吉林大学学报(医学版)  2016, Vol. 42 Issue (03): 517-522

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吴嫣然, 杨陆一, 刘军, 殷红, 牟胤赫, 夏小雪, 滕蓉
WU Yanran, YANG Luyi, LIU Jun, YIN Hong, MOU Yinhe, XIA Xiaoxue, TENG Rong
类金刚石涂层与未涂层镍钛丝在人工唾液中耐腐蚀性能的比较
Comparison of corrosion resistance abilities between diamond-like carbon coated and uncoated nickel titanium wire in artificial saliva
吉林大学学报(医学版), 2016, 42(03): 517-522
Journal of Jilin University (Medicine Edition), 2016, 42(03): 517-522
10.13481/j.1671-587x.20160319

文章历史

收稿日期: 2016-03-20
类金刚石涂层与未涂层镍钛丝在人工唾液中耐腐蚀性能的比较
吴嫣然1, 杨陆一1 , 刘军2, 殷红2, 牟胤赫1, 夏小雪1, 滕蓉1    
1. 吉林大学口腔医学院正畸科, 吉林 长春 130021;
2. 吉林大学超硬材料国家重点实验室, 吉林 长春 130021
摘要: 目的: 比较类金刚石涂层(DLC)镍钛丝和未涂层镍钛丝在不同pH值和氟离子(F-)浓度的人工唾液中的耐腐蚀性能,为DLC在正畸治疗中的应用提供依据。方法: 采用射频磁控溅射技术在镍钛丝上制备DLC,激光拉曼光谱(Raman)对镍钛丝进行表征;DLC镍钛丝作为实验组,未涂层镍钛丝作为对照组,2组镍钛丝分别浸泡在4组不同F-浓度和pH值的人工唾液中,即pH7+0%F-组、pH7+0.2%F-组、pH7+0.5%F-组和pH5+0.5%F-组。采用电化学工作站经典三电极体系绘制动电位极化(Tafel)曲线,并测定2组镍钛丝的自腐蚀电位(Ecorr)和腐蚀电流密度(Icorr);扫描电镜(SEM)观察2组镍钛丝经人工唾液腐蚀前后表面形态学。结果: Raman显示D峰和G峰,表明镍钛丝表面已镀有DLC。电化学腐蚀实验,与pH7+0%F-组比较,pH7+0.2%F-组DLC镍钛丝的Ecorr降低(P<0.05),Icorr升高(P<0.05);未涂层镍钛丝的Ecorr降低(P<0.05),Icorr升高,但差异无统计学意义(P>0.05)。与pH7+0.5%F-组比较,pH5+0.5%F-组DLC镍钛丝和未涂层镍钛丝的Ecorr降低(P<0.05),Icorr升高(P<0.05)。在同组人工唾液中,实验组镍钛丝的Ecorr均高于对照组(P<0.05),Icorr均低于对照组(P<0.05)。实验组和对照组镍钛丝的Tafel曲线随F-浓度增加和pH值降低依次向左偏移,提示耐腐蚀效果降低;SEM观察到腐蚀后镍钛丝表面有点状腐蚀,且对照组镍钛丝表面点状腐蚀多于实验组。结论: DLC镍钛丝耐腐蚀性较未涂层镍钛丝有所增强,但pH值降低和F-浓度增大均会降低其耐腐蚀性。
关键词: 类金刚石涂层    镍钛弓丝    人工唾液    电化学腐蚀    
Comparison of corrosion resistance abilities between diamond-like carbon coated and uncoated nickel titanium wire in artificial saliva
WU Yanran1, YANG Luyi1 , LIU Jun2, YIN Hong2, MOU Yinhe1, XIA Xiaoxue1, TENG Rong1    
1. Department of Orthodontics, Stomatology Hospital, Jilin University, Changchun 130021, China;
2. State Key Laboratory of Superhard Materials, Jilin University, Changchun 130021, China
Abstract: Objective: To compare the corrosion resistance abilities between diamond-like carbon (DLC)coated nickel-titanium arch(NiTi) wires and uncoated NiTi wires in the artificial saliva with different pH values and fluoride(F-)concentrations, and to provide the basis for the application of DLC in the orthodontics treatment. Methods: The DLC coated NiTi wires were prepared by radio-frequency magnetron sputtering technique. Raman spectrum was used to characterizate the NiTi wires. The DLC coated wires were taken as experiment group, and the uncoated NiTi wires were taken as control group, and the NiTi wires in two groups were exposed to four kinds of artificial saliva as four groups, pH7+0%F- group: pH 7+0.2% F- group,pH7+0.5% F- group,and pH5+0.5% F- group.The potentiodynamic polarization (Tafel)curves of NiTi wires in two groups were measured by the classic three electrode system of electrochemical workstation,and the corrosion potential (Ecorr) and the corrosion current density (Icorr)of the NiTi wires in two groups were detected; scanning electron microscope(SEM) was used to observe the morphology of the NiTi wires in two groups before and after corrosion with artificial saliva. Results: The Raman spectra results showed the typical D peak and G peak,which indicated that the NiTi wires had been coated by DLC. The electrochemical corrosion test showed that compared with pH7+0% F- group,the Ecorr of DLC coated NiTi wires in pH7+0.2% F- group was decreased(P<0.05)and the Icorr was increased(P<0.05);the Ecorr of uncoated NiTi wires was decreased(P<0.05),and the Icorr was increased,but there was no significant difference(P>0.05).Compared with pH7+0.5% F- group, the Ecorr of DLC coated NiTi wires and uncoated NiTi wires in pH5+0.5% F-group were decreased(P<0.05)and the Icorr were increased(P<0.05). Meanwhile,in the same group of artificial saliva,the Ecorr of NiTi wires in expiment group was apparently higher than that in control group(P<0.05)and the Icorr was lower than that in control group(P<0.05). The Tafel curves of NiTi wires in two groups were moved to the left with the increasing of F- concentration and the decreasing of pH value,which indicated that the corrosion resistance ability was decreased. Under scanning electron microscope, much pitting corrosion was observed on the surface of NiTi wires in control group than experiment group. Conclusion: The corrosion resistance ability of DLC coated NiTi wires is higher than that of uncoated NiTi wires,but the increasing of F- concentration and the decreasing of pH value can decrease the corrosion resistance ability of NiTi wires.
Key words: diamond-like carbon    Nickel-titanium arch wires    artificial saliva    electrochemical corrosion    

