Synthesis and In Situ Thermal Induction of β-Sheet Nanocrystals in Spider Silk-Inspired Copolypeptides

Spider silk, known for its exceptional tensile strength, extensibility, and toughness, continues to inspire advancements in polymer and materials science. Despite extensive research, synthesizing materials that encompass all these properties remains a significant challenge. This study addresses this challenge by developing high molecular-weight multiblock synthetic copolypeptides that mimic the hierarchical structure and mechanical properties of spider silk. Using autoaccelerated ring-opening polymerization of <i>N</i>-carboxyanhydrides, we synthesized copolypeptides featuring transformable β-sheet blocks. These blocks retain a helical structure during synthesis but transition into β-sheet nanocrystals in situ during solvent-free thermal mechanical processing. Compression molding was employed to induce hierarchical ordering within the copolypeptide films, resulting in a solid "liquid crystalline" structure that undergoes a temperature-induced α-to-β structural transformation. This transformation integrates β-sheet nanocrystals throughout the helical block matrix, significantly enhancing the material's mechanical performance. Our innovative synthesis and processing strategy, which involves alternating sequences of α-helical and β-sheet blocks with various β-sheet-forming NCAs, enables the customization of diverse mechanical characteristics. These advancements not only deepen our understanding of the fundamental design principles of spider silk but also pave the way for a new generation of high-performance, silk-inspired synthetic copolypeptides with broad application potential.