kem porous pva

8/13/2019 KEM Porous PVA

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KeyEngineeringMaterialsVols.264-268200a) p. 2079-2082onlineat http lwvwtt.scienilfu net@2004Traw TechPublications, wilzerland

Preparationf PorousBioceramicsy a SimplePVA'ProcessingA. C. Tas

TurkishAcademy f Sciences, taturkBulvariNo.221 06100Ankara,TurkeyKevwords: bioceramic,alcium hosphate, orosity, olyvinyl lcohol, alcinationAbstract. A robust procedure of preparing macro- and micro-porous calcium phosphatebioceramics s presented.The method involved the simple blending of a water soluble polymer(PVA, polyvinyl alcohol) solutionand a fine calcium phosphatepowder, followed by immediate nsitu gelation and then calcination at high temperatures o burn off the polymer to form theinterconnected orosity. Porous shapes evenmorselsor blocks) areobtainedwith porosity over thevariable range of 35 to 70Vo, with macropores anging from 100 to 1000 pm. Samplecharacteizationwas performed via X-ray diffraction, quantitativechemical analysis, optical andelectronmicroscopy,and compressive trengthmeasurements.IntroductionEighty percentof bone (whose norganicpart is mainly a phaseof alkali (Na and K) and alkalineearth (Mg) element-doped,nonstoichiometric and carbonated-apatitic calcium phosphate) iscomprised f dense orticalbone,within which is found the highly porousand vascular ancellousbone 20Vo). owever, he cancelloustrabecular) one s responsibleor 88Vo f the amountof thenormalbone urnoveror remodeling,mainly owing to its macroporous100 pm< pores


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2080 EuroCeramics ll l

temperature or 6 h, followed by cooling back to RT in 6 h. The porous chunk obtainedwas cut into**ull"t pieces by using a diamond saw to produce the desired shapes. Compressive strength,rrrasu."m"nts on the cut sampleswere performed with an Instron machine, and morphology andphaseconstinrdonof thosewere evaluatedby using scanningelectronmicroscopy(JSM-640'Jeol)andpowder XRD (D-5000,Siemens),espectively.

ResultsMacro- and micro-porosity on the fracture surfacesof the p-TcP ('\ilhitlockite) samplesproducedby using the above procissing recipe are shown in Figure I below. The characteristiccellularmorpnology with smaller holes present n eachcell facilitates the nterconnectivity of the pores.Thedense-loofing walls (as seen n Figs. la and lb) are also porous as depicted by the higbermagnificationphotomicrographs f Figs' lc and ld.

FigureLSEM picturesof porousTCP blocks;(a) and(b) interconnected acropores,c) wall areaenlarged,d)microporouswallsseparatehemacroporesrom oneanotherCompressivetrength f rectangUlarlocks 2 x 2 x 1 cm) cutfrom the calcinedgel-cast hunkhasbeen-foundobe24 * 3 MPa. n comparisono thestrength9] of trabecularones 2 to 10MPa),this porousWhitlockitematerialhasthe unique eatureof beingquite strong n spiteof its highporoiity(around 5-70Vo),easuredy theArchimedes'echnique10]'


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KeyEngineering aterials ols.264-268 2081

The raw material we used n producing the bioresorbable(higher than 60Vo n vivo resorption n 4months and more than 85Vo n around 1 year) B-TCP samples was a chemically processed,commerciallyavailable(Article 1.02143,Merck KGaA) submicroncalcium phosphatepowder witha Ca/Pmolar ratio in the vicinity of 1.50, whoseXRD data s shown in Fig. 2 by the bottom trace(a). The raw material actually consists of two phases,CaHPO+ and microcrystalline calcium-deficient hydroxyapatite (CDHA: Cas(HPO+XPO4)5(OH)).orous blocks (whose SEM picturesweregiven in Fig.l) obtainedwere single-phaseB-TCP, as shown by the middle trace(b) inFig.2.

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Figure 2.XRD data:(a) raw materialused or the data shown n this article, * indicates he peaksofthephaseCaHPO+, emainingpeaksareof CDHA, (b) data or porousblocks producedasdescribedin the experimentalsection,single-phaseB-TCP, (c) data or porousblocks quenched rom the hightemperature, ingle-phase -TCP

B-TCP is known to resorbquite fast in the body, owing to its high solubility. However, the high-temperature olymorphof TCP, namely,a-TCP, doesnot resorbas fast as B-TCP [11]. Alpha-TCPhas another interesting property, and it hydrolyzes itself in human plasma (and in general, inaqueoussystems)nto CDHA [12]. Whence his transformation in vitro or in vivo) is significantlycomplete, he product will not simply dissolveaway (as doesB-TCP) within the first few monthsfollowing the implantation. Therefore,porous cI-TCP based mplants will transform themselvesinto CDHA while retaining their macro-porous structure, and they will resorb in vivo by theosteoclasticaction, which takes place at a pH value of 3 to 4. If an implant material is justdissolving at the bone defect-sitewithin a short period of time, then it will obviously be quite farfrom providing a biomechanicallysoundhealingphaseduring the boneremodelingprocess.


