含水核之奈米膠囊的製備與其體外釋離之研究

Abstract

近年來，對於藥物載體的發展尤其是奈米顆粒受到相當的重視。奈米顆粒的粒徑範圍在10~1000 nm，且為奈米圓球和奈米膠囊的集合名詞。以聚氰基丙烯酸烷基酯（polyalkyl cyanoacrylate，PACA）為材質之奈米膠囊，具有生體相容性及生體可分解性，且聚合過程簡便，因此被廣泛地研究，希望能成為有效的藥物載體系統，以應用在藥物標的、癌症治療、基因治療、眼和口藥物傳遞需求等。 以水、界面活性劑（Span 80/ Tween 80，45/56 w/w混合物）及正己烷以8.08： 25.25：66.67重量比所組成的w/o奈米液滴系統為界面聚合的場所，其平均液滴大小約為53.20 nm，將模式藥aminophylline置於內相中，再以氰基丙烯酸乙酯（ethyl 2-cyanoacrylate，ECA）單體為聚合反應之單體，聚合完成後去除油相、界面活性劑和未反應的單體而得包覆水溶性藥物aminophylline的PECA奈米膠囊。當單體溶液添加量對水相體積比為1：40（配方A）和1：80（配方B）時，產率約達九成。 由FTIR和DSC的結果，可知 PECA奈米膠囊的主體為PECA聚合物。含藥奈米膠囊之IR圖譜同時具有PECA奈米膠囊與aminophylline的官能基特性，其DSC實驗結果發現aminophylline與PECA存在某種交互作用。 以SEM觀察PECA奈米膠囊，發現其為圓球形狀，且其平均粒徑較以DLS分析經純化後分散在反應媒液之奈米膠囊粒徑小。由DLS結果發現含藥奈米液滴系統（1 mg/mL和3 mg/mL）之平均液滴粒徑分別為58.77 nm 和60.90 nm 均較未含藥液滴系統之平均粒徑53.20 nm來的大，此現象亦可見於含藥奈米膠囊平均粒徑大於未含藥奈米膠囊平均粒徑。以相同條件的奈米液滴系統但不同單體量聚合形成之未含藥和含藥奈米膠囊，在配方A（單體量高）所得之平均粒徑分別為72.54 nm和82.70 nm均較配方B（單體量低）所得之平均粒徑分別為62.54 nm和66.10 nm為大，這可能是增加單體添加量，聚合後會形成較厚的聚合物外壁而有較大的粒徑。 在探討PECA奈米膠囊的藥物包覆率及載藥能力實驗，發現以相同藥物使用濃度為內相的液滴系統，在配方A所製備的含藥奈米膠囊之包覆率較配方B所得含藥耐米膠囊高。在藥物使用濃度1∼15 mg/mL的條件下，配方A包覆率1.81%∼44.76% 而配方B包覆率0.38%∼25.05%。究其原因，發現內相中加入aminophylline（1∼15 mg/mL）後，內相液滴的pH值由pH 3.0增加pH 3.5∼pH 8.3，而使ECA聚合速度過快，尚未及分散均勻即已產生聚合反應，而有未被包覆的內相液滴在經3000 rpm離心後，仍大量存在於正己烷層的現象，而致包覆率結果嚴重偏低。 在aminophylline奈米膠囊之藥物釋離研究結果顯示，所製得之奈米膠囊，均具有延緩藥物釋放的效果。在所有pH值下（3.0、7.4、9.0），配方B-1（單體量低）對於配方A-1和A¬-3（單體量高）均有較快之藥物釋出率，可能與膠囊壁厚度有關。溶離液的酸鹼度對aminophylline從PECA奈米膠囊中釋放亦有顯著影響，在不同pH值0.01M磷酸緩衝液下之藥物釋出率大小為pH 9.0 > pH 7.4 > pH 3.0，在第144小時的總釋離量亦分別可達到90%、80% 和60%，這可能和在較高的pH值環境下，PECA聚合物有較快的降解速度及aminophylline有較高的溶解度有關。由藥物釋離實驗之數據經模式分析及曲線揉合的結果顯示，藥物釋離的速率決定步驟應該是在藥物由奈米膠囊中釋出的步驟，而非在藥物通過透析膜的步驟。

Over the past few decades, development of drug carriers such as nanoparticles has caught a lot of attention. Nanoparticle varies in size from 10 nm to 1000 nm and is the collective name for nanosphere and nanocapsule. Poly (alkyl cyanoacrylate) (PACA) nanocapsules have gained extensive interest as drug carriers because of the biocompatibility and biodegradability of the polymer and the simplicity of the polymerization process. The applications attempted to achieve by these carriers include drug targeting, cancer chemotherapy, gene therapy, ocular and oral drug delivery, etc. Therefore, PACA nanocapsule was considered to be a good candidate for the successful exploitation of the drug carrier. Poly (ethyl 2-cyanoacrylate) (PECA) nanocapsules were prepared by interfacial polymerization of a water-in-oil (w/o) nanodroplet system, composed of water, surfactant mixture (Tween 80/ Span 80, 44/56 w/w) and hexane (8.08:25.25:66.67 w/w). The monomer used was ethyl 2-cyanoacrylate (ECA). After removing the oil phase, surfactant and un-reacted monomer, PECA nanocapsules were then obtained. Yields of the production of PECA nanocapsules were about 90%. Results of FTIR and DSC support that the obtained nanocapsules were mainly the products of PECA polymer. Functional IR peaks from PECA nanocapsule and aminophylline were observed in the IR spectrum of aminophylline-loaded nanocapsule. Interaction may exist between aminophylline and PECA in drug-loaded nanocapsule as indicated by DSC results. The morphology of nanocapsules was spherical in shape as seen by SEM. Particle sizes of the nanocapsules estimated by photographs of SEM were significantly lower than the values determined from DLS. The size of droplet in drug-loaded nanodroplet system was larger than the size of droplet in drug-unloaded nanodroplet system. The size of nanocapsules from formulation A (high monomer mass) was larger than those from formulation B (low monomer mass). This may be due to that the higher the monomer mass, the thicker the PECA polymeric wall surrounding the water core. The encapsulation efficiency of aminophylline-loaded PECA nanocapsules were in the range of 1.81% to 44.67% and 0.38% to 25.05% for formulation A and B at various aminophylline concentrations in aqueous phase respectively. The reason for such low encapsulation most likely is that the unstable w/o nanodroplet systems and the alteration of the pH of inner phase, in which higher pH (pH 3.5~ pH 8.3) observed at high drug concentration of aminophylline (1~15 mg/mL). The polymerization of ECA was too faster to be able to disperse evenly in the system before polymerization occurred and hence, leading to low encapsulation efficiently. The results of drug release study of PECA nanocapsules showed that the obtained nanocapsules exhibited sustained release characteristics. Drug-loaded nanocapsules from formulation B-1 had a faster drug release in all pH conditions (3.0, 7.4 and 9.0) than those from formulation A-1 and A-3. The release rates under 37 ℃ and 0.01 M PBS at different pH were in the order of pH 9.0 > pH 7.4 > pH 3.0 for all nanocapsules. This may partially due to the facts that the high PECA nanocapsules degradation and the high aminophylline solubility in alkaline pH conditions. When fitting the drug release profiles to simple mathematical model, it is suggested that limited step of drug release was drug releasing from PECA nanocapsules.