Stability determination of solid lipid nanoparticles (SLN (TM)) in aqueousdispersion after addition of electrolyte

The contribution of mono-, di- and trivalent ions to the destabilization of solid lipid nanoparticle (SLN(TM)) dispersions was investigated, i.e. part icle growth and subsequent formation of semi-solid gels. Sodium, calcium an d aluminium chloride were added in varying concentrations to a Compritol fo rmulation which had proved to be highly sensitive towards destabilizing eff ects. Dispersions containing up to 10(-3) m sodium chloride remained stable for 14 days. The same concentrations of calcium or aluminium induced sligh t and rapid particle growth, respectively. Generally, a pronounced destabil izing effect was observed with increasing electrolyte concentration and inc reasing valence. Higher concentrations of electrolyte (10(-2), 10(-1) m) in duced gelation of the systems. The extent of solidification was highly depe ndent on the crystallinity of the lipid phase. The recrystalization indices of the gels were distinctly higher compared to the liquid systems. Additio nally, unstable modifications, being present in liquid dispersions, were tr ansformed into stable ones with increasing solidification. The mechanisms o f the destabilizing effect of the electrolytes are reduced electrostatic re pulsion and transformation of the lipid Compritol to the beta' modification promoting gel formation.