Polymer‐clay nanocomposite hydrogels with multiple responses to multiple stimuli

Abstract Hydrogels are widely studied for their stimuli‐responsive properties. They adapt to external stimuli, including physical, chemical and biological ones. To enhance adaptability in complex environments, multi‐responsive hydrogels have been developed, which either react to multiple stimuli independently or cooperatively (multistimuli‐response) or exhibit multiple responses triggered by single or multiple stimuli (multi‐response). Their properties depend on polymer type, molecular weight, cross‐linking, and water content, which affect mechanical behavior and response. To address their inherent fragility, polymer‐inorganic nanocomposite hydrogels integrate the advantages of both components, yielding enhanced functionalities. Among various nanofillers, smectites have been extensively studied for improving mechanical strength and responsiveness. Polymer‐smectite nanocomposite hydrogels exhibit enhanced elasticity, toughness, thermal stability, gas barrier properties, and responsiveness to external stimuli, expanding their applications in biomedical engineering, environmental remediation, and smart materials. This review discusses the fundamentals of polymer‐smectite nanocomposite hydrogels, their design strategies, and the role of smectite in enabling multi‐responsive behavior. The classification based on the site of responsiveness (polymer network and smectite) is presented, highlighting the important role of smectite in controlling the response and potential applications. Finally, challenges are addressed, emphasizing smectite's role in advancing next‐generation smart materials.