Bioinspired Tough and Strong Fibers with Hierarchical Core-Shell Structure

Strong and tough bio-based fibers are attractive for both fundamental research and practical applications. In this work, strong and tough hierarchical core-shell fibers with cellulose nanofibrils (CNFs) in the core and regenerated silk fibroins (RSFs) in the shell are designed and prepared, mimicking natural spider silks. CNF/RSF core-shell fibers with precisely controlled morphology are continuously wet-spun using a co-axial microfluidic device. Highly-dense non-covalent interactions are introduced between negatively-charged CNFs in the core and positively-charged RSFs in the shell, diminishing the core/shell interface and forming an integral hierarchical fiber. Meanwhile, shearing by microfluidic channels and post-stretching induce a better ordering of CNFs in the core and RSFs in the shell, while ordered CNFs and RSFs are more densely packed, thus facilitating the formation of non-covalent interactions within the fiber matrix. Therefore, CNF/RSF core-shell fibers demonstrate excellent mechanical performances; especially after post-stretching, their tensile strength, tensile strain, Young's modulus, and toughness are up to 635 MPa, 22.4%, 24.0 GPa, and 110 MJ m(-3), respectively. In addition, their mechanical properties are barely compromised even at -40 and 60 degrees C. Static load and dynamic impact tests suggest that CNF/RSF core-shell fibers are strong and tough, making them suitable for advanced structural materials.