Rehydration of Nanocellulose Films in an Aqueous Silk Fibroin Solution for Facile Fabrication of Strong Composites

Utilizing the swelling behavior of the cellulose nanofiber network structure in water, we present a facile approach to prepare cellulose nanofibrils (CNFs)/regenerated silk fibroin (RSF) composites with improved mechanical properties and biocompatibility by rehydrating CNF films in RSF water solutions. Two rehydratable nanocellulose film structures were employed: one featuring random-in-plane distributed CNF (ROCNF) and the other containing nematic-ordered CNF (NOCNF). These films were rehydrated to facilitate the infiltration of RSF, resulting in composites where RSF interpenetrates the CNF network. The composites showed a higher density, enhanced optical transparency, and synergistically increased modulus, yield strength, and tensile strength, in contrast to the neat CNF films. Particularly, the NOCNF80/RSF20 composites exhibited a Young’s modulus of 20.1 GPa and a tensile strength of 429 ± 17 MPa in the dry state and a Young’s modulus of 78.6 MPa and a tensile strength of 1.66 MPa in phosphate-buffered saline (PBS). Biocompatibility assessed by an in vitro cell test confirmed the ability of the CNF/RSF composites to support the adhesion and growth of L929 fibroblasts, highlighting the potential for various applications as biomedical materials. This approach provides promising opportunities for producing strong and functional CNF-based composites with water-soluble polymers and latexes for diverse applications in different fields.