High-Strength Films Consisted of Oriented Chitosan Nanofibers for Guiding Cell Growth.

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.