Dual-Material 3-D-Printed Wearable Sensors Based on FBG Technology for Physiological and Biomechanical Monitoring in Back Pain Assessment

In recent years, wearable devices for monitoring physiological and biomechanical parameters have gained increasing attention, particularly for assessing individuals suffering from back pain. This condition can influence respiratory rate (RR) and heart rate (HR), making their continuous, non-invasive monitoring valuable for back pain mitigation strategies. Fiber Bragg Grating (FBG) sensors are well suited for wearable sensing due to their flexibility, multiplexing capability, and biocompatibility, although their fragility remains a limitation. A promising solution involves integrating FBG sensors into 3D-printed components, a technique that offers cost-effectiveness, ease of fabrication, and high reproducibility. In particular, the Fused Deposition Modeling (FDM) technique enables the fabrication of components using two distinct materials, to combine the specific advantages of each material. Despite the potential of dual-material 3D printing technology, this approach is still underexplored in the scientific literature. This study presents the design and fabrication of two identical wearable sensors based on FBG technology manufactured using FDM. The novelty is to combine the benefits of two materials: thermoplastic polyurethane (TPU), to enhance the sensors’ strain response, and polylactic acid (PLA), to provide greater rigidity in the anchoring region to the human body. This solution allowed optimizing static and dynamic performance of the sensors. In addition, preliminary tests on healthy subjects highlighted the capability of the proposed systems to monitor cardio-respiratory activity (in particular RR and HR) and flexion-extension movements of the back.