镍钛弓丝(镍钛丝)以其独特的超弹性、形态记忆功能和良好的生物相容性在正畸治疗中应用了几十年[1]。然而,镍钛合金在口腔中能否长期存在仍有争议,因为在不同pH值和氟离子(F-)浓度的口腔唾液中,镍钛合金均可通过离子析出或者电化学腐蚀作用使材料降解[2, 3]。其腐蚀产物会导致诸多健康问题,例如过敏反应、毒性反应和致癌作用[4]。此外,镍钛丝较其他正畸弓丝有较高的摩擦系数[5],腐蚀后其表面粗糙程度相对增大,不利于牙齿的轻力移动。为改善正畸弓丝的长期生物相容性和摩擦学性能,已有许多不同表面处理方法应用到正畸弓丝上[6, 7, 8, 9]。类金刚石涂层(diamond-like carbon,DLC)以其优越的性能,例如超硬、低摩擦、化学惰性和耐腐蚀等[10],不仅广泛应用于工业产品,在生物医学领域也得到越来越多的关注。1993年,Kusy等[11]将DLC应用于正畸领域,证实该涂层可以较大程度降低多晶氧化铝/β钛丝间的摩擦力。近几年,人们利用化学气相沉积或者物理气相沉积等方法将DLC应用到托槽和正畸弓丝等材料上,研究其生物安全性以及摩擦学性能等[12, 13, 14],但是对于DLC涂层镍钛丝在不同pH值和F-浓度的人工唾液中的电化学腐蚀性能的相关研究尚未见报道。本研究利用射频磁控溅射技术在镍钛丝上制备DLC涂层,比较其与未涂层镍钛丝在不同pH值和F-浓度的人工唾液中的耐腐蚀性能。

