(7.6)--Novel Magnesium Alloys Developed机械工程材料机械工程材料.pdf

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1、Novel Magnesium Alloys Developed for Biomedical Application:A ReviewNan Li,Yufeng Zheng*State Key Laboratory for Turbulence and Complex System and Department of Materials Science and Engineering,College of Engineering,Peking University,Beijing 100871,ChinaManuscript received November 11,2012,in revi

2、sed form December 25,2012,Available online 9 February 2013There is an increasing interest in the development of magnesium alloys both for industrial and biomedicalapplications.Industrial interest in magnesium alloys is based on strong demand of weight reduction oftransportation vehicles for better f

3、uel efficiency,so higher strength,and better ductility and corrosionresistance are required.Nevertheless,biomedical magnesium alloys require appropriate mechanical properties,suitable degradation rate in physiological environment,and what is most important,biosafety to human body.Rather than simply

4、apply commercial magnesium alloys to biomedical field,new alloys should be designedfrom the point of view of nutriology and toxicology.This article provides a review of state-of-the-art ofmagnesium alloy implants and devices for orthopedic,cardiovascular and tissue engineering applications.Advances

5、in new alloy design,novel structure design and surface modification are overviewed.The factorsthat influence the corrosion behavior of magnesium alloys are discussed and the strategy in the futuredevelopment of biomedical magnesium alloys is proposed.KEY WORDS:Biomaterials;Magnesium alloys;Biodegrad

6、ation;Mechanical property;Biocompatibility1.IntroductionMagnesium alloys for biomedical applications are in spotlightrecently.They have advantages over traditional metallic mate-rials,ceramics and biodegradable polymers.For mechanicalproperties,metals are more suitable for load-bearing applicationsc

7、ompared with ceramics or polymer because of their high me-chanical strength as well as high fracture toughness.The den-sities of magnesium(1.738 g/cm3)and magnesium alloys(1.75e1.85 g/cm3)are very similar to that of human cortical bone(1.75 g/cm3),while the density of biomedical titanium alloyTi6Al4

8、V is 4.47 g/cm31.For biocompatibility,magnesium ionsare present in large amount in the human body and involved inmany metabolic reactions and biological mechanisms.The hu-man body usually contains magnesium approximately 35 g per70 kg body weight and the daily demand for magnesium is about375 mg2.Ma

9、gnesium alloys are promising candidates for or-thopedicandcardiovascularimplantsandhaveattractedincreasing attention since there is no requirement for a secondaryremoval surgery.Potential of commercial magnesium alloys as biodegradableimplant materials were evaluated.Witte et al.3investigatedin vivo

10、 corrosion of 4 magnesium alloys and found that thecorrosion layer of all the alloys displayed an accumulation ofbiological calcium phosphates and all alloys increased the newlyformed bone compared to the polymer.According to this study,LAE442 exhibited the lowest corrosion rate,while AZ31,AZ91and W

11、E43 were found to degrade at similar rates3.Gao et al.4reported that ZK60 alloy lost 3.1%of its original mass afterProf.Yufeng Zhengs research is concerned with development of new kind of biomedical metallic materials,includingbiodegradable magnesium alloys and iron-based alloys,b-Ti alloys with low

12、 elastic modulus,nickel-free Ti-based shapememory alloys,nanocrystalline metals and alloys and bulk metallic glasses,and their medical devices in dentistry,or-thopedics and interventional therapy.He has published over 230 SCI journal papers since 1998,with the citation of over3100 times and h-index

13、of 26.He edited 7 books and book chapters,and owned 27 Chinese Invention Patents.He wasgranted with over 30 projects including the National Basic Research Program of China and the National Science Fund forDistinguished Young Scholars.He served as a member of the editorial board of Journal of Biomedi

14、cal Materials ResearchPart B-Applied Biomaterials(Wiley),the associate editor board of Materials Letters(Elsevier),the editor board of Journalof Materials Science&Technology(Elsevier)and Acta Metallurgica Sinica(English Letters)(Springer).*Corresponding author.Prof.,Ph.D.;Tel./Fax:86 10 62767411;E-m

15、ail address:(Y.Zheng).1005-0302/$e see front matter Copyright?2013,The editorial office ofJournal of Materials Science&Technology.Published by ElsevierLimited.All rights reserved.http:/dx.doi.org/10.1016/j.jmst.2013.02.005Available online at SciVerse ScienceDirectJ.Mater.Sci.Technol.,2013,29(6),489e

16、502soaking in a simulated body fluid(SBF)for 242 h,while themass loss of Mge5.6Zne0.55Zre0.9Y alloy was merely 1.7%,indicating that the addition of the alloying element Y improvesthe corrosion resistance of ZK60 alloy.Heublein et al.5implanted 20 AE21 stents into coronary arteries of 11 domes-tic pi

17、gs.The main limit of the AE21 stents was that theirdegradation occurred faster than expected as the loss of me-chanical integrity occurred between 35 and 56 days after im-plantation.Then Mario et al.6and Peeters et al.7reported theresults of animal experiment and first clinical study of LektonMagic

