Injectable Thermoresponsive Hydrogels for Antibacterial Applications: Design Strategies, Antibacterial Mechanisms, and Biomedical Applications

Injectable thermoresponsive hydrogels provide flowable precursors that form local depots on warming, offering a route to sustained antibacterial delivery in irregular tissue defects. This narrative review examines how thermal gelation, carrier architecture, and anatomical conditions jointly determine antibacterial exposure. It distinguishes polymer phase separation from macroscopic gelation, injectable precursors from topical and instilled formulations, and bacterial killing from biofilm and host-repair outcomes. Representative studies are compared by composition, delivery, thermal behavior, release conditions, microbiological endpoints, and animal model. Three design considerations emerge: gelation must occur within a practical administration window; drug availability depends on both the carrier and its local residence; and the required balance of retention, clearance, and tissue compatibility differs across wounds, infected bone defects, periodontal pockets, and ocular surfaces. Direct loading, particle-in-gel depots, contact-active components, and light-mediated treatments address different parts of this problem and require distinct efficacy and safety measurements. Current evidence supports preclinical antibacterial and regenerative applications, while heterogeneity in exposure and outcome measurements limits comparison across platforms. Progress toward clinical use depends on connecting formulation manufacture and material fate with local antibacterial exposure and indication-specific outcomes.