A new water robot is created that reacts to light

The centimeter-long robot, whose weight is 90% water, moves without complicated equipment, hydraulics, or electricity. Instead, it is activated by light and moves in the direction of an external rotating magnetic field.

Resembling a four-legged octopus, the robot operates inside a tank filled with water. This makes it ideal for use in aquatic environments.

“Conventional robots are typically heavy machines with a lot of equipment and electronics that cannot safely interact with soft structures, including humans,” explains Samuel E. Stupp, who led the experimental study. “We have developed soft materials with molecular intelligence so that they can behave like robots of any size and perform useful functions in tiny spaces, underwater or underground.”

“By combining walking and steering, we can program specific sequences of magnetic fields that remotely control the robot and guide it along paths on flat or inclined surfaces,” added Monica Olvera de la Cruz, who led the theoretical work in the study. “This programmable feature allows the robot to be guided through narrow aisles with challenging routes.”

The new research builds on Stupp’s previous work to create “robotic soft matter” that mimics living sea creatures. In a previous study, robotic material could bend for several minutes and crawl along the surface, taking one step every 12 hours. However, today the robot moves at the speed of a human – about one step per second – and reacts to magnetic fields. They force these materials to follow certain trajectories.

By combining reactions to light and magnetic fields, the researchers have developed a robot that can lift a load and deliver it to its destination on foot or by rolling. It then drops the weight in a new location, either reshaping it, allowing the smooth weights to gently slide off the robot, or performing a spinning “breakdance” to dislodge and release more sticky objects.

The secret to the robot’s precise movement and maneuverability lies in its water-filled structure and built-in frame made of aligned ferromagnetic nickel filaments. The soft component is a network built at the molecular level, with parts that allow it to respond to light, hold, or expel water inside. They also have the necessary rigidity to react quickly to magnetic fields.

A team at Northwestern University used chemical synthesis to program molecules inside the hydrogel to react to light. When exposed to light, the robot’s molecules become hydrophobic. This makes the robot “come to life” by leaning from a flat to a standing position. The researchers found that this bend allows the material to respond quickly to rotating magnetic fields, activating its ability to walk quickly. When the light is turned off, the molecules return to their original state, and the robot becomes flat. But it is ready at any time for a new cycle of activity under the magnetic field when the LED is pointing at it.

Stupp and Olvera de la Cruz are confident that these developments will be useful in the future as intelligent biomaterials for highly advanced medicine.

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