Published online 13 December 2005 | Nature | doi:10.1038/news051212-4

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Robotic snail takes ceilings in its stride.

This robot loosely imitates a snail's movements with five moveable parts on its artificial 'foot' and clay in place of slime. © AIP/MIT/Chan, B. et al

A robotic snail that can climb smooth vertical walls and traverse ceilings has oozed into action.

The mechanical mollusc was developed by a team of engineers at the Massachusetts Institute of Technology, led by Anette Hosoi. They built the robot to test out mathematical models of how snails move and stay stuck to surfaces, but they also hope that robotic snails might one day find a use in the real world.

Land snails generally get around by contracting their single foot, which sits on top of a bed of sticky slime. A region of compressed muscle travels from the back of the snail's foot towards the front, while the snail's attachment to the surface stops it from sliding backwards. When the compression reaches the very front of the foot it is released, allowing the snail to stretch out to its full length, slightly ahead of its original position. This allows the animal to inch forwards.

To loosely imitate this process, the artificial gastropod has five movable segments lined up on its underside. One by one, each of these sections moves forwards along a track on the robot's body. After all five have advanced, the body itself slides forward, returning the segments to their original positions.

Good gel

The team tested out their snail on a tilting platform, covered with a 1.5-millimetre-thick layer of slime made from Laponite, a type of clay that forms a clear, sticky gel when mixed with water.

As the engineers increased the incline, they saw that the snail took the hill in its stride, continuing to plod along even when the surface was vertical. When the platform was flipped over so that the robot was upside down, it still made steady progress.

The secret to this gravity-defying stunt is apparently to keep the snail as light as possible (just 31.6 grams), while ensuring that the Laponite has just the right stickiness. They publish their findings in the November issue of Physics of Fluids1.

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So has the world been crying out for a robotic snail? "One can easily argue that snail locomotion is slow, slimy and inefficient," admit the researchers in their paper. But they also point out that because gastropods have only one foot, it is much easier to build mechanical analogues of snails than of two-footed people or four-footed animals.

And although they are slow, snails can crawl over pretty much anything, making them extremely versatile at getting around different environments.

The group has now developed mathematical models to come up with the optimum weight and slime characteristics for a robotic snail. Hosoi says that these should help to build a second generation of robosnails that are much faster and more manoeuvrable.