Mechanically strong all-chitin filaments: Wet-spinning of β-chitin nanofibers in aqueous NaOH

Herein, a facile wet-spinning strategy was used for the fabrication of mechanically strong all-chitin filaments from an aqueous NaOH solution using β-chitin nanofibers (β-ChNFs). It is hypothesized that to reach high mechanical performance it is important to preserve the crystalline structure of chitin during fabrication. To explore this possibility, β-ChNFs were disintegrated from squid pens by a mild procedure and showed a uniform diameter of 10-25 nm, length of a few microns, and a high aspect ratio of more than 200. An interesting finding was that gel-like β-ChNF filaments were directly formed in aqueous NaOH without using any organic or ionic agents. The gelation of β-ChNFS under alkali treatments contributed to the construction of strong nanonetworks and thus facilitated the formation of high-strength filaments. The resulting all-chitin filaments showed a high tensile strength and Young's modulus of 251.3 ± 12.45 MPa and 12.1 ± 0.72 GPa, respectively, which were further investigated for utilization as flexible sensors. The advantages of this strategy included the lack of use of any toxic solvents and the achievement of high mechanical performance for the all-chitin filaments. We believe that this wet-spinning approach may promote the functional utilization of chitin to develop high-strength filaments in smart textiles, biosensors, and structural reinforcements.