실험변수로전류, 전압, 주파수, 전해질, 열처리등의조건을달리한실험군들의거칠기, 미세구조, 결정구조등을조사하고, 이를인공체액 (SBF; simulated body fluid) 에침지 ( ; soaking) 하여표면성질및산화막의변화가골과직접결합하는생체활성도 (bioacti

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1 대한치과보철학회지 :Vol. 45, No. 1, 2007 양극산화에의한티타늄산화막의표면특성및생체활성에관한연구 단국대학교치과대학보철학교실 이상한ㆍ조인호 Ⅰ. 서론임플랜트와생체조직간의긴밀하고도생체친화적인반응을이끌어내기위하여임플랜트의표면조성, 구조, 산화막의두께및형태등의표면특성 (surface characteristics) 이매우중요하다. 티타늄은재료자체의우수한생체친화성으로치과임플랜트영역에서가장중요한재료로연구되어왔으나, 티타늄과생체조직간의최적의친화성을가져다주는이상적인표면처리방법은아직도많은논의와연구가필요한실정이다. 임플랜트가장기적으로성공적인임상결과를얻기위해서는골과임플랜트가유착된골계면을얻어야하며, 성공적인골유착을얻기위한필요조건으로서 Albrektsson 등 1) 은임플랜트재료의생체적합성, 임플랜트디자인, 임플랜트의표면특성, 임플랜트식립부위숙주골의상태, 외과적수술방법, 수술후임플랜트에대한하중조건등의 6가지요소들이임플랜트골유착에영향을미치는조건이라고발표하였다. 그중에서도임플랜트의표면특성에대한연구가주로이루어지고있으며, 최근의임상경향은어떻게하면전체치료기간을줄일수있는지에대한관심이집중되어그에따른티타늄의표면처리에관한많은연구들이진행되고있다. 2-5) 표면을개선시키기위한표면처리방법은크게세가지로분류할수있다. 3) 첫째, 물질첨가방법으로는하이드록시아파타이트, 티타늄입자등을플라즈 마분사 (TPS), 화학적진공침착 (CVD), 물리적진공침착 (PVD) 하는방법들이있고, 둘째, 표면삭제방법으로는산부식, 알칼리처리, 화학적혹은전기-기계적인부식, 다양한미세입자를이용한블라스팅하는방법등이있으며, 마지막으로, 표면의성상을변경하는방법으로 e-beam 열처리, 레이저처리, 이온임플랜테이션, 양극산화법등을들수있다. 6) 결국이러한일련의과정을통하여임플랜트표면의형태와성질에변화를주어서궁극적으로는골과의유착을증진시키는데그목적이있다고하겠다. 7) 현재까지많이연구되어온대부분의표면처리방법은티타늄표면의거칠기를조절하는것에초점을맞추고있으며, 8,9) 표면거칠기가증가할수록표면적이넓어지므로골과임플랜트표면간에생체-기계적인결합력이증진된다고믿어왔었다. 10) cp-티타늄의표면처리방법중의하나인양극산화법은최근주목받고있는표면처리방법으로서, 비교적간단한공정으로산화막의두께, 구조, 구성, 미세형태등을다양하게변형시킬수있으며, 산화물의생물학적인성상까지도조절할수있다. 11) 본연구는위와같은선학들의연구결과들에기초하여치과용임플랜트로사용되는티타늄금속의적용에대한연구로서임플랜트표면의물리, 화학, 미세구조적인특징과이것의생체반응간의상관관계를고찰하여골유착에가장효과적인양극산화표면처리방법과제작조건을제시하고자하였으며, 85

$시편제작 2) 표면산화물성분및결정구조분석 (Crystallographic assay of titania) 시편표면의결정구조를관찰하고, 산화막을구성하고있는산화물들을조사하기위하여표면의형태를중점적으로볼수있는박막-X선회절분석기 (Thin Film X-ray Diffractmeter, RINT-2500, Rigaku Co.$

