Double Emulsion-Templated Nanoparticle Colloidosomes with Selective Permeability

Colloidosomes are microcapsules whose shell consists of densely packed colloidal particles. Their physical properties such as permeability, mechanical strength, and biocompatibility can be precisely controlled through the proper choice of colloids and preparation conditions for their assembly. The high degree of control over their physical properties makes colloidosomes attractive structures for encapsulation and controlled release of materials ranging from fragrances and active ingredients to molecules produced by living cells. The conventional approach to preparing colloidosomes involves two steps: first, colloidal particles are introduced into the continuous phase of a water-in-oil emulsion. The particles self-assemble at the interface between the two immiscible liquid phases and form a colloidal shell structure. Subsequently, the colloidal shell structures, templated by the water droplets dispersed in the oil phase, are transferred to an aqueous phase either by centrifugation or repeated washing. This strategy has been used to create colloidosomes with particles ranging from 5 nm to several microns in diameter. The colloidosome structures must be mechanically stabilized to successfully transfer them into an aqueous phase; however, even with this stabilization, the transfer processes are not efficient, often leading to damage of the original structure. In addition, the size distribution of colloidosomes prepared by the conventional technique is rather broad, as polydisperse emulsions are typically used as templates. A narrow size distribution for colloidosomes is especially important for the encapsulation of active pharmaceutical ingredients where delivery of an exact amount is critical. Thus, it is important to develop a more convenient and direct means to create monodisperse and fully controllable colloidosomes, in particular, eliminating the transfer step. In this work, we demonstrate that nanoparticle colloidosomes with selective permeability can be prepared from monodisperse double emulsions as templates. Monodisperse