Rheology of nanostructured lipid carriers (NLC) suspended in a viscoelastic medium.

Colloidal lipid nanoparticle dispersions have been characterized by rheological measurements using two different nanostructured lipid carrier (NLC)-based formulations intended for cosmetic application of substances like sunflower oil and alpha-tocopherol. This study has shown that rheological and viscoelastic properties of aqueous NLC dispersions are quantitatively very different depending on the composition of the oil phase and the temperature of storage despite similar or even identical particle size. NLC were loaded with 30% active ingredient relative to the particle mass. Stearyl alcohol was used as lipid matrix and the particle sizes determined by photon correlation spectroscopy were in the range 210-270 nm. In general, sun flower oil-loaded NLC dispersions showed distinctly higher storage modulus (G'), loss modulus (G") and complex viscosity (eta*). Storage at lower temperature (4 degrees C versus 20 degrees C) delay the build up of a microstructure affected not only by size and stabilizer but also loaded ingredient and storage history after preparation, i.e. storage at room temperature accelerates the build up of a final suspension structure.