Argonne scientists design self-assembled "micro-robots"

August 9, 2011 By Louise Lerner

( -- Alexey Snezhko and Igor Aronson, physicists at the U.S. Department of Energy's (DOE) Argonne National Laboratory, have coaxed "micro-robots" to do their bidding.

The robots, just half a millimeter wide, are composed of microparticles. Confined between two , they assemble themselves into star shapes when an alternating is applied. Snezhko and Aronson can control the robots' movement and even make them pick up, transport and put down other non-magnetic particles—potentially enabling fabrication of precisely designed functional materials in ways not currently possible.

The discovery grew out of past work with magnetic "snakes". This time, however, Snezhko and Aronson suspended the tiny ferromagnetic particles between two layers of immiscible, or non-mixing, fluids.

The video will load shortly

Without a magnetic field, the particles drift aimlessly or clamp together. But when an alternating magnetic field is applied perpendicular to the liquid surface, they self-assemble into spiky circular shapes that the scientists nicknamed "asters", after the flower.

Left to their own devices, the asters don't swim. "But if you apply a second small magnetic field parallel to the surface, they begin to move," said Aronson. "The field breaks the symmetry of the asters' hydrodynamic flow, and the asters begin to swim."

The video will load shortly

By changing the magnetic field, the researchers discovered they could remotely control the asters' motion.

"We can make them open their jaws and close them," said Snezhko. "This gives us the opportunity to use these creatures as mini-robots performing useful tasks. You can move them around and pick up and drop objects."

They soon discovered that the asters form in two "flavors"; one's flow circulates in toward the center of the aster, and the other circulates outward. They swim in opposite directions based on flavor. These properties are useful because scientists can play the flows against one other to make the asters perform tasks.

For example, four asters positioned together act like a miniature vacuum cleaner to collect free-floating particles.

The asters can pick up objects much larger than themselves; in one video, an aster picks up a glass bead that weighs four times as much as the aster itself.

"They can exert very small forces on objects, which is a big challenge for robotics," Aronson explained. "Gripping fragile objects without smashing them has always been difficult for conventional robots."

The microrobots occupy a niche between laser-powered manipulation and mechanical micromanipulators, the two previous techniques developed for manipulation at the microscale. "You can grab with lasers, but the force is much smaller," Snezhko explained. "These asters' forces are more powerful, but they can handle items much more delicately than mechanical micromanipulators can."

The materials can even self-repair; if particles are lost, the aster simply re-shuffles itself.

The research is a part of the ongoing effort, funded by the DOE, to understand and design active self-assembled materials. These structures can assemble, disassemble, and reassemble autonomously or on command and will enable novel materials capable of multi-tasking and self-repair.

"For us, this is very exciting. This is a new paradigm for reconfigurable self-assembled materials that can perform useful functions," Aronson said.

The study, "Magnetic Manipulation of Self-Assembled Colloidal Asters", has been published in Nature Materials.

Explore further: Argonne scientists use bacteria to power simple machines (w/ Video)

More information: Nature Materials (2011) doi:10.1038/nmat3083

Related Stories

Sophisticated nano-structures assembled with magnets (Video)

February 18, 2009

( -- What do Saturn and flowers have in common? As shapes, both possess certain symmetries that are easily recognizable in the natural world. Now, at an extremely small level, researchers from Duke University ...

Precision control of movement in robots

May 16, 2008

A research team from the Department of Electricity and Electronics at the University of the Basque Country’s Faculty of Science and Technology in Leioa, Spain, led by Victor Etxebarria, is investigating the characteristics ...

Bacteria mix it up at the microscopic level

November 2, 2009

( -- Many hands -- or many flagella -- make light work. In studies of the motion of tiny swimming bacteria, scientists at the U.S. Department of Energy's Argonne National Laboratory found that the microscopic ...

Recommended for you

Shocks in the early universe could be detectable today

October 27, 2016

(—Physicists have discovered a surprising consequence of a widely supported model of the early universe: according to the model, tiny cosmological perturbations produced shocks in the radiation fluid just a fraction ...

Bubble nucleus discovered

October 27, 2016

Research conducted at the National Superconducting Cyclotron Laboratory at Michigan State University has shed new light on the structure of the nucleus, that tiny congregation of protons and neutrons found at the core of ...

Neutrons prove the existence of 'spiral spin-liquid'

October 27, 2016

Magnetic moments ("spins") in magnetic solids are capable of forming the most diverse structures. Some of them are not only of interest from a scientific point of view, but also from a technical standpoint: processors and ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.