layers consisting of a gel of ionic liquid containing single-wall carbon nanotubes. The name comes from the similarity of the gel to the paper that can be made by filtering carbon nanotubes, the so-called buckypaper. Electrorheological fluid Electrorheological fluids change the viscosity of a solution with the application of an electric field. The fluid is a suspension of polymers in a low dielectric-constant liquid. With the application of a large electric field the viscosity of the suspension increases. Potential applications of these fluids include shock absorbers, engine mounts and acoustic dampers. Ionic polymer-metal composite Ionic polymer-metal composites consist of a thin ionomeric membrane with noble metal electrodes plated on its surface. It also has cations to balance the charge of the anions fixed to the polymer backbone. They are very active actuators that show very high deformation at low applied voltage and show low impedance. Ionic polymer-metal composites work through electrostatic attraction between the cationic counter ions and the cathode of the applied electric field, a schematic representation is shown in Figure 3. These types of polymers show the greatest promise for bio-mimetic uses as collagen fibers are essentially composed of natural charged ionic polymers. Nafion and Flemion are commonly used ionic polymer metal composites. Stimuli-responsive gels Stimuli-responsive gels (hydrogels, when the swelling agent is an aqueous solution) are a special kind of swellable polymer networks with volume phase transition behaviour. These materials change reversibly their volume, optical, mechanical and other properties by very small alterations of certain physical (e.g. electric field, light, temperature) or chemical (concentrations) stimuli. The volume change of these materials occurs by swelling/shrinking and is diffusion-based. Gels provide the biggest change in volume of solid-state materials. Combined with an excellent compatibility with micro-fabrication technologies, especially stimuli-responsive hydrogels are of strong increasing interest for microsystems with sensors and actuators. Current fields of research and application are chemical sensor systems, microfluidics and multimodal imaging systems. Comparison of dielectric and ionic EAPs Dielectric polymers are able to hold their induced displacement while activated under a DC voltage. This allows dielectric polymers to be considered for robotic applications. These types of materials also have high mechanical energy density and can be operated in air without a major decrease in performance. However, dielectric polymers require very high activation fields (>10 V/µm) that are close to the breakdown level. The activation of ionic polymers, on the other hand, requires only 1-2 volts.