A 3D-printed multi-parametric wearable system for monitoring breathing activity and low back movements

Among many applications of Fiber Bragg gratings (FBGs) in healthcare, non-invasive monitoring via wearable devices is one of the most popular. Their compact size, lightness, immunity to electromagnetic interference, and high strain sensitivity make them ideal for various applications, including vital sign monitoring and human motion analysis. Wearables based on FBGs consist of silicone substrates and, more recently, 3D-printed structures that enclose gratings to improve FBG adaptability to the human body or compliance with the human skin. 3D-printed wearables provide greater design flexibility, rapid prototyping, and customization than their silicone counterparts.This study presents a wearable strain sensor that combines the advantages of FBG technology with those of additive manufacturing to monitor vital signs and joint movement. We focused on the breathing activity and the low back movement detection. To this purpose, the design of the proposed 3D-printed sensor features a dog bone shape to optimize the FBG response to strain. In addition, the 3D-printed matrix includes lateral openings for the insertion of the anchorage mechanisms (i.e., elastic fabric), ensuring high wearability and adaptability to different body anthropometries. The sensor was fabricated via fused deposition modeling and the sensitivity to strain was evaluated by performing a metrological characterization. Lastly, a pilot test on a healthy volunteer assessed its feasibility in monitoring respiratory rate and low back movements showing promising capacities.