Hydrothermal Effect on Mechanical Properties of Nephila pilipes Spidroin.

Hsuan-Chen Wu,Hwo-Shuenn Sheu,I-Min Tso,Jen-Chang Yang,Liang-Yu Chang,Aditi Pandey,Thomas Chung-Kuang Yang,Chieh-Yun Hsu

doi:10.3390/polym12051013

Abstract

The superlative mechanical properties of spider silk and its conspicuous variations have instigated significant interest over the past few years. However, current attempts to synthetically spin spider silk fibers often yield an inferior physical performance, owing to the improper molecular interactions of silk proteins. Considering this, herein, a post-treatment process to reorganize molecular structures and improve the physical strength of spider silk is reported. The major ampullate dragline silk from Nephila pilipes with a high β-sheet content and an adequate tensile strength was utilized as the study material, while that from Cyrtophora moluccensis was regarded as a reference. Our results indicated that the hydrothermal post-treatment (50–70 °C) of natural spider silk could effectively induce the alternation of secondary structures (random coil to β-sheet) and increase the overall tensile strength of the silk. Such advantageous post-treatment strategy when applied to regenerated spider silk also leads to an increment in the strength by ~2.5–3.0 folds, recapitulating ~90% of the strength of native spider silk. Overall, this study provides a facile and effective post-spinning means for enhancing the molecular structures and mechanical properties of as-spun silk threads, both natural and regenerated.

Highlights

Spider silks are protein fibers consisting of hierarchically synergized protein motifs that account for outstanding mechanical properties and biocompatibility [1,2,3]
The liquid crystalline model describes the transformation of liquid silk protein into fibers formed within the spinning duct of spiders, which in turn is accompanied by increasing shear forces that lead to the formation of intermolecular secondary structures
The spidroin-aligned secondary structures (α-helices, random coil, and β-turns) govern the mechanical properties, e.g., hydrophobic antiparallel β-sheets that provide strength and β-spirals that offer the elasticity of the spider silks [9,11,13,14,15,16,17]

Summary

Introduction

Spider silks are protein fibers consisting of hierarchically synergized protein motifs that account for outstanding mechanical properties (toughest material in nature) and biocompatibility [1,2,3]. It is generally recognized that the extraordinary performance of the spider silk resides in the well-organized inter- and intra-molecular chains of silk proteins. Those hierarchically supra-molecular silk structures are greatly controlled by the sophisticated spinning process occurring in the spinning ducts of the spiders. The liquid crystalline model describes the transformation of liquid silk protein into fibers formed within the spinning duct of spiders, which in turn is accompanied by increasing shear forces that lead to the formation of intermolecular secondary structures. The spidroin-aligned secondary structures (α-helices, random coil, and β-turns) govern the mechanical properties, e.g., hydrophobic antiparallel β-sheets that provide strength and β-spirals that offer the elasticity of the spider silks [9,11,13,14,15,16,17]

Methods

Results

Conclusion