**1. Introduction**

222 Smart Actuation and Sensing Systems – Recent Advances and Future Challenges

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Electroactive polymers (EAPs), known as artificial muscles, can generate large deflections under an electrical stimulus (Bar-Cohen 2000, 2004). Due to the similarities with biological muscles, in terms of achievable stress and strain, EAPs have great potential to be used as actuators in bio-inspired robots, bio-medical devices, and micro/nano manipulation systems. Ionic polymer-metal composites (IPMCs) are an important category of ionic EAPs (Shahinpoor & Kim, 2001, 2005; Kim & Shahinpoor, 2003, 2003; Shahinpoor et al, 2003; Kim et al, 2007; Nemat-Nasser & Li, 2000; Nemat-Nasser, 2002), which can work well under a low actuation voltage (1 to 2 Volts) in a sodium salt-water environment.

As shown in Fig. 1, an IPMC consists of one ion exchange membrane, such as Nafion (DuPont), sandwiched in between two thin metal electrodes (Shahinpoor & Kim, 2001). When the IPMC is hydrated, the positive ions in the Nafion polymer, such as sodium and calcium ions, bring water molecules and migrate to the cathode side under an electric field, whereas the negative ions are permanently fixed to the carbon chain (Nemat-Nasser & Li, 2000). The ion transportation and water migration introduce swelling in the cathode side and shrinking in the anode side, which eventually causes bending motion of the IPMC (Shahinpoor & Kim, 2001).

IPMCs can also be used for electrolysis. Electrolysis of water occurs when a relatively high voltage (> 1.6 V) is applied between the cathode and anode (Shaaban, 1994; Shimizu et al, 2005). The water molecules are decomposed into hydrogen and oxygen gases. IPMC enhanced electrolysis of water is due to several reasons; (i) ion transport brings high dense of water close to cathode side (Shahinpoor & Kim, 2001); (ii) the strong electrical fields

© 2012 Chen et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

established on the boundary (Nemat-Nasser & Li, 2000; Nemat-Nasser, 2002) breaks down of the water molecules; and (iii) the porous platinum electrodes (Shahinpoor & Kim, 2001) on the surface acts as a stable electrolysis catalyst (Millet et al, 1989).

**Figure 1.** Actuation mechanism of IPMC (Chen & Tan, 2008).

In this chapter, the advantages and challenges of IPMCs as applied to bio-inspired engineering are discussed. A bio-inspired robotic manta ray integrated with IPMCs as artificial muscles and a novel buoyancy control device using IPMCs as an electrolysis generator are presented.
