One‐Shot Multimaterial 3D Printing of a Flexible Spine for a Robotic Fish Prototype

Bioinspiration is shaping the development of next‐generation robotic systems, particularly bioinspired swimmers capable of complex locomotion in unstructured environments at minimum energetic expense. However, their development is still limited by multistep fabrication processes requiring manual assembly of compliant and stiff components. This work proposes the one‐shot multimaterial additive manufacturing (AM) of an electromagnetically (EM) actuated soft robotic fish capable of carangiform swimming, integrating polylactic acid (PLA) structural elements with a thermoplastic polyurethane (TPU) compliant spine through interlocked T‐shaped interfaces. Three TPU grades (80A, 85A, and 95A Shore hardness) are evaluated to optimize actuation performance. Among them, the TPU 85A prototype achieves the highest tail‐tip deflection while reducing the required actuation voltage (−46.67%), power consumption (−67.25%), and temperature rise (−47.68%). Finite element simulations of the soft robotic fish show good agreement with experimental bending behavior for all tested materials. Underwater tests performed across actuation frequencies from 0.5 to 5 Hz reveal a monotonic reduction in bending amplitude due to hydrodynamic load, while the mean tail‐tip oscillation speed increases with frequency, reaching a 2.85× enhancement between the lowest and highest actuation frequencies.