王 哲,史向陽
(東華大學化學化工與生物工程學院,上海201620)
靜電紡有機/無機雜化納米纖維載藥體系的構建及其生物醫(yī)學應用
王 哲,史向陽
(東華大學化學化工與生物工程學院,上海201620)
納米纖維具有極大的比表面積、可控的多孔二級結構等一系列優(yōu)良特性,使其在環(huán)境保護、能源利用、催化劑、藥物載體、組織工程支架材料等領域得到了廣泛應用。通過靜電紡技術制備的納米纖維主要有有機納米纖維、無機納米纖維、以及有機/無機雜化納米纖維3類。結合作者課題組之前的研究成果積累,綜述了各種不同的靜電紡有機/無機雜化納米纖維載藥體系的構建及其生物醫(yī)學應用。著重介紹了如何將藥物負載在無機納米顆粒(埃洛石、鋰皂石、羥基磷灰石、介孔二氧化硅等)的表面或內部并進而和高分子混紡形成雙載體納米載藥纖維的過程和相關藥物緩釋機理,并探討了有機/無機雜化納米纖維載藥體系的生物醫(yī)學應用,尤其是在抗菌和抗腫瘤方面的治療應用。文章最后對該領域的研究方向和前景作了展望。
靜電紡;雜化納米纖維;藥物載體;生物醫(yī)學應用
近年來,納米載藥體系的研究和應用得到了人們廣泛的重視[1-4]。在納米載藥體系中,藥物分子通常均勻分散于載體基質中或者吸附于載體表面,得到的載體-藥物復合體除了起到攜帶藥物的作用外,還可以影響和控制藥物的釋放動力學,更有利于其藥效的發(fā)揮[3]。納米科技和藥物載體結合的研究源于20世紀60~70年代,當時,英國學者Bangham將磷脂分散在水中,輔以超聲波等手段處理后,通過顯微鏡觀察發(fā)現(xiàn)了脂質體[5]。后來,Ryman和Gergoriadis又分別在模擬生物膜的基礎上,將酶和藥物等包裹在脂質體中,開啟了將脂質體用于藥物載體的研究[6]。此后,包括納米顆粒[7-8]、納米纖維[9-10]、納米管[11-12]、納米棒[13]在內的一系列的納米級藥物載體被相繼開發(fā)出來。在這些納米材料中,納米纖維具有表面形貌可控、表面容易修飾[14-16]、載藥操作簡單、對藥物藥效影響較小等一系列優(yōu)點[17-19],因而倍受研究者們的關注。
常用的制備納米纖維的方法主要有拔拉法、模板合成法、熱致相分離法、自組裝法、乳液聚合法和靜電紡絲法等[20]。其中拔拉法的不足在于其要求聚合物有較好的粘性,能承受外力的拉扯作用,且單位時間內只能生產單根纖維,產量低,應用受到了限制;模板法需要額外的模板,操作過程較復雜;自組裝法操作步驟繁瑣。靜電紡絲技術是目前唯一能夠大量地制備連續(xù)的納米纖維的方法[21],因而受到了研究者的青睞。
自從Kenawy等人于2002年報道了將靜電紡納米纖維用作藥物載體的研究后,基于靜電紡納米纖維的藥物負載體系得到了長足的發(fā)展[18,19,22]。截止目前,通過靜電紡技術制備藥物載體的方法主要包括傳統(tǒng)靜電紡絲法、同軸靜電紡和乳液靜電紡等[9,22-26]。傳統(tǒng)靜電紡絲法即將藥物簡單地和高分子溶液混合,然后將混有藥物的高分子溶液直接紡絲。在制備過程中,藥物通常會均勻分散在纖維中,形成“藥物-基質”結構。此結構中,藥物和基質間的作用力不強,常常伴有藥物突釋現(xiàn)象的發(fā)生,且隨著釋放時間的延長,藥物的釋放速度降低,影響藥效的發(fā)揮。同軸靜電紡和乳液靜電紡是兩種改進的靜電紡絲技術。采用這兩種技術制備的載藥納米纖維,藥物往往存在于纖維內部,形成所謂的“核-殼”結構,藥物處于核層,高分子層處于殼層。在這種“核-殼”結構中,藥物首先要從核層釋放到殼層,再從殼層擴散到纖維外,才可以完成對藥物的釋放。殼層的纖維對藥物起到了額外的屏障作用,因此可以控制藥物釋放速度[10,26]。但是,這兩種靜電紡絲技術仍然存在著一定的弊端。同軸靜電紡需要進行大量的儀器參數(shù)和溶液參數(shù)調試;而采用乳液靜電紡技術時內層的溶劑很難徹底揮發(fā),殘留的溶劑將會影響纖維的細胞相容性和藥物藥效[27]。因此,需要探索以靜電紡為基礎的更加新穎的藥物載體制備方法。
大量研究表明,一些無機納米材料如埃洛石納米管(Halloysite Nanotubes,HNTs)[28-32]、碳納米管(Carbon Nanotubes,CNTs)[33-40]、羥基磷灰石[41-42]、鋰皂石[7,43-44]、介孔二氧化硅[45]等具有高的比表面積、高的表面活性和良好的生物相容性,對多種化學物質及生物活性大分子有較強的吸附能力,是藥物的良好載體。但這些納米材料載藥后多以粉末形式存在,易發(fā)生團聚,無法實現(xiàn)器件化,而且大多存在比較明顯的突釋現(xiàn)象。
