Polymer gels as EAPs: How to start experimenting with them

Electromechanically active polymers (EAP) show great potential for many actuator applications. In this context, hydrogels which are also considered as active polymers have shown also actuator and sensor applications due to their volume phase transition. Nevertheless, in the general term of electromechanically active polymers there is not an exact definition about what is an active polymer. Hydrogels can be considered as active polymer materials not only because of their volume phase transition but also due to their electrical and dielectric properties depending on their internal or chemical modification. The most spread definition of hydrogels is that they are soft and wet materials which show very intriguing properties regarding their volume phase transition. Applications of hydrogels are tightly restricted due to their relative mechanical weakness. In the past 10 years a lot of research has been done in the field of modifying the mechanical properties of hydrogels in order to adapt these materials to daily life requirements. They have been used as sensors and actuators in many fields of science and engineering including microfluidics and biomedicine. In this chapter, we briefly present the main properties of hydrogels, some of the methods used to characterize them as well as the principal applications from an engineering and general point of view. This chapter could be used as a general introduction to the topic of hydrogels, more specifically thermal responsive ones, and also represents an opportunity for all those who want to enter to the field of hydrogels.