Chapter 7: Hygroresponsive Movements of Plants and Soft Actuators

Plants can generate motions even with dead cells and tissues. Their motions are passively driven via the volume change of the cells and tissues, which can swell by absorbing moisture. In this chapter, we introduce the physical principles behind hygroresponsive deformation of plants, with particular interest in how such porous plant tissues as found in motile seed awns can program their deformations with structural constraints. Then we introduce soft actuators inspired by the botanical hygroscopic movement mechanisms. We survey artificial hygroresponsive actuators, compare the performances of biological and artificial actuators, and discuss applications of the bio-inspired actuators.