A chance discovery in a petri dish led a Caltech researcher to develop a new, extremely temperature-sensitive type of artificial skin.

The material could be used on prosthetic devices to sense temperature change or as a bandage that would alert a nurse or doctor about a developing infection in a wound.

Pectin-based artificial skin. Credit: CaltechProf. Chiara Daraio and her team were fabricating synthetic woods when they created a material that produced an electric response to temperature changes. The component responsible for this quality turned out to be pectin, the ingredient that makes jelly jell.

She and her research team worked to produce a thin, transparent, flexible film from pectin and water. This film can be as thin as a human hair, or about 20 micrometers. The pectin molecules have a weakly bonded double-strand structure containing calcium ions. Increasing temperature causes the bonds to break, freeing the positively-charged calcium ions.

This release of ions acts to decrease the film’s electrical resistance, detected by electrodes embedded in the film.

The new “skin” senses temperature similarly to the way a pit viper does. The snakes use their pit organs to detect prey by sensing body heat. An increase in ambient temperature causes expansion of ion channels in sensory nerves, allowing calcium ions to flow.

Other electronic skins can sense very small (one-tenth of a degree Celsius) temperature changes over a five-degree range. The pectin-based skin’s response is two orders of magnitude larger than that of these other skins over a 50 degree range.

Daraio and her team are working on extending the temperature range sensitivity to 90 degrees Celsius. With an increased range, the material could be appropriate for industrial robots and temperature sensors.