Cilia protrude from a microorganism's body, propelling it through liquid environments by repeatedly reaching forward then sweeping back. They don't do so all in unison, but instead start moving separately, one after the other, creating waves that travel down the length of the microbe.

Researchers have created larger-scale artificial cilia before, but the systems have tended to be quite mechanically complex, and too big to incorporate into small devices. A team from The Netherlands' Eindhoven University of Technology, however, recently created a tiny soft-bodied robot that utilizes a much smaller, simpler form of cilia.

To do so, the scientists combined a liquid polymer with carbonyl iron powder particles, then poured that mixture into an array of 50-micrometer-wide cylindrical holes which served as the molds for the cilia. As the polymer proceeded to cure into a rubbery consistency, magnets placed below the molds caused the iron particles to align themselves differently in adjacent cilia – this gave each cilium different magnetic qualities.

The finished 4-mm-long robot consisted of a solid polymer base, with the cilia protruding from one side. When it was placed with the cilia facing upwards – in a water/glycol solution – the application of a rotating magnetic field caused the cilia to move back and forth in waves. This allowed the device to operate somewhat like a pump, as the moving appendages caused the liquid to rapidly flow over it.

When the robot was flipped over, so the cilia were on the bottom, their movement allowed the device to scuttle across a flat surface. It could even crawl up a 45-degree slope, and carry an object weighing 10 times its own weight. And when the direction of the rotating magnetic field was reversed, the robot likewise reversed the direction in which it was travelling.