Hydrogel Sensors for Human Body Detection: Principles, Materials, and Application Frontiers

Hydrogel-based sensors are increasingly recognized as enabling technologies for real-time, accurate, and minimally invasive human monitoring, driven by the growing needs in healthcare for aging populations, early disease screening, and sports/rehabilitation assessment. Unlike conventional rigid sensors, hydrogels provide tissue-like softness, high water content, and intimate biointerfaces, offering superior conformability, hydration, and biocompatibility for long-term skin-interfaced and implantable/in vivo sensing. This Review presents a systematic overview of hydrogel material systems and their sensing applications for human body detection. We first summarize natural polymer hydrogels (e.g., gelatin, alginate, and chitosan) and discuss their biofunctionality and intrinsic limitations, followed by synthetic hydrogels (e.g., PAAm, PVA, and PHEMA) highlighting tunable mechanics, stability, and antibiofouling potential. We then focus on functional composite and smart-responsive hydrogels, including conductive composites, stimulus-responsive networks, and nanoreinforced architectures, emphasizing structure–property–signal transduction relationships. Representative applications are categorized into wearable sensors for external use, including physiological signal monitoring, motion/force sensing, and biochemical analysis of sweat and interstitial fluid, and implantable/in vivo sensor for tissue engineering monitoring, drug release tracking and disease-related biomarker detection, and emerging human–machine interfaces. Finally, we discuss optimization strategies for key performance metrics (mechanical matching, sensitivity/limit of detection, and long-term stability/biofouling resistance), identify core challenges across complex internal/external environments, and provide perspectives on next-generation materials innovation, technology convergence, and system-level integration toward practical clinical translation.