Stanford University material scientists have devised the first synthetic, plastic skin that is conductive, sensitive to touch, and capable of repeatedly self-healing at room temperature. The most immediate applications are in the realm of smart, self-healing prosthetic limbs that are covered in this synthetic skin — but in the long term, the plastic might be used to make self-healing electronic devices, or you might even elect to replace your fingertips (or other piece of skin) with the synthetic, bionic equivalent.

There are two important innovations here: a synthetic material that can repeatedly self-heal, and the fact that it’s electrically conductive — meaning it can detect changes in pressure and temperature (i.e. it’s sensitive, like real skin). We’ll tackle the self-healing bit first.

The Stanford team, led by Zhenan Bao, started with plastic polymer that’s held together with hydrogen bonds. In the world of chemistry, hydrogen bonds are special because they’re much weaker than covalent or ionic bonds, and readily break and reform. Water is probably the best example of hydrogen bonding: You can easily split a droplet of water in two, and yet they readily join back together (self-heal). In short, the plastic that Stanford created can be cut in half — and then, when the segments are placed next to each other, they join back together within 30 minutes at room temperature.

To make the plastic conductive, the team simply mixed in some microparticles of nickel. The nickle particles bond with the polymer and allow electricity to flow across the skin, effectively jumping between the nickle particles like stepping stones. The nickle also increases the mechanical strength of the synthetic skin. Curiously, the team tried using carbon nanotubes instead of nickel, but they did not play well with the polymer and thus didn’t increase conductivity.

The end result is an electrically conductive, self-healing synthetic skin. In testing, the researchers cut the skin in half with a scalpel, then pushed it back together. Within a few seconds, the skin had regained 75% of its mechanical strength and conductivity — within 30 minutes, the skin was fully restored. As far as its electrical properties go, the skin is fairly conductive, and its electrical resistance changes depending on pressure and tension. For example, if you had a prosthetic hand covered in this skin, it would theoretically be possible to convert an incoming handshake into electrical signals that are then wired into your nervous system.

Beyond prosthetics, this polymer could also be used to coat wires — and if they break, the polymer would self-heal and restore conductivity. This could be a useful fallback in electrical/computer systems that cannot fail, or in sprawling systems with very hard-to-reach wiring. (See: Liquid metal capsules used to make self-healing electronics.)

The team is now working on a stretchy and transparent version of the self-healing plastic, which would increase its potential uses dramatically. Before we know it, your smartphone or tablet might have a self-healing touchscreen display.

Research paper: doi:10.1038/nnano.2012.192 – “An electrically and mechanically self-healing composite with pressure- and flexion-sensitive properties for electronic skin applications”