雜化纖維通常是指由不同類別材料組成的納米纖維,如聚合物/無機納米顆粒雜化纖維[46-49]、聚合物/聚合物雜化纖維[50-52]等。由于摻雜了部分功能性物質,雜化纖維通常會顯示出更多優(yōu)良性能,例如催化性能增強[53-55]、機械性能提高[56-57]、藥物包裹能力[58]以及細胞相容性[18]增強改善等。正是因為具有上述優(yōu)良性能,雜化纖維在組織工程[59-60]、催化劑[53,54,61]、傳感器[62-63]和藥物載體[64]等領域具有廣泛的應用前景。
基于以上研究現(xiàn)狀和問題,作者課題組及其他研究團隊將載藥納米管或納米顆粒與高分子紡絲液混合電紡,制備了一系列新型的有機/無機雜化納米纖維雙重載藥體系。一方面雙重載藥體系有效地延長了藥物的擴散歷程;另一方面,負載的無機成分可有效地提高纖維的機械性能。本文主要從負載藥物的生物功能方面,綜述了有機/無機雜化納米纖維載藥體系負載抗生素類藥物和抗腫瘤類藥物方面的研究進展。
2010年,作者課題組Qi等[65]報道了將鹽酸四環(huán)素(Tetracycline Hydrochloride,TCH)作為模型藥,首先將其負載到一種天然呈納米管狀結構的鋁硅酸鹽礦物埃洛石(Halloysite Nanotubes,HNT)的表面或內部空腔制成TCH/HNTs,然后將載藥效率最優(yōu)的TCH/HNTs與聚乳酸-羥基乙酸(Polylactic-co-glycolic Acid,PLGA)混紡,制備了HNTs/PLGA雙載體藥物緩釋系統(tǒng)。實驗結果表明,載藥納米管TCH/HNTs的加入沒有影響到PLGA纖維均勻光滑的結構,與PLGA纖維的直徑相比,TCH/HNTs/PLGA纖維的直徑變細(圖1)。TCH/HNTs載藥粉末和靜電紡TCH/PLGA混紡載藥納米纖維都存在明顯的初始突釋現(xiàn)象(圖2),24 h后TCH釋放率分別是89.4%和83.8%,48 h后兩者TCH釋放率基本上都趨于一個平臺。然而,靜電紡TH-1/PLGA(1%TCH/HNTs/PLGA)和TH-2/PLGA(2%TCH/HNTs/PLGA)載藥納米纖維沒有明顯的初始突釋現(xiàn)象(圖2),24 h后,分別釋放18.6%和16.3%的TCH。另外,兩種載藥纖維體系表現(xiàn)出很好的TCH持續(xù)釋放效果,緩釋28 d后,釋放的TCH分別為65.2%和61.3%,緩釋42 d后,分別有77.6%和68.5%的TCH釋放。體外抑菌實驗表明,從TCH/HNTs載藥粉末及靜電紡載藥纖維中釋放出來的藥物保持了其生物功能。由于TCH/HNTs被成功地封裝到PLGA纖維內部,使得HNTs和PLGA作為TCH的雙重載體進一步延緩了TCH的釋放速度。釋放過程中,一部分TCH從HNTs表面解吸附,一部分TCH從HNTs內部緩慢釋放,然后再通過PLGA纖維基體慢慢擴散到緩釋液中。總之,靜電紡TCH/HNTs/PLGA雙載體納米纖維載藥體系是一個很好的藥物控釋器件,不僅可以延緩TCH的釋放,同時又實現(xiàn)了載藥體系的器件化。
圖1 靜電紡PLGA纖維(a)、TH-1/PLGA(b)、TH-2/PLGA(c)及TCH/PLGA(d)納米載藥纖維的SEM照片和纖維直徑分布直方圖[65]Fig.1 SEM micrographs of the electrospun PLGA(a),TH-1/PLGA(b),TH-2/PLGA(c),and TCH/PLGA(d)nanofibers,and the corresponding fiber diameter distribution histograms[65]
