Engineers and scientists from the California Institute of Technology (Caltech) and ETH Zurich have developed a temperature detecting artificial skin that could be used for prosthetic limbs in amputees.

A team led by Chiara Daraio at Caltech created a material from fabricating synthetic woods in a petri dish; the material has an electrical response to temperature changes. The scientists discovered that it was pectin, a long-chain molecule in plant cell walls, that was responsible for temperature sensitivity.

“Pectin is widely used in the food industry as a jellifying agent; it’s what you use to make jam. So it’s easy to obtain and also very cheap,” says Daraio, a professor of mechanical engineering and applied physics.

The research team used the pectin to create a thin, transparent, flexible film of pectin and water that could be as thin as 20 micrometers, the same diameter of human hair. The pectin molecules break their double-strand calcium ion structures when exposed to temperature increases. When the bonds break, the strands release positively charged calcium ions.

When there is an increase in the positively charged calcium ions, there is a decrease in electrical resistance from the material. A multimeter connected to electrodes embedded in the film can detect the electrical changes and sense temperature.

Other electronic skins can usually sense temperature changes of less than a tenth of a degree Celsius in a range of 5 degrees. The Caltech developed skin can sense temperature changes within a range of 45 degrees.

The Caltech artificial skin can detect temperature changes between 5 and 50ºC. The team hopes they can increase the range to max out at 90º.

The pectin film senses temperatures in a way similar to how vipers sense their prey in the dark—by detecting radiating heat. In the pit organs of a viper, ions in the cell membrane of sensory nerve fibers expand as temperatures increase. When the ions flow, electrical impulses are triggered.

The artificial skin could be used to graft onto prosthetic limbs amputees and restore temperature sensing. The film can also be used to alert doctors and nurses of a temperature increase in wounds, which could be a sign of infection.

The research was funded by the Swiss National Science Foundation and was published online on Feb. 1 in the Science Robotics journal.

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