Preparation,microstructure and degradation behavior of Mg−2Zn−0.4Sc−0.2Zr alloy wire

A biodegradable Mg−2Zn−0.4Sc−0.2Zr(ZK20−0.4Sc)alloy wire with a diameter of 0.5 mm was prepared by a combination of hot extrusion and cold-drawing.The average grain size of ZK20−0.4Sc alloy wire on the longitudinal section along the drawing direction is approximately 7.3μm.The texture results show relatively strong<1020>and weak<1010>fiber texture components parallel to the drawing direction.The ZK20−0.4Sc alloy wire exhibits better mechanical properties with the tensile strength,yield strength and elongate of(329±2)MPa,(287±2)MPa and(14.2±0.5)%,respectively.The better mechanical properties are mainly attributed to the grain refinement strengthening,dislocation strengthening and precipitation strengthening.With the immersion time increasing to 14 d,the corrosion type transfers from filament corrosion and pitting corrosion to severe localized corrosion.

Effect of heat treatment on microstructure, mechanical properties and in vitro degradation behavior of as-extruded Mg-2.7Nd-0.2Zn-0.4Zr alloy

Mg-2.7Nd-0.2Zn-0.4Zr （mass fraction, %） alloy was designed for degradable biomedical material. The ingots of the alloy were solution treated and then hot extruded. The extruded rods were heat treated with aging treatment, solution treatment and solution＋aging treatment, respectively. Microstructures of the alloy were observed by optical microscopy （OM） and scanning electron microscopy （SEM）. Mechanical properties at room temperature were tested. In vitro degradation behavior of the alloy immersed in simulated body fluid was measured by hydrogen evolution and mass loss tests. The degradation morphologies of the alloy with and without degradation products were observed by SEM. The results show that the grains grow apparently after solution treatment. Solution treatment improves the elongation of as-extruded alloy significantly and decreases the strength, while aging treatment improves the strength and reduces the elongation of the alloy. The yield ratio is reduced by heat treatment. The in vitro degradation results of the alloy show that solution treatment on the as-extruded alloy results in a little higher degradation rate and aging treatment on the alloy can reduce degradation rate slightly.

Degradation Behavior of Electrochemical Performance of Sealed-Type Nickel/Metal Hydride Batteries

The degradation mechanism of electrochemical performance of sealed type nickel/metal hydride batteries was investigated. The results indicate that the degradation behavior of Ni/MH battery is not only owing to the lack of electrolyte, but also the deterioration of the active materials on the positive and negative electrodes of Ni/MH batteries. Scanning electron micrographs (SEM), X ray diffraction (XRD) and laser granularity analyses are presented. The particle pulverization and oxidation during charge/discharge are identified as the main causes for deterioration of the negative and positive electrode in nickel/metal hydride batteries, as well as the cross section cracking of both anode and cathode.

Effects of Sr addition on microstructure, mechanical properties and in vitro degradation behavior of as-extruded Zn-Sr binary alloys

The microstructures,mechanical properties and in vitro degradation behavior of as-extruded pure Zn and Zn-x Sr(x=0.1,0.4,0.8 wt.%)alloys were investigated systematically.For the microstructure and mechanical properties,Sr Zn13 phase was newly formed due to the addition of 0.1 wt.%Sr,improving the yield strength,ultimate tensile strength and elongation from(85.33±2.86)MPa,(106.00±1.41)MPa and(15.37±0.57)%for pure Zn to(107.67±2.05)MPa,(115.67±2.52)MPa and(20.80±2.19)%for Zn-0.1Sr,respectively.However,further increase of Sr content led to the deterioration of the mechanical properties due to the stress concentration and cracks initiation caused by the coarsening Sr Zn13 particles during tensile tests.For in vitro degradation,since micro galvanic corrosion was enhanced owing to the formation of the inhomogeneously distributed Sr Zn13 phase,the corrosion mode became non-uniform.Corrosion rate is gradually increased with the addition of Sr,which is increased from(11.45±2.02)μm/a(a=year)for pure Zn to(32.59±3.40)μm/a for Zn-0.8Sr.To sum up,the as-extruded Zn-0.1Sr alloy exhibited the best combination of mechanical properties and degradation behavior.

