Effects of anodic oxidation and hydrothermal treatment on surface characteristics and biocompatibility of Ti–30Nb–1Fe–1Hf alloy

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AppliedSurfaceScience258 (2012) 6190–6198

ContentslistsavailableatSciVerseScienceDirect

Applied

Surface

Science

j o ur na l ho me p age :w w w . e l s e v i e r . c o m / l o c a t e / a p s u s c

Effects

of

anodic

oxidation

and

hydrothermal

treatment

on

surface

characteristics

and

biocompatibility

of

Ti–30Nb–1Fe–1Hf

alloy

Shih-Fu

Ou

a,b,c

_,

_Hsin-Hua

_Chou

d,e

_,

_Chao-Sung

_Lin

f

_,

_Ching-Jui

_Shih

a

_,

_Kuang-Kuo

_Wang

b,g,∗∗

_,

Yung-Ning

Pan

a,∗

a_Department_of_Mechanical_Engineering,_National_Taiwan_University,_Taipei_106,_Taiwan b_Research_Center_for_Biomedical_Devices,_Taipei_Medical_University,_Taipei_110,_Taiwan

c_Research_Center_for_Biomedical_Implants_and_Microsurgery_Devices,_Taipei_Medical_University,_Taipei_110,_Taiwan d_School_of_Dentistry,_College_of_Oral_Medicine,_Taipei_Medical_University,_Taipei_110,_Taiwan

e_Department_of_Dentistry,_Taipei_Medical_University_Wan-fang_Hospital,_Taipei_116,_Taiwan f_Department_of_Materials_Science_and_Engineering,_National_Taiwan_University,_Taipei_106,_Taiwan

g_Department_of_Materials_and_{Optoelectronic}_Science,_Center_for_nanoscience_and_{nanotechnology,}_National_Sun_Yat-Sen_University,_Kaohsiung,_804,_Taiwan

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received15October2011

Receivedinrevisedform20February2012 Accepted21February2012

Available online 28 February 2012 Keywords: Anodicoxidation Hydrothermaltreatment Hydroxyapatite Ti–Nballoy

a

b

s

t

r

a

c

t

Anodicoxidationfollowedbyhydrothermaltreatmenthasbeenwidelyappliedforsurfacemodiﬁcation oftitaniumalloystoprecipitateacrystallinehydroxyapatite(HA)layerinordertoachieveimproved osteoconduction.Amajorityofthestudiesintheliteratureimposedrelativelyhighpowerstoenhance CaandPintheanodicoxideﬁlm(AOF).However,highpowershavebeenfoundtocausedeteriorationof theadhesivestrengthinoneoftheauthor’spreviousstudy.Inthisstudy,anewelectrolytecomprising calciumacetatemonohydrate(CA),␤-glycerophosphatedisodiumpentahydrate(␤-GP)andHApowder wasdeveloped,andtheTi–30Nb–1Fe–1HfalloywasanodizedinthisHA-containingelectrolytetoa relativelylowvoltage.ResultsshowthattheAOFanodizedintheHA-containingelectrolyteexhibitsa betterHAformingabilityduringhydrothermaltreatment,attributingtothepresenceofHApowderin theelectrolytethateffectivelyenhancesboththeCacontentandCa/PratiointheAOF.Ontheotherhand, theadhesivestrengthwaslittleaffectedduetothedecreaseinsizeofthecratersresidingintheAOF.With respecttothebiologicalresponses,notmuchdifferenceinbiocompatibilityofthetreatedanduntreated Ti–Nbsurfaceswasobtained.However,theanodizedandhydrothermallytreatedsurfacepromotesthe attachmentofcells.

