4.6 Materials and fabrication of the robots in applications

The robotic fin (Figure 4b) comprises two Double Bellows and a PVC sheet (160 mm × 75 × mm 0.5 mm). All the frames and connectors in this application are 3D-printed (DSM IMAGE8200 pro, WeNext Technology Co., Ltd., China), including the mounting base of the force sensor (LSB201, FUTEK Advanced Sensor Technology, Inc., USA). The robotic fin, the force sensor, and the sensor mounting base are fabricated and fixed on the 6-DOFs manipulator (JAKA Zu 7, JAKA Robotics, China) to adjust and stabilize the position conveniently. Then, we immerse the robotic fin in the water tank (600 mm × 400 mm 450 mm, water depth 300 mm) to investigate the actuation performance (Figure S8a).