Bioinspired Stiffness-Controlled Protein Filaments Through Molecular Self-Assembly of Protein-Based Rod-Coil Block Copolymers

Natural materials such as collagen, microtubules, and muscle fibers exhibit exceptional mechanical properties, including reversible stretchiness, toughness, and fatigue resistance. These properties stem from their complex hierarchical structures, which are formed through the self-assembly of stiffness-controlled filaments and fibrils. Achieving an understanding of this self-assembly process and the mechanisms that generate the stiffness of these filaments is essential for replicating the structural hierarchies and mechanical properties observed in natural fibers. Proteins, which provide highly controllable monomer units and diverse functionalities, can be engineered to facilitate the self-assembly of bioinspired filaments. However, a major challenge in this process is controlling the stiffness of these self-assembled protein filaments. While proteins hold great promise for forming these structures, the methods for fine-tuning their stiffness during self-assembly remain elusive.<br/> <br/>Here, we present bioinspired stiffness-controlled protein filaments achieved through the molecular self-assembly of designed protein polymers composed of coil-like and rod-like structures. Using molecular dynamics simulations, biosynthesis, and characterization techniques, we discovered that the coil-like protein component imparts high flexibility to the filament structures, generating curvature, while the rod-like protein component enhances stiffness. This finding prompts the investigation of the fundamental relationship between the chain topology of designed protein polymers and their composition, structure, and length, as well as their interdependence. Our work provides valuable insights into the scientific principles underlying protein filaments, paving the opportunity for the development of biomimetic hierarchically structured protein fibers. These advancements have the potential to advance healthcare applications, including drug delivery, tissue engineering, and regenerative medicine.