Fused filament fabrication of gyroid TPU/MWCNT nanocomposite sensors with tunable piezoresistive response: Proof-of-concept integration into a 3D-printed smart midsole

Functional architected polymer nanocomposites that combine mechanical compliance, tunable electrical conductivity, and piezoresistive response are highly attractive for wearable electronics and personalized sensing technologies. However, the coupled effects of conductive-network density and lattice geometry on the electromechanical performance of fused-filament-fabricated (FFF) elastomers remain insufficiently understood. Here, thermoplastic polyurethane (TPU) containing 2, 3, and 4 wt.% multiwalled carbon nanotubes (MWCNTs) was melt-extruded into conductive filaments feedstock and printed into gyroid triply periodic minimal surface (TPMS) lattices with unit cell sizes of 4, 5, and 6 mm. Increasing MWCNT loading improved electrical transport and stiffness, raising Young’s modulus from 14.20 ± 0.19 to 18.88 ± 0.29 MPa, while reducing elongation at break from 659.5 ± 41.33 to 503.14 ± 34.02%. Fracture-surface scanning electron microscopy revealed increasingly interconnected nanotube networks, supporting the observed structure–property trends. Under compression, the gyroid lattices showed stable piezoresistive responses governed by filler loading and architecture. The optimal design, TPU/MWCNT (2wt.%) with a 5 mm unit cell, achieved a gauge factor of 1.24 ± 0.03, sensitivity of 0.55×10-3 kPa-1, hysteresis of 8.17 ± 0.74%, and stable operation over 100 cycles. Four optimized FSR sensors were integrated into a 3D-printed wireless midsole for real-time gait monitoring, demonstrating the potential of architected TPU/MWCNT nanocomposites as customizable functional materials for wearable electronics and smart footwear applications