Nanomaterials help spiders spin tougher silk

Italian and UK researchers have found a way to make Spider silk stronger, using various spider species and carbon nanotubes or graphene.

The research team, led by Professor Nicola Pugno at the University of Trento, Italy, succeeded in having their spiders produce silk with up to three times the strength and ten times the toughness of the regular spider silk.

Humans have used silkworm silks widely in textiles for thousands of years and, in the last few decades in biomedical applications, but recently research has focussed on spider silk, as it has extremely promising mechanical properties. For example, it is among the best spun polymer fibres in terms of tensile strength, ultimate strain, and toughness, even when compared to synthetic fibres such as Kevlar.

Prof Pugno explained: “We already know that there are biominerals present in in the protein matrices and hard tissues of insects, which gives them high strength and hardness in their jaws, mandibles and teeth, for example. Our study looked at whether spider silk’s properties could be ‘enhanced’ by artificially incorporating various different nanomaterials into the silk’s biological protein structures.”

To do this, the team exposed three different spider species to water dispersions containing carbon nanotubes or graphene. After collecting the spiders’ silk, the team tested its tensile strength and toughness.

Prof Pugno said: “We found that the strongest silk the spiders spun had a fracture strength up to 5.4 gigapascals (GPa), and a toughness modulus up to 1,570 joules per gram (J/g). Normal spider silk, by comparison, has a fracture strength of around 1.5 GPa and a toughness modulus of around 150 J/g.”

The researchers say this is the highest fibre toughness discovered to date, and the strength is comparable to that of the strongest carbon fibres or limpet teeth. They add that it is early days for the research, but the results could pave the way to exploiting the naturally efficient spider spinning process to produce reinforced bionic silk fibres. These silks’ high toughness and resistance to ultimate strain could be used in applications such as parachutes.

Prof Pugno added: “This process of the natural integration of reinforcements in biological structural materials could also be applied to other animals and plants, leading to a new class of ‘bionicomposites’ for innovative applications.”

Author
Tom Austin-Morgan

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