Self-Assembling, Flexible Microbots Under Development By Michigan Researchers

Chuck Bednar for redOrbit.com – Your Universe Online
In what they are calling a step towards building microscopic robots, researchers from the University of Michigan have demonstrated how chains of self-assembling particles could act like tiny, electrically-activated muscles.
Writing in the latest edition of the journal Nature Materials, chemical engineering professor Michael Solomon and his colleagues explained that these so-called “microbots” would be smaller than a grain of sand and could be especially beneficial to the medical and manufacturing industries. However, they noted that much work needs to be done before the machines can become a reality.
However, according to LiveScience reporter Charles Choi, the microbots could one day be able to travel through a person’s bloodstream to fight diseases or crawl into bombs in order to diffuse them. Before that is possible, however, the researchers need to find ways to allow them to move autonomously and exert force on other objects, Solomon said.
In their new study, however, the Michigan team reports that muscles created from self-assembling chains of microscopic particles could ultimately help power these miniature robots, Choi said. The researchers began with spherical particles made up of a combination of polystyrene, then stretched them in a machine until they were about the same shape of rice grains (approximately 0.6 microns wide and 3 microns long.)

After the particles were stretched out, one side of each was coated with gold to turn them into what is known as a Janus particle (a particle with two different sides, named after the two-faced Roman god Janus). When placed in saltwater, the gilded halves of each Janus particle are attracted to each other. The more salt in the water, the stronger the attraction became, with the ideal concentration being about half the amount found in the sports drink Powerade.
When left to their own devices, the particles wound up forming short chains of overlapping pairs, averaging roughly 50 to 60 particles per chain, the researchers said. However, when exposed to an alternating electric current, the chains appeared to add new particles indefinitely. By expanding and contracting, the fibers could work like little muscles, and Solomon told Choi that his team had “extended and retracted them many times.”
“The findings point the way toward a new class of reconfigurable materials made of micron-size particles – materials that can be triggered to morph and change shape in response to changes in environment or on demand,” study co-author Sharon Glotzer, a computational physicist and chemical engineer at the university, told Live Science.
In a statement, Glotzer added that the researchers want the devices “to work like little muscles. You could imagine many of these fibers lining up with the field and producing locomotion by expanding and contracting.” The force generated by the fibers is approximately 1,000 times weaker than human muscle tissue per unit area, but the Michigan researchers think it may be enough for microbots to be able to swarm together, lift loads and perform other tasks.
Solomon told Choi that the next step will be to organize groups of those chains into bundles, and get them to behave similar to how biological muscles do. While actual microscopic robots could be several years away, the researchers believe that their Janus particles could be used to create electronics capable of rewiring themselves on demand.
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