Employing spinning conditions to control the mechanical response of spider silk fibers

Spider silk is an extraordinary bio-material known for its exceptional combination of strength, stiffness, and extensibility. As such, it inspires the design of high-performance biomimetic fibers. Interestingly, experimental evidence suggests that the mechanical response of silk fibers is highly sensitive to the spinning conditions (which include naturally spun fibers, fibers forcibly silked in air, and fibers forcibly silked in water), as well as the reeling speed and silking stress. On a microstructural level, this occurs since the spinning environment, process, and conditions affect the intercrystallite distance, the initial chain length, and the network alignment. In this work, we present a microscopically motivated energy-based model that links the spinning conditions to the microstructure, and therefore enables a better understanding of its influence on the macroscopic mechanical behavior. Our model captures key physically interpretable features of the silk network, including the role of intermolecular hydrogen bonds, chain alignment, initial chain stretch, and crystallite size. The proposed framework is validated against various experimental data of uniaxially stretched silk fibers retrieved under different spinning conditions. These findings offer a mechanistic foundation for the rational design of synthetic silk-like fibers with tunable mechanical properties through controlled processing, highlighting the critical interplay between microstructure and macroscopic performance.