The advantage of the second generation technology is the increased loading
with actives compared to SLN and firmer inclusion of the active inside the particle
matrix during the shelf life. By preparing the particles from a solid lipid, especially
highly purified solid lipids, the particle matrix tends to form a relatively perfect crystal
lattice leaving limited space to accommodate the active. This limits the loading capacity
and can lead to expulsion of active from the lipid matrix during storage. In contrast,
the use of a lipid mixture with very differently structured (sized) molecules distorts
the formation of a perfect crystal. The particle matrix contains many imperfections
providing space to accommodate the active in molecular form or as amorphous
clusters. One could state that “the perfectness” of the NLC system is its “imperfectness”
in its crystalline structure. In the second half of the nineties, there was an increasing
interest in investigating the SLN for dermal application, especially for cosmetic use
(52, 53). Interesting cosmetic molecules were incorporated such as e.g. retinol and