Spinning Beta Silks Requires Both pH Activation and Extensional Stress

Abstract

Synthetic silk production has undergone significant technological and commercial advances over the past 5 years, with fibers from most labs and companies now regularly matching the properties of natural silk by one metric or another. Yet the fundamental links between silk protein processing and performance remain largely unresolved and fiber optimization is commonly achieved through non-natural methods. In an effort to address this challenge, data that closes this loop of processing and performance is presented by spinning a native silk feedstock ex vivo into a near-native fiber using just two naturally occurring parameters; pH activation and extensional flow (i.e., spinning rate). This allows us to link previous experimental and modelling hypothesis surrounding silk's pH responsiveness directly to multiscale hierarchical structure development during spinning. Finally, fibers that match, and then exceed, natural silk's mechanical properties are spun and understood by rate of work input. This approach not only provides energetic insights into natural silk spinning and controlled protein denaturation, but is believed will help interpret and improve synthetic silk processing. Ultimately, it is hoped that these results will contribute towards novel bioinspired energy-efficient processing strategies that are driven by work input optimization and where excellent mechanical properties are self-emergent.

Fiber Formation and Mechanical Properties of Bombyx mori Silk Are Regulated by Vacuolar-Type ATPase

“…The rheological properties of silk are also affected by the pH, and lowering the pH induces the formation of a gel . Recent evidence shows that the pH activation prior to extensional flow is essential for the processing of native silk proteins . Furthermore, the pH gradient shortens the distance between molecules, the aggregation and interaction of the silk protein molecules improve the hydrophobicity of the silk protein.…”

“…36 Recent evidence shows that the pH activation prior to extensional flow is essential for the processing of native silk proteins. 38 Furthermore, the pH gradient shortens the distance between molecules, 39 the aggregation and interaction of the silk protein molecules improve the hydrophobicity of the silk protein. The increased hydrophobicity further induces the water removal of the silk protein and increases the concentration of silk.…”

Biomimetic Microadhesion Guided Instant Spinning

“…It was explored that the silkworm spinning was achieved by the pulling of nascent silk fibers (Figure b). ,, The silkworm first spits out the silk coated with sericin to adhere to the wood surface. The silkworm swings its head up and pulls the silk out of the adhesion spot.…”

Charge screening wormlike micelles affects extensional relaxation time and noodle formation

“…1,7 Forming well-defined structures that can maintain sufficient tensile stress to be useful relies on both a pushing force and a pulling force, as reported for effective silk formation. 8,9 A suitable self-assembling molecule that can be used to form well-defined noodles is 1ThNapFF (Figure 1a). 7 At high pH, wormlike micelles (WLM) are formed as the terminal carboxylic acid is deprotonated.…”

“…1,7 Forming well-defined structures that can maintain sufficient tensile stress to be useful relies on both a pushing force and a pulling force, as reported for effective silk formation. 8,9…”