Transformation of vesicular into cubic nanoparticles by autoclaving of aqueous monoolein/poloxamer dispersions.
The ultrastructure of aqueous colloidal dispersions of the cubic monoolein/poloxamer 407/water phase, in particular the particle size distribution and presence of an additional vesicular fraction, highly depends on composition and preparation parameters. Therefore, the effect of autoclaving on such dispersions was investigated. Before autoclaving at 121 degrees C, a dispersion of 4.6% monoolein/0.4% poloxamer predominantly consists of cubic particles beside a fraction of non-cubic particles. The small vesicular particles disappear almost completely upon autoclaving whereas larger particles with cubic structure remain in the sample. In contrast, a 4.4% monoolein/0.6% poloxamer dispersion contains predominantly small vesicular particles before heat treatment. After autoclaving, the majority of the particles is larger and of cubic structure and only a few small non-cubic particles remain. The effect can already be observed at short autoclaving times (e.g., 5 min) but a temperature of at least 90 degrees C is required to induce a major change in the ultrastructure. Results from temperature dependent small angle X-ray diffraction investigations indicate that temperatures corresponding to an isotropic phase are required for particle transformation. Heat treatment of monoolein/poloxamer dispersions can thus be used to transform vesicular dispersions into dispersions of cubic phase or to improve the cubic/non-cubic particle ratio in dispersions already containing particles with cubic internal structure.
Wörle
Gert
G
Institute of Pharmacy, Department of Pharmaceutical Technology, Friedrich-Schiller-University Jena, Lessingstrasse 8, D-07743 Jena, Germany.
Siekmann
Britta
B
Koch
Michel H J
MH
Bunjes
Heike
H
D003102:Colloids; D004355:Drug Stability; D005989:Glycerides / Q000737:chemistry*; D006358:Hot Temperature; D050866:Liquid Crystals / Q000737:chemistry*; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry*; D010316:Particle Size; D020442:Poloxamer / Q000737:chemistry*; D044366:Transition Temperature; D014867:Water / Q000737:chemistry*
D003102:Colloids; D005989:Glycerides; D014867:Water; D020442:Poloxamer; C005953:monoolein