Arresting Microphase Separation Encodes Material Mechanics by Sculpting Microarchitectures and Local Polymer Enrichment

Abstract Mechanical properties are central to material functionality. Although aqueous two‐phase systems (ATPS) can generate microarchitectures in soft materials such as hydrogels, their influence on mechanics, particularly toughness and energy dissipation, remains poorly understood. Here, diverse microarchitectures are systematically engineered within materials via ATPS‐induced local polymer enrichment, which yielding inverse globular, globular, and spinodal patterns, and revealing that each microarchitecture exhibits distinct mechanical behaviors. Most notably, spinodal hydrogel designs improve load distribution, increase fracture resistance, and promote efficient energy dissipation. These insights are used to develop and introduce single polymer phase separation (SPPS) as an innovative strategy to sculpt microarchitectures by tuning the ionic concentration, which overcomes traditional limitations of dual polymer systems. This novel approach enables scalable, low‐complexity, and chemically clean control over stiffness, toughness, and energy dissipation, independent of secondary polymers. Beyond mechanical advantages, spinodal architectures also support enhanced cell migration and biological activity. These findings demonstrate that microarchitectural design, rather than total polymer composition alone, dictates hydrogel mechanics. ATPS and SPPS provide robust and scalable methods to encode distinct mechanical and functional properties via microarchitecture variations into hydrogels, opening opportunities across tissue engineering, biofabrication, soft electronics, and food engineering.