Preparation of transparent fibroin nanofibril-reinforced chitosan films with high toughness and thermal resistance

Silk fibroin nanofibrils can be obtained through fibrillation of fibroin fibers using wet-mechanical methods with a strong shear force. These nanofibers possess favorable mechanical properties and high thermal stability due to the secondary beta-sheet structure of native fibroin. Consequently, ductile chitosan composite films with high thermal stability and optical transparency were successfully fabricated through reinforcement with native fibroin nanofibrils. The crystallinity of the composite films increased with the fibroin nanofibril ratio. Furthermore, the swelling ratio of the composite film decreased with the increasing fibroin nanofibril ratio, suggesting the pres-ence of interactions, such as hydrogen bonding and/or electrostatic interactions, between chitosan and fibroin nanofibrils. This composite film can be used in environments with high moisture content and high temperatures and is anticipated to be utilized in a wide range of applications (e.g., food packaging, cosmetics, and biomaterials).