Mesoscale structure development reveals when a silkworm silk is spun

Area of Science:

• Biomaterials Science
• Polymer Science
• Textile Engineering

Background:

• Silk fiber mechanical properties arise from a complex multi-scale hierarchical structure formed during spinning.
• Understanding the sequential events in silk spinning is crucial for controlling fiber properties.

Purpose of the Study:

• To investigate the mesoscale structural changes during silk fiber formation.
• To identify and characterize the distinct stages of silk structure development.
• To define the consolidation phase and the role of transient water pockets.

Main Methods:

• Ex vivo processing of Bombyx mori silkworm silk solution to arrest the spinning process.
• Analysis of mesoscale structures, including the emergence and disappearance of 'water pockets'.
• Modeling and validation of post-draw processing effects on mechanical properties and hierarchical structure.

Main Results:

• Identified three key stages: gelation, fibrilization, and consolidation.
• Characterized 'water pockets' as transient structures resulting from protein dehydration, phase separation, and nanofibril assembly.
• Demonstrated that nanofibril coalescence during consolidation removes water pockets and refines hierarchical structure.
• Validated that post-draw processing enhances mechanical properties.

Conclusions:

• The consolidation phase is critical, marked by water pocket removal via nanofibril coalescence.
• Insights into spinning events enable a robust definition of 'spun' silk.
• Understanding these stages allows for better control over silk fiber properties and potential applications.