A nanofibril network model of biological silks

Biological silks produced by, for examples, spiders and silkworms exhibit exceptional mechanical properties, including high strength, toughness, and extensibility, which arise from their optimized hierarchical structures. Understanding the relationship between their structures and properties is crucial for the design of bioinspired materials. However, it remains a challenge to recapitulate their macroscopic mechanical behaviors of biological silks with a micromechanical model that integrates the physical mechanisms of deformation and failure, such as molecular unfolding and nanofibrous remodeling. In this paper, we propose a nanofibril network (NFN) model to analyze the deformation, damage, and fracture processes of biological silks. The NFN model reveals how molecular unfolding affects the deformation and fracture of biological silks at the nanofibrous scale. It is observed that molecular unfolding consecutively occurs, evolving into band or elliptical morphologies with increasing tensile strain. Intermolecular hydrogen bonds tend to stabilize the expansion of unfolding zones. The NFN model also unveils how the instability of molecular unfolding is suppressed by nanofibrous architecture and how intermolecular hydrogen bonds interact with intramolecular unfolding to toughen the biological silk. This work provides a theoretical tool for studying and designing biomimetic nanofibrous materials.