Quirks & Quarks

Stitching up surgical cuts with slug slime

The Dusky Arion slug produces a sticky goo to protect itself from small predators, but the defensive goo turns out to have excellent qualities as a medical adhesive

A glue produced by a slug to defend itself could be a useful medical adhesive

The Dusky Arion slug excretes a sticky goo to protect itself from hungry predators. The defensive goo turns out to have excellent qualities as a medical adhesive. (Andrew Smith)
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The Dusky Arion slug produces a sticky goo from its back to protect itself from being eaten by small predators. The defensive goo turns out to be both tough and stretchy -- excellent qualities in a medical adhesive.

Medical grade super-glue is sometimes used in hospitals and surgical suites as a substitute for stitches or staples. 

But while this glue can be useful in this kind of application, it isn't perfect. It dries stiff and hard, while human tissue is flexible and soft. So glued wounds can't handle stress and strain that comes as we move.

That's why Andrew Smith, a professor of biology at Ithaca College in New York, thinks that an accidental discovery he made could lead to a better surgical glue.  

And it was all inspired by slug slime.

A serendipitous discovery

Smith was met with a pleasant surprise when he moved to Ithaca, New York, a few years ago to start a new job. He found a rusty, orange slug in his backyard, and instinctively went to pick it up.

"It's markedly different from other slugs," said Smith. "And as soon as I touched it, it started oozing orange goo off its back."  He found his fingers were glued together by the slug mucus which was not only ultra-sticky, but also stretchy as well.

Smith, who by remarkable coincidence had spent years studying biolgically inspired glues, realized this was a perfect combination for medical adhesives.

The thumb-sized mollusk turned out to be the Dusky Arion Slug, a species that can be found in northern temperate regions around the world.

"[The mucus] is a defensive secretion," explained Smith. "If you're a small predator and try to bite it, you'd get a face full of glue."

Sticky slug glue: the defensive secretion produced by the dusky slug

A slug slime that's strong and flexible

The mucus is able to stay sticky for a long time, even though it's made of 97 per cent water, which Smith said is unusual.

He studied the makeup of the slug glue in detail, and found a double network structure in the material that's different from other strong man-made gels like super glue.

He describes the polymer chains as a crosslinked net that can be pulled and stretched 10 times its length, but the interwoven double-layer design makes it very hard to break.

"If you have a combination of thickness and extensibility, it can take 100 to 1,000 times of energy to fracture," said Smith.

Sticky orange goo extracted from slug. (Rebecca Falconer and Andrew Smith)
 

A bio-inspired medical adhesive

Another group has already created a synthetic version of the slug glue and demonstrated that it can work in animal tissues. 

It was able to seal a hole in a pig's heart, and it held together for thousands of beats.

There could be significant benefits to a better surgical glue. Most wounds today are closed with sutures or staples, which work well but are not perfect. Punching holes in the skin can lead to infection if the seal is not perfect. Sutures and staples can also lead to tearing, scarring, and pain.  

"The ideal is to make something that sets rapidly," said Smith. "You could literally just squirt it into a wound, seal it up and have it heal and that takes away the time involved in doing stitches. One day that we could replace stitches with a with a variety of different glues with different properties."

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