具非均向結構的奈米纖維與聚胜肽之奈米複合型水凝膠：合成、製程與性質的研究

Abstract

視神經組織具有獨特的非均向結構而呈現突出的機械強度與功能性。而在所有用於組織工程的人工軟質材料之中，水凝膠為首選的材料由於其仿生的三維結構以及彈性的機械性質。視神經預期的機械性質應在數百至兩萬帕斯卡的範圍裡，含水量應高於90 %，而順向規則結構應超過70 %。多種方式已被建立以製備出具有順向性的水凝膠，像是自組裝的胜肽或是在磁場下的高分子。然而，其複雜的合成製作使得大規模生產與高成本的議題很困難去解決。因此，本研究的目標是開發以簡易方式製備水凝膠具有順向性結構。我們合成水溶性胜肽型聚電解質並與容易排列順向性的奈米纖維進行交聯，所形成的奈米複合型水凝膠。並進一步對材料的基層面有系統地探討其化學組成、形貌與性質之關聯。 首先，選擇正電荷奈米纖維(CNF+)並與聚胜肽進行交聯。使用鈉鹽的谷氨酸苯酯-谷氨酸無規共聚物(poly(r-benzyl-L-glutamate)40-r-poly(L-glutamic acid)60, PBGA60-Na)是因為其包含谷氨酸的神經刺激因子。水凝膠藉著混合不同量的CNF+與PBGA60-Na以靜電荷與氫鍵作用力而形成。在剪切力下製備水凝膠具有順向規則的結構。接下來，水凝膠的形貌以偏光光學顯微鏡、小角度X光散射、掠角廣角度X光散射與X光三維影像進行鑑定。以流變儀與物性測試儀來研究水凝膠的機械性質。本文特別使用小角度X光散射的技術來定量研究凝膠態的奈米纖維溶液、水凝膠的交聯網路結構、結構上的纖維束半徑、動態關聯長度與順向性。最後，結構與機械性質可以關聯並解釋。 當水凝膠的CNF+含量增加時，其形貌在順向規則下具有從稀疏纖維結構至緊密狀的變化。在固定0.5 wt. %的交聯劑，其機械性質會隨著CNF+含量從1.0 wt. %至3.2 wt. %的增加而提升高達7倍(18476.67帕斯卡)。當化學組成在3.2 wt. %的CNF+與0.5 wt. %的交聯劑時，其複合材料具有最佳的機械性質(18476.67帕斯卡)、含水量(97.53 %)以及順向規則結構(74.17 %)。此水凝膠未來適合用於視神經再生的應用。

The optic nerve of eye exhibits hierarchical aligned structure with unique anisotropic mechanical strength and functional performances. Among the artificial soft materials for tissue engineering, hydrogel is preferred material due to its biomimetic three dimensional structure and elastic mechanical property. The desired mechanical properties of optic nerve should be in the range of several hundreds to twenty thousands Pascal. The water content should be higher than 90 %. The aligned structure should be more than 70 %. Many approaches have been developed to fabricate hydrogel with aligned structure such as self assembled peptide or polymer under magnetic field. However, those approaches are complicated, low yield, and high cost. The goal of this research is to develop facile method for hydrogel with anisotropic structure. We synthesize water soluble peptide based polyelectrolyte which is crosslinked with easily aligned cellulose nanofibrils to form nanocomposite hydrogel. We further investigate the relationships among chemical composition, morphology and property of the material systematically. First, the cationic cellulose nanofibrils (CNF+) was selected to be crosslinked with polypeptide. The sodium salt of poly (r-benzyl-L-glutamate)40-r-poly(L-glutamic acid)60 (PBGA60-Na) was used because it contains neurotransmitter of glutamate. The hydrogel was formed by mixing different amount of CNF+ and PBGA60-Na through static charge and hydrogen bonding. The hydrogel with anisotropic structure was fabricated under shear force. Next, the morphology of the hydrogel was evaluated by polarized optical microscope, small angle X-ray scattering, grazing-incidence wide angle X-ray scattering and X-ray tomography. The mechanical properties of the hydrogel were studied by rheometer and texture analyzer. We used small angle X-ray scattering technique to quantify the gel-like cellulose nanofibrils solution, hydrogel crosslinked network structure, cellulose bundle radius, dynamic correlation length, and anisotropy in particular. Last but not least, the hydrogel structure could correlate with the mechanical property. When the content of CNF+ is increased in the hydrogel, the morphology is changed from sparse fibrillar structure to dense one with anisotropy. At fixed crosslinker concentration of 0.5 wt. %, the mechanical property can be seventh fold (18476.67 Pascal) upon increasing the content of CNF+ from 1.0 to 3.2 wt. %. The composite exhibits the best mechanical property (18476.67 Pascal), water content (97.53 %) and anisotropic structure (74.17 %) at the composition of 3.2 wt. % of CNF+ and 0.5 wt. % of crosslinker. This hydrogel will be suitable for the application of optic nerve regeneration.