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Stretchy sensors are useful for many applications, including monitoring human health and emulating artificial muscles in soft robots. One big problem with these sensors is that they don’t last that long as they twist, stretch, and otherwise deform.
Now, a team of researchers in Belgium have created a highly durable, stretchable sensor with remarkable self-healing capabilities—to the point that it can heal itself after being cut completely in half and still work at near-perfect performance. The results are described in a study published 16 July in IEEE Sensors Journal.
Lead author Rathul Sangma is a Ph.D. candidate at Vrije Universiteit Brussel who is affiliated with Imec. He says his team was motivated to develop a reliable, stretchable sensor for health monitoring, rehabilitation, and motion tracking because “these systems often endure repeated strain or accidental damage. Existing stretchable sensors can fail under such conditions, leading to unreliability and waste.”
Self-Healing Polymer Sensors for Wearables
To create their durable sensor, Sangma and his colleagues decided to use a polymer with a chemical bonding mechanism called Diels–Alder crosslinks. These chemical bonds are reversible, meaning they can break when damaged and reform upon recontact. “When the material is cut, the broken bonds become reactive and, when properly realigned, [they] reconnect, restoring the polymer’s original structure,” says Sangma.
In experiments, the researchers showed that the polymer could be cut in half and self-heal at room temperature over the course of roughly 24 hours. The self-healing process could be sped up to just four hours when the sensor was placed in an oven at 60 °C.
Even after being stretched to the point of breaking and then healed six times, the sensor worked at 80 percent capacity.
Smart wearables could benefit from stretchable sensors capable of recovering their functionality even after sustaining significant damage. BruBotics/YouTube
Embedded within the polymer is a liquid metal called Galinstan, which acts as conductor. While you might expect the liquid metal to spill out when the polymer is severely damaged, the researchers found that the loss of Galinstan was minimal. They suspect that the liquid metal oxidizes when exposed to air, and the resulting oxide creates a thin, protective barrier that prevents the liquid from escaping. The oxide barrier is broken down once the two pieces of the sensor are mechanically reconnected.
“This mechanism is remarkably analogous to how human veins form a clot after rupture to prevent further blood loss,” Sangma says. “Here, the oxide acts as a temporary seal that preserves the integrity of the system until healing is complete.”
In a series of tests, the researchers explored how pristine and damaged sensors experienced drift, which is the gradual change in a sensor’s signal over a long period of continuous stretching and relaxing. The results show that a pristine sensor subjected to repeated stretching through 800 cycles drifted less than 5 percent, while a sensor that had been cut in half and stretched the same number of times drifted less than 10 percent.
“This dual healing—both in structure and electrical functionality—is what makes our design stand out,” Sangma says.
The tests also show that the materials can be recycled with high efficiency once the device finally reaches the end of its operational life. “Over 95 percent of the sensor material can be recovered and reprocessed—an important step toward eco-friendly wearables,” says Sangma.
The research team is actively exploring opportunities to commercialize their sensor, with the aim of using it for medical rehabilitation, sports performance monitoring, and soft robotic systems. They have established a spin-off company, Valence Technologies, to commercialize the materials.
Moving forward, the researchers are looking to scale the sensor so that it can track full body movements, and they would like to conduct long-term durability testing in real-world environments, such as seeing how the sensor performs when exposed to sweat.
