By: Henry Fountain
SALT LAKE CITY — Along one wall of Russell J. Stewart’s laboratory at the University of Utah sits a saltwater tank containing a strange object: a rock-hard lump the size of a soccer ball, riddled with hundreds of small holes.
It has the look of something that fell from outer space, but its origins are earthly, the intertidal waters of the California coast. It’s a home of sorts, occupied by a colony of Phragmatopoma californica, otherwise known as the sandcastle worm.
Actually, it’s more of a condominium complex. Each hole is the entrance to a separate tube, built one upon another by worm after worm.
P. californica is a master mason, fashioning its tube, a shelter that it never leaves, from grains of sand and tiny bits of scavenged shell. But it doesn’t slather on the mortar like a bricklayer. Rather, using a specialized organ on its head, it produces a microscopic dab or two of glue that it places, just so, on the existing structure. Then it wiggles a new grain into place and lets it set.
What is most remarkable — and the reason these worms are in Dr. Stewart’s lab, far from their native habitat — is that it does all this underwater.
“Man-made adhesives are very impressive,” said Dr. Stewart, an associate professor of bioengineering at the university. “You can glue airplanes together with them. But this animal has been gluing things together underwater for several hundred million years, which we still can’t do.”
Dr. Stewart is one of a handful of researchers around the country who are developing adhesives that work in wet conditions, with worms, mussels, barnacles and other marine creatures as their guide. While there are many possible applications — the Navy, for one, has a natural interest in the research, and finances some of it — the biggest goal is to make glues for use in the ultimate wet environment: the human body.
It is too early to declare the researchers’ work a success, but they are testing adhesives on animal bones and other tissues and are optimistic that their approaches will work. “I would have moved on to something else if I didn’t think so,” said Phillip B. Messersmith, a Northwestern University professor who is developing adhesives based on those made by mussels and is testing whether they can be used to repair tears in amniotic sacs, among other applications.
While some skin sealants — mostly of the cyanoacrylate, or superglue, variety — are on the market, their effectiveness is limited. They often cannot be used, for example, on incisions where the skin is pulled or stretched, or must be used in tandem with sutures or staples. Adhesives strong enough to hold skin together under tension, or repair bone or other internal tissues — without inviting attack by the body’s immune system — have eluded researchers.
Nature shows how it can be done, said J. Herbert Waite, a professor at the University of California, Santa Barbara, who did much of the early work of identifying the adhesives that mussels use to stick to rocks and other surfaces. But researchers should view nature’s approach as a general guide, he said, rather than a precise pathway.
“In my view of bioinspired research or materials, I almost always don’t think it’s safe to be slavishly wed to the specific chemistry,” Dr. Waite said, “but rather to distill the important concepts that can then be mimicked.”
So the goal of these researchers is not to duplicate natural adhesives that work well underwater, but to imitate them and make glues that are even better suited for humans. “We want to take elements of the structural adhesives that chemists have made and combine them with the unique elements that nature has used,” Dr. Stewart said.
Synthetic adhesives might not only work better, but they should also be able to be produced in large quantities. Marine organisms make their glues in very small amounts — the typical dollop from a sandcastle worm, for example, is on the order of 100 picoliters. Even if it could somehow be collected before it set, it would take roughly 50 million dollops to make a teaspoon.
“At the end of the day, the single biggest reason to do this is you can get more stuff,” said Jonathan Wilker, an associate professor of inorganic chemistry at Purdue University who works on analogues of mussel adhesives and studies oysters, barnacles and other organisms as well.
But there are several hurdles to making glues that work underwater, Dr. Wilker said. “One is that whenever the surface is really wet, you’re going to be bonding to the surface layer of water, rather than the surface itself. So it’s going to lift off.”