PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES

Scientists have developed a vibrating gel that creeps, crawls and slithers just as worms, snails and snakes do. Manoj K. Chaudhury of Lehigh University and his colleagues describe their artificial creepy-crawly--a hydrogel rod made out of the polymer acrylamide and water--in a report published online this week by the Proceedings of the National Academy of Sciences.

The researchers animated the two-centimeter-long tube by placing it on a vibrating glass plate covered in silicon rubber, with a liquid layer forming between the surface and the "snail." Vibrating the plate at specific intervals resulted in snail-like movement. The scientists then made small incisions in the rubber contacting the underside of the gel rods, which allowed them to move more quickly. The greater the number of incisions, the faster the artificial snails traveled (see image); an optimal angle for the cuts enabled the greatest speed. With further tweaking the gel moved in the manner of a snake, undulating from side to side, and an earthworm, inching along.

The main difference between the artificial snail and the regular garden variety is that the fake one requires an external source to drive its movements. Similar soft solids have so far shown promise for applications including sensors and actuators. The authors note that periodic pulses much like the ones they manufactured through vibrations can be generated by a variety of methods. "Artificially actuated gels that respond to various stimuli such as electromagnetic fields, temperature, and chemical oscillations," they conclude, "point toward applications to situations requiring the autonomous motion of soft solids on surfaces."