1. Introduction

Titaniumpossessesgoodbiocompatibilityandhasbeenusedas

implantmaterialsince1950s[1].Nowadays,titaniumanditsalloys

havebeenwidelyappliedinhardtissuereplacements,especiallyfor

artiﬁcialhip.Nevertheless,forlong-termimplantationloosening

oftheprostheticdevicescausedby“stressshieldingeffect”ofthe

insertedimplantonadjacentbonecanoccur[2].In1992,Sumner

andGalantepointedoutthatthemainreasonforstressshielding

effectisanunsymmetricalloading-stresstransferfromimplantto

neighboringboneduetotheirmismatchstiffness[3].Toalleviate

thiseffect,␤-Tialloyswithlowelasticmodulus,i.e.,Ti–13Nb–13Zr

∗ Correspondingauthorat:1,RooseveltRoad,Section4,Taipei106,Taiwan. Tel.:+886223659940;fax:+886223631755.

∗∗ Correspondingauthorat:ResearchCenterforBiomedicalDevices,Taipei Medi-calUniversity,Taipei101,Taiwan.

E-mailaddress:[email protected](Y.-N.Pan).

[4]andTi–11.5Mo–6Zr–2Fe[5]hadbeendeveloped.Inaddition

toelasticmodulus,thetensilestrengthofimplantsshouldalsobe

consideredforhardtissuereplacement.Thepresentauthorshave

developedtheTi–30Nb–1Fe–1Hfalloywithhighstrengthandlow

elasticmodulus(UTS:914MPa,0.2%proofstress:862MPaandE:

62GPa),whichisexpectedtobemoresuitableforimplant

applica-tions[6].

Althoughtitaniumanditsalloysareregardedtohavegood

bio-compatibility,thebondingbetweenTiimplantsandbonetissuesis

notsufﬁcient.Thisbondingisattributedtoamechanical

interlock-ingoftitaniumsurfacedefectsandporesinthebones.Accordingly,

thisbioinertsurfaceneedsanextrasurfacemodiﬁcationbycoating

abioactivematerialsuchashydroxyapatite(HA)onit.Plasmaspray

isthemostwidelyusedtechniquetofabricateHAcoating,andthe

HA-coatedimplanthasbeendemonstratedtohavesimilar

histo-logicalreactionsassinteredHAbulkinanimaltest[7,8].Butthere

areseveraldrawbacksintheplasmasprayedHA coatingdueto

itscomposition[9,10].ThestructureofplasmasprayedHAcoating

comprisesanadditionalcalciumphosphate(␣-and␤-tricalcium

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S.-F.Ouetal./AppliedSurfaceScience258 (2012) 6190–6198 6191

Table1

Theelectrochemicalparametersandthedesignatedsamplecodes.

Electrolyte Composition(ml/l) pH Anodizingvoltage(V) Anodizingtime(s) Powersupply(J/cm2₎ _Code

CA ␤-GP HA

CAGPelectrolyte 0.2 0.04 7.8 100 5.6 16 CAGP100

230 40.3 350 CAGP230

300 108.5 1233 CAGP300

HAelectrolyte 0.3 0.04 0.05 7.8 230 40.4 349 HA230

phosphate,tetracalciumphosphate andoxyhydroxyapatite) and

anamorphousphasethatareinducedbyhightemperature

ther-molysisandrapid coolingrespectively.Thesephases arehighly

bioresorbableandbiodegradable.Hence,thebondingstrengthof

HAcoatingdecreaseswithincreasingcontactperiodinthebody

ﬂuid[11].

Asmentionedearlier,fabricatingahighcrystallineHAcoating

whichcanadheretightlytothesubstrateisimportant.In1995,

IshizawaandOginodevelopedamethodtoformacrystallineHA

layerusingaTisubstratewithsufﬁcientadhesivestrengthto

sus-tainmorethan300daysofimmersioninTribuffersolution[12,13].

Theprocessconsistedoftwosteps:(1)forminganoxideﬁlmthat

containsCaandPbyanodicoxidation,andthen(2)hydrothermally

treatingthisoxideﬁlmtoprecipitateHAcrystalsonthesurface.

SuchaHAlayerexhibitsasmuchosseoconductionasa

plasma-sprayedHA[14,15]andimprovestheinitialcellattachment[16,17].

