Nonspherical colloidosomes with multiple compartments from double emulsions.

Colloidosomes are hollow capsules whose walls are composed of densely packed colloidal particles. Colloidosomes are typically prepared by creating particle-covered water-in-oil (W/O) emulsion droplets. These particle shells in the oil phase are subsequently transferred into an aqueous phase to generate the colloidosomes. We recently reported a new approach to fabricate monodisperse colloidosomes by using double emulsions as templates. Water-in-oil-in-water (W/O/W) double emulsions with a core–shell structure are created using a glass capillary microfluidic device. Hydrophobic SiO2 nanoparticles, suspended in the oil phase, become the wall of colloidosomes upon removal of the oil. The functionality and physical properties of colloidosomes such as permeability, selectivity, and biocompatibility can be precisely controlled by suitable choice of colloidal particles and processing conditions. Such versatility makes these colloidosomes attractive candidates for applications in encapsulation and delivery of foodstuffs, fragrances, and active ingredients. Further advantages could be obtained from colloidosomes and capsules with a non-spherical geometry, or with multiplecompartments. Nonspherical particles can pack more densely than spherical ones. Nonspherical capsules, therefore, can be used to store a larger amount of encapsulated materials compared to spherical capsules. Nonspherical capsules could also facilitate the delivery of encapsulated materials through constrictions; red blood cells (RBC) are one of many examples in nature where a nonspherical compartment is utilized. In addition to the nonspherical nature, multiple-compartment colloidosomes would enable encapsulation and storage of multiple types of cells andmaterials in a single capsule without risk of cross contamination. Colloidosomes that have been reported to date, however, are spherical in shape, and have only one compartment. Interfacial tension between the two immiscible phases favors minimizing the surface area and thus leads to the formation of spherical droplets. This tendency naturally limits the fabrication process to the generation of spherical colloidosomes. Moreover, the traditional method of using simple W/O emulsions to template colloidosomes leads to generation of spherical colloidosomes with only one compartment. In this report, we demonstrate the generation of nonspherical colloidosomes with multiple compartments. We use glass capillary microfluidics to prepare W/O/W double emulsions with different morphologies. These double emulsions have a different number of internal aqueous drops in the oil drop. Hydrophobic SiO2 nanoparticles, suspended in the oil phase, and poly(vinyl alcohol) (PVA), dissolved in the continuous aqueous phase, stabilize the double emulsions. The nanoparticles in the oil phase eventually become the shell of colloidosomes upon the removal of the oil. During the oil removal, the internal W/O interface retains their spherical shapes whereas the outer O/W interface deforms; this process leads to the generation of nonspherical colloidosomes with multiple compartments (Scheme 1). A glass capillarymicrofluidic device that combines a co-flow and a flow-focusing geometry is used to generate double emulsions with controlled morphology (see Supporting Information, Scheme S1). W/O/W double emulsions with a different number of internal aqueous drops per oil drop (n) were generated by controlling the flow rates of three phases independently as shown inFigure 1. The outerO/Winterface was stabilized by a partially hydrolyzed PVA in the continuous phase and the inner W/O interface was stabilized by 15-nm hydrophobic SiO2 nanoparticles; the nanoparticles dispersed in theoilphaseadsorbedto the twoW/Ointerfacesasevidencedby communications