A cut, a muscle tear or even a fracture are all injuries that the human body can eventually repair by itself. At VUB, researchers are looking for the same kind of self-healing properties for damage-sensitive soft robots. “You can compare self-healing materials with our skin,” says Seppe Terryn. “If we cut ourselves with a sharp knife, all kinds of processes immediately start in our body to heal the wound. The blood coagulates, the immune system protects itself against infections and new skin cells close the wound. Self-healing materials do something similar. When damaged, they recover under the influence of light or heat until they reach their original state. They are already used in coatings for certain expensive cars that automatically remove scratches. But they also offer an interesting solution for soft robots.”
Terryn developed a special material consisting of rubbery polymers with a built-in healing capacity that takes effect after heating. “At a microscopic level, the polymer can be compared to a 3D cobweb,” Terryn explains. “When the robot cuts itself, the web breaks. We can repair it by heating the polymer to 80° Celsius. At that temperature, nodes in the cobweb come loose and increase the mobility of the polymer, causing the cut to fill. When the material cools down again, the cobweb reforms and the injury is gone. After forty minutes the fracture is closed and after one night the robot is as good as new. Thanks to this solution, a broken robot is no longer a disaster, which is still the case today due to complicated repairs.”
He tested his self-healing material on three vulnerable parts of soft robots: a gripper, a robot hand and an artificial muscle. These resilient, air-pressurised parts were subjected to controlled damage. The damage could be fully repaired, without leaving any weak spots, and the robots were then able to fully resume their tasks.
Supported by the European Union
This unique research is part of a larger international partnership between VUB, University of Cambridge, L’Ecole Supérieur de Physique et de Chimie Industrielles de la ville de Paris (ESPCI-Paris), the Swiss Federal Laboratories for Materials Science and Technology (Empa) and the Dutch polymer producer SupraPolix, which received €3 million of European support last summer. The ultimate goal of this prestigious collaboration is to build a robot that can feel damage itself via sensors or software and then repair itself.