1 材料与方法 1.1 主要试剂和仪器

0.018*0.025镍钛丝(日本TOMY公司 ),人工唾液各成分试剂(中国实验室试剂耗材采购网公司),去离子水、无水乙醇和丙酮(北京化工厂)。射频磁控溅射器(中国科学院沈阳科学仪器股份有限公司),CHI920 C型电化学工作站(上海辰华公司),超声清洗机(CLEAN-01 型,宁波蓝野医疗器械有限公司),pH 计(美国Thormo 公司),电子天平(MP500Z 型,上海舜宇恒平科学仪器有限公司 ),场发射扫描电子显微镜电镜(SEM,XL30 ESEM FEG,美国FEI公司),激光拉曼光谱(H30434型,英国Renishaw公司)

1.2 人工唾液的配制和分组

采用 Fusayama-Meyer 型人工唾液配方,电子天平分别称出0.4 g KCl、0.4 g NaCl、0.906 g CaCl2·2H2O、0.696 g NaH2PO4·2H2O、0.005 g Na2S·9H2O、1.00 g 尿素,用去离子水配至 1 000 mL,以NaOH和HCL调整pH值,NaF调整F-的浓度。将人工唾液分为pH7+0%F-组、pH7+0.2% F-组、pH7+0.5% F-组和pH5+0.5% F-组。

1.3 样品的制备和分组

截取0.018*0.025 TOMY镍钛丝末端较平直部分,长约20 mm,逐级经600#和1 200#砂纸打磨,丙酮、无水乙醇、去离子水依次超声清洗5 min,干燥备用。从中随机选取24段镍钛丝在其较宽的2个面上制备DLC涂层(该工作由吉林大学超硬材料国家重点实验室完成)作为实验组,射频磁控溅射涂层的工艺参数为偏压-100 V,射频电源功率120 W,气体选用氩气(Ar),流量为20 SCCM,工作气压为1.0 Pa,基体温度为125℃,沉积时间为60 min。膜厚度为±1 μm。随机选取24段未经涂层处理的镍钛丝作为对照组。所有实验用样品的一端以自凝塑料包埋连在导线上,通过计算弓丝长度,使每个样品的暴露面积相等,同时较窄的2个面涂布抗酸指甲油。实验组和对照组镍钛丝分别随机浸泡在4组配好的人工唾液中,每组6根。样品在新鲜配制的人工唾液中浸泡24 h。

1.4 2组镍钛丝自腐蚀电位(Ecorr)和腐蚀电流密度(Icorr)的测定

采用CHI920 C型电化学工作站和Origin软件绘制动电位极化(Tafel)曲线。所用介质为室温下的人工唾液,研究电极为待测样品,参比电极为饱和甘汞电极,辅助电极为铂片。先测量研究电极的开路电位(OCP),待OCP稳定后(上下波动不超过5 mV)进行电位Tafel扫描并绘制Tafel曲线,此时比较稳定的开路电位电压值即为Ecorr,描绘Tafel曲线时选用的极化电位范围为开路电位上下200 mV,扫描速度设定为5 mV·s-1,找出Tafel曲线阳极和阴极的线性部分,其切线交点对应的电流值即为腐蚀电流,腐蚀电流与样品暴露表面面积的比值即为Icorr。

1.5 SEM观察各组镍钛丝表面形态学

从实验组和对照组随机选取3根样品,采用SEM观察2组镍钛丝经人工唾液腐蚀后表面形态学,并与腐蚀前的表面形态学进行对比。

1.6 统计学分析

采用SPSS 17.0统计软件对数据进行统计学分析。各组镍钛丝的Ecorr和Icorr均以 ± s表示。2组镍钛丝在不同组人工唾液中的Ecorr和Icorr比较采用单因素方差分析;不同种镍钛丝在同组人工唾液中的Ecorr和Icorr比较采用t检验。以α=0.05为检验水准。

2 结 果 2.1 DLC涂层镍钛丝的拉曼光谱图

在1 350 cm-1和1 520 cm-1处分别出现2个相对宽化的波峰(图 1),而出现明显变宽的D峰(约1 358 cm-1)和G峰 (约1 582 cm-1)是DLC结构的典型特征之一,证明在镍钛丝上覆盖的为DLC涂层。

