In the shallow waters along rocky shores, a small marine creature quietly grows teeth stronger than steel. These teeth don’t come from a machine shop or a high-temperature furnace. They form inside the mouth of a chiton – a mollusk that grazes on algae – and they’re replaced every few days.
A new international study has revealed the process behind this extraordinary feat. The work was led by scientists from the University of California, Irvine, along with Japan’s Okayama and Toho universities.
The research not only explains how chiton teeth form but also opens the door to new ways of making advanced materials for everyday use.
Nature’s low-key armor tank
Chiton are marine mollusks that are related to clams and snails. They spend most of their lives clinging to rocks in the intertidal zone – the strip of shoreline that’s alternately covered and exposed as the tide shifts.
At first glance, a chiton might not look like much. Its body is protected by eight overlapping plates, like a tiny suit of armor, with a leathery girdle around the edges. This flexible shell lets the animal curl into a ball when pried from a surface, shielding its softer underside.
Chitons move slowly, grazing on thin layers of algae that grow on rocks. To do this, they use a radula – a ribbon-like tongue lined with rows of hard teeth.
These teeth scrape against stone in a repetitive grinding motion that would quickly wear down most other materials. For a chiton, it’s just part of breakfast.
Chiton teeth on a molecular scale
The team found that a chiton’s secret lies in specialized iron-binding proteins called RTMP1. These proteins travel into developing teeth through tiny channels known as microvilli.
The timing and placement of these proteins are precisely controlled, ensuring each new tooth grows with an architecture that can withstand the creature’s constant scraping of algae from rocks.
“Chiton teeth, which consist of both magnetite nanorods and organic material, are not only harder and stiffer than human tooth enamel, but also harder than high-carbon steels, stainless steel, and even zirconium oxide and aluminum oxide – advanced engineered ceramics made at high temperatures,” said co-author David Kisailus, UC Irvine professor of materials science and engineering.
“Chiton grow new teeth every few days that are superior to materials used in industrial cutting tools, grinding media, dental implants, surgical implants and protective coatings, yet they are made at room temperature and with nanoscale precision. We can learn a lot from these biological designs and processes,” Kisailus explained.
There are more than 900 chiton species around the world. They live mostly in intertidal coastal regions, from places like Crystal Cove and Laguna Beach to the Northwest U.S. coastline and off Hokkaido, Japan.
The researchers discovered that RTMP1 proteins are found in chitons from many different locations, hinting at a shared evolutionary solution for controlling iron oxide formation.
A step-by-step molecular assembly
When the project began, the scientists didn’t know exactly how or when these proteins reached the forming teeth. By combining advanced imaging and biological tools, they found the proteins start in surrounding tissues and move into the tooth through nanostructured tubules.
Inside, the proteins attach to a chitin scaffold – a fibrous material that shapes the magnetite nanorods. At the same time, iron stored in another protein, ferritin, is released into the tooth.
This iron binds to the RTMP1 and crystallizes into highly aligned magnetite rods. The result is an ultrahard tooth built with remarkable precision.
Kisailus said the research not only deepens our understanding of how living things handle iron but also gives engineers fresh ideas for creating new materials.
Lessons for technology and sustainability
“The fact that these organisms form new sets of teeth every few days not only enables us to study the mechanisms of precise, nanoscale mineral formation within the teeth, but also presents us with new opportunities toward the spatially and temporally controlled synthesis of other materials for a broad range of applications, such as batteries, fuel cell catalysts and semiconductors,” said Kisailus.
These applications include new approaches toward additive manufacturing – such as 3D printing – and synthesis methods that are far more environmentally friendly and sustainable, he noted
The project combined cutting-edge electron microscopy, X-ray analysis, and spectroscopy with genetic and molecular biology methods to map out the complete process of tooth formation.
“By combining biological and materials science approaches through wonderful, global efforts, we’ve uncovered how one of the hardest and strongest biological materials on Earth is built from the ground up,” concluded Professor Kisailus.
The full study was published in the journal Science.
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