Tailored carbon nanotubes (CNTs)/ thermoplastic polyurethane (TPU) composite pressure sensors via optimized 3D printing for smart wearable electronics

The advancement of wearable electronics relies on the development of lightweight, flexible, and durable sensors capable of real-time detection. Thermoplastic polyurethane (TPU) offers excellent elasticity and comfort but lacks intrinsic conductivity. Unlike, conventional bulk CNT/TPU composite printing, which incorporates CNTs directly into the filament and may affect printability and flexibility, or simple surface coating methods, which may suffer from weak CNT adhesion during repeated deformation. This study proposes a post-printing CNT surface embedding strategy. The approach combined ultrasonication cavitation-enabled treatment and thermal-assisted process to improve CNT attachment, conductive network formation, and interlayer bonding in 3D printed TPU structures. Two TPU grades (TPU89A and TPU92A) were extruded into filaments and compared with commercial TPU95A. Samples were fabricated using fused deposition modeling with honeycomb infill patterns at 20%-60%. Following immersion in a 1% CNT suspension, ultrasonication treatment, and thermal treatment at 120 °C, SEM-EDS and Raman spectroscopy confirmed CNT incorporation on the TPU surface, with carbon content increasing from 63.85% wt% to 76.71 wt% and distinct D (1325 cm −1 ) and G (1582 cm −1 ) bands. X-ray tomography verified homogeneous CNT dispersion and reduced interlayer voids. Low-density structures (20%) exhibited higher deformability due to greater porosity, while 60% infill provided improved rigidity and contact stability. Among the TPU grades, TPU89A exhibited superior flexibility, enhancing CNT contact variation under pressure. Electromechanical testing revealed sensitivities of 17.82, 21.01, and 41.81 kPa −1 for 20%, 40%, and 60% infill, respectively, within the effective 0-0.002 MPa. Higher infill enabled denser conductive pathways, outperforming TPU92A (30.76 kPa −1 ) and TPU95 (37.43 kPa −1 ). Cyclic compression confirmed stable and repeatable ΔR/R 0 signal over 1000 cycles at 50% elongation. When attached beneath a shoe insole, the sensor effectively detected variations during walking, and running. The optimized TPU89A_HN60_CNT composite achieved enhanced sensitivity, flexibility, and preliminary durability, showing its potential as a function prototype for wearable and tactile-sensing applications.