Figure 9.

Stimuli-responsive actuator performance defined by the specific actuation stress and the actuation strain. Symbols in black refer to (partially) metal actuators, whereas (partially) organic actuators are found in white, and human muscle actuators are colored green. The metal and organic actuators are colored according the external stimuli applied, that being humidity (swelling, blue), light (orange), and photothermal/electro-heating (red). Commodity polymer-based composite and bilayer actuators are built from PA6, PET, PE, and PP. In accordance with future applications, robotics are considered to demand large specific actuation stresses, whereas smart textiles are anticipated to benefit from a larger actuation strain. Data were taken from refs (3, 4, 64, 69, 72, 75, 77, 84, and 97−101).