Soft sensing technologies offer a less invasive way to measure the internal states. They have the potential to revolutionize wearable devices, haptic interfaces, and robotic systems.
However, due to their poor resilience, high energy consumption, and omnidirectional strain responsivity, such technologies have numerous challenges in the deployment.
Recently, scientists from the University of Cambridge reported developing self-healing, biodegradable, 3D-printed materials that sense strain, temperature, and humidity. What’s more, they can partially repair themselves at room temperature.
Earlier versions of the self-healing robots needed to be heated to heal. Unlike those, the newly developed materials can heal at room temperature, which would make them more useful for real-world applications.
David Hardman from Cambridge’s Department of Engineering, the paper’s first author, said, “We started with a stretchy, gelatine-based material which is cheap, biodegradable and biocompatible and carried out different tests on how to incorporate sensors into the material by adding in lots of conductive components.”
Instead of using carbon ink, scientists used salt in the printing sensors. Printing sensors containing sodium chloride – salt– resulted in a material with the properties they were looking for. Salt is soluble in the water-filled hydrogel. Therefore, it gives a uniform channel for ionic conduction – the movement of ions.
When scientists measured the electrical resistance of printed material, they found that changes in strain resulted in a highly linear response. This could be used to calculate the deformations of the material.
Adding salt also enabled sensing of stretches of more than three times the sensor’s original length to incorporate the material into flexible and stretchable robotic devices.
Thanks to their long-term strength and stability without drying out, the newly developed self-healing materials are preferable to many existing alternatives. They are cheap and easy to make: 3D printing or casting.
Co-author Dr. Thomas George-Thuruthel, also from the Department of Engineering, said, “It’s a really good sensor considering how cheap and easy it is to make. We could make a whole robot out of the gelatine and print the sensors wherever we need them.”
- Hardman, D., George Thuruthel, T. & Iida, F. Self-healing ionic gelatin/glycerol hydrogels for strain sensing applications. NPG Asia Mater 14, 11 (2022). DOI: 10.1038/s41427-022-00357-9