Effect of small changes in sintering temperature on varistor properties and degradation behavior of V-Mn-Nb-Gd co-doped zinc oxide ceramics

The effect of small changes in sintering temperature on microstructure, electrical properties, dielectric characteristics, and degradation behavior of V-Mn-Nb-Gd co-doped zinc oxide ceramics was investigated. With the increase of sintering temperature, the densities of the sintered pellets decreased from 5.54 to 5.42 g/cm3 and the average grain size increased from 4.1 to 11.7 μm. The breakdown field(E1 m A) decreased noticeably from 7138 to 920 V/cm with the increase of sintering temperature. The varistor ceramics sintered at 900 ℃ exhibited excellent nonohmic properties, which were 66 for the nonohmic coefficient and 77 μA/cm2 for the leakage current density. Concerning stability, the varistors sintered at 900 ℃ exhibited the strongest accelerated degradation characteristics, with ΔE1 mA =-9.2% for DC accelerated degradation stress of 0.85 E1 m A at 85 °C for 24 h.

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.

The effect of different coatings on bone response and degradation behavior of porous magnesium-strontium devices in segmental defect regeneration

Regeneration of long-bone segmental defects remains a challenge for orthopedic surgery.Current treatment options often require several revision procedures to maintain acceptable alignment and achieve osseous healing.A novel hollow tubular system utilizing magnesium-strontium(Mg-Sr)alloy with autogenous morselized bone filled inside to repair segmental defects was developed.To improve the corrosion and biocompatible properties,two coatings,Ca-P and Sr-P coatings,were prepared on surface of the implants.Feasibility of applying these coated implants was systematically evaluated in vitro and in vivo,and simultaneously to have a better understanding on the relationship of degradation and bone regeneration on the healing process.According to the in vitro corrosion study by electrochemical measurements,greater corrosion resistance was obtained for Ca-P coated sample,and attributed to the double-layer protective structure.The cytotoxicity and alkaline phosphatase(ALP)assays demonstrated enhanced bioactivity for Sr-P coated group because of the long-lasting release of beneficial Sr^(2+).At 12 weeks post-implantation with Mg-Sr alloy porous device,the segmental defects were effectively repaired with respect to both integrity and continuity.In addition,compared with the Ca-P coated implant,the Sr-P coated implant was more proficient at promoting bone formation and mineralization.In summary,the Sr-P coated implants have bioactive properties and exceptional durability,and promote bone healing that is close to the natural rate,implying their potential application for the regeneration of segmental defects.

Binary Zn–Ti alloys for orthopedic applications:Corrosion and degradation behaviors,friction and wear performance,and cytotoxicity

Zinc(Zn)and its biocompatible and biodegradable alloys have substantial potential for use in orthopedic implants.Nevertheless,pure Zn with a hexagonal close-packed crystal structure has only two independent slip systems,therefore exhibiting extremely low elongation and yield strength in its ascast condition,which restricts its clinical applications.In this study,as-cast Zn–xTi(titanium)(x=0.05,0.10,0.20,and 0.30 wt.%)binary alloys were hot-rolled and their microstructures,mechanical properties,wear resistance,and cytocompatibility were comprehensively investigated for orthopedic implant applications.The microstructures of both as-cast and hot-rolled Zn–xTi alloys consisted of anα-Zn matrix phase and a TiZn16 phase,while Zn–0.2 Ti and Zn–0.3 Ti exhibited a finerα-Zn phase due to the grainrefining effect of Ti.The hot-rolled Zn–0.2 Ti alloy exhibited the highest yield strength(144.5 MPa),ultimate strength(218.7 MPa),and elongation(54.2%)among all the Zn–x Ti alloys.The corrosion resistance of Zn–xTi alloys in Hanks’solution decreased with increasing addition of Ti,and the hot-rolled Zn–0.3 Ti alloy exhibited the highest corrosion rates of 432μm/y as measured by electrochemical testing and 57.9μm/y as measured by immersion testing.The as-cast Zn–xTi alloys showed lower wear losses than their hot-rolled counterparts.The extracts of hot-rolled Zn–x Ti alloys at concentrations of≤25%showed no cytotoxicity to MG-63 osteosarcoma cells and the extracts of Zn–xTi alloys exhibited enhanced cytocompatibility with increasing Ti content.

