Evaluation of Reproducibility in 3D-Printed Strain Sensors Manufactured by Fused Deposition Modeling

Fused deposition modeling (FDM) 3D printing has gained significant attention due to its advantages, such as rapid prototyping, customization, low cost, and the ability to produce flexible sensors with complex geometries. In this context, sensors reproducibility emerges as a key requirement, since only sensors that consistently exhibit comparable performance can ensure accurate and reliable measurements. This aspect is particularly crucial in biomedical and industrial applications, where the lack of reproducibility may compromise data comparability, hinder calibration procedures, and ultimately limit the translation of 3D-printed sensors from laboratory prototypes to realworld deployment. Despite its importance, reproducibility has received limited attention in the literature, leaving a significant gap that must be addressed to fully exploit the potential of FDM technology. This study presents the design, fabrication, and metrological characterization of single-layer strain sensors, investigating FDM-printed devices made of thermoplastic polyurethane (TPU) loaded with conductive carbon black (CB). Three configurations were tested: bare sensor (BS), tape-integrated sensor (TS), and siliconeintegrated sensor (SS), with three samples each. Metrological characterization included quasistatic tensile and cyclic tests at different frequencies. Calibration curves showed very low standard deviations (<0.69%), demonstrating good reproducibility across all sensor configurations. During cyclic tests, the response of different samples exhibited similar and overlapping trends, with hysteresis errors consistently comparable and on the same order of magnitude (4%). These results demonstrate that CB-TPU sensors can be reproducibly fabricated and reliably integrated into substrates, improving robustness and durability.