Mussels and barnacles in the intertidal near Newquay, Cornwall, England. Photo by Mark A. Wilson. Department of Geology, The College of Wooster.
BOSTON — I learned this weekend that mussels, those brainless, hard-shell mollusks that and are found in intertidal marine areas (and taste great when simmered in white wine), possess a phenomenal sticking power that if mimicked could advance important surgeries.
A group of scientists presented their research on the topic at the American Association for the Advancement of Science, or AAAS, annual meeting in Boston this weekend. (More to come from that conference in the coming weeks.)
Mussels are unmatched in their ability to attach firmly to surfaces that are wet. Adhering to wet surface is a tricky thing to master not only in nature, but also in a factory or a lab. Take nearly any man-made adhesive or two-part epoxy from the hardware store and try applying it to a fish aquarium — or anything wet. As soon as water’s involved, game’s over.
“It’s a very, very common obstacle,” said Herbert Waite, a molecular biologist with the University of California at Santa Barbara. “For an organism to have figured out not only to learn how to remove all the surface water, but to keep the bond intact, is really remarkable.”
Waite began studying mussels in the late 70s, and spent the next 20 years characterizing the proteins that they use, he told the audience Saturday at a press conference on the subject.
“It seemed a fascinating, heroic kind of system to work on, where these little creatures that don’t even have a brain and live in the high-energy intertidal can survive in this environment purely by their ability to hunker down on hard surfaces,” Waite said, adding that everyone thought he was crazy when he first started focusing his research on mussels.
But he wasn’t crazy. Scientists have since borrowed from Waite’s research to develop synthetic polymers similar to the mussel proteins that they believe could have some very useful applications in medicine.
The mussels produce a glue-like liquid that solidifies into a strong adhesive. The substance is stored in glands in their soft tissue. When secreted, it seals strong, silk-like fibers called byssal threads, also produced by the mussel, to rocks or other hard surfaces.
Researchers are still trying to nail down exactly how they do it. It appears to rely heavily on converting an amino acid to a dopa — an amino acid precursor similar to the ingredient used in medication for Parkinson’s disease — “that has the ability to displace surface water,” Waite said.
Inspired by the industrious sea creature and by Waite’s research, Phillip Messersmith, a materials scientist at Northwestern University is attempting to synthesize polymers that mimic the complicated proteins that these mussels secrete. His main goal: to develop adhesives that would work as a sealant in surgery.
“In almost all situations in a surgical environment where you would want to bond two tissues together or seal a hole in a membrane tissue or bond a medical device to a tissue, the tissue is wet,” Messersmith said during the press conference. “So those concepts from the mussel and how the mussel goes about attaching to wet surfaces, we’re trying to adapt and develop into synthetic materials.”
Messersmith’s team has developed a technique that he believes could aid a number of surgical procedures. Among them, eyelid transplants and correction of a ruptured fetal membrane, or amniotic sac, during pregnancy. They have progressed the farthest on this latter procedure, which they’re attempting on rabbit fetuses. (Rabbits make good models, because the mothers carry up to five to 10 fetuses at a time.)
The rupture of a fetal membrane, Messersmith explained after the conference, is a dangerous problem with no real treatment.
“Right now, treatment of premature rupture of membranes is bedrest,” he said.
To mimic membrane ruptures, scientists poke holes in the fetal membranes of rabbits and then patch them up with a cotton-ball like plug sealed off by the synthetic polymers. Without repair, 30 to 40 percent of the fetuses survive. With repair, that number jumps to 80 percent.
Of course, the hope that their polymer will aid these complications is still mostly a dream. Researchers need to determine that the polymers are safe to use surgically on humans. And it’s unclear whether the success will translate from rabbits to humans. Their next step is to step up the research to pig fetuses, a better model for humans.
Other potential applications for the sealant could include eyelid surgery or prenatal corrections to fetuses with spina bifida.
Sidenote: Emily Carrington, a biologist at the University of Washington, studies mussel’s superstrong byssal fibers. She calls them nature’s bungee cords. Her team has found that the quality of fibers that mussels produce changes with the seasons. The strength of the fiber is 60 percent weaker when the water temperature elevates to 8 degrees Celsius, she said.
“As an organism in the intertidal zone, they’re competitive because they can firmly attach to the rocks and they exclude others. So if they can’t attach well, they’ve lost their competitive edge,” Carrington said.
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Patti Parson and David Pelcyger contributed to this report.