<p>Liquid-liquid phase separation (LLPS) has emerged as a fundamental mechanism for intracellular organization and dynamic regulation, while nanoscience provides precise tools for designing matter at the nanoscale. LLPS-driven condensates behave as dynamic, nanoscale hydrogel-like networks, offering a unifying physical framework that bridges biological phase behavior with synthetic soft materials. Their convergence opens new opportunities for engineering adaptive and functional materials. This review provides an integrative perspective on the LLPS-nano interface, illustrating how LLPS principles enable the rational design of responsive and self-regulating nanomaterials. We synthesize established and hypothesized mechanistic insights into how nanoparticle properties, including surface chemistry, geometry, and responsiveness, modulate phase behavior and shift condensate assembly and energetics. Advanced nanoscale characterization techniques are highlighted for resolving condensate architecture and mechanics with molecular precision. We further highlight emerging functional applications in programmable biomedical therapeutics, drug delivery, advanced nanomaterials, catalytic systems, and environmental remediation, illustrating how LLPS-inspired design can bridge molecular interactions with macroscopic performance. Finally, we propose a forward-looking roadmap combining multiscale modeling, dynamic imaging, and data-driven materials design to advance LLPS from a biological phenomenon to a predictive design principle for creating responsive and susainable materials.</p> Graphical abstract <p></p>