Studying spider silk, NSF-supported researchers learn about the properties of this sticky material, and their findings could lead to new bio-adhesives and glues that work under water.
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Ali Dhinojwala and Vasav Sahni consider themselves materials scientists, not biologists. They study surfaces, friction and adhesion. Nevertheless, they have discovered that understanding how nature makes things stick sometimes means getting up close and personal with the creatures responsible.
ReplyDeleteWhen they recognized, for example, the stickiness of spider silk, "we thought there'd be nothing sexier than working in this area," Sahni said. "Little did I realize that working with spider silk meant working with spiders, too. Big, scary spiders."
Making fresh samples "involved working with newly-spun spider webs in which the spider would be waiting for its prey," he added. "Then I was informed that the spiders I am working with are non-poisonous, which calmed me down a little."
Anyone who comes into direct contact with a spider web knows how sticky it is, the result of a glue-like substance the spider produces from one of the glands in its stomach. But, until recently, scientists did not understand how the glue behaved.
Dhinojwala, a professor and chair of the department of polymer science at the University of Akron in Ohio, and Sahni, a doctoral candidate there, joined with Todd Blackledge, professor of biology, to try to figure out the properties of the microscopic substance that orb-weaving spiders deposit along the round rings of silk they spin as part of their webs. Those droplets--three times thinner than the diameter of a single hair--capture the flies and other insects that spiders eat.
"It's not just the stickiness," Dhinojwala said. "We wanted to better understand the adhesion--how elastic is it? How stretchy is it? The objective was not to determine what it was made up of, but how it behaves and why is it so sticky?"
The drops are composed of highly entangled polymers, which are physically or chemically cross-linked and transmit forces very efficiently. Under a microscope, the researchers pulled on individual glue drops while measuring their force-extension behavior--not easy to do using a tiny probe.
ReplyDeleteThey found the material to be both viscous and elastic, valuable properties for catching fast-flying, incoming insects--and in keeping the victims trapped long enough for the spider to subdue, and devour, them.
The material's consistency is not quite liquid, nor like honey, nor even like silly putty. "It feels like chewing gum," Dhinojwala said. "It just keeps stretching and stretching."