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The Risø National Laboratory in Denmark has a new way of powering artificial
limbs, robot grippers or toys (EP 1026192). It uses a chemical mix that can be
triggered into rapid and reversible changes of size and shape. A conducting
polymer such as polypyrrole is mixed with a pH-sensitive gel. Feeding a
3-volt pulse to electrodes buried in the polymer changes the surface ion
concentration, which alters the pH of the gel and creates a volume
change of up to 800 per cent in less than a second. The reaction is reversible.