Researchers for engineering materials often find ideas among sea creatures--mother-of-pearl for smooth surfaces, clams with their inherent glue findings, and shark's skin that provides inspiration for non-drag materials in water use. A recent study from the University of Copenhagen found that a sea urchin cousin, the heart urchin, is a model for sturdy but lightweight materials. Their report was recently published in the journal Acta Biomaterialia.

Known as sea potatoes, the heart urchin or Echinocardium cordatum measures around 5 cm in diameter and is, yes, heart-shaped. It burrows in sand. Like the ordinary kind of sea urchin, these creatures have soft centers but exoskeletons made of calcium carbonate protect them. Those shells also can really taking a wave thrashing, it turns out, according to a release.

After assistant professor Dirk Müter noticed that the thin sea-potato shells were not blemished despite being bounced around by waves on beaches, he and colleagues used X-ray microtomography to make 3D images of the material make-up of the shells, without breaking them into pieces. They were able to see the structures at less than one-thousandth of a millimeter of distinction, which made it possible to glean why the shells were so strong, the release confirmed.

The calcium carbonate involved is chalky, but it consists of more air than chalk. In it are a huge number of microscopic openings that are given structure by thin calcium carbonate struts. In a cubic millimeter, there are between 50,000 and 150,000 struts, and sometimes the shells are 70 percent air, said a release.

As it happens, these heart urchin shells can be up to six times sturdier than chalk.
"We found an example of a surprisingly simple construction principle. This is an easy way to build materials. It allows for great variation in structure and strength. And, it is very near optimal from a mechanical perspective," Müter said in the release.

It's likely, Müter and colleagues said in the release, that their findings can later be applied to making shock-absorbent materials perform better, and other outcomes.

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