UC Berkeley

Silkworm silk fibers have been in use for over 5000 years in clothing and textiles. These fibers are unwound from the cocoon that is spun by the worm to protect itself during metamorphosis. More recently, spider silk has received a significant amount of research attention due to its exceptional mechanical properties. Spider silk has a breaking strength comparable to steel (>1GPa), and an extensibility closer to nylon (>30%), giving it an extremely high toughness (energy to breakage). Unlike silkworms, however, spiders cannot be farmed for mass silk cultivation. Therefore, a tremendous amount of effort has been put forth toward understanding how silk fibers are spun, and how to reproduce them artificially. The problem is two-fold: silk protein must be obtained (generally through dissolution of cocoons) and that protein must be spun into a fiber. All spinning efforts to date have failed to produce native-quality fibers, and it has become apparent that the complexity of the silk gland is crucial to replicate during the spinning process. Furthermore, efforts to process silk proteins have led to the realization that silk protein provides a unique platform material for a wide variety of biotechnologies. This dissertation focusses on the processing of silk proteins into fibers and various microstructures. Simulations of flow in the spider and silkworm silk gland demonstrate the importance of gland geometry on fiber formation. A hydrodynamic focussing system is developed to spin silkworm fibers, as well as extended to form silk microspheres. A biomimetic microfluidic system is developed that mimics the silk gland geometry and also allows mass transport into and out of the silk solution during spinning. Finally, dissolved silkworm silk is demonstrated to be a useful material for the high fidelity and high aspect ratio molding of nano- and micro-structures.