2 실험변수로전류, 전압, 주파수, 전해질, 열처리등의조건을달리한실험군들의거칠기, 미세구조, 결정구조등을조사하고, 이를인공체액 (SBF; simulated body fluid) 에침지 ( ; soaking) 하여표면성질및산화막의변화가골과직접결합하는생체활성도 (bioactivity) 에미치는영향을알아보고자하였다. Ⅱ. 연구재료및방법 1. 시편제작 2) 표면산화물성분및결정구조분석 (Crystallographic assay of titania) 시편표면의결정구조를관찰하고, 산화막을구성하고있는산화물들을조사하기위하여표면의형태를중점적으로볼수있는박막-X선회절분석기 (Thin Film X-ray Diffractmeter, RINT-2500, Rigaku Co., Tokyo, Japan) 를이용하여각시편표면에생성된산화막의결정구조들을관찰하였고, 특징적인회절피크 (2θ) 는 JCPDS (Joint Committee on Power Diffraction Standards) 를참고로비교하여분석하였다. cp-티타늄 (ASTM cp-grade 1, Hyundai Titanium Co., Ltd., Inchoen, Korea) 을직경 10 mm, 두께 1 mm의디스크형태로제작하고, 일정한표면거칠기를유지하기위하여순차적으로 1200번까지 emery paper로연마하였으며, 초음파세척기에 5분간아세톤용액으로세척하고상온에서건조하였다. 2. 표면처리 1) 양극산화처리실험군은총 7 개의군으로구성하였고, 1 군은대조군으로아무런표면처리를하지않았으며, 나머지각군의실험조건 (Table Ⅰ) 및실험에사용된장비 (Fig. 1) 는다음과같이하였다. 2) 열처리열처리가여러가지특성에미치는영향을알아보기위하여위모든군들을 furnace상에서 1 분에 5 씩 600 까지올려서 1 시간동안열처리하고상온에이르기까지천천히냉각시켰다. 3) 표면거칠기측정 (Roughness measurements) 시편표면의형상을관찰하고표면거칠기 (Sa, Sq) 를측정하기위하여 AFM (Atomic Force Microscope, EasyScan E-AFM, Nano-Surf Co., Switzerland) 을사용하였다. 측정면적은 68.5 μm 68.5 μm으로설정하였으며, 각시편당 3 곳을측정하여이수치들의평균값및표준편차를구하였다. Sa, Sq는 3 차원표면거칠기측정값으로 Sa는표면의평균에서높이편차의절대값의평균이며, Sq는표면의평균에서높이편차의제곱의평균이다. 4) 인공체액에침지각군의생체활성도 (bioactivity) 를알아보기위하여실험실에서제조된 SBF 용액에 1 주일간 (168 시간 ) 침지하였다. 침지한후증류수로세척하고건조시켜분석하였다 (Table Ⅱ, Ⅲ). (-) (+) 3. 실험방법 cooling water in sample holder 1) 표면관찰및형태분석 (SEM analysis of micro-porosity) 시편은주사전자현미경 (Scanning Electron Microscope, S-2500 CS, Hitachi Co., Tokyo, Japan) 으로표면의형태를각각 1000 배및 5000 배로관찰하였다. Ti sample cooling water out stirrer Fig. 1. Schematic drawing of anodizing apparatus. 86

