The Effect of the Loading–Unloading Cycles on the Tensile Behavior and Structures of Spider Tubular Gland Silk

There exists a significant correlation between the microstructural evolution and the mechanical properties of fibers during repeated loading and unloading cycles. Nevertheless, the influence of deformation and the duration of intervals on the structural and tensile behavior of spider silk after repeated stretching at a given strain value has been rarely reported, with the exception of studies focusing on the major ampullate gland silk (Mas) of the spider. In order to investigate the effects of repeated stretching on the structural and mechanical behavior of spider tubular gland silk (Tus), the tensile properties and the changes in semiquantitative protein secondary structure of Argiope bruennichi Tus during loading–unloading cycles were characterized. The results indicate that the typical tensile behavior curves of Tus were irreversibly modified to resemble those of Mas, demonstrating a clear yield region accompanied by a necking phenomenon. The Tus displays remarkable characteristics of repeated stretching and mechanical memory, and it is capable of reproducing the tensile behavior of fibers subjected to one stretch, independent from its previous loading history. The above phenomenon may be caused by repeated stretching leading to the damage and reconstruction of protein structures, including an increase in α-helix content and the rearrangement of spider-silk proteins, enabling them to reproduce their mechanical behavior. These findings may provide valuable insights for the biomimetic design of novel fiber materials, such as the spider silk gut, through the artificial stretching of spider silk glands.