Injectable biomedical hydrogels: In situ construction and service stability

Injectable hydrogels are widely used for minimally invasive biomedical interventions because they can form in situ within irregular defects, confined cavities, and wet tissue interfaces. However, their practical performance depends on the coordinated control of precursor delivery, triggering of gelation, initial network formation, and service stability under physiological conditions. This review presents a construction-oriented perspective that moves beyond conventional classifications based on material source or crosslinking chemistry. We discuss how precursor design, the injection window, gelation kinetics, the physiological microenvironment, and functional integration regulate in situ construction and subsequent performance. We further analyzed key dimensions of service stability, including volume stability, mechanical robustness, interfacial adaptability, degradation, drug release, and biocompatibility, with representative applications in wound repair, hemostasis, tissue filling, and regenerative therapy. Finally, we outline future directions for developing injectable hydrogels with tunable gelation behavior, durable wet-state stability, controlled degradation and release, and clinically relevant properties such as syringe/catheter compatibility, sterilization tolerance, storage stability, and batch-to-batch reproducibility.