesium alloys

The clinic applications of bioabsorbable magnesium(Mg)and its alloys have been significantly restricted owing to their poor corrosion resistance.Besides elemental alloying,surface modification and functionality is a major approach to increasing corrosion resistance for magnesium alloys.This article reviews the cutting-edge advances and progress of biodegradable surface coatings upon Mg alloys over the last decades,aims to build up a knowledge framework of surface modification on biodegradable Mg alloys.A considerable number of conversion,deposition,mechanical and functional coatings and their preparation methods are discussed.The emphasis has been placed on the composition of chemical conversion and deposited coatings to overcome the disadvantages of adhesion,corrosion resistance and biocompatibility of a single coating for biomedical materials.The issues have been addressed on the integration of the structural and functional factors of the composite coatings.

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,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.

Corrosion resistance of Mg−Al LDH/Mg(OH)2/silane−Ce hybrid coating on magnesium alloy AZ31

An environmentally-friendly hybrid coating on AZ31 magnesium alloy substrates was reported.The synergic effect was studied on Mg−Al-layered double hydroxide Mg−Al LDH/Mg(OH)2-coated AZ31 magnesium alloy via an in-situ steam coating process and a subsequent combined surface modification of bis-[triethoxysilylpropyl]tetrasulfide(BTESPT)silane and Ce(NO3)3.The microstructure and composition characteristics of the hybrid coatings were investigated by means of X-ray diffraction(XRD),scanning electronic microscopy(SEM),Fourier transform infrared spectrophotometry(FT-IR)and X-ray photoelectron spectroscopy(XPS).The corrosion resistance of the coated samples was evaluated by potentiodynamic polarization(PDP),electrochemical impedance spectrum(EIS)and hydrogen evolution rate during immersion in 3.5 wt.%NaCl solution.The results show an improved corrosion resistance of the alloy in the presence of BTESPT silane and Ce(NO3)3.This is most likely due to the synergistic effect of steam coating and silane coating to enhance the barrier properties of hybrid coating.In addition,the formation mechanism and anti-corrosion mechanism of coatings were discussed.

Advances in hydroxyapatite coatings on biodegradable magnesium and its alloys

Magnesium is a candidate metal for biodegradable implant applications for its biodegradation tendency and excellent biocompatibility.Unfortunately,the high degradation rate of magnesium and also its localized degradation in physiological conditions are the main issues for its successful implant applications.The degradation rate of magnesium has been reduced to some degree via alloying,but the localized degradation susceptibility is a great concern.For many years,hydroxyapatite(HAp),a biocompatible ceramic material,has been extensively used for bio-implant applications.Recently,a substantial amount of research has been carried out on coating HAp on magnesium-based materials for improved degradation resistance in particular and also to enhance the biocompatibility.This review article focuses on the different methods of HAp coating on magnesium-based materials and also the recent cutting-edge advancements made in the coating process for improved degradation resistance and biocompatibility.The mechanical stability of the HAp coated magnesium-based materials is also discussed.

Corrosion resistance and superhydrophobicity of one-step polypropylene coating on anodized AZ31 Mg alloy

Superhydrophobic coatings have been considerably used in corrosion and its protection of metallic Mg.And the comprehensive performance(hydrophobicity,bonding strength,and corrosion resistance,etc.)of the top coating may be highly dependent on the physical and chemical properties of the primer or under coat.Herein,an integrated superhydrophobic polypropylene(PP)coating was fabricated on the micro-arc oxidized Mg substrate via one-step dipping.Surface morphologies and chemical compositions of the composite coating were examined through Fourier transform infrared spectroscopy(FT-IR),X-ray diffraction(XRD),and field-emission scanning electron microscopy(FESEM)together with X-ray photoelectron spectroscopy(XPS).The surface wettability of the coating was determined by contact angle and sliding angle.The corrosion-resistant performance was evaluated via electrochemical and immersion measurements.The results showed that the hybrid coating possessed micron-scaled granular structure on the surface with a high water contact angle of 167.2±0.8°and a low water sliding angle of 2.7±0.5°.The corrosion resistance of superhydrophobic coating was obviously enhanced with a low corrosion current density of 8.76×10^(−9)A/cm^(2),and the coating still maintained integrity after 248 h of immersion in 3.5wt%NaCl aqueous solution.The MAO coating provides better adhesion of PP to the surface.Hence,the superhydrophobic coating exhibited superior bonding strength,corrosion resistance and durability.

