Scientists have been cooking up all kinds of strange things in the lab lately, from diamonds to meat to human retinas. And now they’ve got a new one ready to roll out: Fake skin. But not just a reasonable facsimile of how skin might look or feel to the touch. The ersatz epidermis mimics some of the most impressive attributes of our largest organ, like the ability to sense subtle pressure and heal itself when cut.
In the last decade, there have been major advances in creating synthetic skin — the scientific quest for "Terminator"-type self-healing materials has been many a researcher's mission. Some of the earlier attempts required impractical high temperatures for self-healing to occur. Others could repair themselves at room temperature, but only once. And importantly, all previous self-healing materials lacked the crucial property of being able to conduct electricity, which is required for sensing and interfacing.
But now, Stanford chemical engineering professor Zhenan Bao and her team have come up with a design that offers both the self-healing ability of a plastic polymer and the conductivity of a metal. The secret? A plastic consisting of long-chain molecules joined by hydrogen bonds, to which nanoscale particles of nickel were added for conductivity and increased mechanical strength.
The result was a polymer with unusual characteristics: the sci-fi ability to repair itself, along with flexibility, conductivity and, for those of you who are tactile-minded, the feel of saltwater taffy.
The molecules easily break apart, but when they reconnect, the bonds reorganize themselves and restore the structure to the pre-break state. The researchers tested the material by cutting a strip of it in half, and then gently pressing it back together. After a few seconds the material returned to 75 percent of its original strength and electrical conductivity. After 30 minutes the material was restored to 100 percent. They repeated the process 50 times, each time it returned to normal. "Even human skin takes days to heal. So I think this is quite cool," said Benjamin Chee-Keong Tee, first author of the paper.
The team also explored how to use the material as a sensor. As described in a release for the material: "For the electrons that make up an electrical current, trying to pass through this material is like trying to cross a stream by hopping from stone to stone. The stones in this analogy are the nickel particles, and the distance separating them determines how much energy an electron will need to free itself from one stone and move to another."
Since the material is flexible, twisting or pulling upon it varies the distance between the nickel particles and, hence, the ease or hindrance with which the electrons can move. It is these subtle changes in electrical resistance that translate information about pressure and tension on the skin, hence, the ability for it to "feel."
The material might be ideal for use in prosthetics, Bao suggested. The researchers also pointed out other commercial possibilities, including coating electrical devices and wires used in hard-to-reach places, minimizing the need for costly repair.
Their findings were published in the journal Nature Nanotechnology.
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