Chemically Programmable Liquid-to-Solid Transitions and Spatial Dynamics in Synthetic Coacervates

Biomolecular condensates undergo dynamic maturation, transitioning from liquid-like droplets to gel-like or solid-like assemblies, exhibiting structural heterogeneity in response to biochemical cues. Synthetic coacervate droplets formed via liquid-liquid phase separation (LLPS) have emerged as simplified models of these condensates and of protocells. Yet, the understanding of complex phase behaviors of liquid-like droplets in both biological and chemical contexts remains less explored, limiting our understanding of biological function and the design of droplet-based soft materials and protocells. Here, we introduce a chemically programmable strategy to dynamically modulate droplet phase transitions through controlled polymer-network cross-linking. Reactive cross-linkers selectively engage polymers within liquid-like droplets, progressively increasing internal microviscosity and inducing a liquid-to-solid transition. Beyond uniform phase regulation, network cross-linking drives spatially heterogeneous phase separation via polymer demixing and Ostwald ripening, with reaction-diffusion dynamics critically shaping both thermodynamically stable and metastable droplets. Using orthogonal cleavable cross-linkers, we further demonstrate chemical control over droplet liquefaction and the generation of multiphasic structures with pathway-dependent configurations. Integration of photoresponsive cross-linkers with digital-micromirror device (DMD) technology enables precise spatial photopatterning of droplet networks. This work establishes a versatile framework for elucidating the structural principles of microphase separation within coacervates and provides a blueprint for designing dynamic soft materials and synthetic protocells.