Stimuli-responsive "smart" interpenetrating polymer network (IPN) hydrogels have gained significant attention in biomedical applications due to their enhanced mechanical strength, biocompatibility, and responsiveness to external stimuli. Traditional single-network hydrogels often suffer from poor mechanical properties and slow response times, prompting the development of IPN hydrogels that combine multiple networks to improve performance. IPN hydrogels are formed by two or more cross-linked networks entangled through physical interactions or topological entanglement, resulting in superior mechanical strength, controlled swelling behavior, and unique properties such as cell adhesion, conductivity, and self-healing. These hydrogels can respond to various stimuli, including temperature, light, pH, salt/ionic strength, and enzymes, enabling applications in drug delivery, biosensors, tissue engineering, and biomedical implants. The design of IPN hydrogels involves two primary mechanisms: retaining original configurations after deformation and dissipating mechanical energy during crack propagation. The interpenetrating structure enhances mechanical properties and allows for the incorporation of diverse network properties, leading to improved performance. IPN hydrogels can be classified based on their network structures, such as polymer blends, graft copolymers, block copolymers, and full/semi-IPNs. Synthetic and natural polymers each offer distinct advantages, with synthetic polymers providing better mechanical properties and chemical stability, while natural polymers offer high biocompatibility and biodegradability. Stimuli-responsive IPN hydrogels exhibit various properties, including thermo-response, light response, pH response, and salt/ionic strength response. These hydrogels can undergo sol-gel transitions in response to environmental changes, enabling controlled drug release and other biomedical applications. The integration of conductive polymers and light-thermal conversion materials further enhances the functionality of IPN hydrogels, making them promising candidates for advanced biomedical applications. Overall, the unique properties and versatility of stimuli-responsive "smart" IPN hydrogels make them valuable materials for a wide range of biomedical applications.Stimuli-responsive "smart" interpenetrating polymer network (IPN) hydrogels have gained significant attention in biomedical applications due to their enhanced mechanical strength, biocompatibility, and responsiveness to external stimuli. Traditional single-network hydrogels often suffer from poor mechanical properties and slow response times, prompting the development of IPN hydrogels that combine multiple networks to improve performance. IPN hydrogels are formed by two or more cross-linked networks entangled through physical interactions or topological entanglement, resulting in superior mechanical strength, controlled swelling behavior, and unique properties such as cell adhesion, conductivity, and self-healing. These hydrogels can respond to various stimuli, including temperature, light, pH, salt/ionic strength, and enzymes, enabling applications in drug delivery, biosensors, tissue engineering, and biomedical implants. The design of IPN hydrogels involves two primary mechanisms: retaining original configurations after deformation and dissipating mechanical energy during crack propagation. The interpenetrating structure enhances mechanical properties and allows for the incorporation of diverse network properties, leading to improved performance. IPN hydrogels can be classified based on their network structures, such as polymer blends, graft copolymers, block copolymers, and full/semi-IPNs. Synthetic and natural polymers each offer distinct advantages, with synthetic polymers providing better mechanical properties and chemical stability, while natural polymers offer high biocompatibility and biodegradability. Stimuli-responsive IPN hydrogels exhibit various properties, including thermo-response, light response, pH response, and salt/ionic strength response. These hydrogels can undergo sol-gel transitions in response to environmental changes, enabling controlled drug release and other biomedical applications. The integration of conductive polymers and light-thermal conversion materials further enhances the functionality of IPN hydrogels, making them promising candidates for advanced biomedical applications. Overall, the unique properties and versatility of stimuli-responsive "smart" IPN hydrogels make them valuable materials for a wide range of biomedical applications.