18、coronary stent(Biotronik,Bulach,Switzerland)madefrom WE43 magnesium alloy,respectively.Based on this LektonMagic coronary stent,Biotronik Company developed 3 genera-tions of absorbable metal stent(AMS):(1)Studies on clinicalimplantation of 71 AMS-1 magnesium stents in the coronaryarteries of 63 pati

19、ents showed that the AMS stents can achievean immediate angiographic result similar to that of other metalstents,and can be safely degraded after 4 months8;(2)AMS-2with new alloy design and stent design maintains longer stentintegrity in animal;(3)AMS-3 stent is a Mg alloy stent coatedwith a fast-de

20、gradable polymer carrier with an anti-proliferativedrug.The first animal trial in porcine model showed promisingresults in terms of safety and efficacy compared to bare AMS Mgstent9.Although commercial magnesium alloys containing aluminumand/or rare earth elements exhibit good mechanical propertiesa

21、nd corrosion resistance,they are not suitable for biomedicalapplications in consideration of toxicity.Aluminum is wellknown as a neurotoxicant.The accumulation of Al has beensuggested to be associated with various neurological disor-ders10.Severe hepatotoxicity has been detected after theadministrat

22、ion of cerium,praseodymium and yttrium11.Toguarantee the biosafety of biodegradable materials,researchershave developed new type of magnesium alloys,choosingelement with no toxicity or low toxicity as alloying elements.This article reviews the progress and development onbiomedical magnesium alloys,m

23、ainly on pure Mg,MgeCa-based,MgeZn-based,MgeSi-based,MgeSr-based and MgeRE-based alloys.We also discussed novel structure design andsurface modification,and proposed the unsolved scientificproblems for the future development of biodegradable magne-sium alloys.2.Purification and Alloying Design of Ma

24、gnesium forBiomedical ApplicationPurificationandalloyingaretwostrategiestoobtainmagnesium-based biomaterials with proper properties.Mechan-ical properties of currently investigated biodegradable magne-sium and magnesium alloys are shown in Fig.1.Fig.2 showstheir corrosion rate and hydrogen evolution

25、 rate.Hemolysis rateand effect of magnesium alloy extract on cell viability aresummarized in Fig.3 and Table 1,respectively.2.1.Pure MgDue to the high chemical activity of magnesium,any of thealloying elements or impurities in its pure form or intermetallicphase will increase the galvanic corrosion

26、of magnesium andmagnesium alloys.The magnesium matrix acts in any case as acathode of the micro galvanic cell and gets dissolved12.Song13and Ren et al.14found that purification remarkablyslow down the corrosion rate of pure magnesium.The corrosionresistance of pure magnesium is relevant to the toler

27、ance limitsof impurities.When the impurity concentration exceeds thetolerance limit,the corrosion rate is greatly accelerated.The mostharmful impurities to pure magnesium are Fe,Cu and Ni,with atolerance limit of 170?10?6,1000?10?6and 5?10?6,respectively15.The tolerance limits are influenced by them

28、ethod of manufacture as well as the presence of a thirdelement.Lee et al.16claimed that the corrosion behavior of puremagnesium depends on the content ratio of impurities,such asFe/Mn ratio,rather than their content values.Grain refinementthrough forging or rolling can also enhance the corrosion res

29、is-tance of pure magnesium.Heat treatment with different tem-peratures and durations may have contrary effects.Ren et al.14reported that the corrosion rate of as-forged high-purity mag-nesium is increased after heat treatment at 773 K for 10 h,whichis caused by the coarsening of grains.However,Kuwah

30、araet al.17found that the MgO layer formed in the heat-treatedprocess at 803 K for 25 h enhances the precipitation of mag-nesium apatite HBSS()solution,so that the corrosion rate of3NeMg is decreased.Duetothehighhydrogenevolutionrate2andhighhemolysisrate(as-castw57%,as-rolled w25%18),pure Mg may not

31、 be a propermaterial for biodegradable vascular stents.For orthopedic applica-tions,althoughpureMgshowstheabilityofinducingtheformationof new bone19,20,the poor mechanical property is a concern.2.2.MgeCa-based alloysCalcium is a major component in human bone and is essentialin chemical signaling wit

32、h cells21.Moreover,magnesium isnecessary for the calcium incorporation into the bone22,whichmight be expected to be beneficial to the bone healing with theco-releasing of Mg and Ca ions.Ca is also beneficial to grain refinement of magnesium alloys.The solubility limit of Ca in Mg is 1.34 wt%23.The M

33、geCaalloys are mainly composed ofa(Mg)phase and Mg2Caphase24.With increasing Ca content,more and coarser Mg2Caphase precipitates along grain boundaries,weakening both themechanical property and corrosion resistance of as-cast MgeCaalloy24,25.After hot rolling or hot extrusion,coarse Mg2Caphase turns

34、 into smaller particles and the grain size is refined,contributing to improved mechanical properties and corrosionresistance24.Referring to Drynda et al.26,the strength of as-extruded binary MgeCa alloys increases with Ca content butthe ductility decreases.Gu et al.27found that the rapid solidifiedM

