Recent advances in the design of hydrogels: Renaissance of the Hofmeister effect

Abstract

The Hofmeister effect has been known for >135 years since Hofmeister and Lewith’s foundational work. Over the past decade, salt treatment induced by the Hofmeister effect in concentrated gelator molecules has attracted considerable interest in designing functional hydrogels without any complicated chemical modifications. Herein, we provide a detailed overview of recent advances in using the Hofmeister effect to regulate the properties of hydrogels, from the perspective of fundamental theories to applications. This review comprehensively emphasizes the main interactions or effects related to specific ions influencing the performance of pre-gel solutions for hydrogel formation. Moreover, this review focuses on the roles of salt ions in regulating the properties and functionalities of hydrogels, including mechanical properties, ionic conductivity, anti-freezing capability, optical properties, printability, analytical sensitivity, and shape memory ability. Additionally, we provide an overview of the potential applications of these hydrogels in various fields. Finally, this review highlights the challenges and opportunities of this approach and proposes potential issues for understanding the Hofmeister effect in designing functional hydrogels. The broad scale and versatility of this approach make it a promising strategy for developing task-specific hydrogels with customized properties and functionalities.