Comparative electromechanical performance of TPU/CB piezoresistive strain sensors fabricated from commercial conductive filaments

• Comparative evaluation of 3D-printed TPU/CB strain sensors fabricated from two commercial conductive filaments (RECREUS and FILI). • RECREUS sensors show higher ductility and negative piezoresistive response; FILI sensors exhibit positive, highly linear behavior at low strain. • TPU/CB/Ag FILI sensors demonstrate minimal baseline drift (<6%) after 500 cycles, confirming superior long-term durability. Commercially available conductive filaments offer a suitable option for rapidly fabricating piezoresistive strain sensors using additive manufacturing technologies. Extending previous work on the RECREUS-based sensors, this study presents a comparative evaluation of the electromechanical performance of strain sensors fabricated from two thermoplastic polyurethane (TPU) filaments loaded with carbon black (CB): RECREUS and FILI. These filaments were processed via fused filament fabrication (FFF) to form TPU/CB sensors. To enhance electrical performance, silver interdigitated electrodes were integrated onto the sensor surfaces using direct ink writing (DIW), resulting in hybrid TPU/CB/Ag configurations. The sensors were characterized under quasi-static and dynamic tensile loading to assess their sensitivity, hysteresis, and durability. Sensors fabricated with RECREUS filament exhibited a negative piezoresistive response and high stretchability, with gauge factors ranging from approximately −18.61 to −0.29 for TPU/CB and from −23.78 to 0.45 for TPU/CB/Ag across the entire strain range. In contrast, FILI-based sensors showed a positive, highly linear response at low strain, with gauge factors of approximately 12–123 for TPU/CB and ≈16 for TPU/CB/Ag. The integration of silver electrodes improved electrical stability and reduced hysteresis in both sensor types. During cyclic loading with small strains between 0.2% and 5%, both materials generated an electrical response proportional to the deformation; however, only the FILI-based sensors kept a stable baseline with minimal drift. After 500 cycles, the FILI sensors showed less than 6% signal drift, compared with 27% drift observed in the RECREUS sensors. These findings highlight the influence of filler dispersion and electrode-to-polymer compatibility on sensor reliability and demonstrate that commercially available filaments with nominally similar compositions can exhibit significantly different electromechanical behavior, affecting sensor reliability.