A SYNTHETIC starfish is flipping somersaults in a fish tank in a Japanese lab. The bizarre creature represents the first steps on the road to new types of artificial muscles for robots and prosthetic limbs.
The five-limbed minibeast is a simple lump of gel cut from a sheet of a polymer called PAMPS. It is the brainchild of Mihoko Otake and her colleagues at the universities of Tokyo and Hokkaido.
PAMPS is an 鈥渆lectroactive鈥� material: in other words, it deforms when placed in an electric field. This happens because charged groups of atoms strung along its long, bendy molecular backbone are attracted to an external charge, forcing them to huddle together.
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The usual way to make the electroactive effect kick in is to immerse the polymer in a conducting solution sandwiched between a pair of parallel electrodes. Otake鈥檚 breakthrough was finding a way to produce complex movement in the starfish-shaped blob of gel with electrodes on one side of it instead of two. 鈥淭his increases the variety of the gel鈥檚 possible motions,鈥� she says.
The researchers achieved this by using a square array of electrodes, which can independently be given a positive or a negative charge. This generates electric fields between neighbouring positive and negative electrodes that can be used to attract and repel parts of the polymer. For example, if an electrode is made negative, positive ions are attracted to it, causing a deformation that bends the polymer (see Graphic).
鈥淲e found that the shape the gel will adopt can be predicted, based on the surrounding electric field,鈥� says Otake. By feeding this information into a computer program that controlled the charge on the electrodes, the researchers were able to produce different motions in different parts of the blob. They have even choreographed a somersault for the starfish.
Having managed to get the polymer starfish moving, Otake says in a forthcoming edition of the journal Robotics and Autonomous Systems that she now hopes to use the technique to produce all sorts of locomotion in robots and prosthetics.
But first Otake hopes to explore less demanding applications: she鈥檚 going on to create robotic sea-cucumbers and manta rays.
Previously, the idea of using long strips of the PAMPS polymer as an artificial muscle was constrained by the need to have two electrodes on either side of it. But Otake hopes it may now be possible to exert more control over such strips by lining artificial muscles with a single array of electrodes, as she has done with the starfish.