Heat-sensitive artificial skin mimics viper organ

Researchers at the California Institute of Technology and ETH Zurich have created an artificial skin that can sense temperature changes, which could enable amputees to sense heat via prosthetics.

(Credit: Thai National Parks)
(Credit: Thai National Parks)

The skin uses a mechanism similar to that of the pit organs in vipers, which allow the snakes to sense prey in the dark by detecting its heat. It was discovered when the team was fabricating synthetic wood in the lab, and created a material with an electrical response to temperature changes. The component responsible was found to be pectin.

“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,” said research lead Chiara Daraio, professor of mechanical engineering and applied physics at Caltech’s Division of Engineering and Applied Science.

Using water and pectin, the team created a thin film just 20 micrometres thick. The pectin molecules have a weakly bonded double-strand structure that contains calcium ions. The bonds break down as temperature rises and the double strands ‘unzip’, releasing the positively charged calcium ions.

The researchers believe that the increased concentration of free calcium ions, combined with their enhanced mobility, causes a decrease in the electrical resistance of the film. This can be detected with a multimeter connected to electrodes embedded in the material. With pit vipers, ion channels in the cell membrane of sensory nerve fibres expand as temperature rises, which allows calcium ions to trigger electrical impulses.

According to the team, this new skin is significantly better than existing synthetic skins at sensing temperature changes. It can detect changes of less than a tenth of a degree Celsius across a 5-degree range. Currently, it can only operate between 5 and 50 degrees Celsius, making it suitable for robotic and biomedical applications. Daraio and her team plan to tweak the fabrication process to extend the range up to 90 degrees, opening up possible industrial applications such as thermal sensors in consumer electronics, or robotic skins to augment human-robot interactions.