Preparation of cell-embedded colloidosomes in an oil-in-water emulsion

Cell encapsulation by locking the interfacial microgels in a water-in-oil Pickering emulsion has currently been attracting intensive attention because of the biofriendly reaction condition. Various kinds of functional microgels can only stabilize an oil-in-water Pickering emulsion, and it is thus difficult to encapsulate cells in the emulsion where the cells are usually dispersed in the continuous phase. Herein, we introduce a facile method for preparing cell-embedded colloidosomes in an oil-in-water emulsion via polyelectrolyte complexation. Escherichia coli (E. coli) was chosen as a model cell and embedded in the thin shell of chitosan/poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AAc)) microcapsules. This is beneficial for expressing cell function because of the little resistance of mass exchange between the embedded cells and the external environment. Cells can be used in biocatalysis or biomedicine and our product will hold great promises to improve the performance in those fields. The synthesis route presents a platform to prepare cell-embedded microcapsules in an oil-in-water Pickering emulsion in a facile and biocompatible way. First, an emulsion stabilized by P(NIPAM-co-AAc) microgels was prepared. Then, the interfacial microgels in the emulsion were locked by chitosan to form colloidosomes. The mechanism of cell encapsulation in this system was studied via fluorescent labeling. The viability of E. coli after encapsulation is ca. 90%. Encapsulated E. coli is able to metabolize glucose from solution, and exhibits a slower rate than free E. coli. This demonstrates a diffusion constraint through the colloidosome shell.