Stable Ultrathin‐Shell Double Emulsions for Controlled Release

Chun‐Xia Zhao, Dong Chen, Yue Hui, David A. Weitz, Anton P. J. Middelberg

Double emulsions are normally considered as meta-stable systems and this limit in stability can restrict application domain. To enhance stability and hence practical application, the outer shell is converted to a mechanically-strong layer, for example a polymeric layer, thus allowing improved performance. This conversion can be problematic for food and drug applications as toxic solvent is needed to dissolve polymer in the middle phase and high temperature is required to remove solvent. Complexity is also high for example involving UV initiation of polymeric monomer cross-linking. In this study, we report the formation of biocompatible, water-in-oil-in-water (W/O/W) double emulsions with an ultra-thin layer of fish oil. We demonstrate their applications in encapsulation and controlled release of small hydrophilic molecules. Without a trigger, the double emulsions remained stable up to months, and the release of small molecules was extremely slow. In contrast, rapid release was achieved by osmolarity shock, leading to a complete release within 2 h. This work demonstrates the significant potential of double emulsions, and provides new insights into their stability and practical application.