Molecular spring: from spider silk to silkworm silk

TL;DR

This study combines theoretical modeling and experimental measurements to uncover the structural reasons behind the different mechanical responses of spider and silkworm silks, highlighting the role of $eta$-sheet splitting in their behavior.

Contribution

It introduces a new combined approach of modeling and experiments to explain the structural basis of silk mechanics, emphasizing the role of $eta$-sheet splitting.

Findings

$eta$-sheet splitting explains stress-strain profiles.

Spider silk's high extensibility is due to tiny $eta$-sheets.

Structural factors account for differences in silk mechanics.

Abstract

In this letter, we adopt a new approach combining theoretical modeling with silk stretching measurements to explore the mystery of the structures between silkworm and spider silks, leading to the differences in mechanical response against stretching. Hereby the typical stress-strain profiles are reproduced by implementing the newly discovered and verified "$\beta$-sheet splitting" mechanism, which primarily varies the secondary structure of protein macromolecules; our modeling and simulation results show good accordance with the experimental measurements. Hence, it can be concluded that the post-yielding mechanical behaviors of both kinds of silks are resulted from the splitting of crystallines while the high extensibility of spider dragline is attributed to the tiny $\beta$-sheets solely existed in spider silk fibrils. This research reveals for the first time the structural factors leading to the significant difference between spider and silkworm silks in mechanical response to the stretching force. Additionally, the combination of theoretical modeling with experiments opens up a completely new approach in resolving conformation of various biomacromolecules.