Behavior of potassium titanate whisker in simulated body fluid

Behavior of potassium titanate whisker in simulated bodyfluidXin Wang,Shuang Jin Liu,Yu Min Qi,Li Chen Zhao,Chun Xiang Cui nKey Laboratory for New Type of Functional Materials in Hebei Province,School of Material Science and Engineering,Hebei University of Technology,Dingzigu Road,Hongqiao District,Tianjin300130,Chinaa r t i c l e i n f oArticle history:Received13November2013Accepted23July2014Available online1August2014Keywords:BiomaterialPotassium titanateSimulated bodyfluidMicrostructurePhase transformationBiocompatibilitya b s t r a c tTwo sintering products containing potassium titanates were fabricated and cultivated in simulated bodyfluid for12days.It was found that the molar ratio of titanium/potassium of potassium titanate is a keyfactor to control the behavior of potassium titanate in bodyfluid environment.Low potassium titanatessuch as K2Ti2O5and K2Ti4O9transformed into calcium titanate due to its intrinsic characteristics of ionexchange.However,potassium hexatitanate was structurally stable adsorbing needle-like hydroxyapa-tite.The experimental results indicated that potassium hexatitanate possesses excellent biocompatibilitywhich is better than low potassium titanates.&2014Elsevier B.V.All rights reserved.1.IntroductionMetallic biomaterials have attracted considerable attentionin recent years due to their good mechanical properties[1–4].Generally,metallic biomaterials such as steels,titanium alloys andmagnesium alloys have good mechanical properties but shortageof biocompatibility than those biological ceramics.Except devel-opment of those low modulus alloys free of toxic elements,another strategy is to modify the surface of metallic materials toimprove their biocompatibility[5–9].Many efforts in chemical orphysical modification on the surface of metals have shown greateffect.For example,making a coating contained hydroxyapatite(HA),titanium-dioxide or potassium titanate(PT)on titaniumalloys has been proven to be a promising methods to improvethe biocompatibility of titanium alloys[10–13].Potassium titanate,which can be rewritten as K2Ti n O2nþ1(orK2OÁn TiO2,n¼1,2,4,6,8),is an important inorganic material,possessing varied structures,good mechanical properties,specialfunctional properties and biocompatibility[14,15].One typical PT,K2Ti6O13or potassium hexatitanate has been used as reinforce-ment in ceramics,polymers and metal matrix bio-composites[16–18].When making a coating containing PT,it is difficult toobtain totally pure PTs such as K2Ti6O13or K2Ti8O17due to thepresence of residual metastable phases such as K2Ti2O5etc.In addition,PT has different chemical behavior with different nvalue.It is thus necessary to study the biocompatibility of differentPTs for developing new biomaterials using PTs.2.Materials and methodPotassium titanate was prepared by sintering the mixture ofraw material powder including potassium carbonate(K2CO3)andtitanium dioxide(TiO2).With a molar ratio of K2CO3and TiO2(K/T)1:3,the sintering sample P13was prepared at9001C for1h toobtain low PT(n r6,e.g.K2Ti4O9).Moreover,with K/T¼1:5(P15),high PT(n Z6, e.g.K2Ti6O13)was expected to be prepared at10001C for1h.The two sintered samples were then immersedinto simulated bodyfluid(SBF)cultivating for12D to evaluate thebiocompatibility and bioactivity of different PTs(S13and S15isthe cultivated sample of P13and P15in this paper,respectively.).The composition of ions in applied SBF is in elsewhere[12].The morphology evaluations of the PT samples before and aftercultivation in SBF were performed on a scanning electron micro-scope(SEM,Philips XL30TMP)and an optical microscope(XDS-1B,COIC,China).The microstructure of potassium hexatitanate aftercultivation in SBF was examined by a transmission electron micro-scope(TEM,Philips Tacnai F20)with an energy dispersive spectro-meter(EDS).The phase composition was investigated by an X-raydiffractometry(XRD,Philips X'pert TMD).3.Results and discussionFig.1shows