Scientists often look to the natural world for inspiration and ideas when creating synthetic materials. Plants and animals can rapidly respond to changes in the environment. An example is the way a Venus flytrap can close quickly when touched by an insect. Researchers have printed liquid metal circuits onto a single piece of soft polymer to create an intelligent material that can curl under pressure or mechanical strain and expand when stretched.
The team says that integrating sensors and moving parts that respond is bulky and typically requires an external computer. They believe liquid metals are the solution to making soft robotics able to mimic autonomous behaviors in nature. Liquid metals can be used to create thin and flexible circuits in soft materials. Some beneficial properties of the liquid metals include that the circuits could rapidly produce heat when an electric current is generated from an electrical source or from pressure applied to the circuit.
When the soft circuits are stretched, the current drops and the material cools. Researchers on the project aim to integrate liquid metal circuits with liquid crystal elastomers, which are polymers able to undergo large changes in shape when heated or cooled. The team applied a nickel-infused gallium-indium alloy onto a liquid crystal elastomer and magnetically moved the liquid metal in the lines to form an uninterrupted circuit.
The team used a silicone sealant that changed from pink to dark red when warmed. When the material responded to a current, the soft material curled as the temperature increased and the film turned redder over time. The materials were used to develop autonomous grippers able to perceive and respond to pressure or stretching applied to the circuits.
Using the gripper, the researchers could pick up small round objects and drop them when the pressure was released, or the material stretched. Scientists on the project also formed the film into a spiral shape. When the pressure was applied to the circuit at the bottom of the spiral, it unfurled with a rotating motion as the temperature increased. Pressure and stretch-sensitive materials could be adapted for use in soft robotics able to perform complicated tasks or locomotion.