Investigation on particle self-assembly in solid lipid-based colloidal drug carrier systems.

Abstract

The effect of spontaneous particle self-assembly into stack-like structures occurring in dispersions of melt-homogenized tripalmitin nanocrystals (solid lipid nanoparticles; SLNs) was studied in dependence of lipid concentration, stabilizer type, stabilizer concentration, and particle size. Tripalmitin nanosuspensions with concentrations ranging from 20 to 200 mg/g were prepared by high-pressure melt homogenization. The formulations were characterized by synchrotron small-angle X-ray scattering (SAXS), photon correlation spectroscopy (PCS), and freeze-fracture transmission electron microscopy (TEM). Dispersions of partly self-assembled particles could be derived both with anionic or cationic surfactants. Particle self-assemblies were observed in such formulations when the tripalmitin concentration exceeds 40 mg/g. Further increase of the lipid concentration enhances particle self-assembly. The tendency to form self-assemblies is also influenced by the particle shape. The interparticle distances in stacked lamellae are determined by the tripalmitin concentration and by the surfactant concentration. Parallel alignment of tripalmitin nanoplatelets is a completely reversible and concentration-dependent effect that can be attributed to the overlap of the exclusion volumes of the anisometric particles. The usefulness of this effect might be explored for the formulation of drug delivery systems.