Degradation behaviors of surface modified magnesium alloy wires in different simulated physiological environments

The degradation behaviors of the novel high-strength AZ31B magnesium alloy wires after surface modification using micro-arc-oxidization （MAO） and subse- quently sealing with poly-L-lactic acid （PLLA） in different simulated physiological environments were investigated. The results show the surface MAO micropores could be physically sealed by PLLA, thus forming an effective protection to corrosion resistance for the wires. In simulated gastric fluid （SGF） at a low pH value （1.5 or 2.5）, the treated wires have a high degradation rate with a rapid decrease of mass, diameter, mechanical properties and a significant increase of pH value of the immersion fluid. However, surface modification could effectively reduce the degradation rate of the treated wires in SGF with a pH value above 4.0. For the treated wires in simulated intestinal fluid at pH =8.5, their strength retention ability is higher than that in strong acidic SGF. And the loss rate of mass is faster than that of diameter, while the pH value of the immersion fluid decreases. It should be noted that the modified wires in simulated body environment have the best strength retention ability. The wires show the different degradation behaviors indicating their different degradation mechanisms, which are also proposed in this work.

In Vivo Study on Degradation Behavior and Histologic Response of Pure Magnesium in Muscles

When an orthopedics device is implanted into bone injury site, it will contact the soft tissue （skeletal muscle, fascia, ligament etc.） except for bone. Magnesium based biodegradable metals are becoming an important research object in orthopedics due to their bioactivity to promote bone healing. In this study, pure Mg rods with and without chemical conversion coating were implanted into the muscle tissue of rabbits. Implants and their surrounding tissues were taken out for weight loss measurement, cross- sectional scanning electron microscopy observation, elemental distribution analysis and histological examination. The results showed that the chemical conversion coating would increase the in vivo cor- rosion resistance of pure Mg and decrease the accumulation of calcium （Ca） and phosphorus （P） elements around the implants. For the bare magnesium implant, both Ca and P contents in the surrounding tissues increased at the initial stage of implantation and then decreased at 12 weeks implantation, while for the magnesium with chemical conversion coating, Ca and P contents in the surrounding tissues de- creased with the implantation time, but were not significant. The histological results demonstrated that there was no calcification in the muscle tissue with implantation of magnesium for up to 12 weeks. The chemical conversion coating not only increased the in vivo corrosion resistance of pure Mg, but also avoided the depositions of Ca and P in the surrounding tissues, meaning that pure magnesium should be biosafe when contacting with muscle tissues,

Degradation behaviors of La–Mg–Ni-based metal hydride alloys:structural stability and influence on hydrogen storage performances

