We all want to find ways to have materials repair themselves. So, when our kids rip their pants, the holes will disappear. Or, when cracks appear in concrete, they will refill the space and keep our structures sound. (Oh, wait, I reported on BacillaFilla some 6 years ago…  and, yet- it’s still not commercially available. Such is the promise of research. Which may portend problems for what I plan to discuss today.)

This need led to using magnetic ink- comprised of microparticles- to see if were able to repair electrochemical sensors, wearable (textile) electric circuits, and batteries. A device that was printed with this ink- where the molecules have specific orientation according to the magnetic field- could be self- repairing. Even if the tear reaches a width of 3 mm (which is a new record for such systems).

Drs. AJ Bandodkar, CS López, AMV Mohan, L Yin, R Kumar and J Wang (UCSD Nanoengineering) published their article, All-printed magnetically self-healing electrochemical devices, in Science Advances.  This development is different from most of those other self-healing systems, in that there is no outside catalyst used and repairs take 50 milliseconds to complete. Those other systems require an external trigger to effect the healing process (the outside catalyst)- and can take several days for complete repair.

The researchers tested their ideas by using the ink to print the devices- and them damaged them by cutting them or pulling them apart. They even repeated the “injury”  at each location some nine times. And, for at least one device, the researchers damaged the products in four separate locations- and it still recovered functionality (with a minimal loss in conductivity).

The ink is comprised of neodymium (a silvery, soft metal, Nd2Fe14B )- which is a critical choice. The particle size is much smaller than the magnetic field they “project” for this material- which is how the tears get “repaired”. Except the magnetic fields of the particles tended to cancel each other out (and, therefore, won’t support the heaing process), probably because the ink was prepared from commercial magnets that were pulverized into powders.

So the researchers printed the ink under the influence of an external magnetic field, which causes the particles to properly align. Then, when the material is cut, the damaged ends can then act as different magnets that attract each other- hence, they self-heal.

The fact that the particles are cheap- and can conduct some electricity (but with pretty poor electrochemical properties)- helps. But, the particles are augmented by the addition of carbon black (normally present in batteries and sensors) to promote their ability to work in electrochemical devices and sensors.

The next step needed is to expand the catalog of inks used. This will afford the development of a wider range of materials.

But, then, again, this could be just like BacillaFilla (the self-repairing concrete mentioned above) – a great research idea that never reaches the marketplace.