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International Conference on Innovative Applied Energy    

E-Proceedings ISBN: 978-1-912532-05-6

St Cross College, University of Oxford, United Kingdom

  


 

Intrinsically Toughest Silk for Energy Applications

 


 

Leng-Duei Koh (1) and Yuan Cheng (2)

1. Institute of Materials Research and Engineering (IMRE), 2 Fusionopolis Way, Innovis, Singapore

2. Institute of High Performance Computing (IHPC), 1 Fusionopolis Way, Connexis, Singapore

  

Paper Abstract

As a highly prized textile material since the ancient time, Bombyx mori (B. mori) silk is being actively explored today for advanced uses in modern applications, ranging from antifouling coating for ships' hulls to futuristic electronics (e.g., e-skins). B. mori silk is produced and spun by the silkworms at the end of their fifth instar, mainly in the raw form of parallel running threads of fibroin coated with sericin.

The mechanical properties of silkworm silk fibroin have been widely studied alongside those of spider dragline silk. Both the silks share similar hierarchical structures but possess significant disparity in their mechanical properties. In our study, we describe a facile feeding technique to enhance the mechanical properties of silk produced by B. mori silkworms, leading to the intrinsically toughest silkworm silk.

The structure of silk (fibroin) may be represented by discrete β-sheet crystallites (hereinafter referred to as crystallites) embedded in a matrix of amorphous chains. Silkworm’s silk typically contains crystallites with the length of about 10 nm or more, and such crystallites are longer than those of spider’s silk (6-6.5 nm). Unlike the lengthy crystallites in the native silkworm silks, the toughest silk obtained in our study contains unprecedentedly short crystallites, which corresponds to short β-chains about half the original length.

The length of crystallites in silk was tunable down to 4.69 nm in length (equivalent to about 13 amino acid residues along the β-chain in the β-sheet), which was only about half the length observed in that of control silk (8.84 nm, equivalent to about 25 residues along the β-chain in the β-sheet). The short β-chains will be able to form less number of hydrogen bonds that enables easy unfolding of β-sheet crystallites upon stretching, rendering the silk with greatly enhanced toughness.

Various earlier approaches have been explored to tune or change the structures in silk in order to alter the mechanical properties of silk, for examples, by artificial spinning (i.e. pulling silk from the spinneret of an insect at a controlled drawing rate) or modulated spinning (i.e. allowing the insect to be spun in an electric field). Unlike the feeding technique as described in our study, the artificial spinning of silk did not significantly change the length of crystallites (i.e. 11.49 nm for the artificially spun silk compared to 11.65 nm for the silk used as the control). Besides, the modulated spinning of silk also did not substantially change the length of crystallites (i.e. 20.2 nm for the modulated silk, 20.4 nm for the silk used as the control).

With substantially improved toughness, the enhanced silk can be applied to e-skins, e-bandages, cosmetics, biosensors, wearable displays, implantable devices, artificial muscles, etc, as future work. Taking further, the enhanced silk can also be applied to harvest energy from the environments through its piezoelectric, triboelectric, pyroelectric, thermoelectric, and photovoltaic effects, and will find applications as advanced smart materials or biogenerators to solve some of the challenges in the energy sector 

Paper Keywords
Silk fibroin, toughness, nanocrystallites, energy storage, energy generator, biomaterial.
Corresponding author Biography

Leng-Duei Koh has authored/co-authored >10 research/review papers in peer-reviewed journals and filed several patents on silk protein technologies, including 1. Colorants-Incorporated Silk for Value-Added Cosmetics (SG Patent Application No. 10201610640X, PCT/SG2017/050629, WO 2018/117964 A1) and 2. Intrinsically Toughest Silkworm Silk (SG Patent Application No. 10201705349U). She is a recipient of awards such as the A*STAR InnoVENT Favourite Product Pitch (team), Singapore Mathematical Olympiad (Gold), Australian Mathematics Competition for the Westpac Award (Distinction), National Youth Achievement Award (NYAA), etc. She is experienced in sericulture as well as the regulation/maintenance of Agri-Food & Veterinary Authority of Singapore (AVA)-accredited Bombyx mori (B. mori) silkworm culture facilities. She has led/co-led several industry-aligned projects with MNCs since 2015 and is currently leading a team researching on silk protein technologies in the Institute of Materials Research and Engineering (IMRE), A*STAR

The International Conference on Innovative Applied Energy (IAPE’18)