The deteriorated degradation resistance of Mg alloy microtubes for vascular stent under the coupling effect of radial compressive stress and dynamic medium

The degradation of Mg alloys relates to the service performance of Mg alloy biodegradable implants.In order to investigate the degradation behavior of Mg alloys as vascular stent materials in the near service environment,the hot-extruded fine-grained Mg-Zn-Y-Nd alloy microtubes,which are employed to manufacture vascular stents,were tested under radial compressive stress in the dynamic Hanks'Balanced Salt Solution(HBSS).The results revealed that the high flow rate accelerates the degradation of Mg alloy microtubes and its degradation is sensitive to radial compressive stress.These results contribute to understanding the service performance of Mg alloys as vascular stent materials.

Preparation of functional coating on magnesium alloy with hydrophilic polymers and bioactive peptides for improved corrosion resistance and biocompatibility

Biodegradable magnesium alloy stents(MAS)have great potential in the treatment of cardiovascular diseases.However,too fast degradation and the poor biocompatibility are still two key problems for the clinical utility of MAS.In the present work,a functional coating composed of hydrophilic polymers and bioactive peptides was constructed on magnesium alloy to improve its corrosion resistance and biocompatibility in vitro and in vivo.Mg-Zn-Y-Nd(ZE21B)alloy modified with the functional coating exhibited moderate surface hydrophilicity and enhanced corrosion resistance.The favourable hemocompatibility of ZE21B alloy with the functional coating was confirmed by the in vitro blood experiments.Moreover,the modified ZE21B alloy could selectively promote the adhesion,proliferation,and migration of endothelial cells(ECs),but suppress these behaviors of smooth muscle cells(SMCs).Furthermore,the modified ZE21B alloy wires could alleviate intimal hyperplasia,enhance corrosion resistance and re-endothelialization in vivo transplantation experiment.These results collectively demonstrated that the functional coating improved the corrosion resistance and biocompatibility of ZE21B alloy.This functional coating provides new insight into the design and development of novel biodegradable stents for biomedical engineering.

A multi-functional MgF_(2)/polydopamine/hyaluronan-astaxanthin coating on the biodegradable ZE21B alloy with better corrosion resistance and biocompatibility for cardiovascular application

The cardiovascular diseases(CVD)continue to be the major threat to global public health over the years,while one of the effective methods to treat CVD is stent intervention.Biomedical magnesium(Mg)alloys have great potential applications in cardiovascular stents benefit from their excellent biodegradability and absorbability.However,excessive degradation rate and the delayed surface endothelialization still limit their further application.In this study,we modified a Mg-Zn-Y-Nd alloy(ZE21B)by preparing MgF_(2) as the corrosion resistance layer,the dopamine polymer film(PDA)as the bonding layer,and hyaluronic acid(HA)loaded astaxanthin(ASTA)as an important layer to directing the cardiovascular cells fate.The electrochemical test results showed that the MgF_(2)/PDA/HA-ASTA coating improved the corrosion resistance of ZE21B.The cytocompatibility experiments also demonstrated that this novel composite coating also selectively promoted endothelial cells proliferation,inhibited hyperproliferation of smooth muscle cells and adhesion of macrophages.Compared with the HAloaded rapamycin(RAPA)coating,our MgF_(2)/PDA/HA-ASTA coating showed better blood compatibility and cytocompatibility,indicating stronger multi-functions for the ZE21B alloy on cardiovascular application.

Corrosion fatigue of the extruded Mg-Zn-Y-Nd alloy in simulated body fluid

Magnesium alloys were considered to be used as biodegradable implants due to their biocompatibility,biodegradability and nontoxicity.However,under the simultaneous action of corrosive environment and mechanical loading in human body,magnesium alloys are easy to be affected by corrosion fatigue and stress corrosion cracking.In this work,the fatigue behavior of the extruded Mg-Zn-Y-Nd alloy used for vascular stents was studied both in air and in simulated body fluid(SBF).It was revealed that the fatigue limit of as-extruded Mg-Zn-Y-Nd alloy in air is about 65 MPa at 10^7 cycles,while there is no limit in SBF and shows a linear relationship between the fatigue life and stress amplitudes.The fatigue crack source in air was formed by the inclusions and defects.However,the stress corrosion and hydrogen embrittlement are the main reasons for the formation of the fatigue initial crack source in SBF.

