Spiders, Doomed Flies, and Tougher Textiles — Just Add Water

A DoD grant will help SDSU’s Gregory Holland further explore spider silk and its possible application toward incredibly tough biomaterials.

By Jeff Ristine

The silk a common variety spider spins to trap its prey is the focus of new San Diego State University research, being supported by the Department of Defense for its potential breakthroughs in producing bioinspired materials U.S. troops may use someday.

Gregory Holland, associate professor of analytical chemistry and an authority on the super-strong properties of spider silk, is studying a specialized silk spun by a spider in the orb weaver family. The species is common to San Diego, found along the trails of Torrey Pines and the Silver Strand, among other areas.

“Lucky us,” said Holland. “They’re in our backyard.”

The U.S. Army Research Office has awarded Holland a $365,000, three-year grant to pursue the work.

Holland and collaborators previously peered into the molecular structure of the silk fibers Black Widow spiders spin, focusing on the gland that kicks off the process of converting a protein-rich liquid into a thread. The fibers are stronger than the material in bulletproof vests.

The new project turns to orb weavers, who spin intricate, circular webs up to three feet across. But it’s not that regular dragline silk Holland is investigating, it’s the much different prey-wrapping silk the spider uses to keep flies, crickets and other tasty morsels in an escape-proof cocoon until feeding time.

“The silk itself has to be very flexible because the spider is moving all around and rotating the prey as it wraps it in silk,” Holland said. “The fly is not dead, it’s moving, so he needs something that’s malleable, not like a steel cable.” Indeed, the initial material extends, stretching up to 60-70% of its original length.

That all changes when the spider vomits onto the silk and prey, “and it’s the primary linchpin of this grant,” Holland said. When the digestive liquid dries, “the silk fibers fuse together and the material becomes really rigid. The silk protein actually changes its structure at a molecular level — going from this flexible, extensible material to a rigid, fixed, matted material. The silk hardens like a straightjacket.”

Spiders rely upon digestive enzymes to trigger the transformation. But Holland’s lab found water has the same effect.

What makes the silk so strong and rigid when the material dehydrates? “That’s what we’re going to learn.”

Different silks are made from proteins with different sequences, Holland explained. So just like the Black Widow dragline silk, the research will look at the atomic and molecular structure of the silk protein starting material, in the gland, as well as the final fiber.