劉 敏,劉愛萍,2,郁建燦,錢國棟
(1.浙江大學硅材料國家重點實驗室,材料科學與工程學院,浙江杭州310027;2.浙江理工大學物理系,浙江杭州310018)
摻雜及分子修飾對類金剛石細胞相容性的影響
劉 敏1,劉愛萍1,2,郁建燦1,錢國棟1
(1.浙江大學硅材料國家重點實驗室,材料科學與工程學院,浙江杭州310027;2.浙江理工大學物理系,浙江杭州310018)
為實現(xiàn)類金剛石(DLC)薄膜在不同使用環(huán)境下生物相容性的可調(diào)性,采用元素摻雜及化學分子修飾對DLC薄膜表面進行改性,借助X射線光電子能譜、拉曼光譜及靜態(tài)接觸角測試表征薄膜的表面形貌和微觀結(jié)構(gòu),探究摻雜及分子修飾對薄膜細胞相容性的影響.結(jié)果顯示:B、N、P、Pt元素摻雜以及3-氨基苯硼酸(APBA)修飾均沒有改變薄膜非晶結(jié)構(gòu),只是提高薄膜有序程度.B、N、P元素的摻入減小了DLC薄膜的接觸角,而N、Pt元素共摻使接觸角變化不大.APBA修飾使各種DLC薄膜的接觸角均減小.B、N、P元素的摻入促進PC12細胞的黏附與增殖,抑制細胞凋亡,而Pt元素的摻入起相反的作用,APBA修飾對細胞生長有明顯促進作用.這說明元素摻雜及分子修飾是調(diào)節(jié)DLC薄膜細胞相容性的有效方法.
類金剛石(DLC)薄膜;摻雜;化學修飾;細胞黏附;細胞增殖
類金剛石(diamond-like carbon,DLC)薄膜具有可低溫沉積、耐摩擦磨損、高硬度、化學性能穩(wěn)定、寬電勢窗口、低背底電流等優(yōu)良特性[1-3],可廣泛用于機械模具和零部件的耐磨保護層、太陽電池減反膜、電化學工作電極等[4-8].DLC薄膜還具有良好的血液相容性與細胞相容性[9-10],可用于構(gòu)建組織工程心臟瓣膜、血管支架、人工骨及其他植入體[11].此外,DLC薄膜具有易于摻雜和表面修飾的特性.大量研究表明:在DLC薄膜中摻入一定量的雜質(zhì)原子(如非金屬元素N、O、Si、F或金屬元素Ti、Co、Mo、W、V等),在不明顯改變薄膜微觀結(jié)構(gòu)的同時,其物理化學及生物相容性能得到較大改善[11].例如,在DLC薄膜中摻雜Si、Ti等元素能有效提高薄膜的耐摩擦磨損能力[12-13].N、B、P等元素的摻入能有效改善薄膜的導電性,拓寬DLC薄膜在場發(fā)射和太陽能電池等方面的應用前景[14-16].P、Ca、Si等元素的摻入有利于改善薄膜的血液相容性,減少血小板在薄膜上的黏附[17-18].在DLC薄膜中摻入具有光催化活性的TiO2納米粒子或Ag元素時,薄膜的抗菌能力有明顯提升[19-20].
目前,基于不同元素摻雜對DLC薄膜細胞相容性的影響及本質(zhì)規(guī)律的研究相對較少,關(guān)于表面修飾改善DLC薄膜細胞相容性的研究也非常有限.為了探究元素摻雜及表面修飾對DLC薄膜細胞相容性的影響機制,本文采用過濾陰極真空電弧沉積系統(tǒng)制備DLC薄膜,并在沉積過程中通入硼烷(BH3)、氮氣(N2)和磷烷(PH3)摻雜源對薄膜進行B、N、P元素的摻雜.通過使用含有鉑粉的碳靶及氣體摻雜源N2,獲得N、Pt共摻的DLC薄膜.此外,實驗中采用3-氨基苯硼酸(3-aminobenzeneboronic acid,3-APBA)對各種摻雜薄膜進行表面功能化,考察摻雜及表面修飾對薄膜親疏水性及微觀結(jié)構(gòu)的影響,探討元素摻雜及表面修飾的薄膜對PC12神經(jīng)細胞黏附、增殖及凋亡等生理活動的影響規(guī)律.
