From aligned structures to enhanced performance: a review on freeze-cast hydrogels and functional applications

Traditional hydrogels lack a uniform isotropic network structure, rendering them unsuitable for applications requiring complex mechanical properties. Freeze casting is a kind of self-assembly technology of polymer chains and functional fillers through directional ice crystal growth and a specific ice crystal template. This approach enables the construction of hydrogels with anisotropic multilevel pore structures, providing an effective pathway to overcome performance limitations. This paper provides a systematic review of research progress in freeze casting technology for preparing high-performance hydrogels. The core fabrication processes for hydrogels utilizing this technique are discussed, including template design, key parameter control for directional freezing, and post-processing enhancement strategies. Hydrogel systems incorporating physical crosslinking, chemical crosslinking, and dual crosslinking mechanisms are summarized. Enhancements in the mechanical properties of hydrogels and their applications in biomedicine, flexible electronics, and green cleaning are reviewed. Finally, challenges in cross-scale precision control and industrial-scale reproducible fabrication are addressed, along with future outlook.