**2.1. Flexible fluidic actuators**

A Flexible Fluidic Actuator generally consists of a flexible shell that transmits potential energy, delivered by the pressurized fluid, into a mechanical force, which then can be used to create a motion.

The flexible fluidic operating principle has a strong background in biomimetics. Gutmann [41, 42] established the "Hydroskelett-Theorie" as an approach to explain evolutionary biology via the concepts of constructional morphology. He understood that the design-principles of hydrosceletts are responsible for the general designs of organisms. Gudo et al. [39, 40] developed this idea further by introducing the term "Engineering Morphology which describes how Gutmann's ideas can be applied to technical design. The biomimetic background of flexible fluidic actuation was specifically discussed in [11, 130]. These works discuss several examples on weevils and spiders and describe how crucial the membrane properties are regarding efficiency and durability of the whole actuation system. The transfer of the evolutionary optimized flexible fluidic drives developed by nature into powerful technical systems is one focus of this work.

A useful classification of Flexible Fluidic Actuators can be made according to their operating principle, or the kind of force they are creating. Here we differentiate between designs that use expansion, contraction or bending directions to drive a system.