1.1 摻雜DLC薄膜的制備與表面修飾
采用過濾陰極真空電弧技術(shù)(FCVA)技術(shù)[21]在導電硅片上沉積DLC及摻雜DLC薄膜.以DLC∶P薄膜的制備為例,以純度為99.99%的高純碳靶為碳源,純度為99.999%的磷烷氣體(PH3)為摻雜源.當沉積室真空度達到2.0×10-4Pa時,通入流量為5 sccm的PH3,碳靶在激發(fā)狀態(tài)下放電并產(chǎn)生碳等離子體,轟擊真空室內(nèi)的PH3,使其電離.多種等離子體在偏壓下一同沉積到氬氣刻蝕的硅片表面.分別改用氮氣(N2,5 sccm)和硼烷(BH3,5 sccm)作為摻雜源,獲得DLC:N及DLC:B薄膜.通過使用含有鉑粉的碳靶及N2摻雜源,獲得N、Pt共摻的DLC:NPt薄膜.調(diào)節(jié)摻雜源氣體流量及沉積時間,可以調(diào)控薄膜成分及薄膜厚度.
摻雜DLC薄膜表面的功能化修飾通過以下步驟實現(xiàn):1)將樣品用丙酮、酒精及去離子水超聲清洗5 min,取出吹干;2)將清洗好的樣品浸泡于混合酸液(V(H2SO4)∶V(HNO3)=9∶1)中72 h,使其表面連接上羧酸基團[22];3)將酸化后的樣品用1 mg/m L的APBA和乙基二甲基胺丙基碳化二亞胺(N-Ethyl-N′-(3-dimethylaminopropyl)carbodiimide,EDAC)的混合溶液浸泡24 h,通過APBA分子的氨基與DLC樣品表面羧基的脫水縮合,在樣品表面修飾上APBA分子.
1.2 不同DLC薄膜的結(jié)構(gòu)表征
使用VG ESCALAB MKII型X射線光電子能譜(XPS)分析不同DLC薄膜的成分和化學態(tài),Mg Kα射線的能量為1 253.6 e V,掃描全譜和元素分譜時能量分析器的通過能分別為50 e V和20 e V.為了探究元素摻雜和表面修飾對薄膜微觀結(jié)構(gòu)的影響,采用Thermo Fisher Scientific DXR激光拉曼(Raman)光譜儀(波長為633 nm)測定DLC薄膜的拉曼光譜.使用靜態(tài)接觸角測量儀(OCA20,GER)測定蒸餾水在薄膜表面的接觸角.室溫下,將1μL蒸餾水輕輕滴在薄膜表面并拍照,再利用SCA20分析軟件測量所得接觸角的大小,共設6組平行實驗.
1.3 不同DLC薄膜的細胞相容性檢測
1.3.1 PC12細胞的培養(yǎng) PC12細胞來源于老鼠的腎上腺嗜鉻腫瘤.培養(yǎng)液使用新鮮配置的胎牛血清(FBS,四季青)體積分數(shù)為10%的達爾伯克(氏)基礎培養(yǎng)基(Dulbecco's minimum essential medium,DMEM),并加入體積分數(shù)1%的青霉素和鏈霉素(P/S,Boster).細胞體外接種密度為1×104個/cm2,每3 d進行一次傳代分瓶.
1.3.2 PC12在不同DLC薄膜上的黏附、增殖與凋亡 將高溫消毒后的不同DLC樣品(8 mm× 8 mm)分別置于24孔板中,在孔中接種800μL PC12細胞(4×103個/孔).將細胞置于37℃、5%(體積分數(shù))CO2的標準條件下培養(yǎng),每2 d更換一次培養(yǎng)液.培養(yǎng)1、3、5 d后,將樣品用PBS沖洗3次,然后用體積分數(shù)為4%的多聚甲醛固定細胞15 min,隨即用5μg/m L的4′,6-二脒基-2-苯基吲哚(4′,6-diamidino-2-phenylindole,DAPI)染色5 min,以觀察細胞核的形貌.將染色后的樣品用PBS沖洗3次后放在共聚焦顯微鏡(CLSM,fluoview FV1000,Olympus)下觀察、拍照.每個樣品隨機選取8個區(qū)域進行拍照,然后對×20照片中細胞的密度及×40照片中細胞的凋亡率進行統(tǒng)計.凋亡細胞的判斷標準為細胞核著色不均勻,發(fā)出刺眼的亮藍色.這是因為在凋亡過程中細胞核會發(fā)生固縮,染色質(zhì)高度凝聚濃縮.共設3組平行實驗.
