A polymeric actuator includes a first and a second electrode layer (2, 3), both containing electrically conductive material and able to change size in at least one direction of deformation under the action of charge injection or ion intercalation. A solid polymer electrolyte layer (4) is interposed between the first and the second electrode layer, in which the solid polymer electrolyte layer is electrically insulating and ionically conductive. The actuator is able to deform by the action of the dimensional changes of the first and second electrode layer. The actuator further includes a passive electrode (5) immersed in the solid electrolyte layer to be electrically insulated relative to the first and second electrode layer, in which the passive electrode is electrically conductive and elastically deformable material, so as to support mechanically the deformations of the actuator induced by the dimensional changes of the first and second electrode layer.