各向異性之生物可降解暨拉伸性殼聚醣-聚胺酯-奈米纖維素複合材料

Abstract

聚胺酯是一種具有生物相容性的高分子彈性體，以其形成的複合材料也具有多樣的性質以及應用性，而殼聚醣是一種自然中含量豐富的天然衍生物，同時具有易於改質的特性，但聚氨酯-殼聚醣複合物仍舊受限於不足的強度以及有限的拉伸性。在此研究中，將奈米纖維素（CNFs）與聚氨酯-殼聚醣複合物進行結合，並製備出具有拉伸性以及各向異性的材料。首先將醛基修飾於生物可降解的聚氨酯鏈末端來形成雙醛基聚胺酯奈米粒子，加入CNFs來形成DP-CNF複合物交聯劑（DPF），再將此水性的DPF與殼聚糖水溶液進行混合來形成聚氨酯-纖維素-殼聚醣（DPFC）的三成份複合物。混合後，DPFC在約33分鐘時於室溫下行成水凝膠，證實了DPF其交聯能力。由DPFC混合物乾燥形成的薄膜能夠在60 ˚C下展現優異的拉伸性（~420.2%）。此外，透過應變-退火的步驟能形成各向異性的薄膜。在200%應變下退火的薄膜有約4.9的彈性各向異性比（elastic anisotropic ratio）。原位小角度/大角度散射分析（SAXS/WAXS）顯示應變-退火過程中微結構的重排以及對齊，進一步證實薄膜的各向異性性質。各向異性的複合物薄膜能夠誘導神經幹細胞的生長方向，也顯示了其具有仿生以及組織工程應用的潛力。

Polyurethane is a family of biocompatible polymeric elastomers, and composites of polyurethane have versatile properties and applications. Chitosan is a naturally derived biodegradable polymer with abundancy and ease of chemical modification. Polyurethane-chitosan composites were recently developed but had insufficient strength and limited stretchability. In the current study, cellulose nanofibers (CNFs) were integrated in polyurethane-chitosan composites to prepare stretchable and anisotropic materials. Biodegradable polyurethane was first synthesized, end-capped with aldehyde to become dialdehyde polyurethane (DP) nanoparticles, and added with CNFs to prepare the DP-CNF composite crosslinker (DPF). The waterborne DPF crosslinker was then blended with chitosan solution to make polyurethane-CNF- chitosan (DPFC) ternary composites. After blending, DPFC may form hydrogel in ~33 min at room temperature, which confirmed crosslinking. Composite films cast and dried from the blends showed good elongation (~420.2%) at 60 ˚C. Anisotropic films were then generated by tension annealing with pre-strain. The annealed films with 200% pre- strain exhibited large elastic anisotropy with ~4.9 anisotropic ratio. In situ SAXS/WAXS analyses unveiled that rearrangement and alignment of the microstructure during tension annealing accounted for the anisotropy. The anisotropic composite films had the ability to orient the growth of neural stem cells and showed the potential for biomimetic and tissue engineering applications.