New Plastic Bleeds Red When Scratched, Then Heals Itself Like Skin

Self-healing materials will eventually fix anything from cell phone screens to car fenders, enabling surfaces to heal on their own in the presence of different types of light. But none of the earlier prototypes we’ve seen work quite like this new plastic: It bleeds red at the site of injury. Then it heals itself, inspired by the properties of tree trunks and human skin.

Marek W. Urban from the University of Southern Mississippi presented a paper on his new co-polymer at the American Chemical Society’s national meeting in San Diego Monday. When it scratches or tears, a red splotch forms around the “wound,” marking the site.

Development of self-healing substances is one of the biggest current research areas in materials science, and we’ve seen a variety of approaches in these pages. Some would seed plastic or metal materials with capsules that break open when damage occurs, while others would stimulate plastics to re-grow chemical bonds using heat or light. This one works in a variety of situations — in the presence of sunlight, visible light from a light bulb, in pH changes or in different temperatures.

Urban’s plastic is made from water-based copolymers, which are more environmentally friendly than other polymers. They contain a type of molecular link that serves as a bridge in the polymer chain. When the plastic is scratched, cut or cracked, these bridges break. Urban’s breakthrough was to design bridges that produce a visible color change — in this case, a red blotch. The copolymer would work as a thin coating on top of other layers of plastic or other material, he said.

Unlike other self-healing materials, this plastic’s healing process can work over and over, he added. It could serve a variety of purposes, from things like nail polish to self-healing car fenders to airplanes. It would improve safety by drawing attention to a structural defect, and it could repair minor defects in the presence of intense light.

“Where degradation occurs or [there is] mechanical damage, the color would start to change,” Urban said.

The Defense Department funded part of his work.