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2082 EuroCeramics ll l

The crystallographicransition rom o-TCP to B-TCP occursat around1l80oC,uponcooling t131.We have been able o totally convert he porousmaterialsof this study nto single-phase -TCP (asshownby the XRD trace abeledas (c) in Fig.2), just by quenching he material rom 1295"C o900'C in 10 minutes. The compressivestrength of porous o-TCP blocks (9 2 MPa) wereobservedo be much ower than hoseof B-TCP,asexpected, nd his s due o the microcracks11]forming in the quenchedporousbody, originating from the significant unit cell volume differencebetween he orthorhombic(a) andhexagonal B) polymorphsof TCP.The cooling/quenching ate to be carefully adjusted and to be employed through the polymorphictransformation emperatureof TCP can in turn be used as a fine-tuning parameter n producingnovel bi-phasic "c[-TCP + B-TCP" bioceramics,with variable degreesof in vivo resorbability. Wehave ound, for instance, hat if we cooledour porousTCP samples rom I295"C to 900"C in 45minutes, nstead of 10 minutes, he end product consistedof a phasemixture of about 70Voa- and30Vop-phases. his materialdoeshave a higher n vivo resorbabilityas compared o pure C[-TCP.The procedure reported here for preparing macroporous calcium phosphateshas also beensuccessfully applied to fine calcium hydroxyapatite (HA) powders, as well as submicron,chemically precipitated CuPzOt powders; the latter of thesepowders has a quite high in vitrosolubility. The use of HA and CazPzOzowdersas the startingmaterials were so selected hat theeasyadjustmentof the CalP molar ratio in the final productover the broad range of 1.0 through 1.6would be feasible.SummarySimple lending f concentratedolyvinylalcohololutions ith submicron-particulatedalciumphosphateowders,ollowedby a suitable olymerburn-out alcination tepwas ound o providea robustand nexpensiveoute or producingmacro-and micro-porous ioceramicmplants.Thissimpleprocesswas ound o be suitableor the manufacturef porousTCP,HA or CazPzOzortheirbi-phasic ixtures)morsels rprismatic locksor clinicalapplications.Referencestll R. Gunzburg,M. Szpalski,N. Passuti nd M. Aebi: TheUseof BoneSubstitutesn SpineSurge y (Springer-Verlag,erm ny,2002).12) P. Sepulveda,.S.Ortega, .D.M. nnocentinindV.C.Pandolfelli:.Am. Ceram. oc.,Vol.83 2000),.3021.t3l M. Trunec nd . Cihlar: . Eur.Ceram. oc.,Vol.22(2002), .2231,.l4l S.L.Morissettend .A.Lewis: . Am. Ceram. oc., ol. 82(1999), . 521.t5l M.A. HuhaandJ.A.Lewis: . Am. Ceram. oc.,Vol. 83(2000), . 1957.16l S. Ghosal, . Emami-Naeini,.P.Harn,B.S.Draskovich ndJ.P.Pollinger: .Am. Ceram.Soc., ol.82 1999), .513.t7l F.S.Ortega, .SepulvedandV.C.Pandolfelli:. Eur.Ceram. oc.,Vol. 22(2002), . 1395t8l M.Zhai, F. Yoshii,T. KumeandK. Hashim: arbohyd.olym.,Vol. 50(2002),p.295.t9l N.O.Engin ndA.C.Tas: .Am.Ceram. oc., ol. 83 2000), . 1581.l10l ASTM Designation 20-00, nnualBookofASTMStandardsAmericanSocietyorTesting ndMaterials, SA2001).t11l J.Wiltfang,H.A. Merten, .A. Schlegel, .Schultze-Mosgau,.R.Kloss,S.RupprechtndP. Kessler: .Biomed.Mater.Res.Appl.Biomater., ol.63 (2002), . 115.Il2l K.S.TenHuisenndP.W.Brown:Biomaterials,ol. 19 1998), .22O9.t13l N. KivrakandA.C.Tas: .Am.Ceram. oc., ol. 81 1998), .2245.

kem porous pva

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