The human skin is not only capable of perceiving touch, it can also sense temperature. Engineering artificial skin needs materials that can feel changes in temperature while being ultra-thin and flexible. Scientists at the Chinese Academy of Sciences have developed a material that can sense the temperature of objects with high accuracy and without directly touching them. This technology has many potential applications but is especially intriguing when it comes to robotics, health monitoring, and prosthetics.
Temperature Is Part of How We Experience the World
Our sense of touch is a vital piece of how we interact with the world around us. Imagine sitting on a beach, seeing the blue ocean, hearing the screeching of seagulls, smelling the salty breeze, and tasting the sweet flavour of ice cream, and feeling the soft sand under your toes. But what if your ability to perceive heat and chill was missing? How would it feel if you could not sense the warm rays of the sun on your skin or the cold touch of the ice cream on your lips? Temperature is a vital dimension of our experiences. Our skin contains special receptors that can discern hot and cold temperatures; they convert it to an electric signal that travels to the brain1. Sensing temperature helps us navigate our world safely, especially when we encounter extreme temperatures. Our skin does a marvellous job of detecting very slight changes in temperature, even without directly touching objects.
Engineering Artificial Skin to Sense Temperature
Scientists are building artificial skin for use in robotics and other fields. To imitate human skin, it must sense not only pressure (touch) but also temperature. Most prototypes for artificial skin could only sense temperature by directly touching an object. However, in multiple circumstances, direct touch can be dangerous. When checking if a plate on a stove is hot, you don’t want to place your hand on it, rather just hover over it to feel the heat from a distance. What we call ‘heat’ is thermal energy.
Thermal energy travels through space as infrared waves. These waves radiate out of anything warm. Our skin can sense these infrared waves using special receptors. Creating artificial skin that can distinguish temperature changes from a distance, necessitates a material that can detect infrared waves from a distance, yet is also very thin and flexible.
Researchers at the Chinese Academy of Science have found a promising solution to this problem2. They used a material called tellurium, a rare metalloid that converts changes in temperature into electricity. When infrared waves hit tellurium it creates a change in voltage, which we can measure and record. The researchers optimized the properties of tellurium by adding ultra-thin copper so that it could detect even smaller changes in temperature. They embedded the tellurium-copper mix into a sheet of polyimide, which is a flexible, light, insulating, and heat-resistant material a bit like plastic. By combining the optimized tellurium with the polyimide, they generated a thin, flexible, and highly sensitive sensor for infrared waves to measure temperature without direct contact.
Applications for New Thermosensory Material
In their publication, the researchers already demonstrated one use-case for their novel temperature sensing technology2: a robotic claw coated with the new material only grabbed a glass if the water inside had a reasonable temperature. If it was too hot or too cold, it did not touch it.
This prototype highlights a potential application in robotics. Robots could use these sensors to detect changes in temperature in their environment, allowing them to navigate more effectively and safely.
Given that this sensor is thin and highly accurate, it could also be integrated into consumer electronics, such as smartphones or smartwatches. On the one hand, it could provide users with more information about their environment, like the temperature of the room they are in. On the other hand, people could use it to monitor their own body temperature as part of health surveillance. This could be incredibly useful for athletes, patients with chronic illnesses, women tracking fertility or elderly people who need a regular assessment of health parameters, including temperature.
Artificial Skin for Prosthetics?
Finally, and perhaps most intriguingly, this innovation could be highly beneficial in prosthetics. Prosthetics to replace lost limbs is a challenging technology. Our movements are guided by feedback from touching and interacting with objects. Adding a sense of touch to prosthetics is still in the early stages but research shows the enormous benefits for patients3. When a person with a prosthetic arm grabs an object, the feedback from touch allows for much better and easier handling. What’s more, having a sense of touch reduces phantom pain. Introducing the component of temperature to touch, could enhance the sensation’s quality because it gives a more realistic feel of the surroundings. It would also enable prosthetic users to better protect themselves from injuries by avoiding handling objects that are too hot or too cold. This could significantly improve their independence and quality of life. One day, a person might sit on the beach, feeling the warmth of the sun and the cold of the ice cream on their artificial arm – feeling as complete as all the other people sharing this experience.
References
- Bensmaia SJ, Tyler DJ, Micera S. Restoration of sensory information via bionic hands. Nat Biomed Eng 2020 74. 2020;7(4):443–455. doi:10.1038/s41551-020-00630-8
- Guo X, Lu X, Jiang P, Bao X. Touchless Thermosensation Enabled by Flexible Infrared Photothermoelectric Detector for Temperature Prewarning Function of Electronic Skin. Adv Mater. 2024;2313911:8-14. doi:10.1002/adma.202313911
- Jabban L, Dupan S, Zhang D, Ainsworth B, Nazarpour K, Metcalfe BW. Sensory Feedback for Upper-Limb Prostheses: Opportunities and Barriers. IEEE Trans Neural Syst Rehabil Eng. 2022;30:738-747. doi:10.1109/TNSRE.2022.3159186