有研究表明,合成性的納米粘土材料鋰皂石(Laponite,LAP)[7,43-44]的內部空腔可以用來高效包裹藥物。按照同樣的設計思路,作者課題組Wang等[66]利用靜電紡絲制備出PLGA/LAP/Amoxicillin(AMX)復合納米纖維。實驗結果表明,LAP對AMX的負載效率隨著AMX濃度的增加而增加,隨LAP濃度的增加而降低。當LAP和AMX的濃度分別為3 mg/mL和2 mg/mL時,LAP對AMX的負載達到最優(yōu)值,為9.76±0.57%。藥物釋放動力學研究表明,AMX從LAP/AMX粉末和PLGA/AMX納米纖維中的釋放都存在著突釋現(xiàn)象。以LAP/AMX納米粉末中的最為明顯,在初始的1 h內AMX的釋放量即接近100%。PLGA/AMX納米纖維中AMX的釋放速度相對較慢,在最初48 h內,大約40%的AMX釋放出來;然后,AMX的釋放速度明顯降低,9 d之后釋放量達到100%。相比之下,PLGA/LAP/AMX納米纖維對AMX的釋放呈現(xiàn)先快速釋放后持續(xù)釋放的特點。在最初24 h內藥物的釋放量約為40%;此后AMX的釋放速度明顯變緩,呈現(xiàn)緩慢釋放特點,15 d后的藥物釋放量為55%。體外抑菌活性評價顯示,PLGA/LAP/AMX載藥納米纖維在固體培養(yǎng)基和液體培養(yǎng)基中均可以有效地抑制金黃色葡萄球菌的生長,表現(xiàn)出良好的體外抑菌活性。這些結果對研究PLGA/LAP/AMX載藥納米纖維在藥物載體、傷口敷料以及組織工程支架材料領域的應用具有重要意義。
圖2 樣品在37℃、pH為7.4的PBS緩沖液中孵育,TCH從TCH/HNTs載藥粉末、靜電紡TH-1/PLGA、TH-2/PLGA及TCH/PLGA載藥納米纖維中釋放的緩釋曲線[65]Fig.2 In vitro release profiles of TCH from TH-1/PLGA,TH-2/PLGA,TCH/PLGA nanofibers,and TCH/HNTs powders.The sampleswere incubated in phosphate buffered saline(PBS)buffer(pH 7.4)at37℃[65]
納米羥基磷灰石(n-HA)是一種很好的無機藥物載體材料,它具有高的比表面積、高的表面活性和良好的生物相容性,并對多種化學物質及生物活性大分子有較強的吸附能力[41-42]。同時,具有納米棒狀結構和高的機械強度,可以作為纖維增強體。作者課題組Zheng等[67]設計并制備了基于n-HA和PLGA的復合納米纖維載藥體系(圖3),并系統(tǒng)地研究了AMX和n-HA在水中的最優(yōu)載藥濃度配比和該復合納米纖維載藥體系的納米纖維直徑、孔隙率、表面親水性、機械性能、模型藥AMX的釋放動力學、細胞毒性、血液相容性以及其對金黃色葡萄球菌的抗菌活性。結果表明,AMX和n-HA兩者濃度分別為2 mg/mL和1 mg/mL時,AMX可達到最優(yōu)負載百分率(20.45%)。通過靜電紡絲法,n-HA納米粉末、AMX/n-HA載藥粉末及AMX被成功地負載到PLGA纖維內部,且對PLGA纖維的形貌、孔隙率和接觸角均沒有明顯的影響。靜電紡n-HA/PLGA、AMX/n-HA/PLGA和AMX/PLGA納米纖維的直徑明顯降低,而n-HA/PLGA和AMX/n-HA/PLGA納米纖維的斷裂強度和楊氏模量相對PLGA納米纖維均有所增加。緩釋實驗結果表明,AMX/n-HA載藥粉末和AMX/PLGA載藥纖維都存在明顯的初始突釋現(xiàn)象,而AMX/n-HA/PLGA雙載體納米纖維載藥體系則避免了突釋現(xiàn)象,并具有很好的持續(xù)釋放效果。體外抑菌實驗表明,靜電紡AMX/n-HA/PLGA載藥纖維氈對金黃色葡萄球菌表現(xiàn)出即時、長效和對載藥量梯度依賴的抑菌活性(圖4)。體外細胞毒性試驗及溶血性試驗也表明AMX/n-HA/PLGA載藥纖維具有良好的生物相容性和血液相容性??傊?,AMX/n-HA/PLGA載藥纖維具有更好的尺寸穩(wěn)定性、機械耐受性、即時長效和載藥量梯度依賴的抑菌活性及很好的生物相容性和血液相容性,可預計其在傷口包覆、術后防粘連和防感染方面將有很好的應用前景。
圖3 AMX/n-HA/PLGA載藥納米纖維的制備過程示意圖(a)及AMX的釋放機理圖(b)[67]Fig.3 Schematic illustration of the encapsulation(a)and release pathways(b)of AMX within n-HA-doped PLGA nanofibers[67]
