Spider dragline silk composite films doped with linear and telechelic polyalanine: Effect of polyalanine on the structure and mechanical properties

Kousuke Tsuchiya,Hiroyasu Masunaga,Keiji Numata,Takaoki Ishii

doi:10.1038/s41598-018-21970-1

Kousuke Tsuchiya, Hiroyasu Masunaga + Show 2 more

Open Access

https://doi.org/10.1038/s41598-018-21970-1

Copy DOI

Abstract

Spider dragline silks have attracted intensive attention as eco-friendly tough materials because of their excellent mechanical property and biomass-based origin. Composite films based on a recombinant spider dragline silk protein (ADF3) from Araneus diadematus were prepared by doping with linear or telechelic poly(l-alanine) (L- or T-polyA, respectively) as a reinforcing agent. Higher tensile strength and toughness of the composite films were achieved with the addition of polyA compared with the tensile strength and toughness of the silk-only film. The difference in the reinforcing behavior between L- and T-polyA was associated with their primary structures, which were revealed by wide angle X-ray diffraction analysis. L-polyA showed a tendency to aggregate in the composite films and induce crystallization of the inherent silk β-sheet to afford rigid but brittle films. By contrast, T-polyA dispersion in the composite films led to the formation of β-sheet crystal of both T-polyA and the inherent silk, which imparted high strength and toughness to the silk films.

Highlights

Natural silk fibers are composite materials composed mainly of multiple proteins along with other minor components such as lipids, glycoproteins, and inorganic salts[1,2]
The recombinant protein of major ampullate spidroin 2 (MaSp2) from Araneus diadematus (ADF3) was used to fabricate composite films doped with polyalanine derivatives
The recombinant spider silk protein was synthesized in Escherichia coli Rosetta (DE3) using pET22b(+) vector (Fig. 1)

Summary

Introduction

Natural silk fibers are composite materials composed mainly of multiple proteins along with other minor components such as lipids, glycoproteins, and inorganic salts[1,2]. The dragline silk proteins compose of a long repetitive middle domain and highly conserved N- and C-terminal domains, and these assemble into higher-order structures to give the silk fiber high tensile strength and toughness. Scheibel et al demonstrated that recombinant spider silk fiber shows excellent toughness as high as that of the natural silk fiber, the profile of the stress-strain curve indicated greater ductility[21]. These recombinant spider silk materials consist of a partial repetitive sequence or a combination of the repetitive domain and terminal domain(s) extracted from the whole sequence of spider silk proteins. The relationship between the mechanical properties and the secondary structures of the composite films was investigated by tensile deformation tests and WAXD analysis

Methods

Results

Conclusion