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Scientists have developed a smart crystal that can heal itself after breaking without any chemical or biological intervention. The crystal relies on its own molecular structure and physical contact to heal—similar to cuts on skin.

Self-healing polymers have been subject to chemists’ investigations for more than a decade and until now have only been observed in softer materials like rubber and plastic.

Pale yellow crystals the size of a baby’s fingernail—and about 0.5 mm thick—were grown in a lab by Patrick Commins, postdoctoral associate researcher at NYU Abu Dhabi and lead author of a paper in the journal Angwandte Chemie International Edition.

Commin says the research with dipyrazolethiuram disulfide crystals was inspired by the relationship between sulfur atoms in soft polymers, which tend to flow toward neighboring sulfur atoms and bond with them easily resulting in self-repair. He decided to test the same bond in crystals.

“What happens when we break the crystal is that we have all these sulfurs moving around and when we press them together they reform their bonds and they heal,” Commins explains.

Commins says the crystal was broken using a machine built specifically to hold tiny objects and that has the capability to break the object cleanly. The two halves of the broken crystal were mechanically brought into contact with each other at room temperature. Twenty-four hours later the crystal was whole again.

The only defect was a superficial mark left behind by the crack in the middle. The percentage of healing was 6.7 percent, which researchers calculated by comparing the amount of force required to break the crystal before and after the healing process.

“This is actually a small breakthrough because it kind of shows a concept that was not considered possible before,” says coauthor Panče Naumov, associate professor of chemistry at NYU Abu Dhabi. “It is the first time we’ve observed that rigid entities like crystals can self-repair. This was not expected. It’s certainly a shift in our understanding of crystals.”

“Crystals found in nature are made from minerals, like calcium and silicates, but this crystal is different,” Commins adds. “The crystal has been made specifically to have many close sulfur-sulfur bonds and they grow in rather small sizes.”

Commins believes this research is just the beginning.

“We think other crystals can do it (self-heal) but no one has actually explored it. We’ve only investigated one aspect of this field. We are expanding upon the subject and are trying to find other self-healing crystals,” he says.

Hideyuki Hara, research scientist at Bruker in Japan, is also a coauthor of the paper.

Source: New York University