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Hard but lightweight ‘bio-metal’ material discovered in sea worm jaws
The marine ragworm Perinereis cultrifera
Steve Trewhella / Alamy
The jaws of some sea worms are made of an exceptionally hard yet lightweight material dubbed a “bio-metal” that could have applications in engineering.
Perinereis cultrifera is a type of ragworm with a long body adorned with bristles. Members of the species also have strong jaws that enable them to crush hard prey such as small crustaceans or other worms. Remnants of their jaws have been found in the fossil record dating back to hundreds of millions of years ago.
Christian Hellmich at TU Wien in Austria and his colleagues have been studying this worm’s jaws for almost a decade, leading them to propose that they are made of a novel material. The molecular structure of each jaw combines proteins and ions of metals such as zinc, giving it characteristics in between those of softer biological materials and metals.
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Most recently, the team performed more than 3300 experiments in which small indentations were made in different parts of the jaw. The way its hardness changed under this pressure followed a pattern typical of metals like copper and silver. But the jaw also exhibited a kind of elasticity that metals cannot have, says Hellmich.
Finally, the researchers developed a mathematical model of bio-metals, which shows how they might respond to strain in a unique way in which microscopic forces arise from the metal ions becoming arranged into lines similar to certain defects in crystals.
The researchers were surprised to uncover so much novelty in the relatively simple animal. Performing mechanical tests on the millimetre-sized jaw was really challenging and required hundreds of hours of preparation and polishing, says Hellmich. “Basically, anything can go wrong,” he says.
“The jaws of bristle worms are incredibly hard yet very lightweight,” says Matthew Lehnert at Kent State University in Ohio. “Many industries, from automobiles to aeronautics, are searching for new ways to develop hard and lightweight materials. The answers are provided in nature!”
“Somehow evolution figured out a way to coax a metal-like mechanical fingerprint out of protein-like ingredients, and studying the worm is how we ask what trick makes that possible,” says Markus Buehler at the Massachusetts Institute of Technology, who didn’t work on the study. The long-term dream outcome of this research is to genetically program materials that would grow in biological systems, he says.
Hellmich and his colleagues are interested in pursuing this goal and their team already includes geneticists and biologists at the University of Vienna. “We are asking questions like, ‘If we knock out a few genes, then how will the jaws be different?’” he says.
Journal Reference:
Biophysics Reviews DOI: 10.1063/5.0325367
Special relativity can warp chemical bonds – now we’ve seen it happen
In some heavy atoms, like those of bismuth (pictured in crystalline form), electrons move at relativistic speedssavva_25/Shutterstock
Albert Einstein’s theory of special relativity can reshape chemical bonds within molecules, and researchers have just seen it happen for the first time.
The theory of special relativity describes how moving at speeds close to the speed of light would affect travellers’ experience of space and time. Because of this, it is usually associated with particle accelerators and spacefaring objects, but within some heavy atoms, electrons experience relativistic speeds too.
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Lai-Sheng Wang at Brown University in Rhode Island and his colleagues have now managed to take an unprecedented look at how this breaks the standard notion of chemical bonds within a charged molecule made from bismuth and carbon.
Within the molecule, a bismuth atom and a carbon atom were connected by three bonds, one of which the researchers expected to be of “sigma” type and two of “pi” type. The difference between these two types stems from electrons’ quantum character – each electron is “smeared” across some region of space, instead of being a tight ball, and whether these regions overlap head on or side by side determines the type of chemical bond they create between the atoms.
In their experiment, Wang and his colleagues mapped the distribution of electrons throughout the molecule, effectively getting a look at its bonds. But instead of seeing electrons distributed in shapes associated with sigma and pi bonds, the team noticed that two of the bonds resembled two different mixes of sigma and pi shapes. “Their characters are different from our normal understanding,” says Wang. “You can’t really call it the sigma and pi.”
His team turned to Kirk Peterson at Washington State University, whose calculations ultimately showed that this mixing was a consequence of electrons near the bismuth nucleus feeling such a strong electromagnetic interaction that they moved at relativistic speeds. He says this effect hadn’t previously been captured in an experiment.
“The hardest thing about [studying] heavy elements is a lack of really good experimental data,” says Peterson. “To have such a beautiful experiment to be able to essentially compare very high-level theory to data is really a luxury.”
Wang says one important part of the new experiment is that he and his colleagues could make the molecule very cold before looking at its electrons. This dampened any jitters and excitations that would have made the final images imprecise.
“As you go down to the bottom of the periodic table, the usual quantum mechanics is no longer sufficient, you need to take into account the effects of relativity,” says Trond Saue at the University of Toulouse in France. He says that all elements in the same row of the periodic table as bismuth are affected by relativistic effects – for instance, gold would be the same colour as silver and mercury would not be liquid without them.
Pekka Pyykkö at the University of Helsinki in Finland says that for bismuth, the relativistic effect on its bonding with carbon could influence how organic bismuth compounds are used in chemical reactions. In fact, a recent study by researchers at the Max Planck Institute for Coal Research in Germany has already shown that relativistic effects help make this heavy metal a good catalyst, or accelerator, of chemical processes.
Wang says that the team now wants to repeat their experiment but swap bismuth for elements close to it in the periodic table to see when exactly special relativity makes the traditional chemical bond structure collapse.
Journal reference:
Science DOI: 10.1126/science.aei1285
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