圖4 在PBS緩沖液中釋放4 d和9 d的AMX/n-HA/PLGA和AMX/PLGA納米纖維氈(所有樣品的AMX初始濃度是60 mg/m L,相對于5 m L的細菌懸浮液)在液體培養(yǎng)基中與金黃色葡萄球菌共孵育24 h得出的抑菌活性的定量分析結果(a),并與空白對照組比較;在PBS緩沖液中釋放4 d(b)和9 d(c)的PLGA(1)、n-HA/PLGA(2)、AMX/n-HA/PLGA(3)和AMX/PLGA(4)納米纖維氈在瓊脂平板上孵育金黃色葡萄球菌6 h,12 h,18 h,24 h得出的抑菌活性的定性分析結果[67]Fig.4 Inhibition of bacterial(S.aureus)growth using AMX-loaded nanofibers(originalunreleased AMX contentwas60 mg/m L relative to the 5 mL bacterial suspension)after 4 or 9 days release after24 h incubation,untreated bacterial solution was set as control;Growth inhibition of bacteria(S.aureus)on agar plate at the incubation time of6 h,12 h,18 h,and 24 h using AMX-loaded nanofibers after 4(b)or 9(c)days release:spots 1~4 represents PLGA,n-HA/PLGA,AMX/n-HA/PLGA,and AMX/PLGA nanofibers,respectively[67]
除此之外,基于高聚物/磁性納米粒子或介孔二氧化硅納米顆粒/抗生素藥物的有機/無機雜化納米纖維載藥體系也相繼被報道。Haroosh等[68]制備并表征了PLAPCL/磁性納米粒子納米纖維,并且用其來負載抗生素類藥物TCH,藥物釋放動力學結果完全符合“Ritger-Peppas and Zeng models”。Hu等[69]用介孔二氧化硅(Mesoporous Silica,MMS)負載布洛芬(Ibuprofen,IBU),然后與PLLA混紡制備得到PLLA-MMS-IBU復合納米纖維。試驗結果表明,布洛芬前12 h的突釋率是PLLAIBU的1/8,并且藥物釋放時間大大延長。動物試驗結果表明,使用PLLA-MMS-IBU在8周時間里發(fā)炎率最低,傷口能夠很好地愈合。因此該長效釋藥膜應用于傷口包覆能夠起到抗炎和預防粘連的作用。
阿霉素(DOX)是目前廣泛使用的抗癌藥物之一[70-72]。自由的DOX在臨床使用時存在毒副作用大等問題[73]。靜電紡納米纖維由于可器件化[74],且可通過調節(jié)纖維形貌、孔隙率和組成有效控制藥物釋放特性[75],在作為抗癌藥物載體應用方面日益受到關注。另外,靜電紡納米纖維作為抗癌藥物載體,可以獲得持續(xù)釋放藥物的效果,具有很好的應用前景。同時,靜電紡納米纖維具有高比表面積、高孔隙率和表面易功能化等特點,作為腫瘤組織部位的支架載體材料具有很多優(yōu)勢[76-78]。
作者課題組Zheng等[79]在制備PLGA/n-HA/AMX復合納米纖維的基礎上,制備了PLGA/n-HA/DOX復合納米纖維。實驗結果表明,PLGA/n-HA/DOX纖維具有很好的DOX持續(xù)釋放效果,同時還表現(xiàn)出在腫瘤滋生的酸性微環(huán)境(pH=5.0~6.0)中相對快速釋放的特性(圖5)。采用MTT法檢測細胞活力的實驗結果表明,在有效的藥物濃度梯度范圍內,DOX/n-HA/PLGA纖維浸漬培養(yǎng)基對人口腔上皮癌細胞(KB細胞)有明顯的殺傷力(圖6)。溶血實驗也表明其具有良好的血液相容性。因此,靜電紡DOX/n-HA/PLGA復合納米纖維抗腫瘤載藥體系在抗腫瘤藥物控釋領域具有巨大的應用潛質。