The present work focuses on the structural stability upon hydrogenation of three typical La-Mg-Ni-based alloys： La2 MgNi9, LaaMgNi14 and La4MgNi19. Structural changes during gaseous and electrochemical cycles were characterized, and the influence of the structure distortion on the hydrogen storage properties was concerned. Hydrogen-induced amor- phization （HIA） and disproportionation of the three alloys have occurred during both the gaseous and electrochemical cycles. Structural stability of the phase structures in the La-Mg-Ni system is found to follow the order： LaNi5- 〉 （La,Mg）5Ni19 〉 （La,Mg）2Ni7 〉 （La,Mg）Ni3 〉 （La,Mg）Ni2. HIA increases thermal stability of the metal hydrides and difficulty to dehydrogenation and leads to degradation of both the gaseous and electrochemical capacities. Interestingly, LaEMgNi9 with poor stability presents elevated discharge capability even at 60 ℃ which can be attributed to increase in the hydrogen desorption capability and inhibition of the self-discharge induced by severe HIA at higher temperatures. In addition, HIA in the electrochemical reactions is obviously weaker than the extent during the gaseous cycles, which is mainly due to the slower hydrogenation speed. The development of HIA in the gaseous and electrochemical process is considered to follow the direct and gradual modes, respectively.

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.

Fe-Zn supersaturated solid solution prepared by mechanical alloying and laser sintering to accelerate degradation

The slow degration of iron limits its bone implant application.The solid solution of Zn in Fe is expected to accelerate the degradation.In this work,mechanical alloying(MA)was used to prepare Fe-Zn powder with supersaturated solid solution.MA significantly decreased the lamellar spacing between particles,thus reducing the diffusion distance of solution atoms.Moreover,it caused a number of crystalline defects,which further promoted the solution diffusion.Subsequently,the MA-processed powder was consolidated into Fe-Zn part by laser sintering,which involved a partial melting/rapid solidification mechanism and retained the original supersaturated solid solution.Results proved that the Fe-Zn alloy became more susceptible with a lowered corrosion potential,and thereby an accelerated corrosion rate of(0.112±0.013)mm/year.Furthermore,it also exhibited favorable cell behavior.This work highlighted the advantage of MA combined with laser sintering for the preparation of Fe-Zn implant with improved degradation performance.

EffectS of sequence of nylon bags rumen incubation on kinetics of degradation in some commonly used feedstuffs in dairy rations

Nowadays, most available information on the degradative behaviour of feeds in ruminants is based on in situ incubation in the rumen, and it is adopted by many feed evaluation systems currently in use for ruminants. However, the outcome of.this technique might be affected by many factors such as sequence of nylon bags incubation in the rumen. The objective of current study was to investigate effects of sequence of nylon bag incubation on degradative behavior of dry matter （DM）, crude protein （CP）, neutral detergent fiber （NDF） and acid detergent fiber （ADF） in some feed ingredients commonly used in dairy rations, including alfalfa haylage, corn silage, corn grain and soybean meal. Four multiparous Holstein lactating cows fitted with permanent ruminal cannulas were used. The nylon bags containing feed samples either were placed in the rumen at once and removed at designated time intervals （all in-gradually out method; AG） or were placed in the rumen at designated time points and retrieved at once （gradually in-all out method; GA）. Fractional rate of degradation of potentially degradable fraction, lag time and effective rumen degradability （ED） of DM and CP were significantly higher in the AG compared to the GA method （P〈0.05）. Fractional rates of DM and CP degradation was higher in alfalfa haylage samples incubated in the rumen using the AG method compared to that using the GA method （0.138 h-1 vs. 0.073 h-1 and 0.002 h-1 vs. 0.1125 h-1, for DM and CP, respectively; P〈0.05）. Due to a higher fractional rate of degradation （Kd） of DM and CP, the ED of DM and CP at different fractional passage rates were higher in the AG than those in the GA method （P〈0.05）. Potentially degradable fraction and lag time of NDF were higher in the AG method compared to the GA method （P〈0.05）. Placing all bags in the rumen at once and removing them at designated time intervals compared with introduction of bags in reverse sequence and removing them all at once led to a lower undegradable fraction （U） of NDF in alfalfa （1.8% vs. 4.0%, respectively; P〈0.05） and corn silage （3.3% vs. 6.7%, respectively; P〈0.05） samples. Potentially degradable fraction of ADF was significantly higher in the AG method compared with the GA method （P〈0.05）. Bag incubation sequence had profound effects on kinetics of degradation of DM, CP and NDF in situ in the feed samples studied. The effects were more evident in the forages （especially alfalfa haylage） than in the concentrate ingredientsnamely corn grain and soybean meal..This experiment is the first time to investigate effects of two methods under the same experiment conditions, providing basic data for the determination of ED.