1.3.3 PC12在不同DLC薄膜上的微管蛋白形貌為了觀察不同DLC薄膜上細胞骨架的形態(tài),對細胞中的微管進行染色.微管是一種具有極性的細胞骨架,是由微管蛋白二聚體組成的長管狀細胞器.經(jīng)過染色,可以看到絲狀微管蛋白從細胞核周圍往細胞質(zhì)延伸.微管蛋白密集、有序地排列且伸長鋪展是細胞生長狀態(tài)良好的特征之一[23].具體染色過程如下:將細胞固定后,用Triton X-100(體積分數(shù)為0.5%,PBS)在室溫下處理2 h,使細胞膜變通透.隨后將細胞用血清(體積分數(shù)為2%,PBS)和白蛋白(體積分數(shù)為2%,PBS)混合液在室溫封閉2 h.封閉后的細胞用連接有Alexa-Fluor 647熒光基團的β-微管蛋白抗體(體積分數(shù)為0.2%,細胞信號傳導)孵化2 h,最后用DAPI(5μg/mL)染細胞核.經(jīng)過封閉處理后,β-微管蛋白抗體可通過抗原-抗體反應特異性的標記細胞中的微管蛋白.將染色后的細胞置于共聚焦顯微鏡下用雙通道觀察,激發(fā)波長分別為405 nm(細胞核)和633 nm(微管蛋白骨架).
2.1 不同DLC薄膜的結(jié)構(gòu)與親疏水性
表1為摻雜及APBA分子修飾后DLC薄膜中各元素的原子百分比.可以看出,DLC:N、DLC:P和DLC:B薄膜中N、P和B元素的原子百分比依次為2%,4%及3%.N、Pt共摻的樣品中Pt元素的原子百分比約為6%,N元素的原子百分比為19%.經(jīng)過酸化及APBA分子修飾后,各樣品表面都檢測到了B和N元素,其中B元素的原子百分比增加了0.3%~1.5%(DLC:P薄膜樣品除外,因為P的2 s峰與B的1 s峰重合).N和B元素的檢出或原子百分比增加說明不同摻雜DLC薄膜表面成功修飾上了APBA分子.
表1 不同類金剛石薄膜樣品中元素種類及原子百分比Tab.1 Type and atomic content of elements in different diamond-like carbon films %
圖1 摻雜及表面修飾的DLC薄膜拉曼光譜Fig.1 Raman spectra of doped and surface-modified DLC films
圖1是摻雜及APBA修飾后DLC薄膜的拉曼(Raman)光譜(拉曼峰強度I隨波數(shù)n的變化).圖中在波數(shù)為900~1 000 cm-1和1 100~1 800 cm-1的峰分別為硅的二階峰和碳的一階峰.碳一階峰可用D峰(峰中心位于1 355 cm-1)和G峰(峰中心位于1 581 cm-1)進行擬合,分別代表sp2雜化碳的呼吸振動和伸縮振動模式[24].從圖1(a)可以看出,元素摻雜既沒有引入額外的振動峰,也沒有改變薄膜的非晶結(jié)構(gòu),只是使碳的一階峰的峰位向低波數(shù)方向移動了15~40 cm-1.這說明元素的摻入增加了sp2雜化碳原子的含量,提高了薄膜有序程度[25].圖1(b)的結(jié)果表明,酸化及APBA修飾后DLC:P薄膜的各峰位及峰強幾乎沒有變化,修飾對DLC:P薄膜結(jié)構(gòu)沒有明顯影響.
圖2是摻雜及修飾后各薄膜樣品的接觸角(θ).結(jié)果顯示,B、N和P元素的摻入減小了DLC薄膜的接觸角,其中P元素的摻入對接觸角的降低效果最為顯著.從XPS數(shù)據(jù)看出,雜質(zhì)元素的摻入使DLC薄膜表面的O元素含量增加.Yokota等[26]發(fā)現(xiàn),DLC薄膜表面的接觸角會隨著N元素的摻入而降低,這與薄膜表面含氧基團的增多有關(guān).可見,DLC:P薄膜中O元素含量增加最多,接觸角降幅最大(約為17°),親水性明顯提高,與Kelly等[22]的研究結(jié)果相符.對于DLC:NPt薄膜,雖然N元素摻入易于提高薄膜的親水性,但是Pt元素的摻入易于增強薄膜的疏水性(θ>130°)[27],兩者共同作用使接觸角變化不大.經(jīng)過酸化和APBA修飾后,各種DLC薄膜的接觸角都降低了約20°~25°.親水性的改善可能與薄膜表面連接的APBA分子中親水性的鄰位羥基有關(guān).
