Hydrogel‐Based Optical Fiber: Sensing Mechanism, Biomedical Applications, and Perspectives

Optical fibers have been widely applied in biomedical sensing technologies, including health monitoring, disease diagnosis, and minimally invasive surgery. However, traditional silica (SiO 2 )‐based rigid fibers face significant challenges in biomedical integration due to their inherent brittleness and limited biocompatibility. In contrast, hydrogel‐based optical fibers have garnered increasing attention in optogenetics, implantable photomedicine, and biomedical sensing, due to their excellent biocompatibility, biomimetic mechanical modulus, and immunity to electromagnetic interference. Here, we provide a comprehensive overview of hydrogel optical fibers for biomedical sensing, emphasizing their fabrication technologies, sensing mechanisms, biomedical applications, current challenges, and future prospects. First, fundamental characteristics and synthetic strategies are introduced, together with the classification of light‐guiding hydrogels. Second, fabrication techniques and sensing mechanisms of hydrogel optical fibers are systematically summarized, focusing on their unique optical modulation modes. Third, a wide range of biomedical sensing applications are highlighted, including the detection of glucose, antibiotics, dopamine, pH, and metal ions. Finally, key challenges and future prospects are discussed, including improving biocompatibility, long‐term reliability, sterilization strategies, multimodal integration, and achieving intelligent therapeutic systems. This review aims to inspire further innovations in hydrogel optical fiber‐based biomedical sensing, and to facilitate the development of next‐generation biomedical sensing platforms for wearable and implantable healthcare devices.