Stanford scientists have for the first time created a synthetic material that can sense subtle pressure and heal itself when torn or cut.
While similar materials have been developed in the past, some have required high temperatures, making them impractical for day-to-day use. For others, repairing a cut changed their mechanical or chemical structure, so they could only heal themselves once. Most importantly, no self-healing material has ever been a good bulk conductor of electricity.
"Before our work, it was very hard to imagine that this kind of flexible, conductive material could also be self-healing," says Chao Wang.
The researchers started with a plastic consisting of long chains of molecules joined by hydrogen bonds. The molecules break apart easily - but when they reconnect, the bonds reorganize themselves and restore the structure of the material. The result is a bendable material.
The addition of tiny particles of nickel increased its mechanical strength; and, because the nanoscale surfaces of the nickel particles are rough, the material is conductive.
When a thin strip of the material is cut in half with a scalpel and the pieces gently pressed back together for a few seconds, it regains 75 percent of its original strength and electrical conductivity. After about thirty minutes, this rises to almost 100 percent.
"Even human skin takes days to heal. So I think this is quite cool," says Benjamin Chee-Keong Tee.
What's more, the same sample could be cut repeatedly in the same place. After 50 cuts and repairs, a sample withstood bending and stretching just like the original.
It's sensitive enough to detect the pressure of a handshake, meaning it could be be ideal for use in prosthetics. It could also be used to coat electrical devices and wires, so that they could repair themselves.