图 1 DLC镍钛丝的拉曼光谱图 Fig.1 Raman spectra of DLC-NiTi wires
2.2 2组镍钛丝的Ecorr和Icorr

随着F-浓度增加,对照组镍钛丝在4组人工唾液中的Ecorr逐渐降低(P < 0.05),Icorr呈升高趋势;与pH 7+0.5% F-组比较,对照组镍钛丝在pH5+0.5% F-组人工唾液中Ecorr降低(P < 0.05),Icorr升高(P < 0.05)。随着F-浓度增加,实验组镍钛丝在4组人工唾液中的Ecorr逐渐降低(P < 0.05),Icorr呈升高趋势;与pH7+0%F-组比较,实验组镍钛丝在pH7+0.2% F-组人工唾液中的Icorr升高(P < 0.05);与pH7+0.5% F-组比较,实验组镍钛丝在pH5+0.5% F-组人工唾液中的Ecorr降低(P < 0.05),Icorr升高(P < 0.05)。

实验组和对照组镍钛丝经4组人工唾液腐蚀后比较,pH7+0.2% F- 、pH7+0.5% F-、pH5+0.5% F-组人工唾液中,实验组镍钛丝的Ecorr均高于对照组(P < 0.05);实验组镍钛丝在pH7+0% F-组人工唾液中的Ecorr也高于对照组,但组间比较差异无统计学意义(P>0.05)。实验组镍钛丝在4组人工唾液中的Icorr均低于对照组(P < 0.05)。

表 1 2组镍钛丝在4组人工唾液中的Ecorr和Icorr Tab.1 Ecorr and Icorr of NiTi wires in two groups under four different kinds of artificial saliva
(n=6, ± s )
Group Ecorr(U/mV) Icorr(nA·cm-2)
Control Experiment Control Experiment
*P < 0.05 vs control group; P < 0.05 vs pH7+0% F- group;#P < 0.05 vs pH7+0.2% F- group; P < 0.05 vs pH7+0.5% F-group.
pH7+0%F- -147.82±8.52 -143.09±5.54 85.23±4.91 74.28±2.88*
pH7+0.2%F- -206.81±4.53 -162.49±4.50*△ 87.69±1.92 82.79±2.29*△
pH7+0.5%F- -308.92±11.82△# -176.48±11.50*△# 90.09±3.45 78.43±5.11*
pH5+0.5%F- -325.47±4.50△#▲ -263.95±4.56*△#▲ 104.72±1.45△#▲ 100.52±1.01*△#▲
2.3 2组镍钛丝在4组人工唾液中的Tafel曲线

对照组镍钛丝在4组人工唾液中的Tafel曲线显示:Tafel曲线随着F-浓度增加和pH值降低依次向左偏移,与pH 7+0.5% F-组比较,pH5+0.5% F-组的Tafel曲线向上偏移(图 2A)。实验组镍钛丝在4组人工唾液中的Tafel曲线显示:Tafle曲线亦随着F-浓度增加和pH值降低依次向左偏移。pH5+0.5% F-组向左、向上偏移较多(图 2B)。对照组的4条Tafel曲线整体比实验组位置偏左。

图 2 2组镍钛丝在4组人工唾液中的Tafel曲线 Fig.2 Tafel curves of NiTi wires in two groups in four different kinds of artificial saliva A:Control group; B:Experiment group.
2.4 SEM观察2组镍钛丝表面形态表现

与腐蚀前比较,对照组镍钛丝经人工唾液腐蚀后可见多处散在凹坑,即点腐蚀;与腐蚀前比较,实验组镍钛丝经腐蚀后可见局部少量点腐蚀。见图 3

图 3 SEM下观察人工唾液腐蚀前后2组镍钛丝表面形态表现(bar=50μm) Fig.3 Morphology of surface of NiTi wires before and after corrision with artificial saliva in two groups observed by SEM(bar=50 μm) A,B: Control group;C,D:Experiment group; A,C: Before corrision;B,D:After corrision.
3 讨 论

DLC涂层的制备方法常规分为2大类:一类是包括离子束沉积、溅射沉积和激光等离子沉积等方法的物理气相沉积;另一类是包括等离子体增强的化学气相沉积。本实验采用射频磁控溅射方法,其优点是低温条件下在镍钛丝上制备DLC涂层,可提高镍钛丝的耐腐蚀性能。金属腐蚀按腐蚀机制可分为电化学腐蚀和非电化学腐蚀2类。口腔环境中的金属腐蚀主要是电化学腐蚀[15],电化学极化测试也是评价医用金属材料抗腐蚀性能的一种有效方法[16],其优点为简便易行和精准度高。本研究采用电化学工作站经典三电极体系测量动电位极化曲线,其测定原理为控制电势电位以较慢的速度连续地改变(扫描),并测量对应电位下的瞬时电流值,以瞬时电流值与对应的电极电势绘图,获得整个极化曲线,即测定研究电极在连续变化电位下的半对数电流值,并在坐标轴上绘成的曲线。

