Development of a hygroscopic soft actuator inspired by botanical movements

Abstract

It is a general notion that animals are motile but plants are not. Thus, most of efforts to develop biologically inspired robots are focused on mimicking motions of animals. However, some plants generate motions without muscles like animals to generate motions. Plants rely on either supply or deprival of water from plant tissues to make motions. Some species of plants such as wild wheat, Erodium, Pelargonium, and pinecones can be actuated when the environmental humidity changes. Their tissues are in general composed of highly oriented two layers, one of which is hygroscopically active while the other is inactive. Inspired by this structure, we fabricated an actuator which generates motions in response to humidity change. We newly developed an electrospinning process which can result in a fibrous layer with fast response rate to humidity cahgne. Using this actuator we demonstrated a simple robot actuated by water vapor, which we named Hygrobot.