the XRD spectra of the prepared potassium titanatesamples.It was found that different PTs were successfully pre-pared by changing K/T.For sample P15,some sharp peakscorresponding to K2Ti6O13and K2Ti4O9can be observed,implyingthat the major phase is K2Ti6O13with some amount of K2Ti4O9asContents lists available at ScienceDirectjournal homepage:/locate/matletMaterials Letters/10.1016/j.matlet.2014.07.1450167-577X/&2014Elsevier B.V.All rightsreserved.n Corresponding author.Tel.:þ862226564125.E-mail address:hutcui@(C.X.Cui).Materials Letters135(2014)139–142residual phase.With a lower K/T,the major phases of P13are K 2Ti 4O 9and K 2TiO 3.Therefore,P15can be regarded as high PT K 2Ti 6O 13whisker and P13is then regarded as low PT K 2TiO 3or K 2Ti 4O 9.Fig.1also displays the XRD spectra of cultivated PT samples in SBF compared with the original samples,showing that the cultivation product of the two samples is quite different.For S15,the XRD spectrum contains such peaks for CaTiO 3,K 2Ti 6O 13and HA as shown in Fig.1.However,for S13,there is only CaTiO 3can be found existing in its spectrum.Fig.2shows the morphologies of the PT samples before and after cultivating in SBF.For P13,it shows a flake pattern for the as-prepared status as shown in Fig.2(a).After cultivating in SBF for 12days,it turns to a block-like pattern which the flake-like product disappeared as shown in Fig.2(c).For P15,the sintering product is a kind of whisker (Fig.2(b))which also keeps the original morphology after cultivation in SBF for 12D (Fig.2(d)),indicating that it is very stable in SBF.Moreover,some small particles can be observed adsorbing on the whiskers as shown in the inset in Fig.2(d).To identify the particles adsorbing on the whiskers,TEM and EDS were used which the results are shown in Fig.3.It was found that the particles around the whisker in Fig.2(d)actually are some clumps formed by a kind of needle-like whisker in nano-scale rich in Ca and P as shown in Fig.3(a).The EDS analysis results (in Fig.3(b))show that the atomic ratio of Ca/P of region C in Fig.3(a)is about 1.7:1(20.6:12.1)near the theoretical value 1.67:1of HA.In addition,the atomic ratio of K/Ti of region C in Fig.3(a)is about 2:7(13.3:46.5shown in Fig.3(c))which is closed to the theoretical value 2:6of K 2Ti 6O 13.Therefore,this result shows that K 2Ti 6O 13whisker in P15keeps a constant chemical composition and can absorb HA nano-whisker,indicating that K 2Ti 6O 13possesses good biocompatibility.It is known that the precipitation of Ca/P ions implies that the cultivated material may possess good biocompatibility or bioac-tivity,as Ca and P are generally regarded as important ions to form HA.In the present work,Ca ions is also precipitated in S13forming CaTiO 3while not HA,which is attributed to ion exchange.The detailed process is that K þin low PT is replaced by Ca 2þfrom SBF,with reactions as:K 2TiO 3þCa 2þ-CaTiO 3þ2K þð1ÞFig.1.XRD patterns of the potassium titanate before and after cultivating inSBF.Fig.2.Morphology of the PT samples.(a)P13,(b)P15,(c)S13and (d)S15.X.Wang et al./Materials Letters 135(2014)139–142140Fig.3.Microstructure of the potassium hexatitanate after cultivation in SBF.(a)TEM image showing a potassium hexatitanate whisker surrounded by hydroxyapatite whiskers,(b)EDS spectrum and the corresponding chemical composition of region B in (a)and (c)EDS results of the whisker C in(a).Fig.4.Morphologies of sample P13after cultivating in pure water for 12D.(a)Optical image with lower magni fication of 50Âfor P13,(b)after water cultivation (c)SEM image of some particles in (b).X.Wang et al./Materials Letters 135(2014)139–142141K2Ti4O9þCa2þ-CaTi4O9þ2Kþð2ÞCaTi4O9þ2Ca2þ-3CaTiO3þTi4þð3ÞIn the process represented by Eqs.