Microstructure and texture evolution of fine-grained Mg-Zn-Y-Nd alloy micro-tubes for biodegradable vascular stents processed by hot extrusion and rapid cooling

Magnesium alloys have narrow available slip result from close-packed hexagonal structure that limit their processing properties.In the recent work,the Mg-2Zn-0.46Y-0.5Nd,as materials for degradable stents,was applied to produce as-extruded micro-tube with an outer diameter of 3.0mm and a wall thickness of 0.35mm by hot extrusion with an extrusion ratio of 105:1 at 653K and rapid cooling.The fine microstructure of the dynamic recrystallization of as-extruded micro-tube could be preserved by rapid cooling such as water-cooled,resulting in more excellent mechanical properties relative to air-cooled micro-tube.The addition of rare earth elements Y and Nd results in continuous dynamic recrystallization dominated the dynamic recrystallization mechanism.During the hot extrusion process,the activation of the non-basal slip system,especially the pyramidal(c+a)slip,could significantly weaken the texture strength,and the as-extruded micro-tube exhibits weak"RE"texture components(011^(-)1)||ED and(1^(-)21^(-)1)||ED.Hence,the magnesium alloy micro-tube prepared by the rapid cooling has fine microstructure and weak texture,which is favorable for further process and governance.

In vitro corrosion properties of HTHEed Mg-Zn-Y-Nd alloy microtubes for stent applications:Influence of second phase particles and crystal orientation

Magnesium(Mg)alloys are promising materials for cardiovascular stent applications due to their good biocompatibility and biodegradability.However,in vitro and in vivo corrosion tests reveal that Mg alloy stents suffer from a rapid corrosion rate and severe localized corrosion,which is limiting their widespread application.To solve the problem of uneven degradation of stents,a HTHE(long-time and high-temperature heat treatment,large-reduction-ratio hot extrusion)process is used to manufacture Mg-Zn-Y-Nd alloy microtubes in this study.The heat treatment is to dissolve alloying elements and reduce the size of SPPs,and the hot extrusion is to acquire fine-grained and strongly textured microtubes.The microstructural characterization shows that coarse second phases in as-cast alloy are refined and uniformly distributed in matrix of microtubes.After hot extrusion,microtubes show strong texture with basal plain oriented parallel to the longitudinal section(LS).The corrosion testing indicates that severe localized corrosion occurs on the cross section(CS)while localized corrosion is alleviated on the LS.Based on the different corrosion properties of the LS and CS,HTHEed microtubes are promising for solving the problems of rapid corrosion rate and severe localized corrosion of Mg alloy stents.

Degradation behavior of ZE21C magnesium alloy suture anchors and their effect on ligament-bone junction repair

Current materials comprising suture anchors used to reconstruct ligament-bone junctions still have limitation in biocompatibility,degradability or mechanical properties.Magnesium alloys are potential bone implant materials,and Mg^(2+) has been shown to promote ligament-bone healing.Here,we used Mg-2 wt.%Zn-0.5 wt.%Y-1 wt.%Nd-0.5 wt.%Zr(ZE21C)alloy and Ti6Al4V(TC4)alloy to prepare suture anchors to reconstruct the patellar ligament-tibia in SD rats.We studied the degradation behavior of the ZE21C suture anchor via in vitro and in vivo experiments and assessed its reparative effect on the ligament-bone junction.In vitro,the ZE21C suture anchor degraded gradually,and calcium and phosphorus products accumulated on its surface during degradation.In vivo,the ZE21C suture anchor could maintain its mechanical integrity within 12 weeks of implantation in rats.The tail of the ZE21C suture anchor in high stress concentration degraded rapidly during the early implantation stage(0-4weeks),while bone healing accelerated the degradation of the anchor head in the late implantation stage(4-12weeks).Radiological,histological,and biomechanical assays indicated that the ZE21C suture anchor promoted bone healing above the suture anchor and fibrocartilaginous interface regeneration in the ligament-bone junction,leading to better biomechanical strength than the TC4 group.Hence,this study provides a basis for further research on the clinical application of degradable magnesium alloy suture anchors.

