Mechanism-guided, target-matched design of a bioinspired hydrogel-filled TPU metamaterial for low-frequency vibration isolation near 128 Hz

An engineered hydrogel-filled TPU metamaterial was designed for 128 Hz isolation. • A double-network hydrogel enabled viscoelastic dissipative tuning. • Final matching depended on resonance placement, hydrogel stiffness, and loss response. • Two-stage refinement yielded a manufacturable TPU 95A HF/SA/PAAm-3 design. • A representative test reached −45.2 dB at 128 Hz and < − 35 dB over 99–149 Hz. Persistent narrow-band vibration near 128 Hz at the flight-controller mounting region presents a critical challenge for compact passive isolation under structural-support constraints in engine-driven agricultural UAVs. Here, we report a target-frequency-oriented engineering strategy for a bone-inspired hydrogel-filled TPU metamaterial that integrates a 3D-printed supporting thermoplastic polyurethane (TPU) lattice with a viscoelastic double-network hydrogel infill. Rather than relying solely on geometric band-gap tuning or bulk hydrogel damping, this framework couples experimentally parameterized hydrogel relaxation with dry-lattice resonance placement and manufacturability correction to match a prescribed operating frequency. In this engineered polymer composite, the TPU skeleton defines the local-resonance architecture, whereas the hydrogel phase provides relaxation-mediated dissipative tuning. Three dry TPU lattices were first screened, and TPU 90A, whose first band gap lay closest to the target-frequency region, was selected as a model scaffold to establish a hydrogel-dependent tuning rule. Comparative studies of SA/PAAm-3, PVA/PAAm-3, and PVA/PAAm(Gly)-2, together with dynamic mechanical analysis (DMA) and stress-relaxation-based viscoelastic characterization, revealed that final target matching is governed not by band gap downshift alone, but by the interplay among lattice-defined resonance placement, hydrogel stiffness, loss response, and relaxation-mediated dissipation. Guided by this principle, a second-stage target-matched refinement was performed on the TPU 95A HF/SA/PAAm-3 composite by further optimizing the skeleton parameters. The final manufacturability-corrected structure exhibited a first band gap covering 128 Hz in a subwavelength regime ( a / λ s = 0.0735 ). In a representative transmissibility test, the final structure maintained transmissibility below − 20 dB over 91–172 Hz and below − 35 dB over 99–149 Hz, reaching − 45.2 dB at the target frequency. These results provide an experimentally parameterized material–structure collaborative framework for engineering manufacturable hydrogel-filled polymer metamaterials under prescribed dynamic-performance constraints.