Effects of ytterbium addition and heat treatment on the mechanical properties and biocorrosion behaviors of Mg-Zn-Zr alloy

Mechanical properties and biocorrosion behaviors in simulated body fluid(SBF)of newly developed Mg-5.8 Zn-0.5 Zr-x Yb(ZK60-X Yb,x=0,1.0,2.0wt%)magnesium alloys in the solution-treated(T4)and artificially-aged(T6)conditions were investigated.The results of mechanical properties show that with Yb addition,the microhardness and the ultimate tensile strength(UTS)of the tested alloys are significantly increased despite a slight decrease in tensile elongation in both T4 and T6 conditions.Especially,after the T6 treatment,the microhardness and the UTS of the samples were further improved,which was mainly attributed to the precipitation strengthening.The biocorrosion behaviors of the tested alloys were studied using electrochemical examinations and immersion tests.The results indicate that the biocorrosion resistance of the tested alloys is significantly improved by Yb addition in both T4 and T6 conditions.Although the corrosion resistance was slightly deteriorated after T6 treatment,the aged ZK60-2.0 Yb alloy still exhibited a favorable corrosion behavior,which was mainly ascribed to the corrosion barrier effect of a more compact and uniform protective film induced by the dispersed nano-scale precipitates.Electrochemical measurements also confirmed these observations.Given the favorable comprehensive performance in mechanical and biocorrosion behaviors,the T6 treated ZK60-2.0 Yb alloy may be considered as a promising candidate for biomedical applications.

Recent research and progress of biodegradable zinc alloys and composites for biomedical applications: Biomechanical and biocorrosion perspectives

Biodegradable metals(BMs)gradually degrade in vivo by releasing corrosion products once exposed to the physiological environment in the body.Complete dissolution of biodegradable implants assists tissue healing,with no implant residues in the surrounding tissues.In recent years,three classes of BMs have been extensively investigated,including magnesium(Mg)-based,iron(Fe)-based,and zinc(Zn)-based BMs.Among these three BMs,Mg-based materials have undergone the most clinical trials.However,Mg-based BMs generally exhibit faster degradation rates,which may not match the healing periods for bone tissue,whereas Fe-based BMs exhibit slower and less complete in vivo degradation.Zn-based BMs are now considered a new class of BMs due to their intermediate degradation rates,which fall between those of Mg-based BMs and Fe-based BMs,thus requiring extensive research to validate their suitability for biomedical applications.In the present study,recent research and development on Zn-based BMs are reviewed in conjunction with discussion of their advantages and limitations in relation to existing BMs.The underlying roles of alloy composition,microstructure,and processing technique on the mechanical and corrosion properties of Zn-based BMs are also discussed.

Biocorrosion resistance of coated magnesium alloy by microarc oxidation in electrolyte containing zirconium and calcium salts

The key to use magnesium alloys as suitable biodegradable implants is how to adjust their degradation rates. We report a strategy to prepare biocompatible ceramic coating with improved biocorrosion resistance property on AZ91D alloy by microarc oxidation （MAO） in a silicate-K2ZrF6 solution with and without Ca（H2PO4）2 additives. The microstructure and biocorrosion of coatings were characterized by XRD and SEM, as well as electrochemical and immersion tests in simulated body fluid （SBF）. The results show that the coatings are mainly composed of MgO, Mg2SiO4, m-ZrO2 phases, further Ca containing compounds involve the coating by Ca（H2PO4）2 addition in the silicate-K2ZrF6 solution. The corrosion resistance of coated AZ91D alloy is significantly improved compared with the bare one. After immersing in SBF for 28 d, the Si-Zr5-CaO coating indicates a best corrosion resistance performance.

In vitro bio-corrosion behaviors of biodegradable AZ31B magnesium alloy under static stresses of different forms and magnitudes

Biomedical degradable materials would be subjected to different degrees and forms of static stress after being implanted in the human body.In this work,the biocorrosion behaviors of AZ31B magnesium alloy under different stress forms with different magnitudes(20~150MPa)were studied.It was found that the corrosion behaviors at stressed conditions were severer than those at unstressed conditions and corrosion rates were obviously accelerated.The biocorrosion behaviors are more sensitive to the effects of tensile loads than to compressive loads.A biocorrosion numerical model on the degradation process of Mg alloy under static loads was established.The corrosion current density(i_(corr))of Mg alloy and the applied static stress(σ)matches a linear relationship of ln i_(corr)~σwell during the early stage(within 24 hrs)while deviated gradually in the latter period of corrosion.This work could provide a guidance and theoretical reference for further researches on the biocorrosion behaviors and practical clinical applications of the biomedical materials subjected to physiological loads.