Effect of Ca Micro-Alloying on the Microstructure and Anti-Corrosion Property of Mg0.5Zn0.2Ge Alloy

Magnesium and its alloys have attracting rising attention as one of biodegradable metallic materials.However,the rapid corrosion and severe localized corrosion still hinder their extensive applications in clinics.In this study,micro-alloying of Ca(≤0.1 wt%)into Mg0.5Zn0.2Ge alloy developed in our previous work was explored to further enhance the corrosion resistance and alleviate the localized corrosion of the alloy.The results reveal that the addition of Ca leads to the transformation of the cathodic Mg_(2)Ge phase in Mg0.5Zn0.2Ca alloy into anodic MgCaGe phase in Ca-containing alloys,thereby changing the galvanic couples in alloys during immersion.The preferential dissolution of MgCaGe phase promotes the participation of Ca and Ge into the formation of corrosion products,resulting in the enrichment of Ca and Ge in the outmost of corrosion product layer,which stabilizes and passivates the corrosion product layer on Mg alloy surface.Additionally,the enrichment of Zn at the corrosion interface seems to further hinder the corrosion of Mg matrix.All of these factors confer a slower and more uniform corrosion on Mg0.5Zn0.2GexCa(x<0.1 wt%)alloy,which provides favorable candidates for the further processing to gain suitable biodegradable Mg alloys.

Passivation of corrosion product layer on AM50 Mg by corrosion inhibitor

The influence of sodium dodecyl sulfate(SDS)on morphology and chemical composition of corrosion product layer formed onα-Mg matrix and cathodic Al-Mn intermetallic was systematically investigated by using FIB and TEM analysis for the first time to disclose the underlying inhibition mechanism.A porous corrosion bi-layer composed of crystalline MgO and Mg(OH)_(2)was observed on both ofα-Mg and Al-Mn intermetallic.It was found that a passive inner layer was deposited onα-Mg after immersion in SDS-containing NaCl solution,which can be ascribed to steady-state growth of magnesium and aluminum oxide under the protection of hydrophobic group of SDS.The inhibition mechanism of the inhibitor was mainly associated with formation of dense oxide layer onα-Mg matrix and preferential adsorption of SDS on the corrosion layer deposited on Al-Mn intermetallic.

Zn content mediated fibrinogen adsorption on biodegradable Mg-Zn alloys surfaces

The protein adsorption has an immense influence on the biocompatibility of biodegradable Mg alloy.In this work,the effect of Zn content on the fibrinogen(Fg)adsorption behavior in Mg-Zn binary alloy was systematically investigated.Experimental results showed that the Fg adsorption amount increased at first and then decreased with the increase of Zn content.The adsorption mechanism was investigated by molecular dynamic and density functional theory simulations.The simulations results showed that Zn with low content existed in the inner layer of Mg alloys due to the lower system energy,which promoted Fg adsorption and the promotion effect was more obvious with the increase of Zn content.When Zn content increased to a higher concentration,parts of Zn atoms started to precipitate in the surface,and the Fg-surface interaction energy started to increase.Moreover,the Zn sites favored the formation of ordered water molecules layers,which inhibit the stable adsorptions of Fg.The inhibition effects of Fg adsorption was enhanced with the Zn content increase.In short,the simulation results explain the experimental phenomena and reveal the microscopic mechanism.This study would provide a significant guidance on the design of biodegradable Mg-Zn alloys.