3 Table I. Treatment conditions of experimental groups in this study Group Voltage Frequency Electrolyte Processing Time(Min.) 1 Control Group 2 0~350 Constant Current DC 0.4M Acetic Acid 2 ⅔ Constant Voltage DC 1M H2SO Hz 0.1M Na2CO Hz 0.1M Na2CO ~ Hz 0.2M Calcium Acetate +0.02M β-glycerophosphate 5 7 0~ Hz 0.2M Calcium Acetate +0.02M β-glycerophosphate 5 Table II. Ionic composition (mm) of SBF and human plasma Na + K + Ca 2+ Mg 2+ Cl - HCO3 - HPO4 2- SO4 2- Plasma ~ ~ ~ ~1.5 SBF* *Simulated Body Fluid Table III. Reagent source of simulated body fluid 25) Reagents Purity Amount/1000 ml NaCl >99.5% g NaHCO3 >99.5% g KCl >99.5% g K2HPO4 3H2O >99.0% g MgCl2 6H2O >98.0% g 1M-HCl - 20 ml CaCl2 >99.9% g Na2SO4 >95.0% g TRIS >99.0% g 1M-HCl ml 실험금속의표면이생체활성도가우수하다면용액내에서골성분과유사한아파타이트의형성을기대할수있는데, 이는 SBF 내에존재하는 Ca 2+, HPO42- 등의이온들이티타늄표면과이온교환반응에의하여, bone-like apatite를형성하는것으로알려져있다 12,13). 5) 인공체액에침지후 SEM, TF-XRD 분석인공체액에 1 주일간침지한후표면형태및결정구조의변화를알아보기위하여주사전자현미경및박막-X선회절분석기로비교분석하였다. Ⅲ. 실험결과 1. 시편표면의주사전자현미경관찰열처리와 SBF 침전을하지않은시편들의 (Fig. 2) 관찰에서 1 군은 native oxide로서, 연마에의해긁힌모습이며, 2 군은오목한산화막의형태를하고있었다. 나머지 3~7 군은모두정도의차이를보이는볼록한형태를보였으며, 특히 3 군은보다더복잡한다공성구조를보이고있었고, 6, 7 군은거친볼록한형태에특히 7 군에서표면에약간의결정성구조 87

의소견을나타내었다. 7 군에서보이는표면의금이간모양은 pore size가성장하면서나타나는결과로서, 이는산화물내의결정이성장하여생기는세라믹파절로생각된다. SBF에 1 주일간침지후소견 (Fig. 3) 에서다른군에서는큰변화를보여주고있지않으나, 3 군에서는하이드록시아파타이트로추정되는결정구조가 침착된모습을보여주고있다.

4 의소견을나타내었다. 7 군에서보이는표면의금이간모양은 pore size가성장하면서나타나는결과로서, 이는산화물내의결정이성장하여생기는세라믹파절로생각된다. SBF에 1 주일간침지후소견 (Fig. 3) 에서다른군에서는큰변화를보여주고있지않으나, 3 군에서는하이드록시아파타이트로추정되는결정구조가 침착된모습을보여주고있다. 3 군의상 ( ) 에서보이는 crack line은시편제작과정상건조처리의과정에서생기는것으로생체내의환경은조직액혹은혈액등으로습한조건이므로, 실제인체내에서는이러한소견이나타날수는없을것으로사료된다. 열처리시편소견에서 (Fig. 4) 비열처리군에비해별다른형태학적인변화는없었고, 대체로조금 Fig. 2. SEM images of each specimen without heat treatment and SBF soaking (left half of each image: 1000 magnifications, right half: 5000 magnifications). Fig. 3. SEM images of each specimen without heat treatment after 1 week soaking in SBF (left half of each image: 1000 magnifications, right half: 5000 magnifications). 88

5 Fig. 4. SEM images of each specimen with heat treatment (left half of each image: 1000 magnifications, right half: 5000 magnifications). Fig. 5. SEM images of each specimen with heat treatment after 1 week soaking in SBF (left half of each image: 1000 magnifications, right half: 5000 magnifications). 더치밀해진양상을보이고있다. 열처리시편을 SBF에 1 주일동안침지한시편들 (Fig. 5) 에서별다른변화는없었다. 2. 시편표면의박막 X선회절분석열처리와 SBF 침전을하지않은시편들 (Fig. 6) 에 서 1 군은 titanium peak만을보이며, 2 군에서부터산화물의 peak가나타나기시작하였는데, 2 군은약간의 anatase peak, 4 군에서는거기에 rutile peak가추가로시작되어 5 군에서 7 군으로갈수록 rutile peak가더욱성장한모습을보이고있다. 특히 7 군에서는 Ca와 P로보이는미세한 peak를볼수있었고, 3 군은 titanium peak는거의보이지않을 89

7. TF-XRD profiles of each specimen without heat treatment after 1 week

6 Fig. 6. TF-XRD profiles of each specimen without heat treatment and SBF soaking. Fig. 7. TF-XRD profiles of each specimen without heat treatment after 1 week soaking in SBF. Fig. 8. TF-XRD profiles of each specimen with heat treatment. Fig. 9. TF-XRD profiles of each specimen with heat treatment after 1 week soaking in SBF. Fig. 10. The graph of Sa and Sq values of each group (unit: μm ). Fig. 11. One 3-dimensional AFM image of roughness and used equipment. 90

