The team’s approach was relatively straightforward. They started with 15 Pholcidae spiders collected from the Italian countryside, which they kept in controlled conditions in their lab. After collecting dragline silk samples to use as a reference, the researchers then sprayed the spiders with a nanotube-infused water solution and measured the strength of the silk they produced.
Some of the spiders spun sub-par silk, and a few of them even dropped dead after being sprayed with the solution. But a few of them proceeded to do something amazing — they produced nanotube-reinforced silk draglines with strength and toughness far beyond any fiber ever created.
To measure the mechanical properties of the silk, the researchers placed each fiber between two C-shaped cardboard holders, and then put them inside a special device that can measure the load on a fiber in a number of different ways.
The results were impressive — if a tad bit confusing. “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,” the researchers explain. That probably doesn’t make much sense to you unless you’re a physicist or an engineer, but to help put those numbers in perspective, one gigapascal (GPa) is equal to 145,037 pounds per square inch (which isn’t exactly the best measurement for tensile strength, but you get the idea). “This is the highest toughness modulus for a fibre,” the team says, “surpassing synthetic polymeric high performance fibers (e.g. Kevlar49) and even the current toughest knotted fibers.”
Obviously, a fiber this strong would have a huge number of potential applications. You could use it to build bridges, bulletproof clothing, and maybe even a space elevator — but there’s still quite a lot of research to be done. Before any of that crazy stuff can happen, the researchers first need to figure out why their method works.
At this point, it isn’t 100 percent clear how the spiders incorporate the carbon nanotubes into their silk. One theory is that the silk becomes coated with nanotubes after it’s spun out. The researchers can’t rule this possibility out until further research is conducted, but they say that it’s unlikely because simply adding an external nanotube coating to the silk wouldn’t have created such a strong fiber.
The other theory — the one that the researchers suspect is more likely — is that the spiders actually ingested the carbon water after being sprayed with it, and the nanotubes ended up being incorporated into their silk as it was spun out. In this way, the nanotubes would be central to the silk cable construction and therefore have the biggest impact on its strength.
And of course, once that issue has been figured out, even more challenges lie ahead. We’ll also need to come up with an effective way to mass produce spider silk (beyond some initial success a few years ago with genetically engineered goats that were made to produce it in their milk). Only then will this material be available for something other than catching overweight flies.
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