Smart synthetic skins have the potential to allow robots to touch and sense what's around them, but keeping them powered up and highly sensitive at low cost has been a challenge.

Now scientists report in the journal ACS Nano a self-powered, transparent smart skin that is simpler and less costly than many other versions that have been developed.

Endowing robots and prosthetics with a human-like sense of touch could dramatically advance these technologies. Toward this goal, scientists have come up with various smart skins to layer onto devices.

But boosting their sensitivity has involved increasing the numbers of electrodes, depending on the size of the skin. This leads to a rise in costs.

Other systems require external batteries and wires to operate, which adds to their bulk. Haixia Zhang and colleagues wanted to find a more practical solution.

The researchers created a smart skin out of ultra-thin plastic films and just four electrodes made from silver nanowires. Other prototypes contain up to 36 electrodes.

Additionally, one component harvests mechanical energy - for example, from the movement of a prosthetic hand's fingers - and turns it into an electric current. Therefore, the skin wouldn't need an external power source.

Testing showed that the skin was highly sensitive. It could "feel" a honeybee as it flew toward and away from the device. It also demonstrated electrical stability, maintaining the same level of output over 30,000 cycles.