The human skin, with all its frailties, turns out to be difficult to recreate, let alone improve on. The main challenge: It manages to be both self-healing and sensitive to the touch, enabling it to send vital information to the brain about temperature and pressure.
But chemists and engineers at Stanford say they are one step closer to developing an electronic skin that has both these properties, and they report this week in the journal Nature Nanotechnology that it could help lead to smarter prosthetics and more resilient, self-repairing electronics.
Their central task was to find a self-healing material (a plastic polymer would ordinarily do the trick) that was also a good conductor of electricity (which typically requires metals). "To interface this kind of material with the digital world, ideally you want it to be conductive," Benjamin Chee-Keong Tee, a researcher on the project, said in a school news release.
They found that a plastic made of long chains of molecules linked up via hydrogen bonds provided weak attractions between differently charged regions of atoms, which result in self-healing. Because the molecules easily break apart and then reorganize to restore their original structure, the result is a flexible material they describe as feeling -- even at room temperature -- like saltwater taffy left in the fridge.
They then embedded tiny particles of nickel into the polymer to increase its strength. Tee calls these rough surfaces "mini-machetes," with tiny electrical fields that enable current to easily flow from one particle to another.
"Most plastics are good insulators, but this is an excellent conductor," said lead researcher and chemical engineering professor Zhenan Bao.
The material is also sensitive enough to detect the pressure of a handshake, whether that pressure be downward or flexing, meaning a prosthetic limb could detect the actual degree of bend in a joint. And coating electrical devices in this material could render those devices capable of getting electricity flowing again if they are damaged.
Bao's team is now concentrating on the next goal: to make the material both stretchy and transparent, so that it could wrap around and overlay electronic devices or display screens.