Crystal hydrogels: Strategies, properties, and applications

Hydrogels, soft materials made from polymer networks capable of absorbing water, demonstrate remarkable compatibility in diverse hybridizations. When the fillers that can undergo reversible crystallization are used for incorporation, the materials’ mechanical properties and functions would be significantly improved. Therefore, these hydrogels, named crystal hydrogels, are emerging as a class of new advanced functional materials. This review offers a comprehensive examination of these materials from five distinct angles. We first discuss their fundamental characteristics and then elaborate on the synthesis methods of crystal hydrogels, categorizing them into three types based on their crystal formation mechanisms. The third section is dedicated to describing the properties of crystal hydrogels. Furthermore, we explore the diverse and remarkable applications that have emerged with the advancement of crystal hydrogels. The review concludes by summarizing the core concepts and assessing the recent opportunities and challenges faced by crystal hydrogels.