Simultaneous effect of strain rate and humidity on the structure and mechanical behavior of spider silk

Kenjiro Yazawa,Hiroyasu Masunaga,Y Norma-Rashid,Ali D Malay,Keiji Numata

doi:10.1038/s43246-020-0011-8

Abstract

Spider dragline silk fibers are important in nature for capturing prey and as a lifeline. However, spider silk is exposed to a range of humidity and deformation conditions, and it is important to understand what effect these have on its properties. Here, we simultaneously investigated the effect of a wide range of strain rates on the structural and mechanical properties of spider silk under different humidity conditions. The toughness of the silk fiber was enhanced under mild humidity and high deformation rate conditions, which occur in the natural habitat of spiders. Structural changes in the fiber upon tension were monitored with a wide-angle X-ray scattering system, showing that during stretching the orientation of the crystalline β-sheets aligned, whereas the crystallite size decreased. These findings help to understand the link between the structural changes and mechanical behavior of spider silk.

Highlights

Spider dragline silk fibers are important in nature for capturing prey and as a lifeline
Dragline silk fibers consist of crystalline β-sheets embedded in amorphous regions consisting of α-helices, β-turns, 310-helices, and random structures; it is possible that the deformation rate can affect the mechanical responses of spider dragline silk
We should consider the effect of humidity to discuss the strain rate-dependent mechanical parameters because the physical properties of spider dragline silk fibers are sensitive to hydration effects[5,11,12,13,14,15,16,17,18,19]

Summary

Introduction

Spider dragline silk fibers are important in nature for capturing prey and as a lifeline. We perform simultaneous WAXS and tensile tests under different strain rates and RH conditions to clarify the relationships between deformation rate and humidity on the mechanical and nanoscale structural properties of spider dragline silk fibers. Tensile tests of dragline silk fibers were conducted at RH43% under different strain rates from 3.3 × 10−5 to 3.3 s−1.

Results

Conclusion