Spinning silk ex vivo

This thesis presents new insights into how strong and tough silk fibres can be spun under benign conditions in Nature. This new knowledge provides inspiration for the development of novel bio-inspired processes and feedstocks that will hopefully be able to produce environmentally friendly high-performance materials.
Silk spinning has fascinated humans throughout history and lately, primarily due to its outstanding property-processing relationship. The mechanical properties of silk fibres easily compete with synthetic fibres but are spun at only ambient conditions without the need for harsh solvents. However, recreating this process has proven challenging to date. Although the main mechanisms such as shear flow as well as pH and the ionic environment are well explored, their interactions especially in the context of extensional flow have not been addressed to date.
Therefore, in this work I investigate the effect of extensional flow on native silk proteins. My findings show that although being the main flow field in fibre spinning, extensional flow alone is not sufficient to create silk fibres at natural spinning speeds. Extending this work by combining both a pH change and subsequent extensional stretching, I have shown that native silk proteins exhibit improved spinnability and ultimately can be spun into fibres that even outperform native silk.
Following, I investigated the effect of metal ions on the flow properties of silk and found that the sensitivity of the silk feedstock to alignment and aggregation can be altered by adding metal ions such as KCl, CaCl2, LiBr and LiCl.