Enhancing water retention in hydrogels under extreme conditions: Strategies, applications and challenges

Hydrogels have garnered significant research interest for their versatile applications in biomedical, electronic, and agricultural fields—attributes intrinsically linked to their high-water-content matrices. However, hydrogel functionality frequently deteriorates under environmental conditions due to dehydration/freezing-induced structural damage, resulting in performance degradation. To address this challenge, various strategies have been developed to enhance the water retention of hydrogels, employing diverse mechanisms and targeting a range of applications. In this review, strategies for improving the water retention of hydrogels and their corresponding cutting-edge applications have been systematically described. Firstly, the states and importance of water in hydrogels are articulated. Subsequently, five core strategies are categorized and mechanistically analyzed across multi-scale: encapsulation, solvent optimization, ionic incorporation, structural design, and combination approaches. Then, the applications and developments of hydrogels are highlighted and mainly categorized into three promising candidates, including biomedical (tissue engineering, dressing, biosensing), electronic (electrolyte, sensor, wearable device), and agricultural (water retainer of soil, nutrient release, vertical farming) fields. Finally, current challenges and future research directions for hydrogels are critically assessed, emphasizing the need for comprehensive solutions and strategic advancements to unlock their full potential in diverse applications.