Multi-layered marble for hydrogel encapsulation.

Hydrophobic skins on fruits play a crucial role in preventing dehydration and shielding against environmental stress. Inspired by this natural structure, hydrophobic encapsulation is widely employed to preserve the functionality and long-term stability of hydrogels. However, instability at the interface between hydrophobic shell and hydrogel remains a critical challenge. Here, we present a hydrogel encapsulation strategy to stabilize the incompatible interface using a concept of liquid marble, where liquid droplet is covered with hydrophobic particles. A uniform nonpolar liquid layer is first formed on the hydrogel surface through interfacial bridges with hydrophobic particles. A secondary hydrophobic particle layer is then deposited onto this liquid layer to prevent leakage, yielding a multi-layered marble (MLM) structure. This MLM-encapsulation is highly versatile, accommodating various hydrogels, liquids, and structural configurations. By maintaining hydrogel performance and functionality across diverse applications, MLM-encapsulation provides a universal and robust solution for overcoming the long-standing interfacial instability problem.