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Caddis Fly Silk May Be Useful Adhesive in Surgery

"Silk from caddis fly larvae may be useful some day as a medical bioadhesive for sticking to wet tissues," said Dr. Russell Stewart, an associate professor of bioengineering at the University of Utah and principal author of a new study of the fly silk's chemical and structural properties. "I picture it as sort of a wet Band-Aid, maybe used internally in surgery--like using a piece of tape to close an incision as opposed to sutures," he added. "Gluing things together underwater is not easy. Have you ever tried to put a Band-Aid on in the shower? This insect has been doing this for 150 million to 200 million years. There's just a fascinating diversity of these insects. Their adhesive is able to bond to a wide range of surfaces underwater: soft and hard, organic and inorganic. If we could copy this adhesive, it would be useful on a wide range of tissue types." Dr. Stewart hopes to make a synthetic version of the caddis fly silk for use as a surgical adhesive. There are thousands of caddis fly species worldwide in an order of insects named Trichoptera that is related to Lepidoptera, the order that includes moths and butterflies that spin dry silk. Because caddis flies are eaten by trout, fly fishermen often use caddis fly lures. Some species of caddis fly spend their larval stages developing underwater, and build an inch-long, tube-shaped case or shelter around themselves using sticky silk and grains of rock or sand (see photo). Some other species use silk, small sticks, and pieces of leaves. In these tube-dwelling species, each larva has a head and four legs that stick out from the tube. The larval case is often conical because it gets wider as the larva grows. A caddis fly larva eventually pupates, sealing off the tube as it develops into an adult fly, and then hatches.

Caddis fly larvae extrude an adhesive silk ribbon out of an organ known as the spinneret. The products of two silk glands converge there, so the extruded adhesive looks like a double ribbon with a seam down the middle. The larvae weave this sticky mesh back and forth around sand grains, sticks, or leaf pieces to create the tubes they occupy.

Aquatic caddis flies and terrestrial butterflies and moths diverged from a common silk-spinning ancestor some 150 million to 200 million years ago. Caddis flies now live around the world in waters ranging from fast streams to quiet marshes.

"The caddis flies' successful penetration into diverse aquatic habitats is largely due to the inventive use by their larva of underwater silk to build elaborate structures for protection and food gathering," the authors said.

The photo shows a caddis fly larva tha has used ribbons of natural sticky silk to stitch together grains of sand and rock (right rear of the photo) for its tube shelter. But when placed in a lab aquarium containing glass beads instead of sand grains, the larva uses its wet silk to add the beads to its tube shelter (center). The photo is by Fred Hayes

This article was published in the week of March 1, 2010, in Biomacromolecules, a journal of the American Chemical Society. [Press release]