Molecular Dynamics Simulation of Self-Assembly and Tensile Deformation of Silk-Mimetic Polymers.

Silk is a natural biopolymer with outstanding mechanical properties due to its nanocomposite microstructure of crystalline β-sheets in an amorphous matrix. However, there remains a lack of understanding of the relationship between amino acid sequence, supramolecular structure formation, and mechanical properties. In this work, we developed a reactive coarse-grained molecular dynamics model to simulate the self-assembly, tensile deformation, and fracture of a segmented copolymer based on the repetitive core domain of spider dragline spidroins. We find that the β-sheet nanocrystal content is determined by the length ratio of β-sheet to non-β-sheet segments. We reveal that the chain length affects the chain-to-chain network connectivity between the nanocrystals. High nanocrystal content and high connectivity improve the strength and stiffness at the cost of extensibility. Toughness does not continue to increase past a threshold β-sheet-to-non-sheet segment ratio. Our findings provide important insights to guide the rational molecular design of silk-mimetic materials.