Advances in bioorganic molecules inspired degradation and surface modifications on Mg and its alloys

Mg alloys possess biodegradability,suitable mechanical properties,and biocompatibility,which make them possible to be used as biodegradable implants.However,the uncontrollable degradation of Mg alloys limits their general applications.In addition to the factors from the metallic materials themselves,like alloy compositions,heat treatment process and microstructure,some external factors,relating to the test/service environment,also affect the degradation rate of Mg alloys,such as inorganic salts,bioorganic small molecules,bioorganic macromolecules.The influence of bioorganic molecules on Mg corrosion and its protection has attracted more and more attentions.In this work,the cutting-edge advances in the influence of bioorganic molecules(i.e.,protein,glucose,amino acids,vitamins and polypeptide)and their coupling effect on Mg degradation and the formation of protection coatings were reviewed.The research orientations of biomedical Mg alloys in exploring degradation mechanisms in vitro were proposed,and the impact of bioorganic molecules on the protective approaches were also explored.

Influence of intermetallic Al-Mn particles on in-situ steam Mg-Al-LDH coating on AZ31 magnesium alloy

The influence of intermetallic Al-Mn particles on the corrosion behavior of in-situ formed Mg-Al layered double hydroxide(Mg-Al-CO32--LDH)steam coating on AZ31 Mg alloy was investigated.The alloy was pretreated with H3PO4,HCl,HNO3or citric acid(CA),followed by hydrothermal treatment,for the fabrication of Mg-Al-LDH coating.The microstructure,composition and corrosion resistance of the coated samples were investigated.The results showed that the surface area fraction of Al-Mn phase exposed on the surface of the alloy was significantly increased after CA pretreatment,which promotes the growth of the Mg-Al-LDH steam coating.Further,the LDH-coated alloy pretreated with CA possessed the most compact surface and the maximum coating thickness among all the coatings.The corrosion current density of the coated alloy was decreased by three orders of magnitude as compared to that of the bare alloy.

Protein conformation and electric attraction adsorption mechanisms on anodized magnesium alloy by molecular dynamics simulations

Protein adsorption preferentially occurs and significantly affects the physicochemical reactions once the biodegradable magnesium alloys as bone replacements have been implanted. To date, interactions mechanisms between Mg implants and proteins remain unclear at a molecular level. Thereby, a combination of molecular dynamic(MD) simulations and experimental exploration is used to investigate the adsorption behavior and conformational change of bovine serum albumin(BSA), a representative protein of blood plasma, upon the surface of microarc oxidation(MAO) coated Mg alloy AZ31. The influences of absorbed proteins on the cytocompatibility of MAO coating are evaluated by virtue of cytotoxicity assay. Results indicate that the negatively charged O atoms(BSA) exhibit strong interaction with Mg^(2+) ions of Mg(OH)_(2), revealing that BSA molecules are ionically adsorbed on the AZ31 surface. Interestingly, MD simulation reveals that MAO coating demonstrates superior ability to capture BSA molecules during the process of adsorption owing to strong electric attraction between the negatively charged O atoms in BSA molecules with Mg atoms of MgO in MAO coating. Moreover, the α-helix part of absorbed BSA molecules on AZ31 substrate and MAO coating markedly decreases with an increase in β-sheet, β-turn and unordered contents, which is attributed to the reduction in the number of hydrogen bonds in BSA molecules. Furthermore, the adsorbed BSA molecules improve the cytocompatibility of MAO coating since the positively charged-NH_(3)^(+) group and β-sheet content of absorbed BSA molecules mediate the cell adhesion by interacting with the negatively charged cell membrane.

In vitro degradation resistance of glucose and L-cysteine-bioinspired Schiff-base anodic Ca−P coating on AZ31 magnesium alloy

A Schiff base(a compound containing a C=N bond)induced anodic Ca−P coating was prepared on AZ31 Mg alloy in a mixed solution of CaCl_(2) and KH_(2)PO_(4) at 60℃ in the presence of glucose and L-cysteine.The microstructure and chemical composition of the coatings were characterized using FE-SEM,FT-IR,XRD,and XPS.The in vitro degradation resistance of the coated samples was evaluated via potentiodynamic polarization(PDP),electrochemical impedance spectroscopy(EIS),and hydrogen evolution test.The experimental results show that the Ca−PSchiff base coating is composed of CaHPO_(4)(DCPA)and hydroxyapatite(HA),whereas HA is not present in the Ca−P coating.The Ca−P_(Schiff base) coating thickness is about 2 times that of Ca−P coating(Ca−P coating:(9.13±4.20)μm and Ca−P_(Schiff base):(18.13±5.78)μm).The corrosion current density of the Ca−P_(Schiff base) coating is two orders of magnitude lower than that of the Ca−P coating.The formation mechanism of the Ca−P_(Schiff base) is proposed.

