Researchers at Carnegie Mellon University, United States, and Kyushu University, Japan, have developed a polymer that can repair itself when irradiated with UV light – over and over again. It is the first material in which capped covalent bonds repeatedly reattach, even allowing fully separated pieces to be fused back together. Other solid self-healing materials can repair themselves one time, or can repair themselves repeatedly, but lack the covalent bonds that increase the material’s strength and stability. The new polymer is cross-linked with trithiocarbonate units, which are carbon atoms bonded to three sulfur atoms, two of which use their special bonding position to attach to another carbon atom. These groups are able to restructure under UV light, so much so that even shredded polymer samples could simply be pressed together and irradiated to be fused into a continuous piece. This self-healing process could be carried out repeatedly on the same sample. The scientists’ findings were reported in the journal Angewandte Chemie.