Researchers from the University of California, Irvine, in collaboration with Okayama and Toho universities in Japan, have conducted a study to understand how chitons—a type of mollusk—develop extremely hard and wear-resistant teeth. Their findings, published in Science, could lead to new ways of producing advanced materials for industrial use.
The research focused on the role of chiton-specific iron-binding proteins called RTMP1. These proteins are transported into developing teeth through nanoscopic tubules known as microvilli. The precise control over where and when these proteins are deposited results in dental structures that are both strong and tough.
“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.”
There are more than 900 species of chitons worldwide. While some can be found near the UC Irvine campus along the California coast, this study examined larger species from the Northwest United States and off Hokkaido in Japan. The team discovered that RTMP1 proteins exist across different chiton populations globally. Kisailus noted this suggests convergent biological design for controlling iron oxide deposition.
Initially unaware of how these iron-binding proteins entered chiton teeth during development, researchers used advanced materials science techniques combined with molecular biology methods to trace their movement. They found that specialized proteins move through nanostructured tubules into each tooth where they bind to preassembled scaffolds made of chitin nanofibers—the biopolymer responsible for shaping magnetite nanorods within the teeth.
Iron stored outside the tooth is released inside as ferritin binds to RTMP1 proteins within the tooth structure. This leads to controlled deposition of nanoscale iron oxide that matures into highly aligned magnetite nanorods responsible for the hardness of chiton teeth.
Kisailus explained that this research advances understanding of cellular iron metabolism while providing insight into synthesizing next-generation advanced materials.
“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,” he said. “This includes new approaches toward additive manufacturing – 3D printing – and synthesis methods that are far more environmentally friendly and sustainable.”
According to Kisailus, combining state-of-the-art electron microscopy, X-ray analysis and spectroscopy with biological techniques like immunofluorescence allowed them to reveal how chiton tooth formation occurs at a molecular level.
“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,” Kisailus said.
Other researchers involved were Michiko Nemoto, Koki Okada, Haruka Akamine, Yuki Odagaki, Yuka Narahara, Kiori Obuse, Hisao Moriya and Akira Satoh from Okayama University; Kenji Okoshi from Toho University also contributed.
Funding for Kisailus’ work came from both the U.S. Air Force Office of Scientific Research and Army Office of Scientific Research.
UC Irvine’s Samueli School of Engineering played an important role in supporting this research as part of its Brilliant Future campaign (https://brilliantfuture.UC Irvine.edu/the-henry-samueli-school-of-engineering), which aims to raise $2 billion through alumni engagement for student success initiatives as well as research projects.
Founded in 1965 (www.uci.edu), UC Irvine is recognized among America’s top public universities by U.S. News & World Report rankings. The university has produced five Nobel laureates across its academic programs serving more than 36,000 students while contributing significantly to Orange County’s economy.
