This article reviews the biomedical applications of stimuli-responsive "smart" interpenetrating polymer network (IPN) hydrogels. Conventional single-network stimuli-responsive hydrogels often suffer from low mechanical strength, limited biocompatibility, and extended response times. To address these issues, researchers have developed stimuli-responsive "smart" IPN hydrogels by introducing a second network, enhancing mechanical strength, biocompatibility, and stimulus responsiveness. The article discusses the design principles, mechanical reinforcement mechanisms, and classification of stimuli-responsive "smart" IPN hydrogels. It also explores their performance characteristics, including thermo-response, light response, pH-response, and salt/ionic strength response. The review highlights the potential of these hydrogels in various biomedical applications, such as drug delivery, tissue engineering, and biosensors, and provides insights into future research directions.This article reviews the biomedical applications of stimuli-responsive "smart" interpenetrating polymer network (IPN) hydrogels. Conventional single-network stimuli-responsive hydrogels often suffer from low mechanical strength, limited biocompatibility, and extended response times. To address these issues, researchers have developed stimuli-responsive "smart" IPN hydrogels by introducing a second network, enhancing mechanical strength, biocompatibility, and stimulus responsiveness. The article discusses the design principles, mechanical reinforcement mechanisms, and classification of stimuli-responsive "smart" IPN hydrogels. It also explores their performance characteristics, including thermo-response, light response, pH-response, and salt/ionic strength response. The review highlights the potential of these hydrogels in various biomedical applications, such as drug delivery, tissue engineering, and biosensors, and provides insights into future research directions.