Funky Flies Offer Model for Surgical Adhesive

An underwater fly that builds a covering of pebbles and sand by gluing them together could point the way for developing a glue that works while wet.

THE GIST

- Caddisflies, related to moths and butterflies, spin silk that is sticky underwater in the larval stage.

- The sticky proteins contain phosphates, which are used in dentistry on crowns and in paint.

- Researchers hope to make a synthetic version that can be used to tape wet tissues together in operating rooms.

Ever try taping something together underwater? Of course not. It wouldn't work.

Don't tell that to the larvae of caddisflies, a large family of underwater insects closely related to moths and butterflies. They spin sticky silk ribbons underwater and use them to trap food or assemble body casings, depending on the species.

New research has uncovered how one type of caddisfly larvae tapes things together underwater. The researchers -- Russell Stewart and Ching Shuen Wang of the University of Utah -- hope the work will lead to the creation of a synthetic version that could be used to hold wet tissues together in an operating room.

Stewart previously worked with another underwater creature -- a marine organism called a sandcastle worm -- that creates dots of glue to paste together the tube of sand grains it calls home.

Stewart's research on the sandcastle worm showed that its glue is made up of highly charged proteins that attract each other so strongly they exclude water, preventing the glue from dissolving underwater.

The proteins also contain phosphate groups, which Stewart says are known to be pretty good adhesion promoters. They are used in dentistry to make things like crowns stick. They are also added to paint to help it stick better to walls.

Stewart decided to investigate caddisflies after Christy Geraci of the Smithsonian Institution in Washington, D.C. showed him some caddisfly specimens.

"I said, 'You can go out to the Provo River and turn over some rocks and find some,'" Geraci said. "We're both fly fishermen, so we knew where to find them."

"They use silk in such amazingly diverse ways, if you look at the array of cases that the make,"Geraci said.

Some stick little bits of sand around their bodies. Others use snail shells. Others make underwater webs that act as sieves to capture food from the water. "They are known as the underwater architects," Geraci said.

Stewart was intrigued by the tiny ribbons of the caddisflies' adhesive he could see under the microscope, crisscrossing the insides of their casings.

Back in Utah, he put on his waders and went looking in the river. He brought specimens back to the lab where he grew them in a tank, giving them clean glass beads with which to make their casings.

This allowed him to collect pure samples of the larvae's adhesive, which he analyzed to determine what it was made of.

"We found pretty early on that there was phosphorous in the fibers, which kind of surprised us," Stewart said. The structure was otherwise similar to moth and butterfly silk, but the phosphorous component was new.

Although the phosphate differentiates the caddisfly larvae silk from moth and butterfly silk, it is a key aspect of what makes sandcastle glue stick underwater.

"It's kind of like they both found the same solution to the same problem," Stewart said.

And, unlike the paint industry, which learned that phosphate makes wet paint stick better fairly recently, "This insect larvae figured this out 150 or 200 million years ago," he added.

Like sandcastle worms, caddisfly larvae also make use of highly charged proteins in their silk. But the silk and the glue have differences, too. "The caddisfly is spinning out these sticky fibers whereas the sandcastle worm is just putting out spots," Stewart said.

Stewart has had success so far making synthetic sandcastle glue that he hopes could be used to piece together tiny shards of bones.

Now, Stewart hopes to make a synthetic material with similar properties to the caddisfly tape that could be used for applications like sticking wet tissues together during or after an operation while the tissues healed.

"Silk is sort of a hot topic in biomaterials," said Jennifer Elisseeff of Johns Hopkins University in Baltimore. Silk is a very popular material from which to build scaffolds to grow tissue on, she said, "so this is probably going to jump out at people."

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