Magnetic control: A setup of electromagnetic coils controlled by a computer allows careful control of the microbots. Carnegie Mellon University

Microscopic machines might one day deliver drugs directly to a sickly cell or a tumor, or allow researchers to fabricate electronics components more easily. But first, scientists need to figure out how to power and control such tiny devices. Methods currently being explored range from piggybacking on bacteria to harnessing magnetic fields.

Magnetic control has shown only limited success, partly because it's hard to control microscopic objects individually. Metin Sitti, an associate professor of mechanical engineering at Carnegie Mellon University (who has previously developed tape that mimics geckos' sticking power and a robot that can stick to a stomach without damaging it), has now come up with such a control technique.

Previously, Sitti showed that a permanent magnet about 200 microns wide can be maneuvered using alternating magnetic fields, allowing it to crawl forward across a surface. Now, by adding electrostatic "traps" to the surface, Sitti can stop or move an individual micro magnet within a group on command.

The microbots move across a glass surface covered with a grid of metal electrodes. When a high voltage is applied to an electrode, it generates a field. In a recent issue of Applied Physics Letters, Sitti, together with Chytra Pawashe and Steven Floyd, shows how these electrodes can be used to anchor one or more microbots while allowing others to continue to move freely around the surface.

The movie below shows several microbots moving across a four-by-four array of electrodes.