The artificial electronic skin project at Stanford University has come a long ways since we first wrote about it back in 2010. It was amazing enough that the synthetic dermis they developed was so sensitive to changes in pressure that it could detect when a fly landed on it. Newer versions included chemical and biological sensors that can detect certain kinds of DNA. Early last year, head researcher and associate professor of chemical engineering, Zhenan Bao, succeeded in creating stretchable solar cells that would power the artificial skin.
The latest skin that Bao and her team have created features some amazing self-healing properties. However, unlike self-healing polymers currently out, the features of Bao’s skin make it stand far apart from the rest. Some self-healing materials require them to be exposed to high temperatures or UV light to activate the healing properties; the Stanford skin healed itself at room temperature by simply pressing the cut pieces together for no more than 30 minutes. Other self-healing materials heal, but their mechanical and/or chemical structures are actually permanently altered, so they can only heal themselves once. The Stanford skin was cut in the same place 50 times and managed to repair itself close to 100 percent of its original strength each time and managed to be an excellent conductor of electricity both before and after the cuts were made.
The secret behind this amazing material, according to the team, is a special combination of a self-healing polymer and a conductive metal:
They started with a plastic consisting of long chains of molecules joined by hydrogen bonds – the relatively weak attractions between the positively charged region of one atom and the negatively charged region of the next.
“These dynamic bonds allow the material to self-heal,” said Chao Wang, another member of the research team. The molecules easily break apart, but then when they reconnect, the bonds reorganize themselves and restore the structure of the material after it gets damaged, he said. The result is a bendable material, which even at room temperature feels a bit like saltwater taffy left in the fridge.
To this resilient polymer, the researchers added tiny particles of nickel, which increased its mechanical strength. The nanoscale surfaces of the nickel particles are rough, which proved important in making the material conductive. Tee compared these surface features to “mini-machetes,” with each jutting edge concentrating an electrical field and making it easier for current to flow from one particle to the next.
If self-healing artificial skin wasn’t amazing enough, it is also pressure and flex sensitive! According to the research team, the material can detect the pressure of a handshake and, if used in a prosthetic, may provide information on a joint’s angle of bend.
Article from Stanford University: Stanford’s touch-sensitive plastic skin heals itself
Journal Abstract from Nature Nanotechnology: An electrically and mechanically self-healing composite with pressure- and flexion-sensitive properties for electronic skin applications