Capillary‐Wave‐Induced ‘Endocytosis’ Enables Programmable Core‐Shell Capsules Formation for Controlled Release

ABSTRACT

Understanding droplet‐liquid pool interactions in immiscible systems is critical for advancing fluidic encapsulation strategies. Here, we uncover a previously unreported ‘endocytosis’ phenomenon in which an aqueous droplet impacts a deep immiscible pool and spontaneously engulfs the pool liquid, forming a stable double‐layered liquid structure. This process origins from the focusing of capillary waves at the droplet‐pool interface and followed by a pinch‐off of a central oil column via Rayleigh‐Plateau instability. We propose a dimensionless criterion for central column formation, determined by whether viscous dissipation of the droplet's kinetic energy. By introducing a UV‐crosslinkable precursor, gelatin methacryloyl (GelMA) into the droplet, we succeed in encapsulating pool liquid into hydrogel capsules with tunable core‐shell ratios by simply adjusting the impact velocity. This enables precise control of release mechanism: thick‐shell capsules exhibit non‐Fickian sustained release, while thin‐shell capsules display delayed burst Case II release upon swelling. The proposed ‘endocytosis’ phenomena offer a surfactant‐free, single‐parameter controlled strategy compared to conventional liquid encapsulation methods, which offers a new opportunity for on‐demand release in drug delivery and responsive materials.