In research that may provide information for future high-performance nanomaterials, a team led by the University of Michigan discovered for the first time how mollusks construct ultra-durable structures with symmetry, whose symmetry surpasses that of any other than a single atom in nature. anything.

Robert Hovden, assistant professor of materials science and engineering at the University of Michigan and the author of the paper, said: “We humans have all the technology and cannot make nano-scale structures as complex as pearls.” “So we can study how pearls are Learn a lot from the chaotic nothingness into this very symmetrical structure."

Research has found that the symmetry of the pearl has become more and more precise as it is constructed, answering centuries of questions about how the disorder at its center has become perfect.

Nacre is a rainbow-colored and extremely durable organic-inorganic composite material that also forms the shell of oysters and other mollusks. It is built on the aragonite fragments surrounding the organic center.

These layers account for more than 90% of the pearl's volume, and as they accumulate from the center outwards, these layers gradually become thinner and more closely matched.

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Perhaps the most surprising finding is that molluscs maintain the symmetry of the pearl by adjusting the thickness of each layer of nacre. If one layer is thicker, the next layer is often thinner, and vice versa. The pearls depicted in the study contained 2,615 carefully matched nacres with a deposition time of more than 548 days.

"These thin and smooth nacres look a bit like sheets with organic matter in between," Hofden said. "Each layer has an interaction, and we assume that this interaction enables the system to correct as it progresses."

The team also discovered detailed information about how the interactions between the layers work. Mathematical analysis of the nacre shows that they follow a phenomenon called "1/f noise", in which a series of seemingly random events are related to each other, and each new event is affected by the previous event. 1/f noise has been proven to control various natural and man-made processes, including seismic activity, economic markets, electricity, physics and even classical music.

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"For example, when you roll a dice, each roll is completely independent and separate from every other roll. But the 1/f noise is different because each event is related to each other. "Hofden said. "We can't predict, but we can see a structure in the chaos. In this structure is a complex mechanism that allows the thousands of layers of pearls to be combined in an orderly and precise manner."

The research team found that the pearl lacks true long-range order—this carefully planned symmetry keeps the hundreds of floors in the brick house consistent. In contrast, pearls exhibit a mid-range order, maintaining about 20 layers of symmetry at a time. This is enough to maintain consistency and durability in the thousands of layers that make up the pearl.

The team collected their observations by studying Akoya “keshi” pearls produced by Pinctada imbricata fucata oysters near the eastern coast of Australia.

They chose these special pearls with a diameter of about 50 mm because they are naturally formed instead of nucleated cultured pearls with artificial centers. Each pearl is cut with a diamond wire saw into a part of 3 to 5 mm in diameter, then polished and inspected under an electron microscope.

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Hofden said that the results of the study published in the Proceedings of the National Academy of Sciences can help provide information for the next generation of materials with precise hierarchical nanoscale structures.

“When we build things like brick houses, we can build them periodically through careful planning, measurement and formwork,” he said. "Molluscs can achieve similar results at the nanoscale by using different strategies. So we have a lot to learn from them, and this knowledge can help us make stronger and lighter materials in the future."

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