By Nneka Nwogwugwu
Northwestern University researchers, for the first time, have discovered a rare mineral hidden inside the teeth of a chiton, a large mollusk found along rocky coastlines.
The iron mineral, called santabarbaraite, had been documented in rocks.
Based on minerals found in chiton teeth, the researchers developed a bio-inspired ink for 3D printing ultrahard, stiff and durable materials.
“This mineral has only been observed in geological specimens in very tiny amounts and has never before been seen in a biological context,” said Northwestern’s Derk Joester, the study’s senior author. “It has high water content, which makes it strong with low density. We think this might toughen the teeth without adding a lot of weight.”
One of the hardest known materials in nature, chiton teeth are attached to a soft, flexible, tongue-like radula, which scrapes over rocks to collect algae and other food.
Having long studied chiton teeth, Joester and his team most recently turned to Cryptochiton stelleri, a giant, reddish-brown chiton that is sometimes affectionately referred to as the “wandering meatloaf.”
To examine a tooth from Cryptochiton stelleri, Joester’s team collaborated with Ercan Alp, a senior scientist at Argonne National Laboratory’s Advanced Photon Source, to use the facility’s synchrotron Mössbauer spectroscopy as well as with Paul Smeets to use transmission electron microscopy at the Northwestern University Atomic and Nanoscale Characterization and Experiment (NUANCE) Center.
They found santabarbaraite dispersed throughout the chiton’s upper stylus, a long, hollow structure that connects the head of the tooth to the flexible radula membrane.
“The stylus is like the root of a human tooth, which connects the cusp of our tooth to our jaw,” Joester said.
“It’s a tough material composed of extremely small nanoparticles in a fibrous matrix made of biomacromolecules, similar to bones in our body.”
Joester’s group challenged itself to recreate this material in an ink designed for 3D printing. Stegbauer developed a reactive ink comprising iron and phosphate ions mixed into a biopolymer derived from the chitin. Along with Shay Wallace, a Northwestern graduate student in Mark Hersam’s laboratory, Stegbauer found that the ink printed well when mixed immediately before printing.
The study, “Persistent polyamorphism in the chiton tooth: From a new biomaterial to inks for additive manufacturing,” was supported by the National Science Foundation (award numbers DMR-1508399 and DMR-1905982), National Institutes of Health (award number NIH-DE026952), Air Force Research Laboratory (award number FA8650-15-2-5518) and Deutsche Forschungsgemeinschaft (award number STE2689/1-1).