Fusion Arrest and Triggered Release of Contents in Coacervates via Oxidation-Assisted Interfacial Coating

Liquid-liquid phase separation (LLPS) generates dynamic coacervate compartments whose fusion and dissolution behaviors are difficult to control without perturbing bulk conditions. Here, we introduce an interfacial polydopamine (pDA) coating strategy that programs the stability and morphological evolution of poly-L-lysine/ATP (pLys/ATP) coacervates. Dopamine oxidation with potassium permanganate (KMnO₄) at the droplet interface yields a thin pDA shell that initially promotes droplet-droplet adhesion and rapid coalescence but subsequently suppresses further coarsening and preserves the size distribution over extended incubation. Microscopic analysis reveals that this coating primarily restructures the interface while retaining a fluid interior, enabling long-lived yet internally dynamic protocell-like assemblies. We further show that the pDA shell can be mechanically actuated by a small bifunctional diamine, which triggers fast centripetal contraction and expulsion of encapsulated contents, whereas a longer PEG-based crosslinker does not elicit such behavior. This chemically simple, two-input scheme establishes a generalizable route to arrest and reactivate LLPS-derived compartments, offering a versatile design element for systems chemistry, protocell models, and LLPS-guided delivery platforms.