7 정도로산화막의구성이 anatase와 rutile로구성된산화물로조성을이루고있으며, 그중에서 rutile의양이더우세함을알수있었다. SBF에 1 주일동안침지후소견 (Fig. 7) 은 3 군을제외한나머지군들에서산화물들의약간의양적성장을보이고있지만 SBF에침지전과비교하여큰변화는없었고, 3 군에서만 bone-like apatite가생성되어있음을관찰할수있었고, titanium peak는전혀보이지않고있다. 열처리시편군 (Fig. 8) 에서는열처리하지않은시편과비교하여결정구조의조성의변화는거의없었으나, 열처리가산화물의양의증가의측면에서약간의기여가있다고보인다. 열처리시편을 SBF 에 1 주일동안침지한결과 (Fig. 9) 결정구조의조성및양의변화는거의없었다. 3. 시편표면의 AFM 관찰및거칠기측정거칠기는 7, 5, 2, 3, 6, 4, 1 군순으로서, 7 군에서가장큰값을, 1 군에서가장작은값을보였으며 (Fig. 10), 7 군과나머지군간에통계학적으로유의성있는차이를보였다 (p<0.05). 그러나생체활성도는유일하게 3 군에서만존재하였으므로, 거칠기와생체활성도간에는상관관계는없는것으로사료된다. 관찰된 AFM의대표적 image와장비사진은 Fig. 11에서보는바와같다. Ⅳ. 총괄및고안치과용임플랜트의여러가지표면처리방법중양극산화법은산화막층의여러가지물리학적인성질을쉽게조절할수있으며, 재현성의수준이높고, 다른표면처리방법들과비교하여비교적적은경비와간단한공정으로제작가능하다는장점들을가지고있다. 15) 그러므로산화막의두께, 구조, 조성, 형태들을제어할수있는매우유용한방법으로, 임플랜트에거칠고, 다공성이며, 매우단단하게부착되는산화막을만들어내는데우수한방법으로보고되고있다. 16) Choi 등 17) 은티타늄의양극산화법의방법들을소개하였는데, 그변수로서일정한전류, 일정한전 압, 주파수, 그리고전해질의다양한종류와농도를변화시키는것들을들고있으며, Ishizawa 등 18) 은전압, 전류, 처리시간, 전해질의농도등의변수를달리하면, 산화막의두께, 미세구조, 거칠기, 결정구조, Ca와 P의농도등을조절할수있다고하였다. 표면거칠기가골유착에미치는영향의측면에서 Wennerberg 19) 는거칠기가증가하면임플랜트와골조직사이의기계적인맞물림의효과가증진된다고하였고, Orton 등 20) 은거친표면의뒤틀림제거력 (removal torque) 이높은이유로기계적맞물림이크고응력분산에유리하며, 임플랜트나사와골조직간의탄성계수의차이를완충하는역할때문이라고하였다. 그러나 Wennerberg 등 21) 의다른연구에서는거친표면을가진임플랜트가골창상부위에서치유능력이우수하며, 골접촉율과뒤틀림제거력에서통계적으로유의한증가를나타내는안정된골유착을가져다주지만, 어느일정한수치를초과한표면거칠기의임플랜트의경우에는골창상치유가오히려제한되기때문에골접촉율이떨어져서골유착에불리하다고보고한바있다. 그러므로 Lim 4) 의연구를토대로임플랜트의표면처리에따른효과의측면에서표면거칠기외에도고려해야할다른여러가지중요한조건이있다고생각할수있으며, 결정의형태와성장, 산화막의구성성분 ( 특히 O/Ti 비율 ), TiO2 결정상의종류등이세포와의반응성에중요한역할을한다고볼수있다. 즉, 본실험의결과중거칠기의수치가가장높았던 7 군에서기대되었던생체활성도를얻어내지못한사실로미루어볼때, Wennerberg 등 21) 의연구결과와같은맥락의하나로, 표면이거칠다고해서반드시우수한생체친화성을보장하지않는다는사실과, 표면거칠기가생물학적반응에서다른표면성질만큼중요하지않다는가설을이끌어내었으며, 표면거칠기는주로물리적인결합에기여하는것으로추정된다고사료된다. 그러므로보다향상된생체활성도를얻기위해서는산화막층의물리화학적성질 ( 미세구조, 미세기공도및상분율, 결정학적방향성등 ) 의개선이필요할것으로사료된다. 본연구에서표면의다공성구조의생체활성도를알아보기위하여인체의혈장과이온의조성과농도가거의유사한 SBF 를이용하였다. 이용액은 TRIS 91

