劉 敏,劉愛萍,2,郁建燦,錢國(guó)棟
(1.浙江大學(xué)硅材料國(guó)家重點(diǎn)實(shí)驗(yàn)室,材料科學(xué)與工程學(xué)院,浙江杭州310027;2.浙江理工大學(xué)物理系,浙江杭州310018)
摻雜及分子修飾對(duì)類金剛石細(xì)胞相容性的影響
劉 敏1,劉愛萍1,2,郁建燦1,錢國(guó)棟1
(1.浙江大學(xué)硅材料國(guó)家重點(diǎn)實(shí)驗(yàn)室,材料科學(xué)與工程學(xué)院,浙江杭州310027;2.浙江理工大學(xué)物理系,浙江杭州310018)
為實(shí)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?fù)诫s及化學(xué)分子修飾對(duì)DLC薄膜表面進(jìn)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(cè)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(duì)薄膜細(xì)胞相容性的影響.結(jié)果顯示:B、N、P、Pt元素?fù)诫s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(jìn)PC12細(xì)胞的黏附與增殖,抑制細(xì)胞凋亡,而Pt元素的摻入起相反的作用,APBA修飾對(duì)細(xì)胞生長(zhǎng)有明顯促進(jìn)作用.這說明元素?fù)诫s及分子修飾是調(diào)節(jié)DLC薄膜細(xì)胞相容性的有效方法.
類金剛石(DLC)薄膜;摻雜;化學(xué)修飾;細(xì)胞黏附;細(xì)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(xué)性能穩(wěn)定、寬電勢(shì)窗口、低背底電流等優(yōu)良特性[1-3],可廣泛用于機(jī)械模具和零部件的耐磨保護(hù)層、太陽電池減反膜、電化學(xué)工作電極等[4-8].DLC薄膜還具有良好的血液相容性與細(xì)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(shí),其物理化學(xué)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(dǎo)電性,拓寬DLC薄膜在場(chǎng)發(fā)射和太陽能電池等方面的應(yīng)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(shí),薄膜的抗菌能力有明顯提升[19-20].
目前,基于不同元素?fù)诫s對(duì)DLC薄膜細(xì)胞相容性的影響及本質(zhì)規(guī)律的研究相對(duì)較少,關(guān)于表面修飾改善DLC薄膜細(xì)胞相容性的研究也非常有限.為了探究元素?fù)诫s及表面修飾對(duì)DLC薄膜細(xì)胞相容性的影響機(jī)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?dú)猓∟2)和磷烷(PH3)摻雜源對(duì)薄膜進(jìn)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(shí)驗(yàn)中采用3-氨基苯硼酸(3-aminobenzeneboronic acid,3-APBA)對(duì)各種摻雜薄膜進(jìn)行表面功能化,考察摻雜及表面修飾對(duì)薄膜親疏水性及微觀結(jié)構(gòu)的影響,探討元素?fù)诫s及表面修飾的薄膜對(duì)PC12神經(jīng)細(xì)胞黏附、增殖及凋亡等生理活動(dòng)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(dǎo)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(dāng)沉積室真空度達(dá)到2.0×10-4Pa時(shí),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?dú)猓∟2,5 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(shí)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(shí)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(tuán)[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(xué)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(shí)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?fù)诫s和表面修飾對(duì)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(zhǎng)為633 nm)測(cè)定DLC薄膜的拉曼光譜.使用靜態(tài)接觸角測(cè)量?jī)x(OCA20,GER)測(cè)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(cè)量所得接觸角的大小,共設(shè)6組平行實(shí)驗(yàn).
