Euglenoid-Inspired Giant Shape Change for Highly Deformable Soft Robots

Nature has exploited softness and compliance in many different forms, from large cephalopods to microbial bacteria and algae. In all these cases, large body deformations are used for both object manipulation and locomotion. The great potential of soft robotics is to capture and replicate these capabilities in controllable robotic form. This letter presents the design of a bioinspired actuator capable of achieving a large volumetric change. Inspired by the changes in body shape seen in the euglena Eutreptiella spirogyra during its characteristic locomotion, a novel soft pneumatic actuator has been designed that exploits the hyperelastic properties of elastomers. We call this the hyperelastic bellows (HEB) actuator. The result is a structure that works under both positive and negative pressure to achieve euglenoid-like multimodal actuation. Axial expansion of 450% and a radial expansion of 80% have been observed, along with a volumetric change of 300 times. Furthermore, the design of a segmented robot with multiple chambers is presented, which demonstrates several of the characteristic shapes adopted by the euglenoid in its locomotion cycle. This letter shows the potential of this new soft actuation mechanism to realise biomimetic soft robotics with giant shape changes.