8 (Tris Hydroxy Methyl Amino Methane) 라는성분으로 ph 7.40을유지하며, 용액내에존재하는 Ca 2+, HPO4 2- 등의이온들이 bioactive titanium surface와이온교환반응에의하여, bone-like apatite를형성한다고알려져있으며, 14,22-24) 생체활성도를가늠하는여러가지방법들 (cell culture, alkaline phosphatase activity test, total protein measurement, type I collage measurement) 중비교적오차범위가작고, 정확한생체활성도를확인하는데유용함을여러연구들에서입증한바있다. 12,25-27) Han 등 28) 은산화막의결정상, 형태, 두께및 Ca와 P의생성등들의변화는양극산화시가해진전압의정도에따라좌우된다고하였고, Song 등 29) 은가해진주파수에의해비슷한결과를보고한바있다. Li 등 30) 도산화막에새로침착되는 Ca의농도와가해진전압에상관관계가있다고하였으며, 본실험의 3 군에서 spark discharge가일어날정도로가혹한조건하의시편에서우수한생체활성도가나타났기때문에, 본연구에서도전압이상당히중요한실험변수로작용했음을짐작할수있다. 3 군에서사용된전해질인황산 (H2SO4) 은강산으로서, 이미공업적으로내산화막을성장시키는데널리이용되어온경위가있으며, 이러한전해질을우선검토해보는것은실험을전개하는방법으로당위성이있다고생각하며, 결과적으로 3 군에서생체활성도가나타났다. 하지만표면에황산의잔류물이극미소량잔류할가능성이있으나, 이잔류물은이온이아닌작용기 (functional group; 어떤화학적성질을표시하는원인이되는기 ) 로화학결합한형태로존재하여실제인체에생물학적인영향은주지않을것으로추정된다. 인체의혈장과본실험에사용된 SBF 용액내에서도황산기 (SO4 2- ) 가존재하여, 이것으로말미암아 Ca와 P의생성을유도한다는연구결과도있다. 31) 결론적으로, 본실험의결과에따라산화막을구성하고있는산화물의두께와양을증가시키는데는황산과같은매우강한산을전해질로사용하고, spark discharge가일어날만큼매우높은전압을가하는등의가혹한실험조건하에서좋은결과를얻었음을알수있었다. 전압과전해질을조절하여산화막에이온 (Ca, P) 을 implantation시킨 6, 7 군관찰결과, 형태학적으 로도복잡한다공성으로우수하며, 산화물 (rutile / anatase) 의양도비교적많았지만, 1주일이내에생체활성도는유도되지않았다. 이는 3 군과비교하여이온이 implantation 되었다하더라고, titanium peak를훨씬능가하는산화물의분포와우수한 ( 잘배향된 ) 결정구조없이는생체활성도를기대할수없음으로추정된다 32,33) (Fig. 12). 생체활성도에영향을미치는산화막내의주된결정구조에대해서여러연구들이있어왔다. Lim 등 3) 과 Yang 등 16) 은티타늄표면의산화막에두종류이상의결정구조가혼재하여있는경우생체친화성이우수하다고하였고, 골과유사한 apatite의형성에있어서 Lausmaa 등 31) 은 rutile이, Son 등 11) 과 Uchida 등 34) 은 anatase가더유효한영향을주었다고보고한바있다. 본연구의결과생체활성도가유도된 3 군의결정구조를살펴보면, rutile과 anatase가혼재하는양상이나, 그중 rutile phase가더우세하다고볼수있다. 이상본연구의결과로미루어생각해볼때, 산화막의결정구조와생체활성도간에밀접한관계 (crystallographic compatibility) 가있는것으로말할수있으며, 향후전압, 전해질, 열처리등의실험변수들의많은조합들중에서최적의조건을밝혀내어서, 보다더우수한양극산화처리된표면을만들수있는무한한가능성이있을것으로생각된다. 결론적으로티타늄표면의산화막의결정구조가생체반응성에미치는영향을분석하여생체에우수한 Fig. 12. Comparison of intensities of titanium peak between group 3 and the rest of groups. 92

