幾丁聚醣複合物奈米結構與可控制藥物釋放行為之研究

Abstract

幾丁聚醣近來在醫藥應用方面受引起很大的注意，因為具有很好的生物相容性使得幾丁聚醣廣泛應用在眼科的局部治療、植入物以及注射藥物領域。而且，由於幾丁聚醣能夠被人體體內酵素(特別是溶解酵素)所代謝，因此也被認為是生物可分解性材料。另外，幾丁聚醣表面帶正電荷的性質使其擁有很好的生物吸附性，在應用上能夠長時間的停留在體內以提升其利用率。幾丁聚醣也擁有能夠幫助傷口癒合以及抗菌等優點。最重要的是，幾丁聚醣大量存在於自然界中讓製作成本變得非常便宜。 幾丁聚醣具有陽離子特性使它能夠形成具有酸鹼敏感與電場敏感特性的聚電解質水膠。本論文的第一部分著重在討論具有電敏感性的幾丁聚醣/奈米黏土複合水膠的合成(第四章)。表面帶負電的黏土顆粒能夠當作幾丁聚醣的交鍊劑來增加複合物的交鍊程度，並且提升其機械強度、膨潤收縮特性和疲勞特性。實驗結果中可以發現，比起純幾丁聚醣來說，複合物在電場不斷開關的循環刺激下能夠擁有較佳的抗疲勞特性。除此之外，我們也利用另一種無機黏土(蒙脫土)來增加幾丁聚醣的抗疲勞特性以及長時效穩定藥物釋放行為(第五章)。脫層後的蒙脫土也能夠當作幾丁聚醣的交鍊劑，結果發現在電場的刺激下，不同的交鍊程度會強烈影響維他命B12的釋放行為。當蒙脫土的含量增加，藥物擴散指數n值和複合物的對於電場的反應性將會減低。另外，具有較高蒙脫土含量的複合物在電場不斷開關的循環刺激下電反應性會減弱，但是能夠擁有較佳的抗疲勞特性。除此之外，在第六章中，利用乳化法和溶膠水膠法的製程可以成功製備出顆粒尺寸介於50-130奈米的幾丁聚醣-四乙氧基矽複合奈米顆粒。四乙氧基矽經過水解縮合反應，能夠和幾丁聚醣形成網狀結構，進而增加藥物的包覆效率，同時也提供較佳的機械強度，使其在電場關閉時不讓藥物流出載體。 幾丁聚醣因為具有氫氧根和氨根的基團，因此可以很容易被用來做為改質的處理，使其在生藥應用上具有很大的利用價值。雙性幾丁聚醣同時擁有親水性和疏水性的特性使其能夠在水溶液中自組裝形成類似微胞狀的團聚物，這樣的特性主要是由於疏水基團分子或疏水基團分子間的作用力所造成的。在第七章中，我們利用親水性甲基羧基基團與疏水性己醯基團的嫁接物，製備出一種新穎的幾丁聚醣衍生物，能夠在水溶液中自組裝形成空心的奈米膠囊。同時也藉由實驗方法鑑定出此雙性幾丁聚醣衍生物的臨界團聚濃度和表面電性。而此自組裝特性和結構穩定性主要來自於分子間作用力和熱力學的作用。而更有趣的發現指出，改變不同的疏水基團鏈長(變化從2個碳到12個碳)或嫁接量，可以操控幾丁聚醣奈米團聚物的自組裝行為(第八章)。從結果中可以發現，嫁接量和碳鏈數的乘積值(XDH × XCn),能夠用來當作一個指標來決定奈米團聚物的結構: 當乘積超過1.5時，奈米團聚物會從實心的結構轉變成空心的結構變化。在藥物傳遞應用中，抗癌藥物小紅莓在此奈米結構下被證明可以大大提升吸附性以及包覆率。

Chitosan (CS) is currently receiving a great of interest for medical and pharmaceutical application. Indeed, it is known for being biocompatible allowing it use in various medical applications such as topical ocular applications, implantation or injection. Moreover, chitosan is metabolised by certain human enzymes, especially lysozyme, and is considered as biodegradable. Due to its positive charges at physiological pH, chitosan is also bioadhesive, which increases retention at the site of application. Chitosan also promotes wound-healing and has bacteriostatic effects. Finally, chitosan is very aboundant, and its production of low cost and ecologically interesting. CS with cationic characteristics is capable to form polyelectrolyte hydrogel that owing pH-sensitivity and electric-sensitivity. The first part in this thesis is focusing on the synthesis of electrostimulus-responsive hybrid composites composed of chitosan (CS) and clay (chapter 4). The addition of negatively charged clay as an ionic cross-linker strongly affect the cross-linking density as well as the mechanical property, swelling–deswelling behavior and fatigue property of the hybrids. Compared with pure CS, a significant improvement in the anti-fatigue property against cyclic electric stimulations of the hybrid was found. In addition, an inorganic phase, MMT, was incorporated in the CS matrix to enhance the anti-fatigue property and corresponding long-term stable release kinetics (chapter 5). The exfoliated silica nanosheets are able to act as cross-linkers to form a network structure between the CS and MMT, and this difference in the cross-linking density strongly affects the release of vitamin B12 under electrostimulation. Further increasing the MMT content reduced both the diffusion exponent n and the responsiveness of the nanohydrogel to electrostimulation. A consecutively repeated ‘‘on” and ‘‘off” operation shows that the electroresponsiveness of the nanohydrogel with higher MMT concentrations was reduced, but its anti-fatigue behavior was considerably improved. In addition, nanoparticles (NPs) with particle size of 50-130 nm composed of chitosan (CS) and tetraethyl orthosilicate (TEOS) were prepared through emulsion and sol-gel process (chapter 6). TEOS that hydrolyzed and condensed to form network structure with the CS improved the drug loading capacity and also provided the mechanical enhancement of the nano-sphere to restrict drug release when the electric field was switched off. In addition, CS appears to be more useful in biomedical applications because of its both hydroxyl and amino groups that can be easily modified. Amphiphilic CS consisting of hydrophilic and hydrophobic segments can form micelle-like self-assemblies due to non-covalent association arising from intra- and/or intermolecular interactions among hydrophobic segments in aqueous media. In chapter 7, a new type of amphiphilic chitosan, which was synthesized through the use of both hydrophilic carboxymethyl and hydrophobic hexanoyl substitutions, was employed to self-assemble into a hollow nanocapsule in an aqueous environment. Critical aggregation concentration (cac) and zeta potential were experimentally identified for the amphiphilic chitosan (CHC). The self-assemble mechanism, together with the corresponding nanostructural stability, of this unique CHC nanocapsule was also proposed in terms of intermolecular interaction and thermodynamic reason. Further, a more interesting finding where through the use of acyl chain of varying chain lengths, from C2 to C12, for intramolecular substitution, the self assembly behavior and the resulting nanostructure of the chitosan nano-aggregate can be well manipulated (chapter 8). It was found that the critical value of (XDH × XCn), i.e., a product of “degree of acyl substitution” and “carbon number of acyl chain”, can be employed as an indicator for structural variation of the nano-aggregates: when (XDH × XCn) exceeded 1.5, the architecture of the nano-aggregates underwent a structural transformation from solid nano-particle to hollow nano-capsules. An improved affinity and capacity of doxorubicin drug encapsulation can be technically designed according to the nature of the resulting nanocapsules for controlled delivery.