Comparison of wax and glyceride solid lipid nanoparticles (SLN (R))

The present study compares solid lipid nanoparticles (SLN) formulated with either wax or glyceride bulk material. While most published data deal with glyceride SLN, little knowledge is reported on wax carriers. The two types were compared with respect to drug encapsulation efficacy, particle size di stribution after production and storage, and crystal packing. The inclusion of retinol as a model drug was investigated. Retinol is chemically unstabl e in water and rather stable in lipid phases. Thus, rapid degradation of re tinol indicates rapid drug expulsion from the carrier. Good stability indic ates an effective drug encapsulation in the lipid phase of the nanoparticle s. Particle size distribution was measured by laser diffractometry. Subcell packing and assignment of polymorphic forms was investigated by WAXS measu rements. Glyceride SLN showed good drug encapsulation, while physical stabi lity was poor. In contrast, wax SLN possessed good physical stability but l acked sufficient drug encapsulation in the solidified state. These differen ces were attributed in part to different crystal packing. Less ordered crys tal lattices favour successful drug inclusion, as in the case of glyceryl m onosterate and glyceryl behenate SLN. The highly ordered crystal packing of wax SLN comprised of beeswax or cetyl palmitate, for instance. leads to dr ug expulsion, but also to superior physical stability. (C) 2000 Elsevier Sc ience B.V. All rights reserved.