Harnessing bistability for directional propulsion of soft, untethered robots

Significance A major challenge in soft robotics is the integration of sensing, actuation, control, and propulsion. Here, we propose a material-based approach for designing soft robots. We show an untethered, soft swimming robot, which can complete preprogrammed tasks without the need for electronics, controllers, or power sources on board. To achieve propulsion, we use bistable shape memory polymer muscles connected to paddles that amplify actuation forces. As a proof of principle, we show that these robots can be preprogrammed to follow specific routes or deliver a cargo and navigate back to their deployment point. The proposed design principle can have a broad impact in soft robotics based on programed materials. In most macroscale robotic systems, propulsion and controls are enabled through a physical tether or complex onboard electronics and batteries. A tether simplifies the design process but limits the range of motion of the robot, while onboard controls and power supplies are heavy and complicate the design process. Here, we present a simple design principle for an untethered, soft swimming robot with preprogrammed, directional propulsion without a battery or onboard electronics. Locomotion is achieved by using actuators that harness the large displacements of bistable elements triggered by surrounding temperature changes. Powered by shape memory polymer (SMP) muscles, the bistable elements in turn actuate the robot’s fins. Our robots are fabricated using a commercially available 3D printer in a single print. As a proof of concept, we show the ability to program a vessel, which can autonomously deliver a cargo and navigate back to the deployment point.