BecausetheoperationalvoltagegreatlyaffectsHA formation

[18–21],mostofthestudiesimposedrelativelyhighpower(high

voltage(>300V)or longtreating time) duringanodicoxidation

to enhance the amount of precipitated HA after hydrothermal

treatment[13,18,19,22,23].However,inourpreviousstudies,the

adhesivestrength betweenanodicoxidation ﬁlm(AOF)andthe

substrate decreased with increasing applied anodic voltage in

constantcurrentmode[20,21,24].Thedeteriorationofadhesive

strengthisrelated tothealignedporesandthecraters existing

withintheAOF[20],signifyingthatanewanodicoxidationprocess

thatcanproduceahighCaandP-containingoxideﬁlmthrough

usingarelativelylowanodizingvoltageisanecessity.

Inthepresentstudy,theTi–30Nb–1Fe–1Hfalloywastreated

withanimprovedanodicoxidationprocessbyadjustingthe

elec-trolytecompositionandoperatinginlowvoltagetoincorporate

enoughamountsofCaandPintotheAOF.Therelationshipbetween

microstructureandadhesivestrengthoftheoxideﬁlmwas

evalu-ated.Furthermore,afterhydrothermaltreatment,thecellresponse

oftheoxideﬁlmwasevaluatedbyinvitrotest.

2. Materialsandmethods

2.1. Samplepreparation

The material used in this study is Ti–30Nb–1Fe–1Hf plate.

10mm× 10mm×1mmcouponswereabradedwithsilicon

car-bonpapersuptograde800,andthenweredegreasedwithacetone

for5minfollowedbyethanolfor3mininanultrasoniccleaner,

andﬁnallydriedinair.Inthisstudy,thesecouponsaredenotedas

Ti–Nbplate.

2.2. Anodicoxidation

Twokindsofelectrolytewereused.Onetypeofelectrolytewas

prepared by dissolving _{␤-glycerophosphate} disodium

pentahy-drate(C3H7Na2O6P·5H2O,␤-GP)andcalciumacetatemonohydrate

[Ca(CH3COO)2·H2O,CA] in accordance withthe prescription of

Ishizawa and Ogino[12],denoted as“CAGP electrolyte”. Inthe

otherelectrolyte,HApowder(Ca/P=1.67)wasaddedintothe

solu-tionwhichcomprised␤-GPandCAindistilledwater,denotedas

“HAelectrolyte”.The␤-GPandCAwascompletelydissolved,but

thedepositionofHA powderinthesolutionwasobserved.The

detailparametersoftwokindsofelectrolytearelistedinTable1.

The solutionwasconstantly stirred using a magnetic stirrerat

25◦C.

TheTi–Nbplatewasgalvanostaticallyanodizedataconstant

currentdensityof50mA/cm2_up_to_a_speciﬁc_voltage_using_a_direct

currentpowersupply(GWinstekGPR-30H10D),andahighdensity

graphiteplatewasusedasthecathode.Theﬂuctuationsofpotential

duringanodizingwererecordedbyanoscilloscope(TektronixTDS

1002)withasamplingrateof20points/s.Afteranodicoxidation,

thesamplewascleansedwithdistilledwaterand thendriedat

roomtemperature.

2.3. Hydrothermaltreatment

Afteranodization,theTi–Nbplateswerehydrothermallytreated

at 250◦C for 6h in an autoclave (volume: 53.6ml) containing

26.8mldistilledwater.Afterhydrothermaltreatment,thesamples

werecleansedwithdistilledwaterfollowedbydryinginastream

ofroomtemperatureair.

2.4. Microstructuralcharacterization

ThesurfacemorphologiesofAOFbeforeandafter

hydrother-maltreatmentwereobservedusingascanningelectronmicroscope

(SEM;Model:PHILIPS XL30).The crystallinityand phase ofthe

AOFwereidentiﬁedviaglancingangleX-raydiffractionusinga

K␣radiationwithanincidenceangleof1◦andatascanningspeed

of2◦/min(XRD;Model:PHILIPSX’Pert,X-raytubePW3373/100

CuLFFDK147515).Themicrostructures oftheAOF were

exam-inedbycross-sectional transmissionelectronmicroscopy(TEM)

andenergydispersivespectrometry(EDS)equippedinTEM.The

compositionsoftheAOFwereanalyzedbyanelectronprobeX-ray

microanalyzer(EPMA).

