The Bio-inspired Design of a Self-propelling Robot Driven by Changes in Humidity

Abstract

Plants use highly reliable nastic movement through the oriented hygroscopic swelling of tissue to autonomously respond to external stimuli. Buildings, on the other hand, use highly unreliable kinematic mechanisms with multiple failure-prone components that are dependent on electromechanical input. Literature describing stimulus-responsive shape-changing actuators focuses primarily on single-stage reversible movements, and therefore provides limited insights into the methodologies needed to achieve directed multistage locomotion. Here we describe a methodology to develop a self-propelling and programmable robot (Hygrobot) capable of flexible locomotion with the cyclic introduction and removal of moisture. Several multi-layer mechanisms were programmed to actuate sequentially with changes in moisture, in a choreographed manner, to generate locomotion. We expect that this approach can advance interest into hygroscopic self-propelled mechanisms, as well as foster further research into the development of more complex kinematic mechanisms, requiring articulated and multi-stage actuation, for direct architectural or robotic implementation.