The role and significance of Magnesium in modern day research-A review

Magnesium is one of the largely available elements in the earth’s crust. It has a low structural density with high specific strength. This unique material property has forced an increase in the use of magnesium and its alloys in various applications pertaining to industrial sector,automobiles, aerospace and biomedical. Since magnesium is a highly reactive metal, it is prone to higher rate of corrosion as compared to its counterparts. Thus, it is essential to analyze the corrosion behavior of magnesium and its alloys in its applications. An appropriate process is to be followed in the design and development of magnesium alloys which overcome the limitations of magnesium and enhance the desired material properties in accordance to their applications. This review paper summarizes the importance of magnesium and its material properties. The influence of various alloying elements on the mechanical properties of magnesium is reviewed. The broad classification of Mg alloys and their behavioral trends are detailed. The corrosion behavior of magnesium and the influence of corrosion products on the material characteristics of magnesium, in aqueous medium, are discussed. The manufacturing techniques of magnesium alloys along with the secondary techniques are also covered. The various applications and the limitations of magnesium in these applications are covered. A complete section is dedicated towards detailing the recent trends of magnesium(Mg) alloys, i.e., the biodegradable nature and applications of Mg alloys. The influence of biocorrosion on Mg alloys and techniques to overcome it have been deliberated. This paper provides a thorough review on recent developments of magnesium with respect to engineering applications.

Graphene nanoplatelets-reinforced magnesium metal matrix nanocomposites with superior mechanical and corrosion performance for biomedical applications

Magnesium(Mg)metal matrix composites(MMCs)reinforced with graphene nanoplatelets(GNPs)have been developed by powder metallurgy(PM).GNPs with different concentrations(0.1,0.2,and 0.3 wt.%),layer thicknesses(5 nm and 9 nm),and particle sizes(15μm and 5μm)were dispersed into Mg powder by high-energy ball-milling processes.The microstructure and mechanical properties of the fabricated composites were characterized using transmission electron microscopy(TEM),scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDX),X-ray diffraction(XRD),Raman spectroscopy(RS),and compression tests.The corrosion resistance was evaluated by electrochemical tests and hydrogen evolution measurements.The cytotoxicity of Mg-GNPs composites was assessed using osteoblast-like SaOS2 cells.The results indicate that GNPs are excellent candidates as reinforcements in Mg matrices for the manufacture of biodegradable Mg-based composite implants.GNP addition improved the mechanical properties of Mg via synergetic strengthening modes.Moreover,retaining the structural integrity of GNPs during processing improved the ductility,compressive strength,and corrosion resistance of the Mg-GNP composites.Cytotoxicity assessments did not reveal any significant toxicity with the addition of GNPs to Mg matrices.This study demonstrates that Mg-xGNPs with x<0.3 wt.%,may constitute novel biodegradable implant materials for load-bearing applications.

Magnesium as Biodegradable Implant Material

Drawbacks associated with permanent metallic implants lead to the search for degradable metallic biomaterials. Magnesium alloys have been highly considered as Mg has a high biocorrosion potential and is essential to bodies. In this study, corrosion behaviour of pure magnesium and magnesium alloy AZ31 in both static and dynamic physiological conditions (Hank's solution) has been investigated. It is found that the materials degrade fast at beginning, then stabilize after 5 days of immersion. High purity in the materials reduces the corrosion rate while the dynamic condition accelerates the degradation process. In order to slow down the degradation process to meet the requirement for their bio-applications, an anodized coating is applied and is proved as effective in controlling the biodegradation rate.

