Direct visualization of shear dependent silk fibrillogenesis

Silk's desirable properties originate from the development of a multiscale hierarchical structure produced during spinning, but little is known regarding the origin of the micro and nano fibrils that are consistent and prominent features of spun fibres. This raises the important question: can shearing alone generate these filaments, or is further input and control by the physiology/morphology of the silk duct required? Combining confocal microscopy with rheology provides unique insights into the direct connection between applied shear and the fibrillation of silk proteins in as close to in vivo conditions as currently possible. Our measurements demonstrate that unlike typical synthetic polymers, native silk proteins are able to spontaneously self-assemble, fibrillate and develop hierarchical structures upon controlled shearing, and that the shear induced fibrilogenesis is accompanied by dramatic changes in the rheological response. These observations suggest that natural spinning may be far less complex than previously assumed.