The smart clothes we hear about today, like shirts and shorts that monitor your health while you run, typically include sensors that have been woven into or clipped onto fabrics. For the most part, these sensors aren’t printed, which can make them more costly and more rigid. “We wanted to make wearable devices that were more skinlike,” said Amay Bandodkar (UCSD BioE, ’16), who is an author of the study. “Just like the human skin is stretchable and self-healing, we wanted to impart a self-healing ability to printed electronics.”

The ink that Dr. Bandodkar and colleagues created includes ground neodymium magnets, which are found in hard drives and fancy refrigerator magnets. “We basically just pulverized these magnets into microscopic particles and incorporated them into the ink,” said Dr. Bandodkar, who is now a postdoctoral fellow at Northwestern University.

Traditionally, attempts to create self-healing materials have relied on a chemical reaction called polymerization. While this has the benefit of actually melding broken fragments back together via chemical bonds (as opposed to magnetic attraction holding two pieces together), self-healing polymer systems have limitations. They often require external inputs like heat, cannot seal large cracks and can take anywhere from hours to days to actually repair themselves.

Using magnetic particles “is a new concept for self-healing,” said Zhenan Bao, an engineering professor at Stanford University who was not involved in the study. Compared to previous approaches, “this method is simple, fast and does not require adding heat, light or other chemicals.”

Magnetic ink is also cheap: Dr. Bandodkar estimated that $10 worth of ink materials can yield hundreds of small devices. The next steps, he said, are to determine the optimal ratios of ink ingredients for specific applications, which could take at least a couple of years.

Ultimately, Dr. Bandodkar thinks that these inks can make their way into everything from solar panels to implantable medical devices. To him, though, one of the coolest applications is just everyday technology anyone can wear. “If you’re wearing a device on your skin and it gets broken as you move around, you don’t have to throw it away,” he said. “Within a few seconds it’s going to self-heal, and you can use it over and over again.”