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Jun 14, 2018 | By Thomas

MIT researchers have designed and 3D printed an array of soft, mechanical critters whose movements can be controlled with a wave of a magnet, much like marionettes without the strings.

Photo: Felice Frankel

A study published on Wednesday in the journal Nature showed that the magnetically manipulated structures were composed of a smooth ring that wrinkles up, a long tube that squeezes shut, a sheet that folds itself, and a spider-like “grabber” that can crawl, roll, jump, and snap together fast enough to catch a passing ball. It can even be directed to wrap itself around a small pill and carry it across a table.

The researchers fabricated each structure from a new type of 3D printable ink that they infused with tiny magnetic particles. Then they fitted an electromagnet around the nozzle of a 3D printer, which caused the magnetic particles to swing into a single orientation as the ink was fed through the nozzle. By controlling the magnetic orientation of individual sections in the structure, the researchers were able to produce structures and devices that can almost instantaneously shift into intricate formations, and even move about, as the various sections respond to an external magnetic field.

Xuanhe Zhao, the Noyce Career Development Professor in MIT’s Department of Mechanical Engineering and Department of Civil and Environmental Engineering, says the group’s technique may be used to fabricate magnetically controlled biomedical devices.

“For example, we could put a structure around a blood vessel to control the pumping of blood, or use a magnet to guide a device through the GI tract to take images, extract tissue samples, clear a blockage, or deliver certain drugs to a specific location. You can design, simulate, and then just print to achieve various functions,” said Zhao.

This type of technology is called soft actuated devices — for instance, hydrogel devices swell when temperature or pH changes; shape-memory polymers and liquid crystal elastomers deform with sufficient stimuli such as heat or light. MIT said these types of soft actuated devices are often slow to respond, and change shape over the course of minutes to hours.

“There is no ideal candidate for a soft robot that can perform in an enclosed space like a human body, where you’d want to carry out certain tasks untethered,” Kim says. “That’s why we think there’s great promise in this idea of magnetic actuation, because it is fast, forceful, body-benign, and can be remotely controlled.”

Instead of making structures with magnetic particles of the same, uniform orientation, the team arranged individual sections with a distinct orientation of magnetic particles. When exposed to an external magnetic field, each section should move in a distinct way, depending on the direction its particles move in response to the magnetic field.

With their new 3D printing method, the researchers can print sections of a structure and tune the orientation of magnetic particles in a particular section by changing the direction of the electromagnet encircling the printer's nozzle during printing.

Photo: Felice Frankel

The team also developed a physical model that predicts how a printed structure will deform under a magnetic field. Other devices MIT developed included a set of “auxetic” structures that rapidly shrink or expand along two directions. They also printed a ring embedded with electrical circuits and red and green LED lights to illuminate in a programmed manner.

“People can design their own structures and domain patterns, validate them with the model, and print them to actuate various functions,” Zhao says. “By programming complex information of structure, domain, and magnetic field, one can even print intelligent machines such as robots.”

 

 

Posted in 3D Printing Application

 

 

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