http://www.newscientist.com/article/dn2 ... Uzz5vlVikoSpider-Man would be so envious. Spiders have woven webs infused with carbon nanotubes and even graphene, raising the prospect of new materials with record-beating properties.
Graphene – sheets of carbon just one atom thick – is one of the strongest artificial materials, and spider silk is one of the strongest natural ones. So Nicola Pugno of the University of Trento, Italy, wondered what would happen if you combined them.
Pugno and his colleagues captured five spiders from the Pholcidae family and sprayed them with a mixture of water and graphene particles 200 to 300 nanometres wide. They also sprayed another 10 spiders with carbon nanotubes and water to compare the effects of the two materials.
Some spiders produced below-par silk, but others got a major boost. The best fibres came from a spider dosed with nanotubes: it was around 3.5 times as tough and strong as the best unaltered silk, spun by the giant riverine orb spider.
From spiders to silkworms
The only natural material that is stronger than orb spider silk is the material that the teeth of molluscs called limpets are made out of, Pugno and colleagues revealed earlier this year. The molluscs' teeth stretch more than the spider silk, but are much less tough, meaning they crack more easily.
The team isn't sure how the graphene and carbon nanotubes end up in the silk. One possibility is that the carbon coats the outside of the strands, but Pugno thinks that would not be enough to account for the increase in strength. Instead, he believes the spiders mop up materials in their environment and incorporate them into the silk as they spin. This comes at a cost, however – four of the spiders died soon after being sprayed.
At this early stage it's not clear how such a material will be used, but one possibility is a giant net capable of catching falling aircraft, suggests Pugno. The team also plans to investigate other ways of producing bionic materials, such as dosing silkworms with artificial substances. "This concept could become a way to obtain materials with superior characteristics," he says.
Original paper:
http://arxiv.org/ftp/arxiv/papers/1504/1504.06751.pdfAbstract
The protein matrix and hard tissues of insects1,2,3,4, worms5,6,7, ants8 and spiders9,10 naturally incorporates metals, such as zinc1,2,3,5,8,9,10, manganese2,3,9and copper6,7. This leads to mechanical hardening of teeth9, jaws5,6,7, mandibles1,2,3,4,8,, ovipositors8 and to an enhancement of silk toughness10. Thus, the artificial incorporation of metals, or even insulating or semiconducting materials, into these protein structures could be exploited to obtain a reinforced matrix. A number of groups reported the introduction of metals, such as zinc1,2,3,5,8,9, titanium10, aluminium5, copper6,7 and lead6 in the protein structure of spider silk through multiple pulsed vapour-phase infiltrations10. This allowed to increase its toughness modulus from 131 MPa8 up to 1.5 GPa10. Biomaterials with increased mechanical or conductive properties could find innovative applications in garment textiles11 and medical nerve regeneration12. It was suggested to coat spider silks with amine-functionalized multiwall carbon nanotubes, to produce electrically conducting fibres9, or with cadmium telluride13, magnetite1 or gold1,2 nanoparticles, for fluorescent13 , magnetic13,14 and electronic applications13,15. However, to the best of our knowledge, the incorporation of materials in the inner protein structure of spider silk has not been achieved to date. Here, we report the production of silk incorporating graphene and carbon nanotubes directly by spider spinning, after spraying spiders with the corresponding aqueous dispersions. We observe a significant increment of the mechanical properties with respect to the pristine silk, in terms of fracture strength, Young’s and toughness moduli. 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, or 1567 J/g, which, to the best of our knowledge, is the highest reported to date, even when compared to the current toughest knotted fibres8. This approach could be extended to other animals and plants and could lead to a new class of bionic materials for ultimate applications.
