Production of synthetic spider silk fibers.

摘要

Orb-weaving spiders produce six different types of silks, each with unique mechanical properties. The mechanical properties of many of these silks, in particular the dragline silk, are of interest for various biomedical applications. Spider silk does not elicit an immune response, making it an ideal material several biomaterials. However, spiders cannot be farmed for their silk as they are cannibalistic and territorial. The most reasonable alternative for producing spider silk fibers is to utilize genetic engineering to produce the proteins in a foreign host and then spin fibers synthetically. Spider silk-like proteins have been expressed transgenic goats on a scale sufficient to spin synthetic fibers. To spin it, the protein is dissolved in a chaotropic to create a viscous spin dope. This spin dope is extruded into a coagulation bath where it forms a fiber. Fibers spun in this manner have poor mechanical properties, nothing like the natural silk, and are water soluble. By applying a post-spin draw, the mechanical properties of the fibers increase and they are no longer water soluble. This increase occurs because important secondary structures known as beta-sheets form and begin to align parallel to the fiber axis. In the past, post-spin draw has been applied by hand to the fibers after spinning. As such, an unacceptable amount of variation has been reported. The long-term goal of this research was to design, test, and optimize a mechanical system that can create consistent, synthetic spider silk fibers. The data here presented show that stretching the fibers during the spinning process has the same effect on the mechanical properties as hand drawing but with better consistency. Another primary goal of this research was to discover how parameters such as solvents, temperature, speed, additives, and post-spin draw, among other variables, affect the properties of synthetic spider-silk proteins extracted from goat's milk. As part of this research, a mechanical system that can perform these treatments while the fiber is being made was designed, built and tested. This system was built with the intent to inform the creation of a commercial spider silk spinning process.