Work started in 2001 and two years later results were published in Nature Materials. Nano tape is one of the first developments of synthetic setae, which arose from a collaboration between the Manchester Centre for Mesoscience and Nanotechnology, and the Institute for Microelectronics Technology in Russia. The shear adhesion allows the tape to be easily peeled off, in the manner a gecko lifts its foot and since the carbon nanotube arrays leave no residue on the substrate, the tape can be reused many times. Nano tapes mimic these structures with carbon nanotube bundles, which simulate setae, and individual nanotubes, which simulate spatulas, to achieve macroscopic shear adhesion and to translate the weak van der Waals interactions into high shear forces. The shear adhesion is achieved by forming and breaking van der Waals forces between these microscopic structures and the substrate. On a gecko's foot, micrometer-sized elastic hairs called setae are split into nanometer-sized structures called spatulas. The best results came from a polyurethane filament brushed in silicone oil droplets, with a maximum extension of a remarkable 1,500%.Geckos show a remarkable ability to climb smooth vertical surfaces at high speeds, exhibiting both strong attachment and easy rapid removal, or shear adhesion, of their feet.

With an understanding of the mechanics of the silk, Elettro’s team put together five synthetic versions. “At that point, the surface tension of the liquid almost is taking over, keeping the entire structure taut and under tension.” “The more you shrink the silk or move the end points closer together, the more the silk buckles and then starts to coil within the droplet.

“It’s actually quite interesting for me, on the spider biology side of things, how they achieve that,” says Douglas Little, a physicist at Macquarie University in Sydney, Australia, who works with spider silk but was not involved in the study. Its secret lies, he discovered, in the way the web spools inside the droplets of glue as a sort of “liquid wire”. “This stretchiness confers spider silk a strength tenfold that of a natural or synthetic rubber,” says Elettro. The study, led by Hervé Elettro from France’s Université Pierre et Marie Curie with colleagues from Oxford University, analysed capture silk – webbing designed to immobilise prey – which can be stretched to three times its web length without breaking and still returns to its original state, with no sagging, when relaxed. The discovery could result in a breakthrough in wire technology for micro-fabrication. But a new study has found that the glue is the reason webs can be stretched to many times its original length while still remaining taut.

The sticky surface of silk produced by Australian Golden Orb Weavers is, like most spider webs, designed to glue insects down long enough for them to become a meal. Scientists have created five synthetic ‘liquid wires’ that mimic the mechanics of spiders’ silk.

New sticky nano technology