Ecorr指在腐蚀体系中无外加电压时测得的稳定状态的开路电位(即稳定电位),能反映腐蚀倾向的大小,即Ecorr越低(负值越大),金属的腐蚀倾向越大;反之,腐蚀倾向越小。虽然利用Ecorr 值可以定性比较合金腐蚀的倾向,但其不能反映合金的实际腐蚀速率,而Icorr是评价合金腐蚀速率的重要参数,依赖于 Tafel外推法原理获得,首先从 Tafel 区呈线性关系的阴、阳极曲线做切线所得交点对应的纵坐标为腐蚀电流,再与暴露表面面积作比即为Icorr。随着F-浓度增大,对照组镍钛丝在4组人工唾液中的Ecorr逐渐降低,即腐蚀倾向逐渐增大;Icorr逐渐升高,即腐蚀速率呈加快趋势;Tafel曲线图可见:随着F-浓度的增大和pH值的降低,曲线依次向左偏移,说明F-的存在及浓度的增大降低了镍钛丝的耐腐蚀性能,这与马长柏等[17]的研究结果一致。pH5+0.5% F-组镍钛丝的Tafel曲线向上偏移表明:酸和F-共同作用使镍钛丝腐蚀倾向增大,腐蚀速率加快,这是因为氟化氢极易与镍钛表面的氧化膜TiO2发生一系列的反应,加速氧化膜的破坏[18]。随着F-浓度增大,实验组镍钛丝在4组人工唾液中的Ecorr降低,即腐蚀倾向逐渐增大,说明F-的存在及浓度的增大也影响了DLC镍钛丝的耐腐蚀性;酸和F-共同作用使DLC镍钛丝腐蚀倾向增大,腐蚀速率加快,具体原因和反应机制有待进一步研究,该趋势也有可能是局部DLC崩解,暴露内部镍钛丝表面,使得实验组DLC镍钛丝在酸性含F-人工唾液中的腐蚀规律与对照组相似。本研究结果显示:DLC涂层一定程度提高了镍钛丝在酸性及含F-人工唾液中的耐腐蚀性能。该结果与Huang等[1]研究结论一致(其研究结果显示:DLC涂层的镍钛弓丝表面粗糙度较未涂层镍钛弓丝减轻91.3%),反映出DLC涂层的保护作用。

对DLC涂层的表面形态学进行观察,除可借助原子力显微镜(AFM)或者3D激光显微镜外,也可借助SEM进行定性观察。本研究采用SEM观察镍钛丝在酸性含F-人工唾液中发生电化学腐蚀前后的表面形态学。在50μm视野下观察到对照组镍钛丝经腐蚀后表面有多处散在的点腐蚀,其原因为F-等阴性因子可以吸附在镍钛丝表面形成的TiO2钝化膜上,发生化学反应使氧原子排挤出去,氧化膜被破坏。此外,合金表面钝化膜成分除了TiO2还有少量碳元素,这些碳元素也会使钝化膜相对不稳定,这也是发生点腐蚀的原因之一。而实验组DLC镍钛丝经人工唾液腐蚀后可以观察到相对少量的点腐蚀,提示DLC可起到一定的保护作用。但是本文作者发现:个别DLC镍钛丝的点腐蚀聚成小段线条,这可能是由于DLC涂层表面局部出现微小裂痕,暴露内部镍钛丝发生腐蚀所致。

本研究结果显示:DLC对镍钛丝的电化学腐蚀有保护作用,但F-浓度增加及pH值降低均会影响其抗腐蚀性。这为探究DLC在正畸领域的应用提供了参考,也为镍钛丝表面的改性奠定了基础,但DLC与镍钛合金的结合强度及其在酸性含F-人工唾液中的反应机制有待于进一步研究。

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