Triple-layered encapsulation through direct droplet impact.

HYPOTHESIS: Multilayer capsules not only provide better protection for the core, but also enable multifunctionalities. However, their fabrication is challenging. Rapid encapsulation by the impact of the droplet is a simplified approach to form the compound droplet with a single shell layer. Therefore, it is worth exploring the potential for multilayer capsule formation with the approach. EXPERIMENTS: We investigate the impact of an aqueous core droplet through a layered liquid pool to form compound droplet and use ultraviolet polymerization to solidify its outer layer. The critical conditions to form the compound droplet are studied. We then explore the protection features of the capsule. FINDINGS: We succeed in fabricating defect-free capsules that featuring a triple-layered structure with a solid outer shell. The corresponding formation dynamics is revealed. We illustrate that the capsule provides reliable protection to the core through fluorescent intensity monitoring, pH level indication and bacteria revival test. Our method can also be adapted to tailor the functionality of the capsule, which is demonstrated by fabricating the magnetically steerable capsule. Our proposed approach offers great potentials for protecting sensitive ingredients and allows great flexibility in customizing capsule functionalities.