Aging Behaviors of Silicone Rubber Composite Materials under Outdoor Environment

We investigated the aging effect on the chemical structure of silicone rubber composite materials under outdoor environment. The variations of low molecular weight siloxanes in silicone rubber were probed by gas chromatography-mass spectrometry during the degradation process. The experimental results indicate that a series of cyclic siloxanes exist in both the virgin and aged silicone rubber samples, while the additional low molecular weight siloxanes（hexamethyl cyclotrisiloxane） only appear in the aged samples. Meanwhile, the total amounts of low molecular weight siloxanes in the aged samples are much less than those in the virgin ones. The loss of low molecular weight siloxanes is induced by the chain scission and depolymerization.

Degradation Characters of La-Mg-Ni-Based Metal Hydride Alloys:Corrosion and Pulverization Behaviors

Degradation behaviors of three typical La-Mg-Ni alloys, La2MgNi9, La1.5Mg0.5Ni7 and La4MgNi19, were studied. La1.5- Mg0.5Ni7 with （La,Mg）2Ni7 as main phase presents better discharge capacity and cycling stability. The three alloys suffer severe pulverization and corrosion after electrochemical cycles, which are considered to be the significant factor attributing to the capacity deterioration. However, the overall corrosion extent of the three cycled alloys aggravates successively, which is inconsistent with the result that LaEMgNi9 presented poor cycling stability and also the assumption that alloy with high Mg content is easy to be corroded. The intrinsic anti-corrosion and anti-pulverization characteristics of the three alloys are mainly focused in this work. Immersion corrosion experiments demonstrate that the Mg-rich phases are more easily to be corroded. The corrosion resistance of the three alloys presents an improved trend which is inversely proportional to abundance of the Mg-rich phases. However, the anti-pulverization abilities present an inverse trend, which is closely related to the mechanical property of various phase structures. LaNi5 with the highest hardness is easy to crack, but the soft （La,Mg）Ni2 is more resistant to crack formation and spreading. Thus, the weaker corrosion of La2MgNi9 after electro- chemical cycling is attributed to the better intrinsic anti-pulverization capability though the anti-corrosion is poor. As La4MgNi19 possesses excellent corrosion resistance, enhancement of the anti-pulverization ability is urgent for improvement in the cycling stability.

In-situ deposition of apatite layer to protect Mg-based composite fabricated via laser additive manufacturing

Biodegradable magnesium(Mg) and its alloy show huge potential as temporary bone substitute due to the favorable biocompatibility and mechanical compatibility. However, one issue deserves attention is the too fast degradation. In this work, mesoporous bioglass(MBG)with high pore volume(0.59 cc/g) and huge specific surface area(110.78 m^(2)/g) was synthesized using improved sol-gel method, and introduced into Mg-based composite via laser additive manufacturing. Immersion tests showed that the incorporated MBG served as powerful adsorption sites, which promoted the in-situ deposition of apatite by successively adsorbing Ca2+and HPO42-. Such dense apatite film acted as an efficient protection layer and enhanced the corrosion resistance of Mg matrix, which was proved by the electrochemical impedance spectroscopy measurements. Thereby, Mg based composite showed a significantly decreased degradation rate of 0.31 mm/year. Furthermore,MBG also improved the mechanical properties as well as cell behavior. This work highlighted the advantages of MBG in the fabrication of Mg-based implant with enhanced overall performance for orthopedic application.

