Limpet Teeth Tell of Daily Grind
The title-holder for strongest biological material goes to a small mollusk.
A limpet’s life is an arduous one. Clinging to rocks with a muscular foot, these little mollusks brace against crashing waves that deliver the food they need to survive. Using a long, tongue-like appendage studded with tiny teeth, limpets scrape against the hard rock surface, gathering algae and pulling it toward their mouth. Talk about a daily grind.
Tiny as the teeth are—each one is as long as a strand of hair is thick—they’re the strongest biological material known to exist, according to a recent paper appearing in the Royal Society journal Interface. In fact, they’re 10 percent stronger than spider silk, the previous title-holder for strongest naturally occurring material.
The mighty teeth are critical to limpet survival. “If the teeth break very easily on the rock surface, that’s it—the limpet can’t feed, and it dies off,” says Asa Barber, an engineer at the University of Portsmouth in England and the lead author on the paper.
Barber first became interested in limpet teeth a decade ago, when he happened upon an image of a tooth’s internal architecture in a structural biology textbook. He noticed that the tooth was composed of very small fibers within a softer, organic material, similar to how engineers embed carbon fibers inside plastic to reinforce it.
Barber eventually decided to study the teeth for himself. He used a scanning electron microscope to locate them along the tongue of a limpet specimen (Patella vulgata), creating the gray-scale version of the image above. (The color was added in later.) Then, he and his team pulled the teeth apart into small samples and applied force to them until they broke—a common method typically used for testing the strength of larger materials. (“Trying to break a small thing apart is generally quite difficult,” says Barber.)
Closer inspection revealed that the tooth’s (relatively) soft outer protein shell is filled with fibers made of a mineral called goethite, which confers strength twice that of the bulletproof material Kevlar.
“It’s another nice example [of] how nature does things so well,” says Timothy Weihs, a materials engineer at Johns Hopkins University, who was not involved in the research. “Over time, nature’s been able to design some pretty well-optimized structures.”
The discovery could help engineers design better dental fillings for when our own teeth fail. It also sheds more light on a creature that often goes unnoticed. “People had sort of disregarded [limpets],” Barber says, so it’s surprising to find “such a unique property from quite a mundane organism.”