Corrosion behavior and mechanical property of Mg-4Li-1Ca alloys under micro-compressive stress

Biomedical materials may suffer from stress-induced corrosion when performing as implant materials at load-bearing sites, bringing about variations in the microstructure, corrosion resistance, and mechanical properties. In this study, the corrosion behavior and mechanical properties of an extruded Mg-4Li-1Ca alloy were investigated under different micro-compressive stresses (0-6 MPa) using a novel homemade loading device. Under 0-3 MPa of micro-compressive stress, the strong basal texture of extruded Mg-4Li1Ca alloys was weakened and the internal stress gradient stimulated grain boundary migration to induce grain growth. Meanwhile, increased stress resulted in the precipitation of second-phase particles and the accumulation of residual stress, accelerating the corrosion rate due to preferential corrosion. However, with increasing stress, the volume fraction of the second phase increased, becoming the dominant factor controlling the corrosion rate, and residual stress was released for samples under 4.5-6 MPa of microcompressive stress. Hence, surface corrosion product films rapidly formed and served as effective physical barriers, weakening the microstructural effect on the corrosion behavior. The yield strength of Mg-4Li-1Ca alloy reached 95.48 MPa under 3 MPa of micro-compressive stress owing to the dual effects of precipitation strengthening and shear-band strengthening. The relationships between microstructure, corrosion behavior, and mechanical property provide a theoretical foundation for understanding the degradation characteristics of the Mg-4Li-1Ca alloy under physiological loading and practical application.

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.

Robust damage warning and healing tracing strategy for anticorrosion coatings on magnesium alloy AZ31enabled by polydopamine fluorophores

Polymeric coatings are susceptible to microdefects that are difficult to detect thus leading to premature failure of metallic components or even catastrophic accidents.Although obtaining considerable progress in damage healing and detecting,it is still challenging for anticorrosion coating to realize warning the damage generation and tracing the healing process simultaneously.This article validates a robust strategy based on damage-induced fluorescence enhancement effect to visualize dynamic damage-healing processes in anticorrosion coatings on magnesium alloy AZ31.Through embedding fluorescent poly-dopamine nanoparticles into thermo-responsive epoxy resin,immediate fluorescence was intensified at coating damages.Localized electrochemical impedance and salt spray results proved that the prepared coating possessed pronounced healing and corrosion protection capability with near-infrared irradiation.Notably,the healing behavior can be traced and visualized based on the decrease in fluorescence intensity.This work opens a new avenue to monitor the failure and self-healing mechanism of anticorrosion coatings,providing guideline for engineering of next generation smart protection materials.

Comparison of microstructure,mechanical property,and degradation rate of Mg-1Li-1Ca and Mg-4Li-1Ca alloys

Mg-1 wt.%Li-1 wt.%Ca(LX11)and Mg-4 wt.%Li-1 wt.%Ca(LX41)alloys share the same hexagonal closed-packed crystalline structure.However,the differences in microstructure,mechanical properties,and degradation rates between the two alloys are not well understood.Hereby,the above three aspects of LX11 and LX41 alloys were studied via optical microscopy,tensile tests,and electrochemical polarization and electrochemical impedance spectroscopy,together with hydrogen evolution.The concentration of the released Mg^(2+),Ca^(2+),and Li+ions was analyzed using a flame atomic absorption spectrophotometer.Results demonstrated that the LX11 alloy was composed of finerα-Mg grains,fewer twins,and smaller volume fractions of the intermetallic phases Mg_(2)Ca than the LX41 alloy.The increasing Li concentration generated a weak decrease in the yield strength of the Mg-Li-Ca alloys,a remarkable increase in elongation to failure,and a stable ultimate tensile strength.The LX11 alloy had better corrosion resistance than the LX41 alloy.The release rate of the cations(Mg^(2+),Ca^(2+),and Li+)varied significantly with time.The release rate of metallic ions in Hank’s solution cannot reflect the true corrosion rate of Mg-Li-Ca alloys due to the formation of the precipitated corrosion products and their difference in solubility.The dealloying corrosion mechanism of the Mg_(2)Ca phase in Mg-Li-Ca alloys was proposed.

Recent advances in biodegradation controls over Mg alloys for bone fracture management: A review

Magnesium(Mg) alloys possess comparable physical and mechanical properties to bone, making them an outstanding candidate of implant materials for bone fracture treatment. In addition to the excellent biocompatibility, and bioactivity, the engagement of Mg alloys is key for a number of biological functionalities in the human body. The unique biodegradation nature of Mg alloy implants implies that it may not require a secondary removal procedure when the expected supporting tasks accomplish, as they may simply and safely "disappear" over time. Nonetheless, the demonstrated drawback of potentially rapid degradation, is an issue that must be addressed appropriately for Mg implants and is consequently given unique attention in this review article. Herein, the critical criteria and the state-of-the-art strategies for controlling the degradation process of Mg alloys are reported. Furthermore, future developments of biodegradable Mg and its alloys systems with satisfactory specifications for clinical trials and deployment,are discussed. This review aims to provide information to materials scientists and clinical practitioners in the context of developing practical biodegradable Mg alloys.