3D-cubic interconnected porous Mg-based scaffolds for bone repair

Mg-based porous materials,as potential bone tissue engineering scaffolds,are considered an attractive strategy for bone repair owing to favorable biodegradability,good biocompatibility and suitable mechanical properties.In this work,3D-cubic interconnected porous Mg–xZn–0.3Ca(x=0,3,6)scaffolds were prepared to obtain desirable pore structures with a mean porosity up to 73%and main pore size of 400–500μm,which pore structures were close to the human cancellous bone.The structure–property relationships in the present scaffolds were analyzed by experiments and theoretical models of generalized method of cells(GMC).Mg–xZn–0.3Ca scaffolds exhibited good compression properties with a maximum above 5MPa in yield strength and about 0.4GPa in elastic modulus.This was attributed to not only the alloy strengthening but also the large minimum solid area.On the other hand,the scaffolds showed undesirable and relatively serious degradation behavior in Hank’s solution,resulting from Zn addition in Mg-based scaffolds and the high surface area ratio in the pore structure.Therefore,surface modifications are worth studying for controlled degradation in the future.In conclusion,this research would explore a novel attempt to introduce 3D-cubic pore structure for Mg-based scaffolds,and provide new insights into the preparations of Mg-based scaffolds with good service performances for bone repair.

Research progress on corrosion behaviors and biocompatibility of rare-earth magnesium alloys in vivo and in vitro

As yet,Mg alloys acting as the medical implants have drawn extensive attention,due to their spontaneous degrada bility,effective load-transmissibility and the excellent biocompatibility,particularly in bone tissue reconstruction and vascular radial-support.Regrettably,they were inevitably affected by the tension/compression-torsion,dynamic erosion and corrosion fatigue under complex service conditions,which lead to premature failure of implantation-materials.Micro-alloying addition is an effective way to delay the rapid degradation,especially in rare-earth micro-composite addition.It can not only reduce intensities of galvanic-corrosion by refining the grain sizes and adjusting the Volta-potentials distribution of the precipitates,but also modify the compositions and biocompatibility of the degradation products.Moreover,the higher compress tress on the surface can improve the stability and densification of the film layer,which enhanced the corrosion resistance.Thus,the latest research progress about in vivo/vitro degradation behavio rs and bioco mpatibility of rare-earth Mg alloys is reviewed;The internal relationships between rare-earth elements,phase features and degradation behaviors of Mg alloys are summarized.Moreover,the effects of rare-earth addition on the film-characteristics are deeply explained,and the induced mechanisms of rare earth elements on the biocompatibility are revealed.

Two-stage degradation and novel functional endothelium characteristics of a 3-D printed bioresorbable scaffold

Bioresorbable scaffolds have emerged as a new generation of vascular implants for the treatment of atherosclerosis,and designed to provide a temporary scaffold that is subsequently absorbed by blood vessels over time.Presently,there is insufficient data on the biological and mechanical responses of blood vessels accompanied by bioresorbable scaffolds(BRS)degradation.Therefore,it is necessary to investigate the inflexion point of degradation,the response of blood vessels,and the pathophysiological process of vascular,as results of such studies will be of great value for the design of next generation of BRS.In this study,abdominal aortas of SD rats were received 3-D printed poly-l-actide vascular scaffolds(PLS)for various durations up to 12 months.The response of PLS implanted aorta went through two distinct processes:(1)the neointima with desirable barrier function was obtained in 1 month,accompanied with slow degradation,inflammation,and intimal hyperplasia;(2)significant degradation occurred from 6 months,accompanied with decreasing inflammation and intimal hyperplasia,while the extracellular matrix recovered to normal vessels which indicate the positive remodeling.These in vivo results indicate that 6 months is a key turning point.This“two-stage degradation and vascular characteristics”is proposed to elucidate the long-term effects of PLS on vascular repair and demonstrated the potential of PLS in promoting endothelium function and positive remodeling,which highlights the benefits of PLS and shed some light in the future researches,such as drug combination coatings design.