圖2 不同DLC薄膜樣品的接觸角Fig.2 Contact angles of different DLC films
2.2 PC12細胞在不同DLC薄膜上的黏附、增殖與凋亡
細胞在材料表面的黏附、增殖與凋亡是衡量材料生物相容性的重要指標.如圖3(a)所示為PC12細胞在不同DLC薄膜上的黏附與增殖,以樣品上現(xiàn)有細胞密度(C)與原種植密度(C0)的比值(C/C0)作為縱坐標.從圖中可以看出,種植1 d后細胞在B、N、P元素摻雜的薄膜上的黏附多于在未摻雜的DLC薄膜,B、N、P元素的摻雜對細胞黏附起到了促進作用,其中摻雜P元素的促進作用最為明顯(約40%).N、Pt元素共摻的薄膜上細胞黏附的數(shù)量明顯低于未摻雜樣品(約降低30%).細胞在各薄膜樣品上的增殖與凋亡表現(xiàn)出了與黏附相似的規(guī)律,即B、N、P元素的摻入促進了細胞在薄膜上的增殖,抑制了細胞的凋亡;而Pt元素的摻入對細胞增殖和凋亡產(chǎn)生了完全相反的作用(見圖3(b)).培養(yǎng)5 d后,與DLC薄膜相比,DLC:P薄膜上的細胞密度提高了約60%,凋亡率(A)降低了約40%.而DLC:NPt薄膜上的細胞密度降低了70%,凋亡率提高了約30%.摻雜后DLC薄膜表面親水性的變化可能是細胞行為改變的一個重要因素.Trantidou等[28]的研究表明:細胞更傾向黏附于親水性的基底上.本文的實驗結(jié)果與文獻[28]的結(jié)論不謀而合,親水性最好的DLC:P薄膜上細胞的黏附與生長最優(yōu).摻雜元素自身的生物相容性可能是影響細胞行為差異的因素之一.文獻[29]的研究表明:B元素具有良好的生物相容性,體內(nèi)適量的B元素能激發(fā)釋放生長因子和細胞因子,加速細胞外基質(zhì)的循環(huán),同時能促進某些RNA和蛋白質(zhì)的合成.N、P元素是構(gòu)成細胞的主要元素,摻入后也能提高材料的細胞相容性[17,22,30-31].Regan等[31]利用DLC:P薄膜可實現(xiàn)細胞的圖案化生長.另外,Pt和Ag元素都是化學惰性的金屬元素,當薄膜中摻雜納米Ag,Ag表面能釋放自由基并與細菌膜上的脂類結(jié)和,破壞膜的功能,表現(xiàn)出抗菌作用[19,32-33].本文實驗中Pt元素對細胞生長的抑制作用可能同樣來自于Pt表面自由基的釋放.
圖3 不同DLC薄膜樣品上的細胞密度和細胞凋亡率Fig.3 Ceu densities and cell apoptosis rates on different DLC films
從圖3(a)還可以看到,培養(yǎng)3 d后,APBA修飾的摻雜DLC薄膜上(DLC:NPt薄膜除外)細胞密度增大了約50%,而DLC:NPt薄膜上細胞密度提高約為70%.APBA在增大細胞密度的同時對細胞凋亡起了一定的抑制作用.培養(yǎng)3 d后,經(jīng)過APBA修飾的摻雜DLC薄膜上(DLC:NPt薄膜除外)細胞凋亡率降低了約20%,而DLC:NPt薄膜上細胞凋亡率降低了約40%(見圖3(b)).APBA修飾對細胞生長的調(diào)控可能與APBA上的鄰位羥基有關(guān).這些鄰位羥基能與細胞膜糖蛋白終端的鄰位羥基發(fā)生脫水縮合,從而增強材料與細胞的相互作用,利于細胞黏附和增殖.如圖4所示為經(jīng)過3 d培養(yǎng)后不同DLC薄膜上細胞生長的光學照片,圖中標尺為100μm,細胞核用DAPI染色.可以看出,摻雜及修飾前后薄膜上細胞密度有明顯差異,相比于未摻雜的DLC薄膜,N、P元素摻雜的薄膜上細胞密度明顯增大,Pt元素摻雜的薄膜上細胞密度減小;經(jīng)過APBA修飾后,DLC:P薄膜上細胞密度明顯增大.
