Recreating Silk's Fibrillar Nanostructure by Spinning Solubilized, Undegummed Silk

Area of Science:

• Biomaterials Science
• Polymer Chemistry
• Textile Engineering

Background:

• Silkworm silk's exceptional toughness stems from its hierarchical nanofibrillar structure.
• Artificial silk fiber production is hindered by differences between native feedstock and processed silk solutions.
• Degumming silk removes sericin, altering its properties and making it difficult to replicate native silk's structure.

Purpose of the Study:

• To develop a method for dissolving silk without degumming, preserving native fibroin and sericin.
• To investigate the liquid-liquid phase separation behavior of undegummed silk solutions.
• To produce and characterize artificial silk fibers from undegummed solutions and compare them to degummed counterparts.

Main Methods:

• Dissolving raw silk without degumming to obtain a solution of intact fibroin and sericin.
• Characterizing the solution's phase behavior, including liquid-liquid phase separation and gelation kinetics.
• Wet spinning of both undegummed and degummed silk solutions into fibers.
• Analyzing fiber properties (strength, toughness) and nanostructure (using ultrasonication).

Main Results:

• Undegummed silk solutions exhibit liquid-liquid phase separation above 10% (wt/wt), enhancing stability and delaying gelation.
• Fibers spun from undegummed solutions were 8x stronger and 218x tougher than those from degummed silk.
• Ultrasonication revealed a hierarchical nanofibrillar structure (≈20 nm) in undegummed fibers, absent in degummed fibers.

Conclusions:

• Preserving the molecular integrity of silk proteins (fibroin and sericin) is crucial for artificial fiber production.
• Liquid-liquid phase separation in undegummed silk solutions facilitates the formation of native-like hierarchical structures.
• This approach offers a new pathway to recreate high-performance silk fibers with properties comparable to native silk.