polyacrylamide was reduced to about half that of the polyacrylic acid in order to allow it to take up more of the water displaced from the polyacrylic acid. This is not yet the ideal muscle system. The current drives the shape change through a pH gradient which arises from electrolysis of water, which cannot be reversible in a closed system. The gas formed also causes instabilities in our system. Other workers have experimented with the release of calcium ions from polypyrrole as an alternative system for swelling and deswelling the gels without electrolysis of water. [10] The gels are also mechanically weak, but much stronger gels can be made by combining polyvinylalcohol with polyacrylic acid. [11] As outlined above, an ideal muscle should show an overall expansion or contraction along one axis in response to an applied field, with no overall volume change. This cannot be achieved with a single centrosymmetric material but is possible with an asymmetric series of layers. We have shown that stacked combinations of gels can be made to give linear contraction in response to applied electric field. In essence the asymmetry of gel stack balances the asymmetry of the applied field to allow a symmetric response. Other swollen polymer combinations should be capable of similar responses.