Hydrogels are soft and wet materials with a three-dimensional porous network structure, capable of swelling to retain a large volume of water and maintaining semi-solid integrity. In general, their diverse structures are mainly determined by the type of polymer matrix, the method and degree of crosslinking, and the three-dimensional structure. However, all different hydrogels share water as their core theme. The water content and organization, both at the surface and within the hydrogels, are crucial factors influencing their many physical properties. Over the past years, their formulations and applications have made transformative advances. But the construction of novel hydrogel systems requires understanding how water molecules or solutes interact with the hydrogel. Herein, this review reexamines hydrogels from the perspective of water and summarizes the states, distribution, and behavior of water within hydrogels, as well as the hydrogel properties imparted by water. We also enumerate the techniques for detecting water in hydrogels and discuss the latest progress in the regulation and design of water-hydrogel systems and their unique role in key applications. Thus, the role of water within hydrogels extends far beyond merely acting as a solvent; it is one of the key factors bridging the structure–function relationship in hydrogels.

中文翻译：

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水：水凝胶的灵魂


水凝胶是具有三维多孔网络结构的柔软湿润材料，能够膨胀以保留大量水分并保持半固体完整性。一般来说，它们的不同结构主要由聚合物基质的类型、交联的方法和程度以及三维结构决定。然而，所有不同的水凝胶都以水为核心主题。表面和水凝胶内部的水分含量和组织是影响其许多物理特性的关键因素。在过去的几年里，它们的配方和应用取得了变革性的进步。但是，构建新型水凝胶系统需要了解水分子或溶质如何与水凝胶相互作用。本文从水的角度重新审视了水凝胶，总结了水凝胶中水的状态、分布和行为，以及水赋予水凝胶的性质。我们还列举了检测水凝胶中水的技术，并讨论了水-水凝胶系统调节和设计的最新进展及其在关键应用中的独特作用。因此，水在水凝胶中的作用远远超出了仅仅作为溶剂的作用;它是弥合水凝胶结构-功能关系的关键因素之一。