biostudies-literatureKobayashi SJapan Society for the Promotion of Science (JSPS), KAKENHI198https://www.ebi.ac.uk/biostudies/studies/S-EPMC12025331biostudies-literatureUnknown10(4)In this study, we investigated the thrust enhancement in a bio-inspired underwater propulsion fin using a shear-stiffening gel. Shear-stiffening gels exhibit velocity-dependent stiffness, i.e., they become stiffer during high-speed deformation and softer during low-speed motion, providing adaptive mechanical properties without requiring complex mechanisms. A "compound joint" incorporating a dilatant compound, a material of shear-stiffening gel, was developed and experimentally evaluated against a "rigid joint" and a flexible "urethane joint". A speed-ratio control strategy was employed to assign faster and slower oscillations during positive and negative thrust intervals, respectively. The results demonstrated that the compound joint achieved a balance between high thrust and stable performance. Its adaptive stiffness effectively reduced deformation during high-speed oscillations, enhanced thrust while maintaining flexibility during low-speed intervals, and minimized thrust fluctuations. Compared with the rigid and urethane joints, the compound joint exhibited a superior balance between a high average thrust and low thrust variation.Biomimetics (Basel, Switzerland)Enhancing Thrust in Underwater Bio-Inspired Propulsion Fin Using Shear-Stiffening Gel.PMC12025331JP18K04047Kobayashi SJonishi YfalseEnhancing Thrust in Underwater Bio-Inspired Propulsion Fin Using Shear-Stiffening Gel.In this study, we investigated the thrust enhancement in a bio-inspired underwater propulsion fin using a shear-stiffening gel. Shear-stiffening gels exhibit velocity-dependent stiffness, i.e., they become stiffer during high-speed deformation and softer during low-speed motion, providing adaptive mechanical properties without requiring complex mechanisms. A "compound joint" incorporating a dilatant compound, a material of shear-stiffening gel, was developed and experimentally evaluated against a "rigid joint" and a flexible "urethane joint". A speed-ratio control strategy was employed to assign faster and slower oscillations during positive and negative thrust intervals, respectively. The results demonstrated that the compound joint achieved a balance between high thrust and stable performance. Its adaptive stiffness effectively reduced deformation during high-speed oscillations, enhanced thrust while maintaining flexibility during low-speed intervals, and minimized thrust fluctuations. Compared with the rigid and urethane joints, the compound joint exhibited a superior balance between a high average thrust and low thrust variation.2025-01-01T00:00:00Z2025 Mar2025-07-01T03:05:49.135Z2025-07-01T03:05:49.135ZS-EPMC120253314027759710.3390/biomimetics10040198