1.3 不同DLC薄膜的細(xì)胞相容性檢測(cè)
1.3.1 PC12細(xì)胞的培養(yǎng) PC12細(xì)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?jǐn)?shù)為10%的達(dá)爾伯克(氏)基礎(chǔ)培養(yǎng)基(Dulbecco's minimum essential medium,DMEM),并加入體積分?jǐn)?shù)1%的青霉素和鏈霉素(P/S,Boster).細(xì)胞體外接種密度為1×104個(gè)/cm2,每3 d進(jìn)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(xì)胞(4×103個(gè)/孔).將細(xì)胞置于37℃、5%(體積分?jǐn)?shù))CO2的標(biāo)準(zhǔn)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?jǐn)?shù)為4%的多聚甲醛固定細(xì)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(xì)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(gè)樣品隨機(jī)選取8個(gè)區(qū)域進(jìn)行拍照,然后對(duì)×20照片中細(xì)胞的密度及×40照片中細(xì)胞的凋亡率進(jìn)行統(tǒng)計(jì).凋亡細(xì)胞的判斷標(biāo)準(zhǔn)為細(xì)胞核著色不均勻,發(fā)出刺眼的亮藍(lán)色.這是因?yàn)樵诘蛲鲞^程中細(xì)胞核會(huì)發(fā)生固縮,染色質(zhì)高度凝聚濃縮.共設(shè)3組平行實(shí)驗(yàn).
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(xì)胞骨架的形態(tài),對(duì)細(xì)胞中的微管進(jìn)行染色.微管是一種具有極性的細(xì)胞骨架,是由微管蛋白二聚體組成的長(zhǎng)管狀細(xì)胞器.經(jīng)過染色,可以看到絲狀微管蛋白從細(xì)胞核周圍往細(xì)胞質(zhì)延伸.微管蛋白密集、有序地排列且伸長(zhǎng)鋪展是細(xì)胞生長(zhǎng)狀態(tài)良好的特征之一[23].具體染色過程如下:將細(xì)胞固定后,用Triton X-100(體積分?jǐn)?shù)為0.5%,PBS)在室溫下處理2 h,使細(xì)胞膜變通透.隨后將細(xì)胞用血清(體積分?jǐn)?shù)為2%,PBS)和白蛋白(體積分?jǐn)?shù)為2%,PBS)混合液在室溫封閉2 h.封閉后的細(xì)胞用連接有Alexa-Fluor 647熒光基團(tuán)的β-微管蛋白抗體(體積分?jǐn)?shù)為0.2%,細(xì)胞信號(hào)傳導(dǎo))孵化2 h,最后用DAPI(5μg/mL)染細(xì)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(yīng)特異性的標(biāo)記細(xì)胞中的微管蛋白.將染色后的細(xì)胞置于共聚焦顯微鏡下用雙通道觀察,激發(fā)波長(zhǎng)分別為405 nm(細(xì)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(cè)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?yàn)镻的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(qiáng)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(jìn)行擬合,分別代表sp2雜化碳的呼吸振動(dòng)和伸縮振動(dòng)模式[24].從圖1(a)可以看出,元素?fù)诫s既沒有引入額外的振動(dòng)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(dòng)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(qiáng)幾乎沒有變化,修飾對(duì)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(duì)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(huì)隨著N元素的摻入而降低,這與薄膜表面含氧基團(tuán)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(duì)于DLC:NPt薄膜,雖然N元素?fù)饺胍子谔岣弑∧さ挠H水性,但是Pt元素的摻入易于增強(qiáng)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(xì)胞在不同DLC薄膜上的黏附、增殖與凋亡
