Harnessing Phase Separation for the Development of High-Performance Hydrogels.

Hydrogels are indispensable for the development of next-generation bioelectronics, soft robotics, and biomedical devices, where their mechanical properties determine performance and reliability. Among strategies to enhance hydrogel mechanics, phase separation enables controlled heterogeneity resulting in gel networks that are reinforced by more than just covalent bonds and polymer entanglements. By regulating the demixing of polymer-rich and solvent-rich domains, phase separation leads to architectures that couple strength, elasticity, and dynamic responsiveness. This article reviews the recent advances in designing high-performance phase-separated hydrogels by linking phase separation behavior within polymer networks to emergent properties such as toughness, fatigue resistance, adhesion, and stimuli-responsiveness. We highlight how mesoscale organization governs multifunctional performance and demonstrate how these principles help resolve the key trade-offs in critical applications, such as high-pressure hemostatic sealants, low-impedance bioelectronics, perfusable tissue engineering scaffolds, and adaptive soft robotics. Finally, we discuss critical challenges, including in situ characterization and scalability, and future opportunities like machine-learning-guided design, which are essential to translate phase separation from a materials heuristic into design rules for reliable, high-performance hydrogel materials.