Extremely strong and tough chitosan films mediated by unique hydrated chitosan crystal structures

Chitosan-based materials have attracted considerable attention owing to their inherent biodegradability, biocompatibility, and antimicrobial properties. However, the establishment of a scalable technology for the fabrication of high-strength and high-toughness chitosan films remains a major challenge. Herein, a new route for the fabrication of high-strength and high-toughness chitosan films mediated by a unique hydrated chitosan crystal structure is reported, using an aqueous KOH/urea solution as a solvent and an aqueous KCl solution as a neutralization bath. The KCl concentration, neutralization temperature, and neutralization time significantly affect the self-assembly and lateral aggregation of chitosan chains and the microstructure and morphology of the chitosan hydrogels and films. Furthermore, stretching orientation endows the chitosan films with a high tensile strength, Young’s modulus, and work of fracture of 579 ± 52 MPa, 18.8 ± 1.5 GPa, and 26.7 ± 6.9 MJ m−3, respectively. To the best of our knowledge, the chitosan films developed in this study are the first example of extremely high-strength and high-toughness chitosan films. We believe that our findings will be useful for the fabrication of polysaccharide-based films with excellent mechanical properties and in broader applications in the fields of biomedicine, flexible bioelectronics, water treatment, and food packaging.