Sometimes science advances at a snail's pace, but in this case that's a good thing: researchers have created a squishy material that combines polymers with liquid metal, demonstrated in a snail-like robot. Developers say this electrically conductive gel could be used to make self-healing electronic circuits and biological monitors for measuring heart and muscle activity—and maybe even lead to robot nervous systems.
The composite substance is stretchy and soft like living tissue. If it breaks or tears, the edges can be touched together to quickly re-form the material's molecular bonds without any additional heat or chemical treatment. And crucially, its developers say, it is the first such material that also conducts electricity well.
These abilities could lead to wire-free medical monitors as well as fully soft robots. “For my research, one thing that's really big is, ‘How do you put multiple functions into a single material?'” says Lillian Chin, who develops soft robotic components as part of her own research at the Massachusetts Institute of Technology. Existing soft-bodied robots, she says, often require at least some rigid metals and silicon components. But soft, flexible living tissues can perform multiple tasks; muscles, Chin notes, both move the body and provide electrical feedback about that movement to the brain.
To build a multitasking artificial substance, researchers began with a tangle of long polymer chains soaked in a solvent to keep them supple, then carefully mixed in microscopic drops of gallium-indium liquid metal as well as tiny silver flakes. This produced a low-density gel dotted with conductive metals, through which enough electricity can flow to, for instance, power a motor.
For a recent study in Nature Electronics, the team used this new material in a monitor for measuring muscles' electrical activity as well as to connect power sources to motors in two basic machines: a snail-like soft robot and a toy car. The material's self-healing ability helped these simple circuits to stand up to wear and tear—and to be easily reconfigured. For example, the team cut the car's power-carrying gel “wires” and shifted their connections to power both movement and a small built-in light.
The snail example shows how one could use such material as a kind of artificial nervous tissue for soft robots, says Carnegie Mellon University mechanical engineer Carmel Majidi, the study's senior author. But truly multifunctional bots will require more intricate uses of the new material.
“In practice, we would want to have digital printing capabilities so we can make much more complex circuits that could interface with microelectronic chips, as well as other types of components that we could actually use in more sophisticated robotics and electronics applications,” Majidi says. “There are so many possibilities that arise when you take machines and robots out of the hard case and engineer them out of materials that are soft and squishy.”