35、ge3Ca alloy ribbons showed much finer grain features,bettercorrosion resistance and improved cell reaction than the as-castMge3Ca alloy ingot.In vitro cytotoxicity test indicated thatMge1Ca alloy does not induce toxicity to L929 cells24.Mge1Ca alloy pins gradually degraded in vivo within 90 days and

36、new bone formed24.Moreover,in the study carried out byKrause et al.28,as-extruded Mge0.8Ca alloy maintained morethan half of their initial volume after being implanted into rabbittibiae for 6 months.2.3.MgeZn-based alloysZn exists in all human body tissues and is one of the mostabundant nutritionall

37、y essential elements in the human body29.Zn is a common alloying element in magnesium alloys with the490N.Li and Y.Zheng:J.Mater.Sci.Technol.,2013,29(6),489e502Fig.2Corrosion rate and hydrogen evolution rate of several kinds ofmagnesium alloys4,18,24,28,33,43,45,67,69.Fig.3Hemolysisrateofseveralkind

38、sofmagnesiumalloys18,24,33,45,50.Fig.1Mechanical properties of pure Mg and MgeCa-based alloys18,24,26(a),MgeZn-based alloys18,33,41,42,46,48(b),MgeSi-based and MgeSr-based alloys18,53,59,60(c),MgeRE-based alloys66,68e72(d)and comparison of mechanical properties of these alloy systems(e).N.Li and Y.Z

39、heng:J.Mater.Sci.Technol.,2013,29(6),489e502491solubility limit of 6.2 wt%23and can effectively improve me-chanical properties of magnesium.Various kinds of MgeZnbased alloys were studied.2.3.1.MgeZn binary alloys.Zhang et al.30e33investigated anextruded Mge6Zn alloy as a biodegradable material.This

40、 alloyconsists of a uniform single phase after solid solution treatmentand hot working,so galvanic corrosion is avoided33.The me-chanical properties of the Mge6Zn alloy is believed to besuitable for implant applications33.The in vitro cytotoxicity ofMge6Zn to L929 cells was found to be Grade 0e1 and

41、 thehemolysis rate is 3.4%30,33,indicating the Mge6Zn alloy ex-hibits good biocompatibility in vitro.The Mge6Zn alloy rodswere implanted into the femoral shaft of rabbits and graduallyabsorbed in vivo at degradation rate about 2.32 mm/y withnewly formed bone surrounding the implant33.The viscerahist

42、ologyexaminationandthebiochemicalmeasurementsproved that the degradation of MgeZn alloy did not harm theimportant organs32,33.In Fig.2,it is noticeable that thecorrosion rate of the Mge6Zn alloy in vivo is one order ofmagnitude higher than that in vitro,and is higher than other Mgalloys.2.3.2.MgeZne

43、Zr,MgeZneY and MgeZneZreY alloys.The addition of Y into magnesium alloys increases the solubilityof the matrix due to its high solubility(8.0 wt%23)in Mg,which enables the harmful elements to dissolve into the matrixand therefore slows down the corrosion rate4.Zr is usually usedas a grain refiner in

44、 magnesium alloys34.Zr shows goodbiocompatibility and osseointegration both in vitro and in vivo,even outperforming titanium35,36.Zhang et al.37investigated the influence of Y content ontensile properties and corrosion resistance of MgeZneY alloyswith low Zn content(1.73e1.98 wt%).The results showed

45、 thatboth tensile strength and elongation increase with increasing Ycontent,due to that the I-phase(Mg3Zn6Y)has better strength-ening effect than the W-phase(Mg3Zn3Y2).The alloys with asingle secondary phase showed a better corrosion resistance thanthose with two secondary phases.ZW21 and WZ21 alloy

46、s arefound to perform good cytocompatibility both in vitro andin vivo with homogeneous degradation and only limited gasformation being observed in vivo38.Gao et al.4found after242 h soaking in SBF,the mass loss of Mge5.6Zne0.55Zre0.9Y alloy was merely 1.7%,while that of Mge5.4Zne0.55Zr(ZK60)was 3.1%

47、,but still larger than that of pure Mg.2.3.3.MgeZneMn alloys.Manganese has no toxic effectexcept after extreme occupational exposure39.It plays a pri-mary role in the activation of multiple enzyme system39.Mndoes not affect the mechanical property of magnesium alloy,butcan improve their corrosion re

48、sistance by removing iron andother heavy-metal elements into relatively harmless intermetalliccompounds23.Zhang et al.40?42investigated the effect of Zn content onmicrostructure,mechanical properties and corrosion behavior ofMgeZneMn alloy.When the Zn content increases from 0 to3 wt%,the grain size

49、decreases from 12 to 4mm and the me-chanical properties increase remarkably.When the Zn content ismore than 3 wt%,the grain size stops decreasing,so the strengthcannot be improved any more and the elongation decreasessignificantly.The best anti-corrosion property is obtained with1 wt%Zn while furthe

50、r increase of Zn content deteriorates thecorrosion property.In vivo study showed that after 18 weeks,about 54%as-cast MgeMneZn(Mge1.2Mne1.0Zn,in wt%)implant had degraded but the degradation of magnesium did notcause any increase in serum magnesium content or any disordersof the kidney after 15-weeks

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