The strength of spider silk is often a source of inspiration for scientists trying to design new types of ultrastrong materials. But at the University of Akron, it's something else about spider silk that inspires. David Lukofsky reports.
Scientists know spider silk is one of nature's most intriguing materials. Pound for pound, spider silk is 3 times stronger than Kevlar-- 5 times stronger than steel. But now a team of scientists from the University of Akron reveals something else about the material. Todd Blackledge is Director of the University of Akron lab that observed the effect with golden orb-web spiders.
"What we found is that silk will cyclically - repeatedly - respond to changes in humidity. When the silk is wetted, it will relax. And then as it dries out, it will contract and pull back," says Blackledge.
Other materials, like wood, do this too. It's why a wooden door could be hard to close on a hot and humid summer day. What's unique about spider silk is that it's also quite strong. A strand of silk smaller than a human hair could lift the equivalent of an aspirin off the ground simply by getting wet. This might not sound like much at first, but researcher Blackledge explains that a bundle of many spider fibers could generate a much larger force.
"Potentially a bundle of fibers that's equivalent to two centimeters thick silk could potentially lift trucks up and off the ground simply by getting wetted and then dried out," says Blackledge.
The discovery marks the first step in making spider silk a competitor in the race toward designing artificial muscles. Other research groups are examining how muscles could be built with special types of plastics that change shape when electrified. But the spider silk appears to have several advantages. One of its biggest is that it doesn't require a direct input of electricity. Instead, the silk could exploit changes in the ambient humidity.
"Let's say you wanted to lift something off the ground, you would simply dry it out to a certain humidity that lifts it the degree you want, and then by maintaining that humidity you maintain that exact level of force potentially indefinitely or at least for a very long time period."
The discovery could serve in applications that require strong forces in tiny spaces. For example, the material might lead to small devices that could travel through the small enclosures of the human body, and eventually open up to release a drug. Non-medical applications might also be possible.
"One of the applications we considered is green energy production. If you have places in the environment where humidity naturally fluctuates, you could potentially set-up silk on little power generating motors that could take the energy contained in the changing humidity and transform it into a form of energy that's more useful to us, like electricity," says Blackledge.
Using the silk on a large scale implies finding a reliable source for the spider silk. But spiders are carnivores -- they can't be farmed easily like caterpillars or other plant-eating creatures. Blackledge says the answer to that problem might be in the field of genetic engineering.
"There are a number of labs throughout the world that are looking to synthesize silk so to insert spider silk genes into other organisms, or to understand the molecular properties of spider silk well enough that we could simply synthesize molecules that mimic those properties."
The full study is published in the current edition of the Journal of Experimental Biology.
David Lukofsky. WOSU News.