M--镍钛形状记忆合金：骨科应用中的有前途的材料

Chapter10©2013BahraminasabandBinSahari,licenseeInTech.ThisisanopenaccesschapterdistributedunderthetermsoftheCreativeCommonsAttributionLicense(),whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedtheoriginalworkisproperlycited.NiTiShapeMemoryAlloys,PromisingMaterialsinOrthopedicApplicationsMarjanBahraminasabandBarkawiBinSahariAdditionalinformationisavailableattheendofthechapter(Geetha,Singhetal.2008;Bahraminasab,Hassanetal.2010).Developingorapplyinganoptimalmaterial,therefore,cancausetheimplanttolastlongerandtoavoidthehugecostrelatedtotheinappropriateorunsuitablechoiceofmaterials.Shapememoryalloys(SMA)haveprovidednewinsightsintobiomedicalareaforcardiovascular,orthopedicanddentalapplications,andformakingadvancedsurgicalinstruments.Thebiomedicalsuccessofthesematerialsisduetotheirunusualproperties,whichmakesthemsuperiortoconventionalmaterials.AmongmanySMAs,NiTialloyisconsideredtobethebestbecauseofitssuperbcharacteristics.NiTialloypossessesmostofthenecessitiesfororthopedicimplantationandisusedinalargenumberofapplications.Therefore,itisworthtohighlighttheorthopedicapplicationsofthismaterial.Thereminderofthischapterisorganizedasfollows;section2discussesonbiocompatibilityofNiTishapememoryalloyinbothbulkandporousforms,followedbyabriefreviewofsomecurrentNiTiapplicationsinsection3.Afterthatsection4introducesoneofthepotentialapplicationsofthismaterialinorthopedics,whichisthefemoralcomponentofkneeprosthesis.Thechapterendswithdiscussionandconclusionininsections5and6,respectively.ShapeMemoryAlloys–Processing,CharacterizationandApplications2622.BiocompatibilityofNiTiEnthusiasmtoapplyNiTiinimplantshasbeentemperedbytheconcernrelatedtoitsbiocompatibility.Biocompatibilityisrelatedtothecapabilityofmaterialtoexistincontactwithhumanbodytissueswithoutcausinganunacceptabledegreeofharmtothebody.Furthermore,thematerialsshouldhavetheabilitytointeractwiththebiologicalenvironmenttoimprovethebiologicalresponse,thetissue-surfacebonding,andtoenhancetheabilitytoundergoaprogressivedegradationwhennewtissuesgrowandheal.OfthetwometalelementsinNiTialloys,titaniumiswellrecognizedtobebiocompatiblewithsuperblong-termcorrosionresistance.IncontrasttoTi,NireleasefromthesurfaceofNiTiimplantshasbeenaconcerningissuebecausethedissolutionandconcentrationofNiionsorweardebrisaboveacertainamountcausessomeallergicreactionandbiocompatibilityproblemsincludingpneumonia,chronicsinusitisandrhinitis,nostrilandlungcancerforpatients(Mantovani2000;Kapanen,Ryhanenetal.2001;MachadoandSavi2003).However,mostofinvivostudiesofNiTiimplantationandinvitroexperimentsexhibitedgoodbiocompatibilityofthismaterial(Castleman,Motzkinetal.1976;Ryhaenen,Kallioinenetal.1998;Kapanen,Ryhanenetal.2001).Thegoodcorrosionresistanceofthismaterialcanbeattributedtoitscrystalstructurestability,whichimpedestheseparationandreleaseofNiions.Therefore,itseemsthattheactualriskoflargeNileachingfromwearandcorrosionphenomenamaypotentiallybeoverexaggerated(Es-SouniandFischer-Brandies2005).ThetitaniumcontentofthesealloysisreadilyoxidizedandcreatesanoutmostprotectivetitaniumoxidelayerwhichactasabarriertochemicalattackandcorrosionandconfinesthediffusionofNiions.Thisoxidelayer,however,isnotpermanentandcanbedepletedbywear,corrosion,andfatigue.Inthissituation,NiTirepassivatesandregeneratetheoxidelayer.Theintegrityoftheprotectivetitaniumoxidelayerisinfluencedbysurfaceroughness,inhomogeneities,residues,porosity,andgeometry.Acertaintoxicityusuallyobservedinvitrostudies,ismostlikelyduetothehigheramountofNiconcentrationsinvitrothatarenotpossibletoachieveinvivo(Shabalovskaya1996).ThebiocompatibilityofNiTialloyshasbeenreportedtobeequalorbetterthanthatoftitanium,Co–Cralloysandstainlesssteels(Shabalovskaya1996;Ryhanen2000;Es-SouniandFischer-Brandies2005).Treatmentssuchassurfaceoxidation,plasmaimmersionionimplantation(PIII),andlasersurfacemodificationreducetheamountofNileachingfromthesurfaceofNiTiimplanttonegligibleamounts.Forexample,atreatmentlikedualelectropolishing(EP)andphotoelectrocatalyticallyoxidation(PEO)makesNiTisuitableforhardtissuereplacements(Chu,Guoetal.2009).Aproblemassociatedwiththismaterial,whichseemstobeimportantfororthopedicimplants,isslowosteogenesisprocessandgrowthofafibrouslayeratinterfaceofbone-