Biodegradation,hemocompatibility and covalent bonding mechanism of electrografting polyethylacrylate coating on Mg alloy for cardiovascular stent

Organic coatings are the most widely employed approach for the promotion of corrosion resistance of magnesium(Mg)alloys.Unfortunately,traditional organic coatings are weakly bonded to Mg substrates due to physical adsorption.Herein,a polyethylacrylate(PEA)coating was fabricated on Mg-Zn-YNd alloy via electro-grafting.The surface structure and chemical composition were characterized by means of scanning electron microscope(SEM),energy dispersive X-ray spectroscopy(EDS),atomic force microscope(AFM)and Fourier transform infrared(FTIR)as well as time of flight-secondary ion mass spectrometer(To F-SIMS).The results showed that the surface roughness of PEA coating was dominated by scan rate;while the coverage and integrity of PEA coating were mainly affected by the monomer concentration and sweep circles.To F-SIMS results indicated that PEA coating was wholly covered on Mg alloy,and the presence of C2H3Mg-fragment confirmed the covalent bond between PEA coating and Mg alloy.In addition,DFT calculation results of the adsorption of EA molecules with Mg substrate agree well with the experimental phenomena and observation,suggesting that the electrons in 3s orbit of Mg atoms and 2pz orbit of C1 atom participated in the formation of covalent bond between PEA coating and Mg substrate.Potentiodynamic polarization curves and immersion test demonstrated that the PEA coatings could effectively enhance the corrosion resistance of Mg alloy.The platelet adhesion results designated that platelets were barely visible on PEA coating,which implied that PEA coating could effectively prevent the thrombosis and coagulation of platelets.PEA coating might be a promising candidate coating of Mg alloy for cardiovascular stent.

Investigation of Mg–Zn–Y–Nd alloy for potential application of biodegradable esophageal stent material

In recent years,due to unhealthy dietary habits and other reasons,advanced esophageal cancer patients are on the rise,threatening human health and life safety at all times.Stents implantation as an important complementary or alternative method for chemotherapy has been widely applied in clinics.However,the adhesion and proliferation of pathological cells,such as tumor cells,fibroblasts and epithelial cells,may interfere the efficacy of stents.Further multiple implantation due to restenosis may also bring pain to patients.In this contribution,we preferred a biodegradable material Mg–Zn–Y–Nd alloy for potential application of esophageal stent.The hardness testing showed that Mg–Zn–Y–Nd alloy owned less mechanical properties compared with the commercial esophageal stents material,317L stainless steel(317L SS),while Mg–Zn–Y–Nd displayed significantly better biodegradation than 317L SS.Cell apoptosis assay indicated Mg–Zn–Y–Nd inhibited adhesion and proliferation of tumor cells,fibroblasts and epithelial cells.Our research suggested potential application of Mg–Zn–Y–Nd alloy as a novel material for biodegradable esophageal stent.

Micro-patterned hydroxyapatite/silk fibroin coatings on Mg-Zn-Y-Nd-Zr alloys for better corrosion resistance and cell behavior guidance

In this study,a micro-patterned hydroxyapatite/silk fibroin(HA-SF)coating was firstly fabricated on the surface of Mg-Zn-Y-Nd-Zr alloy by template-assisted electrospraying technique coupling with spin coating technique.Two types of micro-patterns were achieved with high contour accuracy,namely HA SF(line-pattern)and HA-SF(dot-pattern).The microstructure,composition,surface wettability and corrosion behaviors of the coatings were investigated by SEM,EDS,FTIR,XRD,water contact angle and potentiodynamic polarization test.The results revealed the hydrophilic nature of coatings and two orders of magnitude reduction of corrosion density(icorr)as compared with that of the substrate.All the micro-patterned surfaces promoted the attachment of MC3T3-E1 cells with visible filopodia after 1 d incubation.In addition,coatings with line pattern exhibited the superior guidance to cell migration as compared to dot pattern,and the preference of cell attachment in the convex zone was observed.In summary,the obtained micro-patterned HA-SF coatings possessed the remarkably improvement of anticorrosion ability and good efficacy in guidance of cell attachment and alignment,which can serve as a promising strategy for cellular response modulation at the interface of magnesium-based implants and bone.

