殼聚醣基導電自癒合水膠之開發及在神經系統之生醫應用

Abstract

基於殼聚醣之自癒合水膠近些年在生醫領域備受關注。這類水膠網絡通常由殼聚醣及其衍生物的氨基和交聯劑材料上的醛基之間產生的動態席夫鹼鍵動態交聯形成。在這些可降解的自癒合水膠中，導電水膠因其與具有電活性的組織，尤其是神經組織，存在一定的交互作用，被視為一種極具潛力的軟材料。對於應用於生醫領域之導電自癒合水膠，其導電性常由導電高分子或者其他金屬/非金屬粒子提供。但不同的導電設計策略及材料選擇會帶給水膠多樣的特性，以符合預期之應用需求。在第一部分中，導電高分子聚吡咯經由殼聚醣修飾後製備成奈米粒子，後加入羧乙基殼聚醣和雙官能化聚胺酯奈米交聯劑系統中，製備出具導電性和可注射性之自癒合水膠及可形狀回復支架。相較於不導電的材料，體外實驗表明導電水膠/支架均為神經幹細胞生長和分化提供適合的環境，並通過皮下植入證實了此導電材料良好的生物相容性及生物降解性。同時，在體外以及斑馬魚腦損傷模型中評估了智能導電水凝膠和支架在神經修復和運動檢測中的潛在功能。在先前導電水膠的基礎上，在第二部分討論了結合導電高分子奈米粒子的殼聚醣–聚胺酯複合薄膜的製備。該導電薄膜具備足夠的導電性、良好的親水性、熱響應拉伸性及有潛力的應變感測性。通過體外實驗驗證具導電性會使薄膜上的神經幹細胞更好的增殖與更傾向膠質神經細胞分化。亦評估了其作為生醫領域作為表面塗層材料的潛力。在第三部分中，將膠體金奈米粒子作為添加物以賦予羧甲基殼聚醣與雙官能化聚胺酯水膠適宜的導電性、穩定的交聯網絡、小針頭注射性及抗發炎特性。同時，通過自己設計的體外抗發炎實驗可知導電水膠具有一定的清除自由基的能力。而後，動物實驗證實，在腦內注射導電水凝膠有助於巴金森氏症大鼠的運動功能的恢復並減輕了組織學上的神經變性。這些發現支持含膠體金奈米粒子的導電水凝膠作為用於神經保護和巴金森氏症治療的很有前途的生物材料。第四部分合成了新型氧化單寧酸修飾的金奈米交聯劑並與羧甲基殼聚醣製備具生物活性的自癒合水膠。經實驗驗證，此自癒合水膠表現出抗氧化、抗發炎、導電以及注射特性，並且可以促進神經幹細胞增殖與向神經元方向分化。在動物實驗中，與包載了藥物的自癒合水膠對比，從電生理、行為學以及組織學等多角度證實了具生物活性的自癒合水膠之於巴金森氏症的治療與包載了藥物的自癒合水膠效果沒有顯著差異。透過第三和第四部分研究可得出，開發結合具生物活性之奈米金的殼聚醣基可注射自癒合自癒合水膠具有作為治療巴金森氏症的新策略的潛力。以上研究提出了設計和開發不同導電來源之殼聚醣基自癒合水膠及相關材料在多種神經系統之生醫應用。

Self-healing hydrogels based on chitosan have attracted much attention in the biomedical field over the past decades. These hydrogel networks are usually formed by dynamic Schiff base bonding between the amino groups of chitosan or its derivatives and the aldehyde groups of the crosslinker. Among the degradable self-healing hydrogels, conductive hydrogels are considered as a promising soft material due to their interaction with electroactive tissues, especially neural tissues. The conductivity of self-healing hydrogels for biomedical applications is often provided by conductive polymers or other metallic/non-metallic particles. However, different design strategies and material choices will impart various functions of conductive hydrogel to satisfy the intended application requirements. In the first part, the polypyrrole, i.e., conductive polymer, was modified by chitosan to form nanoparticles, which were then added to a system of carboxyethyl chitosan and difunctional polyurethane to produce self-healing hydrogel and shape-recoverable scaffold with conductivity and injectability. Compared with the non-conductive ones, in vitro experiments demonstrated that the conductive hydrogels/scaffolds provide a suitable environment for the growth and differentiation of neural stem cells, and the good biocompatibility and biodegradability of the conductive materials were demonstrated by subcutaneous implantation. Meanwhile, the potential functions of the smart conductive hydrogel and scaffold in neural repair and motion sensing were evaluated in vitro and in a zebrafish brain injury model. The second part discussed the preparation of chitosan-polyurethane composite films incorporating conductive polypyrrole/chitosan nanoparticles, based on the conductive hydrogels in previous section. The conductive film has sufficient conductivity, good hydrophilicity, thermoresponsive stretching, and potential strain sensing properties. In vitro experiments have demonstrated that the conductivity resulted in better proliferation of neural stem cells and a greater tendency for glial cell differentiation on the film. In the third part, the colloidal gold nanoparticles were used as additives to endow the self-healing hydrogel composed of carboxymethyl chitosan and dialdehyde polyurethane with suitable conductivity, stable crosslinking network, tiny gauge needle injectability, and anti-inflammatory properties. In addition, a self-designed in vitro anti-inflammatory assay revealed that the conductive hydrogel has the capability to scavenge reactive oxygen species. Then, animal experiments confirmed that intracerebral injection of conductive hydrogel promoted motor function recovery and reduced histological neurodegeneration in Parkinsonian rat model. These findings support the use of conductive self-healing hydrogel containing colloidal nanogold as a convincing biomaterial for neuroprotection and Parkinson's disease treatment. The fourth part synthesized a new oxidized tannic acid-modified gold nano-crosslinker with carboxymethyl chitosan to prepare a bioactive self-healing hydrogel. The self-healing hydrogels were characterized to possess antioxidant, anti-inflammatory, conductive, and injectable properties, as well as to promote the proliferation and neuronal differentiation of neural stem cells. In animal experiments, the effects of the bioactive self-healing hydrogel on the treatment of Parkinson's disease were found comparable to the drug-loaded self-healing hydrogel from electrophysiological, behavioral, and histological perspectives. The development of chitosan-based injectable self-healing hydrogels incorporating bioactive gold nanoparticles has the potential to be a new strategy for treating Parkinson's disease. The above studies suggest the design and development of chitosan-based self-healing hydrogels or related materials with different sources of conductivity for multiple therapeutic applications in the nervous system.