圖5 DOX/n-HA載藥粉末、靜電紡DOX/n-HA/PLGA(1% DOX,質量分數(shù),相對于PLGA)復合載藥納米纖維及DOX/PLGA(1%DOX,質量分數(shù),相對于PLGA)混紡載藥納米纖維在PBS(pH=7.4,37℃)(a)和醋酸鹽(pH=5.4,37℃)(b)緩沖液中DOX的緩釋曲線[79]Fig.5 In vitro release profiles of DOX from DOX-n-HA particles,electrospun DOX-PLGA(1%DOX,mass fraction,relative to PLGA)and DOX-n-HA-PLGA(1%DOX,mass fraction,relative to PLGA)nanofibers.The samples were incubated in(a)PBS buffer(pH=7.4)and(b)acetate buffer solution(pH=5.4)at 37℃[79]
圖6 KB細胞在純培養(yǎng)基、n-HA粉末、靜電紡PLGA、n-HA/PLGA纖維氈及純DOX、DOX/n-HA載藥粉末及DOX/PLGA和DOX/n-HA/PLGA載藥納米纖維氈的浸漬培養(yǎng)基中培養(yǎng)1 d后的MTT檢測結果,用未經(jīng)任何處理的KB細胞作為對照[79]Fig.6 MTT viability assay of KB cells treated with pure DOX,and the releasemedium of DOX-n-HA powder,DOX-PLGA and DOX-n-HA-PLGA composite nanofibers with different DOX contents for 24 h. Untreated KB cellswere used as control,the PLGA nanofibers,n-HA nanoparticles,and n-HA-PLGA nanofibers without DOX loading were also treated under similar conditions and compared with those materials loaded with DOX[79]
除此之外,基于高聚物/介孔二氧化硅納米顆粒和Au納米粒子/DOX的有機/無機復合納米纖維載藥體系也相繼被報道。Qiu等[80]將DOX首先負載于介孔二氧化硅納米顆粒(Mesoporous Silica Nanoparticles,MSNs)中,然后與Poly(L-Lactic Acid)(PLLA)混合紡絲制備得到PLLA/DOX@MSNs復合納米纖維。試驗結果表明,復合納米纖維能夠長期穩(wěn)定釋放DOX,并且比MSNs和PLLA單獨載藥有更好的殺滅Hela細胞的能力。Yan等[81]利用靜電紡的方法首先制備出包含Au納米顆粒(AuNPs)的PVA/CS納米纖維,然后把DOX負載到復合納米纖維上。結果表明,納米纖維對藥物有很高的封裝率,通過控制交聯(lián)時間,可以很好地控制藥物的釋放速率。Hou等[82]首先在介孔二氧化硅中封裝NaYF4:Yb3+、Er3+,然后負載DOX,最后與含有吲哚美辛的Poly(ε-caprolactone)(PCL)和gelatin混合紡絲,制備得到了雙載藥納米纖維,結果表明吲哚美辛釋放較快,而DOX表現(xiàn)出持續(xù)釋放的特點。
本文系統(tǒng)地介紹了有機/無機雜化納米纖維載藥體系的構建及其生物醫(yī)學應用,尤其是在抗菌和抗腫瘤治療方面的應用。綜述了幾種通過靜電紡方法制備的有機/無機雜化納米纖維載藥體系,它們的共同優(yōu)勢是制備工藝簡單、自身可降解、生物相容性好及機械性能高,同時實現(xiàn)了無機納米粒子的器件化,對所負載藥物都能夠實現(xiàn)緩慢釋放,而藥物的治療效果則不受影響。這些優(yōu)點使有機/無機雜化納米纖維載藥體系在近年來得到了廣泛的研究與發(fā)展。
隨著納米纖維載藥體系研發(fā)的不斷深入,有機/無機雜化納米纖維載藥體系的應用潛力已得到廣泛認同。但將該體系進一步應用于體內試驗的相關研究仍將是一項富有挑戰(zhàn)意義的課題??傊袡C/無機雜化納米纖維載藥體系已經(jīng)展示出了美好的前景,為藥物緩釋體系帶來了很大的突破,為術后防感染和癌癥治療提供了很好的平臺體系。相信經(jīng)過研究者們的努力,有機/無機雜化納米纖維載藥體系將拓展用于多種不同藥物的負載與控釋,用于多種不同疾病的治療。