Microstructure and Mechanical Properties of Friction Stir Welded 1.5GPa Martensitic High-Strength Steel Plates

In this study, 2.4 mm thick high-strength martensitic steel plates with a tensile strength of 1500 MPa were friction stir welded at various welding speeds of 40, 60, 80, 100, 120 mm/min and a constant rotation speed of 300 rpm. Sound joints could be obtained when the welding speed was 40, 60 and 80 mm/min, while a kissing bond was found in the joint welded at 100 and 120 mm/min. It was revealed that the peak temperature exceeded A C3(the end temperature at which all ferrite transformed to austenite when the steel was heated) for all the welding conditions and martensitic structures were fi nally formed in the stir zone of the joints. A signifi cant decrease in hardness was located in the heat-aff ected zone, which had a transitional microstructure from tempered martensite near base metal to a mixed structure containing hard martensite, soft ferrite and bainite near stir zone. For the sound joints, the specimen was fractured in the heat-aff ected zone during tensile tests and the highest tensile strength could reach about 1058 MPa.

Preparation of Biodegradable Mg/β-TCP Biofunctional Gradient Materials by Friction Stir Processing and Pulse Reverse Current Electrodeposition

Mg alloys,as a new generation of biodegradable bone implant materials,are facing two tremendous challenges of enhancing strength and reducing degradation rate in physiological environment to meet clinical needs.In this study,tricalcium phosphate(β-TCP)particles were dispersed in Mg–2 Zn–0.46 Y–0.5 Nd alloy by friction stir processing(FSP)to produce Mg-based functional gradient materials(Mg/β-TCP FGM).On the surface of Mg/β-TCP FGM,the hydroxyapatite(HA)coating was prepared by electrodeposition.The effects of FSP and electrochemical parameter on the microstructure,microhardness,bonding strength and corrosion performance of the Mg/β-TCP FGM were investigated.After four passes of FSP,a uniform and fine-grained structure was formed in Mg/β-TCP and the microhardness increased from 47.9 to 76.3 HV.Compared to the samples withoutβ-TCP,the bonding strength of the Mg/β-TCP FGM increased from 23.1±0.462 to 26.3±0.526 MPa and the addition of degradableβ-TCP contributed to the in situ growth of HA coating.The thickness of HA coating could be dominated by controlling the parameters of electrodeposition.According to the results of immersion tests and electrochemical tests in simulated body fluid,it indicated that the degradation rate of the Mg/β-TCP FGM could be adjusted.

Clarifying effect of welding conditions on microstructure and mechanical properties of friction stir spot-welded DH590 automotive high-strength steel plates

Friction stir spot welding was successfully applied to the 1.2-mm-thick DH590 dual-phase steel plates by using a polycrystalline cubic boron nitride rotating tool.During welding,the rotation speed ranged from 600 to 1000 r/min and the penetration depth ranged from 0.1 to 0.3 mm.In the spot joints,the size of the stir zone increased with the increase in rotation speed as well as the penetration depth of the tool.Comparing with the banded ferrite and martensite structure of the base metal,a mixed microstructure of ferrite and tempered martensite,refined bainite structure and coarse martensite structure were found in the heat-affected zone,thermomechanically affected zone and stir zone of the joints,respectively.Two kinds of interfacial shapes were formed between the upper and lower steel plates,and the formation of the bonded interface was dominated mainly by the penetration depth of the rotating tool rather than the rotation speed.It was revealed that the joints with straight interfaces showed higher shear tensile loads comparing with those with hook-like interfaces.Shear tensile tests showed that the maximum shear tensile load reached about 15.56 kN when the rotation speed and penetration depth were set as 800 r/min and 0.3 mm,respectively.The specimen was fractured through plug failure mode with a total elongation of about 5.6 mm.