Paper-thin magnetic muscles bring origami robots to life for medical use

A new 3D printing technique can create paper-thin “magnetic muscles,” which can be applied to origami structures to make them move.

By infusing rubber-like elastomers with materials called ferromagnetic particles, researchers at North Carolina State University 3D printed a thin magnetic film which can be applied to origami structures. When exposed to magnetism, the films acted as actuators, which caused the system to move without interfering with the origami structure’s motion.

This type of soft magnet is unique in how little space it takes up, said Xiaomeng Fang, assistant professor in the Wilson College of Textiles and lead author of a paper on the technique published in Advanced Functional Materials.

“Traditionally, magnetic actuators use the kinds of small rigid magnets you might put on your refrigerator. You place those magnets on the surface of the soft robot, and they would make it move,” she said. “With this technique, we can print a thin film which we can place directly onto the important parts of the origami robot without reducing its surface area much.”

Scientists designed their primary robot to deliver medicine to ulcers inside the human body, using an origami pattern called Miura-Ori. The technique allows a large flat surface to fold into a much smaller area. The magnetic “muscles” are attached to facets of the origami—when exposed to a magnetic field, they help the origami open up and navigate to the ulcer location.

The Miura-Ori design is well-suited to administering medicine, Fang said, because it can be ingested as a small object and then open to deliver medicine with its entire surface area.

Researchers tested the robot using a mock stomach made of a plastic sphere filled with warm water. Guiding the robot through the stomach using external magnetism, researchers successfully maneuvered it to an ulcer site, deployed it into its unfolded state, and secured it in place by externally attached soft magnetic films. This setup enabled controlled and steady drug release over time, for a safe and noninvasive procedure which allows patients to carry out daily activities as normal.

Previous attempts to use ferromagnetic particles have struggled to generate enough force to move robots, Fang said, because they were not able to pack enough particles into the rubber solution. Adding a large quantity of particles turns the liquid rubber black, which absorbs the UV used to solidify the solution and keeps it from curing properly. Thermal energy can also help solidify the rubber, so researchers added a hot plate underneath the collecting plate to augment their UV light.

“Adding the hot plate meant that we could use a much higher concentration of ferromagnetic particles than usual, which was the real breakthrough,” Fang said. “The more particles you are able to use, the more magnetic force you are able to generate.”

Using a different Miura-Ori origami pattern, researchers also created a second robot designed to crawl forward. When placed in a magnetic field, muscles placed at specific areas of the robot cause it to contract, with the front section raising up and the rear drawing in closer. When the field is turned off, the motion of returning to its original position pushes the robot forward—a single “step.”

This crawling origami robot is capable of traversing obstacles up to 7 millimeters high with speed adjustable via magnetic field strength and frequency, and adapting to diverse terrains, including sand.

Taken together, these two robots demonstrate the significant potential of soft magnetic actuators and origami structures in robotics, Fang said.

“There are many diverse types of origami structures that these muscles can work with, and they can help solve problems in fields anywhere from biomedicine to space exploration,” Fang said. “It will be exciting to continue to explore more applications for this technology.”