Table2

Samplecodesforsurfaceswithdifferenttreatmentsinvitrotest.

Code Electrolyte Anodizingvoltage(V) Dielectricbreakdown Hydrothermaltreatment

Control

CAGP100 CAGPelectrolyte 100 Before

CAGP300 CAGPelectrolyte 300 After

HYT-CAGP CAGPelectrolyte 300 After 250◦_C–6_h

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6192 S.-F.Ouetal./AppliedSurfaceScience258 (2012) 6190–6198

2.5. Adhesiontest

TheattainmentoftheadhesivestrengthoftheAOFwascarried

outaccordingtoASTM-C633-01standard[25]byusingatensiletest

machine(CHUNYEN;Model:CY-6040A4)ataconstantcross-head

speedof1.2mm/minwith1.5kginitialforce.Eachsampleconsisted

oftwoplateswhichwereanodizedtoaspeciﬁcvoltage,thatwere

boundedusingepoxyglue(LIONBONDEA2000N).Theoverlapping

areaofthetwoplateswas20_×10mm2_._The_samples_were_cured

at150◦C for45min.Theadhesionstrengthwasreportedasthe

averageof10adhesiontestresults.

2.6. Cellculture

FivetypesofTi–Nbsurfacewereevaluatedinvitrotocompare

cellcount,alkalinephosphatase(ALP)activityandcelladhesion.

Thesamplesincludeduntreated,anodizedbeforeandafter

dielec-tricbreakdownaswellasanodizedandhydrothermallytreated.

The sample codes were listed in Table 2. The test specimens

(10mm×10mm×1mm)wereplacedintoa24-wellpolystyrene

plate.Beforecellculture,allthespecimenswereshinedby

ultravio-letray(UV)for24h.Thetestspecimensweresterilizedandwashed

severaltimeswithDulbecco’smodiﬁedEagle’smedium(DMEM,

Gibco)andphosphate-bufferedsaline(PBS,0.1M,pH7.2).The

cul-turemediumconsistedofDMEMcontaining10%fetalbovineserum

(FBS),100␮g/mlofstreptomycin,and100units/mlofpenicillin.

TheMG-63cellsuspensionwithadensityof1×104_cells/ml_was

addedintotheculturewell.500mlculturesolutionand50␮l

3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolimbromide(MTT)

labelsolutionwereaddedintoeveryculturewellbeforeplacingthe

plateinsideaculturechamberat37◦Cinahumidiﬁedatmosphere

of95%airand5%CO2.Theculturemediumwaschangedeverythree

days.Thetestspecimenswereculturedforvariousperiodsoftime,

i.e.,8h,24h,72h,120hand168h.Theextentofadhesionof

MG-Fig.1. Potential–timeresponsesofTi–NballoygalvanostaticallyanodizedinCA+GP andHAelectrolytes.

63cellsonthesurfacesofspecimenswasevaluatedthroughthe

observationsofcellmorphologiesbyusingSEM.Theproliferation

behaviorwasdeterminedbyperformingMTTassaytoobtainthe

cellopticaldensity(OD)bytheplatereader(ELISA,DYNEX-MRXII)

at=595nm.Finally,thedifferentiationbehaviorwasestimated

bymeasuringthealkalinephosphatase(ALP)activityofthecells

afterculturingthemforvariousperiodsoftime.

3. Results

3.1. Potential–timeresponses

Fig. 1 shows the potential–time response during

galvanos-taticanodizing.TheanodicpotentialforCAGP electrolyteraised

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6198 S.-F.Ouetal./AppliedSurfaceScience258 (2012) 6190–6198

propertybyanodizinginanelectrolytecontainingHApowder

fol-lowedbyhydrothermaltreatment.

Acknowledgment

TheauthorsaregratefultotheResearchCenterforBiomedical

DevicesandResearchCenterforBiomedicalImplantsand

Micro-surgeryDevicesTaipeiMedicalUniversity,Taiwanforthesupport

inbiocompatibilityexperiments.

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