Worm’s Jaws Show Mettle: Zinc links may inspire new materials

Since biology excels at making strong and hard substances, such as bone, teeth, and seashells, scientists who design new materials often try to emulate nature’s inventions. For Galen D. Stucky of the University of California, Santa Barbara and his colleagues, the microstructures of marine worms’ jaws harbor clues for making synthetic materials. Unlike the bony jaws of mammals, these worms’ chops are made primarily of protein.

JAW INNARDS. X-ray absorption (top) shows the highest concentration of zinc (dark area) near the tip of a clam-worm jaw. A light-microscope image of the jaw, about 3 millimeters long, appears at bottom. H. Lichtenegger, et al./PNAS

Stucky and his coworkers recently reported that the tiny jaws of the bloodworm, Glycera dibranchiata, contain the copper chloride mineral called atacamite, which makes the structures particularly strong (SN: 11/9/02, p. 302: Available to subscribers at Worm’s teeth conceal odd mineral material).

In an upcoming issue of the Proceedings of the National Academy of Sciences (PNAS), the researchers compare the bloodworm’s jaws to those of the clam worm, Nereis limbata, a sand- and mud-dwelling scavenger. Although the protein compositions of the two worms’ jaws are similar, the jaws of Nereis contain zinc instead of copper.

Using a variety of tests, Stucky and his coworkers found that the properties of the clam worm’s jaw vary with its zinc content. As the concentration of zinc increases, so do the jaw’s hardness and stiffness. The clam-worm jaws are especially hard near the tips, says Stucky, but even there, they’re still softer than bloodworm jaws.

The researchers also found that the zinc in clam-worm jaws isn’t in a mineralized form, as is the case for much of the copper in the tip of the bloodworm jaws. Instead, the team determined that clam-worm jaws are hard wherever zinc cross-links protein networks.

Stucky and his coworkers suggest that each animal’s jaw composition suits the mechanical demands of its eating habits. The clam worm, which scavenges food, may not require jaws as hard as those of the bloodworm, which thrusts its jaws into prey to inject venom.

In the future, notes materials researcher Mehmet Sarikaya of the University of Washington in Seattle, investigators might discover more specifically how the zinc-based cross-linking occurs in clam worms and why the animals rely on zinc rather than on another metal. Within such knowledge, Sarikaya says, scientists might find clues for designing their own hardy composites of proteins and metals.

Stucky says his group is already taking steps toward creating flexible and light-weight materials inspired by the worm. The researchers are also examining the hard beaks of octopuses and squid, which are protein based like the worms’ jaws yet contain little or no metal.

Materials scientists can learn a lot from animals, says Arthur Heuer of Case Western Reserve University in Cleveland, where he has studied the conch shell for clues to materials design. Says Heuer: “Nature has had hundreds of millions of years to experiment.”


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