Self-assembled micro-robots have been created by Alexey Snezhko and Igor Aronson, physicists at the U.S. Department of Energy's (DOE) Argonne National Laboratory.
The robots, just half a millimeter wide, are composed of microparticles. Confined between two liquids, they assemble themselves into star shapes when an alternating magnetic field 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.
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."
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."
The cylinder had split. At first he couldn't tell if it had been the impact or deliberate internal mechanisms at work. From the rent, an ooze of metal bits was sliding. Squatting down, O'Neill examined them.
The bits were in motion. Microscopic machinery, smaller than ants, smaller than pins, working energetically, purposefully - constructing something that looked like a tiny rectangle of steel.