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Construction of Drug-Loaded Electrospun Organic/Inorganic Hybrid Nanofibers for Biomedical Applications
WANG Zhe,SHIXiangyang
(College of Chem istry,Chemical Engineering and Biotechnology,Donghua University,Shanghai201620,China)
The distinctive features of nanofibers(such as huge surface area to volume ratio,controllable porous secondary structure,etc.)enable them to be widely used in the fields of environmental protection,energy,catalysts,drug delivery,and tissue engineering scaffolds.Nanofibers prepared by electrospinning technology mainly include organic nanofibers,inorganic nanofibers,and inorganic/organic hybrid nanofibers.In this review,based on our previouswork associated with electrospun hybrid nanofiber systems,the construction of various drug-loaded electrospun organic/inorganic hybrid nanofiber systems for biomedicalapplications has been reviewed.In particular,this review mainly introduces processing of loading drugmolecules onto orwithin various inorganic nanoparticles(e.g.,halloysitenanotubes,laponitenanodisks,nanohydroxyapatite,mesoporous silica,etc.)and subsequent electrospinning with polymers to form electrospun hybrid nanofiber-based double drug carrier systems,and the associated mechanisms related to the sustained release of the encapsulated drugmolecules.The biomedical applications of the drug-loaded hybrid electrospun nanofibers,especially antibacterial and antitumor therapy applications have also been reviewed.The review ends with a brief outlook of the future directions and prospects of this research area.
electrospinning;hybrid nanofibers;drug carriers;biomedical app lications
TB383
A
1674-3962(2014)11-0661-08
2014-04-03
上海高校特聘教授(東方學者)支持計劃
王 哲,男,1989年生,碩士研究生
史向陽,男,1970年生,教授,博士生導師,Email:xshi@dhu.edu.cn
10.7502/j.issn.1674-3962.2014.11.03