First Evidence of Fungal Strains Isolated and Identified from Naphtha Storage Tanks and Transporting Pipelines in Venezuelan Oil Facilities

Biocorrosion, as well as the biodeterioration of crude oil and its derivatives, is one of the major environmental, operational and economic problems in the Venezuelan oil industry. Fungal contaminants are able to produce large quantities of biomass and synthesize peroxides and organic acids, causing severe damage on metal surfaces and promoting the contamination and biodeterioration of fuels. No evidences regarding fungal strains have been reported to be associated to petroleum naphtha, widely used as a diluent of extra heavy crude oil (EHCO) in the exploitation processes of the Orinoco Oil Belt, the biggest proven reserve of EHCO worldwide. The aims of this paper were to isolate and identify fungal strains from the naphtha storage tank and the naphtha distribution network from an oil field operator in Venezuela. The results showed the isolation of four different fungal strains. The molecular identification by 28S rRNA sequencing and phylogenetic tree analysis allowed us to identify the presence of: 1) a new uncultured Ascomycota fungus species BM-103, with high identity to novel hyphomycetes Noosia banksiae and Sporidesmium tengii, in the naphtha storage tank;2) two yeasts, Rhodotorula mucilaginosa BM-104 (Phylum Basidiomycota) and Wickerhamia sp. BM-105 (Phylum Ascomycota), in a highly damaged naphtha pipeline branch and;3) Cladosporium cladosporioides BM-102 (Phylum Ascomycota) in a cluster oil well. DNA fingerprinting analysis using ERIC-PCR primers pairs also allowed us to detect the presence of R. mucilaginosa BM-104 right in the access of the studied naphtha system. Interestingly, R. mucilaginosa and C. cladosporioides were previously reported as predominant fungal contaminants of diesel and jet fuel and of kerosene and fuel storage systems, respectively. This paper represents the first evidence of fungal strains isolated and identified from the naphtha systems in the Venezuelan oil industry. The results obtained are discussed.

Amino Acid Composition of Tightly Bound Exopolymeric Substances Produced by Corrosion-Related Bacteria in Presence of Mild Steel

The composition of tightly bound exopolymeric substances (EPS) obtained from biofilm and plan- ktonic cell subpopulations of Stenotrophomonas maltophilia 5426 UKM was analyzed to study an impact of mild steel presence in the cultivation medium. The overall protein production was found to increase in the presence of a steel coupon. Some amino acids such as lysine, valine, iso-leucine, tyrosine and phenylalanine were found to be secreted in higher amounts in the presence of mild steel, while its absence leads to an increase of arginine, asparagine, serine, glutamine, proline, glycine, cysteine, leucine, methionine production levels. Biofilm cells EPS contained more arginine, glycine, cysteine, valine, methionine and leucine, comparing to EPS of planktonic cells. The chang- es of tightly bound EPS aggregation around the cells induced in the presence of steel coupons were revealed by transmission electron microscopy. The results suggested the transition of S. maltophilia 5426 UKM cells from planktonic to biofilm lifestyle to be a complex process involving more than a single step.

Biodegradable magnesium materials regulate ROS-RNS balance in pro-inflammatory macrophage environment

The relationship between reactive oxygen and nitrogen species(ROS-RNS)secretion and the concomitant biocorrosion of degradable magnesium(Mg)materials is poorly understood.We found that Mg foils implanted short term in vivo(24 h)displayed large amounts of proinflammatory F4/80+/iNOS+macrophages at the interface.We sought to investigate the interplay between biodegrading Mg materials(98.6%Mg,AZ31&AZ61)and macrophages(RAW 264.7)stimulated with lipopolysaccharide(RAW 264.7^(LPS))to induce ROS-RNS secretion.To test how these proinflammatory ROS-RNS secreting cells interact with Mg corrosion in vitro,Mg and AZ61 discs were suspended approximately 2 mm above a monolayer of RAW 264.7 cells,either with or without ^(LPS).The surfaces of both materials showed acute(24 h)changes when incubated in the proinflammatory RAW 264.7^(LPS) environment.Mg discs incubated with RAW 264.7^(LPS) macrophages showed greater corrosion pitting,while AZ61 showed morphological and elemental bulk product changes via scanning electron microscopy-energy dispersive X-ray spectroscopy(SEM-EDX).X-ray photoelectron spectroscopy(XPS)analysis showed a reduction in the Ca/P ratio of the surface products for AZ61 disc incubated with RAW 264.7^(LPS),but not the Mg discs.Moreover,RAW 264.7^(LPS) macrophages were found to be more viable in the acute biodegradative environment generated by Mg materials,as demonstrated by calcein-AM and cleaved(active)caspase-3 staining(CC3).^(LPS) stimulation caused an increase in ROS-RNS,and a decrease in antioxidant peroxidase activity.Mg and AZ61 were found to change this ROS-RNS balance,independently of physiological antioxidant mechanisms.The findings highlight the complexity of the cellular driven acute inflammatory responses to different biodegradable Mg,and how it can potentially affect performance of these materials.

