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Biomedicine

Bone-setting Glue

A new adhesive, inspired by aquatic worms, could help repair shattered bone.

Shattered bones pose a difficult problem for surgeons, who currently must use tiny screws and plates to hold fragments in place long enough for the break to heal. But a new glue, which has the sticking power to adhere to bone, could one day help orthopedic surgeons fix difficult breaks, researchers announced today at the American Chemical Society conference in Washington, DC.

King of the castle: Sandcastle worms (shown here), which build themselves a house of sand, inspired a novel adhesive that could one day be used to glue broken bones back together.

Making glue that sticks to bone and other wet surfaces has proven a particularly complex task–either it slides right off, or it dissolves into the surrounding liquid. Russell Stewart, lead researcher and biomedical engineer at the University of Utah, found his inspiration for the glue in the tiny sandcastle worm. The worm builds its tube-shaped home on the ocean floor using sand grains and bits of shell, cemented into place piece by piece like brick and mortar.

“The worm has to overcome several problems when putting a sandcastle together underwater,” Stewart says. “Its adhesive has to adhere to wet surfaces, and when it’s secreting that adhesive under water, it has to prevent it from just dissolving into the ocean.” Although the glue starts out as fluid, it must harden into a solid. “The worm has solved all of these problems, and we’re trying to copy those solutions,” he says.

Stewart and his colleagues found that the sandcastle worm uses changes in pH level to trigger the glue to harden. Inside the worm, where the pH is low, the glue is a fluid. Exposure to seawater, which has a higher pH, slowly causes the glue to solidify. After a little tinkering, the researchers recreated a synthetic version of the worm’s adhesive–a polyacrylate glue that is water soluble but doesn’t dissolve in liquid, is at least as strong as Super Glue, and is twice as strong as the worm’s original glue. Cell culture experiments showed no sign of toxicity; early tests in rats appear to back that up and also show no unusual immune reaction.

“There’s a significant need in the clinic for better glues,” says Jeffrey Karp, a biological and chemical engineer at Brigham and Women’s Hospital in Boston. And while there are some very strong medical grade glues available, he notes that they also tend to be highly inflammatory. The need for an adhesive that can bond bone and align small fragments without inflammation is a pressing one. What’s more, Karp says, the new adhesive is unique in that it can be applied to a wet surface without migrating away from the injury site. “Glues tend to be very messy, and surgeons have great difficulty manipulating them in wet environments,” he says. “It’s difficult to place them directly on the site of interest.”

A close bond: A scanning electron microscope image of two glass beads cemented together by a sandcastle worm and removed from the worm’s tube (inset). The larger image is a close-up of the connection, which was made using the worm’s adhesive.

Stewart and his colleagues believe the adhesive can be used as a complement to wires, pins, and plates–large pieces could be held in place with hardware, while small pieces could be glued back in. And in cranial-facial fractures, where using pins and screws can cause permanent cosmetic damage, the glue could potentially be injected with a syringe, avoiding open surgery.

“One of our challenges is to hold very small pieces in very precise alignment. We just need to hold them there until they heal, just six weeks,” says Thomas Higgins, an orthopedic surgeon at the University of Utah’s School of Medicine who specializes in joint fractures and has consulted with Stewart on the adhesive’s clinical applications. “To have something that is liquid and would assume a more rigid state when you put it [in the body], that would be much more easily applicable and much more versatile than what we use now,” he says. “This is still preliminary, but it shows a lot of promise.”

Beyond bonding bones, the adhesive holds promise for a number of wet-environment applications–everything from mending cracked teeth to repairing corrosive cracks on ships out of dry dock. “It will be really interesting for a dentist or orthopedic surgeon to consider [this type of material] as a strategy for bone and tooth repair,” says Herbert Waite, a biochemist at the University of California, Santa Barbara who was not involved in the research.

Karp notes that there’s still a lot of work to be done. “Just the idea of forming glue in the presence of blood may be very different than forming it under seawater or under lab conditions,” he says. But he believes that the group is off to a good start. “I think it’s a really interesting and novel approach, to better understand the biology of the sandcastle worm to create new adhesives,” Karp says. “Evolution is the best problem solver. There’s nothing that can compete with it.”

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