Scientists create self-healing, touch-sensitive plastic for prosthetic limbs

Scott Sutherland
November 13, 2012

Professor Zhenan Bao, and her team from Stanford University, have succeeded in creating a plastic that combines touch sensitivity and the ability to self-heal at room temperatures, making it an ideal material for the construction of artificial limbs, and potentially for self-repairing electronic devices.

There have been many advances in self-healing artificial skin over the past 10 years, however there have been drawbacks to many of these discoveries. Some materials required high temperatures to self-heal, making them impractical, while others could only heal once because the repairing process changed their chemical or mechanical structure. Also, none of these materials were good conductors of electricity, which not only is a crucial property for touch-sensitivity, but also for interacting with electronic devices.

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"To interface this kind of material with the digital world, ideally you want them to be conductive," said Benjamin Chee-Keong Tee, a PhD candidate in Stanford's Bao Research Group, according to Science Daily.

To make the material able to repeatedly self-heal, they used long chains of molecules that are strung together with weak hydrogen bonds. This allows the chains to break apart relatively easily, but they join back together just as easily. A cut in the material takes roughly 30 minutes to completely and seamlessly heal itself.

"Even human skin takes days to heal. So I think this is quite cool," said Tee.

Plastics tend to be good insulators, meaning that electricity does not flow freely within them, so for the material to be conductive, the team embedded it with 'nickel nanostructured microparticles' — particles that are between 0.1 and 100 micrometres in size, with structure on their surface or inside that is much smaller. These nickel microparticles allow electrons to be passed between them, thus setting up a current across the material. This flow of electricity allows the material to be touch-sensitive, because putting pressure on the material, or bending or stretching the material changes the distance between the microparticles, and thus how easily electrons are passed between them (particles close together pass electrons easier and particles farther apart). This information can be interpreted and used to determine downward pressure, allowing the 'skin' to sense a touch, a handshake, and tension, to tell how far a limb is rotated or how far a joint is bent.

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The researchers also see this material becoming useful for coating electrical wires and electronic devices, allowing them to repair themselves. The research is published in the November 11 issue of Nature Nanotechnology.