9 반응성을가진표면처리방법을알아내는것은앞으로의계속적인과제로사료된다. Ⅴ. 결론 1. 표면처리한모든군들에서형태학적으로다공성구조를나타내었고, 2 군을제외한나머지군들은대체로거친볼록한형태를나타내었으며, 산화물의양이많고결정성이우수한군들이형태학적으로도양호한것으로나타났다. 2. 양극산화법과열처리를동시에처리한결과, 결정구조의구성에는영향을주지않았으나, 전체적인산화물 (rutile / anatase) 의양의증가에는기여하였다. 3. 거칠기는 7, 5, 2, 3, 6, 4, 1 군순으로서, 7 군 (1000 Hz pulse, 460V) 에서가장큰값을, 1 군 (machined, 대조군 ) 에서가장작은값을보였으며, 7 군과나머지군간에통계학적으로유의성있는차이를보였으나 (p<0.05), 7 군에서는 1주일이내에생체활성도가나타나지않았다. 4. 전압과전해질을조절하여산화막에이온 (Ca, P) 을 implantation시킨군관찰결과, 형태학적으로도우수하며, 산화물도소량생성되었지만, 1주일이내에생체활성도는유도되지않았다 군에서유일하게생체활성도가나타났고, 산화막의구성은순수 titanium peak가보이지않을정도로, 주로 rutile 계열의산화물로이루어져있었으며, 특히 rutile의결정구조중에서비정상적으로 [101] 면이배향되어있었고, 이면을중심으로 bone-like apatite가형성되었음을알수있다. 양극산화법의여러가지실험조건중전압, 주파수, 전해질등을변화시켜산화막을조절한결과, 산화막의표면형상, 표면미세기공도, 제 2 상 (Ca/P) 의생성, 결정구조, 두께등을제어할수있었으며, 더나아가 in vitro에서생체활성도까지유도할수있었다. 그러므로양극산화법은산화막의물리적성질은물론, 생물학적인성질까지개선시킬수있는매우유용한표면처리방법으로생각될수있으며, 향후보다더적극적인생체실험을통하여이를입증하는노력이필요하리라사료된다. 참고문헌 1. Albrektsson T, Bra nemark P-I, Hasson HA, Lindstrom J. Osseointegrated titanium implants. Acta Orthp Scand 1981;52: Kim WS, Cho IH. On the surface characteristics and stability of implant treated with anodizing oxidation. 2003; College of dentistry, Dankook university, Ph. D thesis. 3. Lim YJ, Oshida Y, Andres CJ, Barco MT. Surface characterizations of variously treated titanium materials. Int J Oral Maxillofac Implants 2001;16: Lim YJ. Effects of heat treatment on the surface characteristics of titanium for implant. 2004; College of dentistry, Seoul national university, Ph. D thesis. 5. Yang SW, Cho IH. On the effect of different surface treatment on the osseointegration and stability of implants. 2003; College of dentistry, Dankook university, Ph. D thesis. 6. de Maeztu MA, Alava JI, Gay-Escoda C. Ion implantation: Surface treatment for improving the bone integration of titanium and Ti6Al4V dental implants. Clin Oral Impl Res 2003;14: Lee JM, Kim YS, Kim CW, Jang KS, Lim YJ. A study on the responses of osteoblasts to various surface-treated titanium. J Korean Acad Prosthodont 2003; 42: Cho DH, Lim JH. A study on the surface roughness and initial stability of various dental implants. J Korean Acad Stomatognathic Function and Occlusion 2000; 16: Kang BS, Cho IH. A histomorphometric and stability of two kinds of implants with different surface roughness. J Korean Acad 93

