Water-in-oil-in-water emulsions are examples of double emulsions, in which dispersions of small water droplets within larger oil droplets are themselves dispersed in a continuous aqueous phase1,2,3. Emulsions occur in many forms of processing and are used extensively by the foods, cosmetics and coatings industries. Because of their compartmentalized internal structure, double emulsions can provide advantages over simple oil-in-water emulsions for encapsulation, such as the ability to carry both polar and non-polar cargos, and improved control over release of therapeutic molecules4,5,6. The preparation of double emulsions typically requires mixtures of surfactants for stability; the formation of double nanoemulsions, where both inner and outer droplets are under 100 nm, has not yet been achieved7,8,9. Here we show that water-in-oil-in-water double emulsions can be prepared in a simple process and stabilized over many months using single-component, synthetic amphiphilic diblock copolypeptide surfactants. These surfactants even stabilize droplets subjected to extreme flow, leading to direct, mass production of robust double nanoemulsions that are amenable to nanostructured encapsulation applications in foods, cosmetics and drug delivery.
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This work is supported by a grant from the National Science Foundation (T.J.D.), a grant from the Human Frontiers of Science Program (T.J.D.), and University of California start-up funds (T.J.D. and T.G.M.). Some of the work was conducted at the National Resource for Automated Molecular Microscopy (NRAMM) which is supported by the National Institutes of Health through the National Center for Research Resources P41 programme. We thank C. Potter and J. Quispe of NRAMM at the Scripps Research Institute, and S. Zhong and D. Pochan of the University of Delaware, for use of cryoelectron microscopy equipment.
Author Contributions J.A.H. synthesized the polypeptides, prepared and characterized the emulsions, designed experiments, and assisted in manuscript preparation. C.B.C and S.M.G. also prepared and characterized the emulsions. Z.L. imaged the emulsions using CTEM. T.G.M. and T.J.D. initiated the project, designed and supervised the experiments, analysed the data, and drafted the manuscript. T.J.D. assembled and finalized the manuscript. All authors discussed the results and commented on the manuscript.
The file contains Supplementary Methods, Supplementary Table 1, Supplementary Figures 1-6 with Legends. Text of synthetic methods and additional details on emulsion preparation. The Supplementary Table gives characterization of block copolypeptide surfactants. The Supplementary Figures show additional details of polypeptide surfactants including variations of amino acid composition, emulsion stability, emulsion size, and control of internal droplet structure. (PDF 1679 kb)
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Hanson, J., Chang, C., Graves, S. et al. Nanoscale double emulsions stabilized by single-component block copolypeptides. Nature 455, 85–88 (2008). https://doi.org/10.1038/nature07197
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