Originally Published MDDI January 2005

R&D DIGEST

Heather Thompson

In another example of nature's superior design, scientists at the University of Adelaide (Adelaide, South Australia) have discovered an adhesive secreted from a rare type of burrowing frog found in Australia.

The frog, which is of the Notaden genus, lives underground for nine months of the year and emerges during the torrential rain season. To protect itself from insect attacks during this vulnerable time, the frog secretes a glue that binds the jaws of biting insects and adheres the insect to the frog's skin.

Every two weeks the frog sheds its skin, as all frog species do. The frog then eats the skin for nourishment, along with any insects stuck to it.

What is intriguing to scientists about the frog's secretion is that it hardens in seconds, even in moist conditions, and still remains flexible. Furthermore, the adhesive appears to be nontoxic, according to Michael Tyler, who discovered the glue.

Tyler is a head researcher at Adelaide. He and orthopedic surgeon George Murell of the University of New South Wales conducted the first experiments using the frog glue to patch the meniscal knee cartilage in sheep. The frog glue held the cut fragments of joints and allowed the body's natural collagen to fill in weak points.

"There is a great need for something strong enough to withstand the forces in the knee to hold the cartilage together until it repairs," says biomaterials expert Rolfe Howlett. Many biological types of glue on the market are too weak to fix body parts that are under large amounts of stress, such as knee cartilage. The frog glue's strength and flexibility make it a promising alternative, says Tyler.

Tyler has spent several years studying the amphibious secretions. He and his team previously found a way to remove the frog skin without harming the animal. Introducing a mild electric shock to the skin induces the frog to create more secretion and allows for easier removal.

Further experiments have shown that the adhesive will stick to plastics, wood, glass, and metal. And it retains its bonds even in moist conditions. Once set, the glue has a porous structure that could allow healing gases, nutrients, and possibly even cells to pass through the structure.

The Adelaide group is currently working on creating a synthetic version of the glue based on unusual proteins found in the secretion. "I cannot put an estimate on a time when a commercial product will be available," says Tyler, "but we have made excellent progress and numerous researchers are contributing."

"We are actively seeking a commercial partner, and our own funding is very limited," he adds.

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