Chitosan has biocompatibility and biodegradability; however, the practical use of the bulk chitosan materials is hampered by its poor strength, which can not satisfy the mechanical property requirement of organs. Thus, the construction of highly strong chitosan-based materials has attracted much attention. Herein, the high strength nanofibrous hydrogels and films (CS-E) were fabricated from the chitosan solution in LiOH/KOH/urea aqueous system via a mild regenerating process. Under the mild condition (ethanol at low temperature) without the severe fluctuation in the system, the alkaline-urea shell around the chitosan chains was destroyed, and the naked chitosan molecules had sufficient time for the orderly arrangement in parallel manner to form relatively perfect nanofibers. The nanofibers physically cross-linked to form CS-E hydrogels, which could be easily oriented by drawing to achieve a maximum orientation index of 84%, supported by the scanning electron microscopy and two-dimensional wide-angle X-ray diffraction. The dried CS-E films could be bent and folded arbitrarily to various complex patterns and shapes. The oriented CS-E films displayed even ultrahigh tensile strength (282 MPa), which was 5.6× higher than the chitosan films prepared by the traditional acid dissolving method. The CS-E hydrogels possessed hierarchically porous structure, beneficial to the cell adhesion, transportation of nutrients, and removal of metabolic byproducts. The cell assay results demonstrated that the CS-E hydrogels were no cytotoxicity, and osteoblastic cells could adhere, spread, and proliferate well on their surface. Furthermore, the oriented CS-E hydrogels could regulate the directional growth of osteoblastic cells along the orientation direction, on the basis of the filopodia of the cells to extend and adhere on the nanofibers. This work provided a novel approach to construct the oriented high strength chitosan hydrogels and films.

中文翻译：

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定向壳聚糖纳米纤维组成的高强度薄膜指导细胞生长

壳聚糖具有生物相容性和生物降解性。然而，松散的壳聚糖材料强度低，妨碍了其实际使用，不能满足器官的力学性能要求。因此，高强度壳聚糖基材料的构建引起了很多关注。在此，通过在柔和的再生过程中在LiOH / KOH /尿素水体系中的壳聚糖溶液制备了高强度纳米纤维水凝胶和薄膜（CS-E）。在温和条件下（低温乙醇），体系不发生剧烈波动，壳聚糖链周围的碱性脲壳被破坏，裸壳聚糖分子有足够的时间平行排列有序排列，形成相对理想的纳米纤维。纳米纤维物理交联形成CS-E水凝胶，借助扫描电子显微镜和二维广角X射线衍射，可以很容易地通过拉伸将其定向以达到84％的最大取向指数。干燥后的CS-E膜可以任意弯曲和折叠成各种复杂的图案和形状。取向的CS-E薄膜甚至显示出超高的拉伸强度（282 MPa），比通过传统的酸溶解方法制备的壳聚糖薄膜高5.6倍。CS-E水凝胶具有分层的多孔结构，有利于细胞粘附，营养物质的运输和代谢副产物的去除。细胞分析结果表明，CS-E水凝胶没有细胞毒性，成骨细胞可以在其表面粘附，扩散和增殖。此外，定向的CS-E水凝胶可以调节成骨细胞沿定向方向的方向生长，这是基于细胞的丝状伪足在纳米纤维上延伸并粘附的基础。这项工作提供了一种新颖的方法来构造定向的高强度壳聚糖水凝胶和薄膜。