Marine Worm Inspires a New Bone Adhesive

The worms live in intertidal surf, building sturdy tube-shaped homes from bits of sand and shell and their own natural glue. Tiny, hair-like cilia brush the sand grains and shell pieces down the tentacles so they can be grabbed by the worm's fleshy, pincer-like "building organ.” The worm then secretes two little dabs of the glue onto the particle, and the building organ puts it onto the end of the tube, holding it there for about 25 seconds, and then testing it to see if the glue is set. The glue is designed to set up and harden within 30 seconds after the worm secretes it.

The researchers developed a synthetic version of the waterproof superglue, using polyacrylate glue protein analogs synthesized with phosphate, primary amine, and catechol sidechains with molar ratios similar to the natural glue proteins. When the polymers are mixed, they form an unusual substance known as a coacervate, which condenses out of the polymer solution and sinks to the bottom of a test tube as a dense solution, which is the foundation of the synthetic glue. Because the solution-within-a-solution does not disperse, it can be sucked up with a syringe. To test the strength of the synthetic glue, the researchers cut cow leg bones collected from grocery stores in cubes measuring 1 cm on a side, sanded the pieces, wetted them, and bonded the pieces together either with synthetic worm glue or with Loctite 401 superglue. The bonded pieces of bone were kept warm and wet for 24 hours. The researcher then tested the strength of the glues by using dull blades to push them in opposite directions until the bond failed. They found that the marine-based glue bond possessed was equal to 37% of the strength of the commercial cyanoacrylate. The study was published in the June 2009 issue of the journal Macromolecular Bioscience.

"It is especially difficult to maintain alignment of small bone fragments by drilling them with screws and wires,” said lead author Russell Stewart, Ph.D., of the department of bioengineering at the University of Utah. "An adjunctive adhesive could reduce the number or volume of metal fixators while helping maintain accurate alignment of small bone fragments to improve clinical outcomes.”

Most synthetic biocompatible polyacrylate and cyanoacrylate adhesives are used to replace sutures for the treatment of superficial skin wounds. However, due to their toxic byproducts, most are unsuitable for bone or deep tissue repairs.

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