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Langmuir. 2016 Nov 15;32(45):11907-11917. Epub 2016 Nov 2.

Effects of High Pressure on Internally Self-Assembled Lipid Nanoparticles: A Synchrotron Small-Angle X-ray Scattering (SAXS) Study.

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Biological and Soft Systems, Cavendish Laboratory, University of Cambridge , JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
Centre for Materials Science, School of Physical Sciences and Computing, University of Central Lancashire , Preston PR1 2HE, United Kingdom.
Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen , DK-2100 Copenhagen, Denmark.
Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic , 162 06 Prague, Czech Republic.
Institute of Inorganic Chemistry, Graz University of Technology , A-8010 Graz, Austria.
School of Food Science & Nutrition, University of Leeds , Leeds LS2 9JT, U.K.


We present the first report on the effects of hydrostatic pressure on colloidally stabilized lipid nanoparticles enveloping inverse nonlamellar self-assemblies in their interiors. These internal self-assemblies were systematically tuned into bicontinuous cubic (Pn3m and Im3m), micellar cubic (Fd3m), hexagonal (H2), and inverse micellar (L2) phases by regulating the lipid/oil ratio as the hydrostatic pressure was varied from atmospheric pressure to 1200 bar and back to atmospheric pressure. The effects of pressure on these lipid nanoparticles were compared with those on their equilibrium bulk, nondispersed counterparts, namely, inverse nonlamellar liquid-crystalline phases and micellar solutions under excess-water conditions, using the synchrotron small-angle X-ray scattering (SAXS) technique. In the applied pressure range, induced phase transitions were observed solely in fully hydrated bulk samples, whereas the internal self-assemblies of the corresponding lipid nanoparticles displayed only pressure-modulated single phases. Interestingly, both the lattice parameters and the linear pressure expansion coefficients were larger for the self-assemblies enveloped inside the lipid nanoparticles as compared to the bulk states. This behavior can, in part, be attributed to enhanced lipid layer undulations in the lipid particles in addition to induced swelling effects in the presence of the triblock copolymer F127. The bicontinuous cubic phases both in the bulk state and inside lipid cubosome nanoparticles swell on compression, even as both keep swelling further upon decompression at relatively high pressures before shrinking again at ambient pressures. The pressure dependence of the phases is also modulated by the concentration of the solubilized oil (tetradecane). These studies demonstrate the tolerance of lipid nanoparticles [cubosomes, hexosomes, micellar cubosomes, and emulsified microemulsions (EMEs)] for high pressures, confirming their robustness for various technological applications.

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