Single-, Dual-, and Multi-Stimuli-Responsive Nanogels for Biomedical Applications Nanogels, composed of cross-linked hydrophilic polymers and water, have an average size of about 100 nm and are used in biomedical applications for drug delivery, tissue engineering, wound healing, and gene therapy due to their environment-sensitive properties. Stimuli-responsive nanogels can respond to external stimuli such as temperature, light, and magnetic fields, or internal stimuli like pH, enzymes, and reduction, enabling on-demand drug delivery. These nanogels are popular for their good hydrophilicity, high drug loading efficiency, flexibility, and biocompatibility. The article discusses the synthesis, properties, and biomedical applications of stimuli-responsive nanogels, as well as the opportunities and challenges for their use in biomedical applications. Nanogels are classified into physically cross-linked and chemically cross-linked types. Chemically cross-linked nanogels are more stable and have better control over morphology, strength, and swellability. They are formed through covalent bonds, while physically cross-linked nanogels are less stable and can undergo sol-gel transitions due to environmental stimuli. Stimuli-responsive nanogels can be designed to release drugs at the target site, improving therapeutic effects and reducing side effects. They have unique properties such as the ability to load and protect small hydrophilic molecules or biological macromolecules, provide prolonged circulation in the blood, and allow for controlled drug release. The synthesis of stimuli-responsive nanogels involves methods such as polymerization of monomers, cross-linking of polymer precursors or natural polymers, and template-assisted nanofabrication. Nanogels can be shaped using "top-down" or "bottom-up" methods. The "top-down" method uses molds to create particles with controlled size, shape, and function, while the "bottom-up" method involves designing molecular structures and assemblies from molecules or clusters. Various stimuli-responsive nanogels have been developed, including pH-responsive, temperature-responsive, and glutathione (GSH)-responsive nanogels, which can release drugs in response to specific environmental conditions. Biomedical applications of stimuli-responsive nanogels include targeted drug delivery, cancer treatment, and tissue engineering. pH-responsive nanogels can deliver drugs to tumor sites with lower pH, while temperature-responsive nanogels can release drugs at body temperature. GSH-responsive nanogels can release drugs in response to redox environments. These nanogels have shown promising results in drug delivery, with high drug loading efficiency, controlled release, and minimal toxicity. They are also used in imaging and diagnostics, with some nanogels being radiopaque for imaging purposes. The article highlights the potential of stimuli-responsive nanogels in biomedical applications and the need for further research to optimize their use in clinical settings.Single-, Dual-, and Multi-Stimuli-Responsive Nanogels for Biomedical Applications Nanogels, composed of cross-linked hydrophilic polymers and water, have an average size of about 100 nm and are used in biomedical applications for drug delivery, tissue engineering, wound healing, and gene therapy due to their environment-sensitive properties. Stimuli-responsive nanogels can respond to external stimuli such as temperature, light, and magnetic fields, or internal stimuli like pH, enzymes, and reduction, enabling on-demand drug delivery. These nanogels are popular for their good hydrophilicity, high drug loading efficiency, flexibility, and biocompatibility. The article discusses the synthesis, properties, and biomedical applications of stimuli-responsive nanogels, as well as the opportunities and challenges for their use in biomedical applications. Nanogels are classified into physically cross-linked and chemically cross-linked types. Chemically cross-linked nanogels are more stable and have better control over morphology, strength, and swellability. They are formed through covalent bonds, while physically cross-linked nanogels are less stable and can undergo sol-gel transitions due to environmental stimuli. Stimuli-responsive nanogels can be designed to release drugs at the target site, improving therapeutic effects and reducing side effects. They have unique properties such as the ability to load and protect small hydrophilic molecules or biological macromolecules, provide prolonged circulation in the blood, and allow for controlled drug release. The synthesis of stimuli-responsive nanogels involves methods such as polymerization of monomers, cross-linking of polymer precursors or natural polymers, and template-assisted nanofabrication. Nanogels can be shaped using "top-down" or "bottom-up" methods. The "top-down" method uses molds to create particles with controlled size, shape, and function, while the "bottom-up" method involves designing molecular structures and assemblies from molecules or clusters. Various stimuli-responsive nanogels have been developed, including pH-responsive, temperature-responsive, and glutathione (GSH)-responsive nanogels, which can release drugs in response to specific environmental conditions. Biomedical applications of stimuli-responsive nanogels include targeted drug delivery, cancer treatment, and tissue engineering. pH-responsive nanogels can deliver drugs to tumor sites with lower pH, while temperature-responsive nanogels can release drugs at body temperature. GSH-responsive nanogels can release drugs in response to redox environments. These nanogels have shown promising results in drug delivery, with high drug loading efficiency, controlled release, and minimal toxicity. They are also used in imaging and diagnostics, with some nanogels being radiopaque for imaging purposes. The article highlights the potential of stimuli-responsive nanogels in biomedical applications and the need for further research to optimize their use in clinical settings.