Soft multitasking robot runs on fumes

Soft robots and medical devices of the future will rely on materials that curl, twist, and stretch in response to a trigger, such as heat or light. But soft actuators made so far perform just one type of motion. Researchers have now made a material that executes multiple actions when exposed to chemical vapors (Chem 2024, DOI: 10.1016/j.chempr.2024.06.016).

The team used the material to make a three-clawed gripper that responds to acetone vapor by grabbing cargo—a cotton ball, in this study. Further exposure to acetone causes the claw to drop the ball.

Scientists have previously made complex actuators by combining multiple materials or triggers, says Niveen M. Khashab, a chemistry professor at King Abdullah University of Science and Technology. To make the new multitasking material, Khashab and her colleagues embedded a polymer film with tiny cage-like molecules that contain urea. The researchers created curved strips of the film such that one side had more urea cages than the other, and then they exposed it to acetone vapors.

The porous polymer absorbs the acetone molecules, which first nestle in the spaces between the urea cages, increasing the material’s volume. The film curves even further because of its uneven cage distribution. After a minute or so, the acetone molecules migrate into the cages, reducing the polymer’s volume. This causes the strips to stretch and flatten.

This is just a proof of concept. Khashab says that by using cages of other sizes and components, researchers could design “soft robots that recognize various molecules—say, toxic chemicals or even viruses—and act on them.”

The actuator’s response to gas is valuable because it eliminates the need for bulky electronics to control actuation, says Carmel Majidi, a mechanical engineering professor at Carnegie Mellon University. More work is needed to make the actuator fast enough to be useful in practical applications, he says. “Nonetheless, it represents an important milestone in the development of chemically responsive soft actuators.”