Researchers from Northwestern University developed a light-powered, life-like material that acts as a soft robot. It is capable of walking at human speed, picking up and transporting cargo to new locations, climbing hills, and even “break dancing,” as the researchers describe it, to release cargo in proper locations. The light-activated robot, which is approximately 1 cm in size, 90% water by weight, and that walks in the direction of an external rotating magnetic field, moves without the addition of complex hardware, hydraulics, or electric power. A chemical synthesis process programs the robot’s molecules, located in a hydrogel — where they can react to light. When exposed to light, the molecules become hydrophobic, or water repellent, allowing their escape. The process caused the robot to bend from a flat position to one that is standing upright. The researchers discovered that this bending enabled the material to respond rapidly to rotating magnetic fields. When exposed to rotating magnetic fields, the embedded skeleton (of aligned ferromagnetic nickel filaments) exerted cyclic forces on the soft molecular network, activating the robots’ legs. The rotating field is programmable to navigate the robot along a predetermined course. “Conventional robots are typically heavy machines with lots of hardware and electronics that are unable to interact safely with soft structures, including humans,” said Samuel I. Stupp, a professor of materials science and engineering, chemistry, medicine, and biomedical engineering who led the experimental research. “We have designed soft materials with molecular intelligence to enable them to behave like robots of any size and perform useful functions in tiny spaces, underwater or underground.” The researchers demonstrated the ability to program distinct magnetic field sequences by combining the robot’s walking and steering motions. Those sequences serve to remotely operate the robot, and hold the possibility to direct it to move about different types of surfaces, added Monica Olvera de la Cruz, a professor of materials science and engineering, chemistry, and chemical and biological engineering who led the theoretical work. “This programmable feature allows us to direct the robot through narrow passages with complex routes,” she said. The robot showed the ability to collect cargo and deliver it to a destination by both walking and/or rolling. By inverting its physical shape — allowing smooth payloads to gently slide off the robot — or performing a spinning “break dance” to dislodge and release stickier objects, the robot successfully delivered cargo to a new location. “The design of the new materials that imitate living creatures allow not only a faster response but also the performance of more sophisticated functions,” Stupp said. “We can change the shape and add legs to the synthetic creatures, and give these lifeless materials new walking gaits and smarter behaviors. This makes them highly versatile and amenable to different tasks.” Stupp and Olvera de la Cruz envision the soft robotic materials being used to create objects for many applications, including chemical production, new tools for environmentally important technologies, and as smart biomaterials for highly advanced medicine. The research was published in Science Robotics (www.doi.org/10.1126/scirobotics.abb9822).
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