Glass formation and properties of Ti-based bulk metallic glasses as potential biomaterials with Nb additions

Ti47Cu38-xZr7.5Fe2.5Sn2Si1Ag2Nbx（x = 0, 1, 2; at%） bulk metallic glasses （BMGs） with superior biocorrosion resistance were synthesized by copper mold casting. Although the minor addition of Nb to the Ti-Cu- Zr-Fe-Sn-Si-Ag BMG slightly decreases the glass-forming ability （GFA）, the Nb-bearing Ti-based alloys could be casted in a bulk glassy rod form with diameters up to 3 mm. It is found that partial substitution of Cu with Nb is effective on enhancing the bio-corrosion resistance of the Ti-based BMG. Potentiodynamic polarization measurements show that Nb addition to Ti-based BMG leads to higher open-circuit potential and pitting potential as well as lower passive current density in Hank＇s solution. Electrochemical impedance spectroscopy （EIS） results indicate that with Nb content increasing, the charge transfer resistance values of the Ti-based BMGs become larger, demonstrating that the surface oxide films are more protective. The Nb-bearing Ti-based BMGs also exhibit good in vitro biocompatibility comparable to that of Ti-6Al-4V alloy. The enhanced bio-corrosion resistance, excellent in vitro biocompatibility and good mechanical properties of the Nb-bearing Ti-based BMGs are favorable for biomedical applications.

Inhibition effect on microbiologically influenced corrosion of Ti-6Al-4V-5Cu alloy against marine bacterium Pseudomonas aeruginosa

With rapid development of marine infrastructures,materials with better biocorrosion resistance and antibiofouling performance will be highly demanded.Ti6Al4V alloy is susceptible to the above.The inhibition to the microbiologically influenced corrosion of Ti6Al4V-5Cu alloy against Pseudomonas aeruginosa was investigated using antibacterial test,electrochemical techniques,surface analysis,and weight loss test conducted for 2.5 months.At a sputtering depth of 0 nm,the passive film of Ti6Al4V-5Cu alloy was mainly composed of ideal oxide TiO_(2).With increasing sputtering thickness to 6 nm,Ti_(2)O_(3)and TiO were detected with a relative fraction of 14.6%and 14.8%,respectively,in the oxide layer of Ti6Al4V-5Cu alloy.In contrast,the outermost layer of Ti6AlV alloy was predominantly composed of TiO_(2)but Ti_(2)O_(3)(22.8%),Al_(2)O_(3)and V_(2)O_(5) were also detected.With increasing sputtering depth to 6 nm,fitting revealed the presence of Ti_(2)O_(3)and TiO with relative fractions of 25.3%and 35.8%,respectively.Yet,a spot of TiO(8%)was also observed at 12 nm in the oxide layer of Ti6Al4V alloy.Although the addition of Cu into Ti6Al4V alloy generated the self-healing property of passive film in the presence of P.aeruginosa,it also reduced resistance to corrosion in general condition.

The influence of alternating cyclic dynamic loads with different low frequencies on the bio-corrosion behaviors of AZ31B magnesium alloy in vitro

The real physiological environment of human body is complicated with different degrees and forms of dynamic loads applied to implanted medical devices due to the daily activities of the patients,which would have impacts on the degradation behaviors of magnesium alloy implants.In this work,the bio-corrosion behaviors of AZ31B magnesium alloy under alternating cyclic dynamic loads with different low frequencies(0.1-2.5 Hz)were specially investigated.It was found that the bio-degradation performances under external dynamic stressed conditions were much severer than those under unstressed conditions and static loads.The corrosion rates were generally accelerated as the rise of cyclic frequency.Hereby a numerical model for the degradation process of Mg alloy was established.The corrosion current density icorr of Mg alloy and the applied loading frequency f matches a linear relationship of ln icorr∝f,which is the result of interactions between the cyclic alternating load and corrosive environment.This work could provide a theoretical reference and an experimental basis for further researches on the biodegradation behaviors of biomedical materials under dynamic conditions.