圖4 不同DLC薄膜樣品上細胞生長3 d后的照片F(xiàn)ig.4 Images of cells on different DLC films after culture for 3 days
2.3 不同DLC薄膜上PC12細胞的微管蛋白形貌
(1)XPS及Raman光譜測試結(jié)果表明,B:N、P、Pt元素的摻入沒有改變薄膜的非晶結(jié)構(gòu),元素摻雜后sp2雜化碳原子增加,薄膜有序程度提高.
圖5 不同DLC薄膜樣品上細胞生長3 d的的微管蛋白形貌Fig.5 Tubulin morphology of cells on different DLC films after culture for 3 days
(2)B、N、P元素的摻入提高了薄膜的親水性,摻P元素薄膜的接觸角降低最為明顯,為17°.
(3)B、N、P元素的摻入促進了PC12細胞在DLC薄膜上的黏附與增殖,抑制了細胞在薄膜上的凋亡;而Pt元素的摻入起了相反的作用.
(4)APBA分子修飾對各摻雜薄膜上PC12細胞的生長起了顯著促進作用(3 d后細胞密度增大約50%),對細胞相容性相對較差的DLC:NPt薄膜作用尤為顯著(約70%).
(5)不同元素摻雜及化學分子修飾對DLC薄膜的細胞相容性的影響不同.可以通過元素摻雜或者化學分子修飾來調(diào)節(jié)DLC薄膜的生物相容性,以滿足其在生物體內(nèi)、外不同環(huán)境對生物相容性需求.
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Influence of doping and molecular modification on cell compatibility of diamond-like carbon film
LIU Min1,LIU Ai-ping1,2,YU Jian-can1,QIAN Guo-dong1
(1.State Key Laboratory of Silicon Materials,School of Material Science and Engineering,Zhejiang University,Hangzhou 310027,China;2.Department of Physics,Zhejiang Sci-Tech University,Hangzhou 310018,China)
DLC film was functionalized by element doping and molecular modification aiming at the biocompatibility regulation of diamond-like carbon(DLC)film for better use in different environment as the substrate material of cell sensor.X-ray photoelectron spectroscopy,Raman spectroscopy and static-state contact angle measurement were applied to characterize the surface morphology and microstructure of DLC film.The effects of element doping and molecular modification on the cell compatibility of the film were explored.Results show that the doping of B,N,P and Pt elements and the modification of 3-aminobenzeneboronic acid(APBA)do not change the amorphous structure of DLC film,but enhance the ordered structure.The doping of B,N and P elements decreases the contact angle of DLC film,while the codoping of N and Pt elements does not lead to obvious change of contact angle.The APBA modification makes the contact angle decrease for different DLC films.Moreover,the doping of B,N and P elements promotes the adhesion and proliferation of PC12 cells and inhibits cell apoptosis.However,the incorporation of Pt element presents the opposite effect.The modification of 3-aminophenylboronic acid can obviously promote the cell growth on the doped DLC surface.Therefore,element doping and molecular modification are effective methods for biocompatibility modulation of DLC film.
diamond-like carbon(DLC)film;doping;chemical modification;cell adhesion;cell proliferation
錢國棟,男,教授.ORCID:0000-0001-7133-2473.E-mail:gdqian@zju.edu.cn
TB 321;Q 24
A
1008- 973X(2015)09- 1790- 06
10.3785/j.issn.1008-973X.2015.09.024
2014- 10- 04. 浙江大學學報(工學版)網(wǎng)址:www.journals.zju.edu.cn/eng
國家自然科學基金資助項目(51272237,51272231,51010002);中國博士后科學基金特別資助項目(2013T60587);中國博士后科學基金資助項目(2012M520063);浙江省博士后基金資助項目(Bsh1201016).
劉敏(1989-),女,碩士生,從事薄膜生物相容性研究.ORCID:0000-0002-5032-4973.E-mail:aipingwz@163.com