細(xì)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(biāo).如圖3(a)所示為PC12細(xì)胞在不同DLC薄膜上的黏附與增殖,以樣品上現(xiàn)有細(xì)胞密度(C)與原種植密度(C0)的比值(C/C0)作為縱坐標(biāo).從圖中可以看出,種植1 d后細(xì)胞在B、N、P元素?fù)诫s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(duì)細(xì)胞黏附起到了促進(jìn)作用,其中摻雜P元素的促進(jìn)作用最為明顯(約40%).N、Pt元素共摻的薄膜上細(xì)胞黏附的數(shù)量明顯低于未摻雜樣品(約降低30%).細(xì)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(jìn)了細(xì)胞在薄膜上的增殖,抑制了細(xì)胞的凋亡;而Pt元素的摻入對(duì)細(xì)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(xì)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(xì)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(xì)胞行為改變的一個(gè)重要因素.Trantidou等[28]的研究表明:細(xì)胞更傾向黏附于親水性的基底上.本文的實(shí)驗(yàn)結(jié)果與文獻(xiàn)[28]的結(jié)論不謀而合,親水性最好的DLC:P薄膜上細(xì)胞的黏附與生長(zhǎng)最優(yōu).摻雜元素自身的生物相容性可能是影響細(xì)胞行為差異的因素之一.文獻(xiàn)[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(zhǎng)因子和細(xì)胞因子,加速細(xì)胞外基質(zhì)的循環(huán),同時(shí)能促進(jìn)某些RNA和蛋白質(zhì)的合成.N、P元素是構(gòu)成細(xì)胞的主要元素,摻入后也能提高材料的細(xì)胞相容性[17,22,30-31].Regan等[31]利用DLC:P薄膜可實(shí)現(xiàn)細(xì)胞的圖案化生長(zhǎng).另外,Pt和Ag元素都是化學(xué)惰性的金屬元素,當(dāng)薄膜中摻雜納米Ag,Ag表面能釋放自由基并與細(xì)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(shí)驗(yàn)中Pt元素對(duì)細(xì)胞生長(zhǎng)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(xì)胞密度和細(xì)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(xì)胞密度增大了約50%,而DLC:NPt薄膜上細(xì)胞密度提高約為70%.APBA在增大細(xì)胞密度的同時(shí)對(duì)細(xì)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(xì)胞凋亡率降低了約20%,而DLC:NPt薄膜上細(xì)胞凋亡率降低了約40%(見圖3(b)).APBA修飾對(duì)細(xì)胞生長(zhǎng)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(xì)胞膜糖蛋白終端的鄰位羥基發(fā)生脫水縮合,從而增強(qiáng)材料與細(xì)胞的相互作用,利于細(xì)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(xì)胞生長(zhǎng)的光學(xué)照片,圖中標(biāo)尺為100μm,細(xì)胞核用DAPI染色.可以看出,摻雜及修飾前后薄膜上細(xì)胞密度有明顯差異,相比于未摻雜的DLC薄膜,N、P元素?fù)诫s的薄膜上細(xì)胞密度明顯增大,Pt元素?fù)诫s的薄膜上細(xì)胞密度減?。唤?jīng)過APBA修飾后,DLC:P薄膜上細(xì)胞密度明顯增大.
圖4 不同DLC薄膜樣品上細(xì)胞生長(zhǎng)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(xì)胞的微管蛋白形貌
(1)XPS及Raman光譜測(cè)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?fù)诫s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(xì)胞生長(zhǎng)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(jìn)了PC12細(xì)胞在DLC薄膜上的黏附與增殖,抑制了細(xì)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(duì)各摻雜薄膜上PC12細(xì)胞的生長(zhǎng)起了顯著促進(jìn)作用(3 d后細(xì)胞密度增大約50%),對(duì)細(xì)胞相容性相對(duì)較差的DLC:NPt薄膜作用尤為顯著(約70%).
(5)不同元素?fù)诫s及化學(xué)分子修飾對(duì)DLC薄膜的細(xì)胞相容性的影響不同.可以通過元素?fù)诫s或者化學(xué)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(duì)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(guó)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(xué)學(xué)報(bào)(工學(xué)版)網(wǎng)址:www.journals.zju.edu.cn/eng
國(guó)家自然科學(xué)基金資助項(xiàng)目(51272237,51272231,51010002);中國(guó)博士后科學(xué)基金特別資助項(xiàng)目(2013T60587);中國(guó)博士后科學(xué)基金資助項(xiàng)目(2012M520063);浙江省博士后基金資助項(xiàng)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