Northwestern scientists create soft robots that can walk and transport goods

The first-of-its-kind tiny robot is nearly 90% water and could be used in the medical or chemical field.

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Image: Northwestern University

A group of professors and researchers at Northwestern University have created an innovative new kind of robot that is soft, can walk on its own, and transport cargo. 

Samuel Stupp, the board of trustees professor of materials science and engineering, chemistry, medicine, and biomedical engineering at Northwestern University, said the robots are the first of its kind and are able to walk at speeds resembling humans while also picking up objects and moving them to new locations. 

Stupp explained in an interview that the centimeter-long robots are able to move without the use of any electricity, hydraulics, or hardware. The effort was supported by the US Department of Energy's Office of Basic Energy Sciences. 

"I had an interest for several years in developing new materials that can emulate features that we expect in living creatures. Three years ago, I started investigating materials that could absorb light and then make shape changes. What we are trying to do is create materials with a brain," he said.

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"We designed a material that is 90% water and 10% contains some very special polymers. When those polymers are hit by visible light, they change their chemical structure immediately and become hydrophobic. So at first, it's got a lot of water inside, but then when the light changes it, it decides that it doesn't like water and expels it. It contracts and curls up and when it curls up, then if there is a magnetic field around it, the magnetic field exerts a force on the material because there is another magnetic component inside and the force makes this new shape walk."

The embedded skeleton of the robot, which is made up of nickel, responds to magnetic fields, allowing it to be controlled without all of the hardware typical robots need to function. 

In a study published in Science Robotics last month by a group of researchers led by Stupp and Monica Olvera de la Cruz, Northwestern's Lawyer Taylor professor of materials science and engineering and chemistry, the scientists wrote that the robot resembled a four-legged octopus. 

"By combining walking and steering motions together, we can program specific sequences of magnetic fields, which remotely operate the robot and direct it to follow paths on flat or inclined surfaces," Olvera de la Cruz said. "This programmable feature allows us to direct the robot through narrow passages with complex routes." 

Olvera de la Cruz explained that her team was able to demonstrate through calculations how to optimize light intensity, magnetic fields, and density of magnetic components in order to predict the movements and behaviors of the soft robotic materials

Stupp said he has spent years working on a concept he calls "robotic soft matter" that resembles sea creatures and only recently was able, with the help of his team, to build robots that could move at the same speed as humans. 

The soft robots can take about one step every second and Stupp explained that they can be steered using magnets and light. 

"Conventional robots are typically heavy machines with lots of hardware and electronics that are unable to interact safely with soft structures, including humans. 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," Stupp said. 

"The design of the new materials that imitate living creatures allows not only a faster response but also the performance of more sophisticated functions. We can change the shape and add legs to the synthetic creatures, and give these life-like materials new walking gaits and smarter behaviors. This makes them highly versatile and amenable to different tasks."

When asked about potential use cases, Stupp said he envisions smaller versions of the robots being used in medicine that can be injected inside of a body to perform tasks that are currently difficult for doctors. 

"For example, one of these micro robots could go in and remove a blood clot from your brain after you have a stroke or clean up blood vessels so that you don't die of heart disease," he said.

"Or we could use them to deliver medicines and have them sort of walk towards a place in your body where you need to deliver medicine locally. Another area is chemical factories that could make different kinds of products using these life-like materials to help make molecules."

He added that the robots could be used for environmental uses as well, particularly in situations like oil spills, where people would need to remove toxic particles from water. He also imagines that the robots would be useful in any situation where very small robots are needed to repair something like a battery. 

Stupp noted that the Department of Energy was interested in the project because they are effectively creating materials that can interconvert different types of energy in a useful way, akin to an artificial muscle. 

"The muscles in your body convert chemical energy from what you eat to mechanical energy so you can lift something. So that's the interconversion of chemical energy to mechanical energy," Stupp said.  

"This interconversion of energy, from one form of energy to another energy, can be the source of great new technologies. And so in this case, we are converting light energy and magnetic energy to mechanical energy. You take light and you make something walk. This is an extremely exciting new frontier in science and technology and we are looking forward to continuing to develop new ideas." 

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