10 Oral and Maxillofac Implants 2001;5: Park KH, Chang IT. Osseointegration of anodized titanium implants. J Korean Acad Prosthodont 2004;42: Son WW, Zhu X, Shin HI, Ong JL, Kim KH. In vivo histological response to anodized and anodized / hydrothermally treated titanium implants. J Biomed Mater Res Part B: Appl Biomater 66B: 2003; Kokubo T, Kushitani H, Sakka S. Solution able to reproduce in vivo surface-structure changes in bioactive glass-ceramic A-W. J Biomed Mater Res 1990;24: Serro AP, Saramago B. Influence of sterilization on the mineralization of titanium implants induced by incubation in various biological model fluids. Biomaterials 2003;24: Kim HM. Ceramic bioactivity and related biomimetic strategy. Current Opinion in Solid State and Materials Science 2003;7: Zhu X, Ong JL, Kim SK, Kim KH. Surface characteristics and structure of anodic oxide films containing Ca and P on a titanium implant material. J Biomed Mater Res 2002;60: Yang B, Uchida M, Kim HM, Zhang X, Kokubo T. Preparation of bioactive metal via anodic oxidation treatment. Biomaterials 2004;25: Choi JW, Kim KN, Heo SJ, Chang IT, Han JH, Baik HK, et al. The effects of various surface treatment methods on the osseointegration. J Korean Acad Prosthodont 2001; 39: Ishizawa H, Ogino M. Characterization of thin hydroxyapatite layers formed on anodic titanium oxide films containing Ca and P by hydrothermal treatment. J Biomed Mater Res 1995;29: Wennerberg A. The importance of surface roughness for implant incorporation. Int J Mach Tool Manuf 1998;38: Orton EC, Polher O, Shenk R, Hohn RB. Comparison of porous titanium-surfaced and standard smooth-surfaced bone plates and screws in an unstable fracture model in dogs. Am J Vet Res 1986;47: Wennerberg A, Ektessabi A, Albrektsson T, Johansson C, Andersson B. A 1-year follow-up of implants of differing surface roughness placed in rabbit bone. Int J Maxillofac Implants 1997;12: Kim HM, Miyaji F, Kokubo T, Nishiguchi S, Nakamura T. Graded surface of bioactive titanium prepared by chemical treatment. J Biomed Mater Res 1999;45: Kim HM, Kokubo T, Fujibayashi S, Nishiguchi S, Nakamura T. Bioactive macroporous titanium surface layer on titanium substrate. J Biomed Mater Res 2000;52: Kim HM, Himeno T, Kawashita M, Lee JH, Kokubo T, Nakamura T. Surface potential changes in bioactive titanium metal during the process of apatite formation in simulated body fluid. J Biomed Mater Res 2003;67A: Kokubo T, Kim HM, Kawashita M. Novel bioactive materials with different mechanical properties. Biomaterials 2003; 24: Kokubo T, Kim HM, Kawashita M, Nakamura T. Bioactive metals: preparation and properties. J Mater Sci Mater Med 2004;15: Takadama H, Kim HM, Kokubo T, Nakamura T. TEM-EDX study of mechanism of bonelike apatite formation on 94

11 bioactive titanium metal in simulated body fluid. J Biomed Mater Res 2001; 57: Han Y, Hong SH, Xu K. Structure and in vitro bioactivity of titania-based films by micro-arc oxidation. Surface and Coatings Technology 2003;168: Song WH, Jun YK, Han Y, Hong SH. Biomimetic apatite coatings on micro-arc oxidized titania. Biomaterials 2004;25: Li LH, Kong YM, Kim HW, Kim YW, Kim HE, Heo SJ, et al. Improved biological performance of titanium implants due to surface modification by micro-arc oxidation. Biomaterials 2004;25: Leonor IB, Kim HM, Balas F, Kawashita M, Reis RL, Kokubo T, et al. Surface charge of bioactive polyethylene modified with -SO3H groups and its apatite inducing capability in simulated body fluid. Key Engineering Materials 2005; : Hench LL. Bioceramics. From concept to clinic. J Am Ceram Soc 1991;74: Hench LL. Bioceramics. J Am Ceram Soc 1998;81: Lausmaa J. Multi-technique surface characterization of oxide film of electropolished and anodically oxidized titanium. Appl Surface Sci 1990;45: Uchida M, Kim HM, Kokubo T, Fujibayashi S, Nakamura T. Structural dependence of apatite formation on titania gels in a simulated body fluid. J Biomed Mater Res 2003;64A: Reprint request to: In-Ho Cho, D.D.S., M.S.D., Ph.D. Department of Prosthodontics, College of Dentistry, Dankook University 7-1, Shinbu-Dong, Chunan, Chungnam, , Korea cho8511@dku.edu 95

