A pit viper

Pit viper-inspired mechanism improves artificial skin's temperature sensing

Image credit: Rushenb

Artificial skin based on the plant-cell saccharide pectin can sense temperature with the greatest accuracy ever achieved.

The material relies on a mechanism similar to the one that pit vipers use to sense warm prey in the dark. It detects radiated heat through ion channels in cell membranes that expand as temperature increases, allowing calcium ions to enter and trigger a reaction.

The skin, described in an article in the journal Science Robotics, can sense temperature changes smaller than 0.01 °C. Earlier artificial skins were only able to register differences an order of magnitude greater. The new material also has a much greater temperature range of more than 45 °C compared to only 5 °C of previously developed electronic skins.

The team of researchers from ETH Zurich and the California Institute of Technology (Caltech) who developed the skin believe it could be used in prosthetics to restore amputees' ability to sense temperature. It could also serve as a temperature-sensitive bandage in wound healing, alerting doctors to signs of infection.

The researchers made the discovery almost by accident. A Caltech team led by Chiara Daraio was cultivating synthetic woods in a petri dish. One of the experimental materials, when tested, was electrically responding to temperature changes. The scientists looked into what was going on inside and found that the temperature response was due to the presence of pectin, a polysaccharide present on plant cell walls.

“Pectin is widely used in the food industry as a jellifying agent; it's what you use to make jam,”Daraio explained. “It's easy to obtain and also very cheap.”

The team further developed the material into a 20 micrometre-thick transparent flexible film containing only pectin and water.

Pectin molecules in the film have a weakly bonded double-strand structure that contains calcium ions. As temperature increases, these bonds break down and the double strands ‘unzip’, releasing the positively charged calcium ions.

Either the increased concentration of free calcium ions or their increased mobility results in a decrease in the electrical resistance throughout the material.

So far, the skin is capable of detecting temperature changes across a range between 5 and 50 °C but the team hopes to be able to increase the range up to 90 °C. This would make pectin sensors useful for industrial applications, such as thermal sensors in consumer electronics or robotic skins to augment human-robot interactions.

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