(1)–(3),aqueous environ-ment may play an important role for the formation of CaTiO3in low PTs due to the presence of a large amount of Ca2þin SBF.It is known that low PT possesses considerable amount of Kþorganiz-ing layered channels favorable for ion-exchange.If there are no adequate free Ca2þsupplying for ion-exchange,low PT cannot transform to CaTiO3.As verification,P13is immersed in pure water for12 D.It shows that the macro morphology of sample P13 changed from irregular particle shape shown in Fig.4(a)to short strip shape shown in Fig.4(b).In fact,this short strip is composed by some bundles of whiskers as shown in Fig.4(c),implying that the low PT in P13has transformed into high PT whisker. Interestingly,the transformation to high PT shown in Fig.4is suppressed in SBF,suggesting that ion environment is important for the behavior of PT.4.ConclusionThe molar ratio of titanium/potassium of potassium titanates is a key factor to control the behavior of potassium titanate(PT)in the simulated bodyfluid.Low PT may transform into calcium titanate due to its intrinsic characteristics of ion exchange in body fluid environment.However,high PT potassium hexatitanate is structurally stable and adsorbing needle-like hydroxyapatite in SBF.It is then demonstrated that potassium hexatitanate possesses excellent biocompatibility which is better than low potassium titanates.AcknowledgmentsThe project was aidedfinancially by Key Foundation Project of Hebei Province Applied and Fundamental Research(No.11965151D).References[1]Ryhänen J,Niemi E,Serlo W,NiemeläE,Sandvik P,Pernu H,et al.Biocompat-ibility of nickel-titanium shape memory metal and its corrosion behavior in human cell cultures.J Biomed Mater Res A1997;35:451–7.[2]Okazaki Y,Gotoh parison of metal release from various metallicbiomaterials in vitro.Biomaterials2005;26:11–21.[3]Staiger MP,Pietak AM,Huadmai J,Dias G.Magnesium and its alloys asorthopedic biomaterials:a review.Biomaterials2006;27:1728–34.[4]Chou D-T,Wells D,Hong D,Lee B,Kuhn H,Kumta PN.Novel processing of Iron-Manganese alloy based biomaterials by inkjet3D printing.Acta Mater 2013;9:8593–603.[5]Hanawa T.In vivo metallic biomaterials and surface modification.Mater SciEng A1999;267:260–6.[6]Puleo D,Nanci A.Understanding and controlling the bone-implant interface.Biomaterials1999;20:2311–21.[7]Liu X,Chu PK,Ding C.Surface modification of titanium,titanium alloys,andrelated materials for biomedical applications.Mater Sci Eng R2004;47: 49–121.[8]Duarte LT,Biaggio SR,Rocha-Filho RC,Bocchi N.Surface characterization ofoxides grown on the Ti-13Nb-13Zr alloy and their corrosion protection.Corros Sci2013;72:35–40.[9]Silva-Bermudez P,Rodil S.An overview on protein adsorption on metal oxidecoatings for biomedical implants.Surf Coat Technol2013;233:147–58. [10]Chu PK,Chen J,Wang L,Huang N.Plasma-surface modification of biomaterials.Mater Sci Eng R2002;36:143–206.[11]Cui CX,Shen YT,Xu YJ,Li YC,Wang R,Wang X,et al.Fabrication and bio-compatibility of K2Ti6O13bio-ceramic coating on the surface of the titanium alloy TiAlxZrxÀ4SnxÀ3.5NbxÀ4.5.Rare Met Mater Eng2003;32:627–30. [12]Cui CX,Liu H,Li YC,Sun J,Wang R,Liu SJ,et al.Fabrication and biocompat-ibility of nano-TiO2/titanium alloys biomaterials.Mater Lett2005;59:3144–8.[13]Satoh K,Ohtsu N,Sato S,Wagatsuma K.Surface modification of Ti–6Al–4Valloy using an oxygen glow-discharge plasma to suppress the elution of toxic elements into physiological environment.Surf Coat Technol2013;232: 298–302.[14]Li YB,Li DX,Xu ZZ,Lin Q,Lan XH,Lu CH,et al.In vitro bioactivity of potassiumtitanate whiskers.Adv Mater Res2008;47:1351–4.[15]Li J,Zhang YC,Zhang M.Low temperature preparation and optical propertiesof K2Ti6O13.Mater Lett2012;79:136–8.[16]Yu D,Wu J,Zhou L,Xie D,Wu S.The dielectric and mechanical properties of apotassium-titanate-whisker-reinforced PP/PA pos Sci Technol 2000;60:499–508.[17]Qi Y,He Y,Cui C,Liu S,Wang H.Fabrication and biocompatibility in vitro ofpotassium titanate biological thinfilm/titanium alloy biological composite.Front Mater Sci2007;1:252–7.[18]Lu Z,Liu Y,Liu B,Liu M.Friction and wear behavior of hydroxyapatite basedcomposite ceramics reinforced withfibers.Mater Des2012;39:444–9.X.Wang et al./Materials Letters135(2014)139–142 142。