Fine-Core Highly Water-Retentive Hydrogel Flexible Optical Fiber for Long-Term Stable Sensing Application

Hydrogel flexible optical fibers (HFOFs) have great potential in environmental monitoring and biomedical applications. However, current HFOFs face significant challenges, including the presence of large amounts of free water and low fiber crosslinking density, which result in poor water retention and environmental tolerance. These issues hinder the stable use of HFOFs as sensing waveguides. This study proposes for the first time a high-water-retention, fine-core HFOF. HFOFs are spun from a polyacrylamide hydrogel material containing glycerol using the drawing spinning method. During the drawing and stretching process, the fiber network porosity decreases, and self-assembly induced by water evaporation generates numerous hydrogen bonds. The hydroxyl groups in the glycerol molecules form hydrogen bonds with water molecules, while a large amount of bound water is generated, thereby enhancing the water retention performance of the HFOFs. HFOF demonstrates excellent water retention (water loss rate: <0.1%/day), stretching performance (500%), light-guiding ability (1.45 dB/cm), and recovery properties (1 min). The highly water-retentive HFOFs are applied in various scenarios, including bionic sensors for vibration detection and flexible sensors for monitoring human respiration and heartbeat. This work offers a new solution for improving the stable use of HFOFs and provides new inspiration for bionic monitoring and wearable human sensors.