12 ABSTRACT SURFACE CHARACTERISTICS AND BIOACTIVITY OF ANODICALLY OXIDIZED TITANIUM SURFACES Sang-Han Lee, D.D.S., M.S.D., In-Ho Cho, D.D.S., M.S.D., Ph.D. Department of Prosthodontics, College of Dentistry, Dankook University Statement of problem: Recently, anodic oxidation of cp-titanium is a popular method for treatment of titanium implant surfaces. It is a relatively easy process, and the thickness, structure, composition, and the microstructure of the oxide layer can be variably modified. Moreover the biological properties of the oxide layer can be controlled. Purpose: In this study, the roughness, microstructure, crystal structure of the variously treated groups (current, voltage, frequency, electrolyte, thermal treatment) were evaluated. And the specimens were soaked in simulated body fluid (SBF) to evaluate the effects of the surface characteristics and the oxide layers on the bioactivity of the specimens which were directly related to bone formation and integration. Materials and methods: Surface treatments consisted of either anodization or anodization followed thermal treatment. Specimens were divided into seven groups, depending on their anodizing treatment conditions: constant current mode (350V for group 2), constant voltage mode (155V for group 3), 60 Hz pulse series (230V for group 4, 300V for group 5), and 1000 Hz pulse series (400V for group 6, 460V for group 7). Non-treated native surfaces were used as controls (group 1). In addition, for the purpose of evaluating the effects of thermal treatment, each group was heat treated by elevating the temperature by 5 per minute until 600 for 1 hour, and then bench cured. Using scanning electron microscope (SEM), porous oxide layers were observed on treated surfaces. The crystal structures and phases of titania were identified by thin-film x-ray diffractmeter (TF-XRD). Atomic force microscope (AFM) was used for roughness measurement (Sa, Sq). To evaluate bioactivity of modified titanium surfaces, each group was soaked in SBF for 168 hours (1 week), and then changed surface characteristics were analyzed by SEM and TF-XRD. Results: On basis of our findings, we concluded the following results. 1. Most groups showed morphologically porous structures. Except group 2, all groups showed fine to coarse convex structures, and the groups with superior quantity of oxide products showed superior morphology. 96

13 2. As a result of combined anodization and thermal treatment, there were no effects on composition of crystalline structure. But, heat treatment influenced the quantity of formation of the oxide products (rutile / anatase). 3. Roughness decreased in the order of groups 7,5,2,3,6,4,1 and there was statistical difference between group 7 and the others (p<0.05), but group 7 did not show any bioactivity within a week. 4. In groups that implanted ions (Ca/P) on the oxide layer through current and voltage control, showed superior morphology, and oxide products, but did not express any bioactivity within a week. 5. In group 3, the oxide layer was uniformly organized with rutile, with almost no titanium peak. And there were abnormally more [101] orientations of rutile crystalline structure, and bonelike apatite formation could be seen around these crystalline structures. Conclusion: As a result of control of various factors in anodization (current, voltage, frequency, electrolytes, thermal treatment), the surface morphology, micro-porosity, the 2nd phase formation, crystalline structure, thickness of the oxide layer could be modified. And even more, the bioactivity of the specimens in vitro could be induced. Thus anodic oxidation can be considered as an excellent surface treatment method that will able to not only control the physical properties but enhance the biological characteristics of the oxide layer. Furthermore, it is recommended in near future animal research to prove these results. Key words : Anodic oxidation, Titania, Bioactivity, SBF (simulated body fluid), Rutile, Crystallographic Compatibility 97

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