Spiders sprayed with water containing carbon nanotubes and graphene flakes have created the toughest fibres ever measured.
A spiders silk is one of the most extraordinary materials known to science and the protein fibres, spun by a spider to make its web, is stronger than almost anything that humans can make today.
The dragline silk spiders use to make the web’s outer rim and spokes matches high-grade alloy steel for tensile strength but is about a sixth as dense. It is also highly ductile and is capable of stretching to five times its length. This combination of strength and ductility makes spider silk extremely tough, matching the strength of state-of-the-art fibres such as Kevlar.
Researchers from the University of Trento in Italy have found a way to incorporate carbon nanotubes and graphene into spider silk to increase its strength and toughness beyond anything that has been seen before. The resulting material has properties such as fracture strength, Young’s modulus, and toughness modulus higher than anything ever measured.
The team started with 15 Pholcidae spiders which they kept in controlled conditions in their lab. After collecting initial web samples, they sprayed the spiders with water which included the nanotubes, measuring the mechanical properties of the silk that the spiders produced.
For each strand of silk, they fixed the fibre between two C-shaped cardboard holders and placed it in a device that can measure the load on a fibre with a resolution of 15 nano-newtons and any fibre displacement with a resolution of 0.1 nanometers.
Emiliano Lepore at the University of Trento working on the project said;
We measure a fracture strength up to 5.4 GPa, a Young’s modulus up to 47.8 GPa and a toughness modulus up to 2.1 GPa. This is the highest toughness modulus for a fibre, surpassing synthetic polymeric high performance fibres (e.g. Kelvar49) and even the current toughest knotted fibres.
How the spiders incorporate carbon nanotubes and graphene flakes into their silk is not clear at this stage. The team use spectroscopic methods to show that the carbon-based materials are present in the fibre but are unable to show exactly how.
One possible theory that the researchers cannot rule out is that the silk becomes coated with these carbon-based materials after it is spun, however the researchers said this is unlikely because the structure would not have the strength they measured. A more likely theory is that the spiders ingest the water along with the carbon-based materials and these are then incorporated into the fibre as it is spun. So the nanotubes and graphene end up in the central part of each fibre, where it can have the biggest impact on its strength.
Although at the early stages the researchers say that a similar approach could be used on other organisms, and this new reinforcing procedure could also be applied to other animals and plants, leading to a new class of bionic materials.