Incorporation of the model drug ubidecarenone into solid lipid nanoparticles

Purpose. The impact of drug incorporation on melt-homogenized tripalmitin nanoparticles is investigated with ubidecarenone as a model drug. The dispersions are studied with respect to their drug loading capacity, localization and physical state of the drug as well as to potential changes of the nanoparticle properties due to interactions between drug and triglyceride matrix. Methods. The investigations were carried out using photon correlation spectroscopy, differential scanning calorimetry, synchrotron radiation X-ray diffraction, ultracentrifugation, and cryo- and freeze-fracture transmission electron microscopy. Results. Ubidecarenone can be incorporated into the dispersions in concentrations higher than 50% of the dispersed phase. The drug is associated with the nanoparticles such that small drug amounts are bound tightly to the carrier matrix while excess drug adheres as a liquid phase to the crystalline particles. Drug incorporation lowers the crystallization and melting temperature of the particle matrix and accelerates the transition of the triglyceride into the stable beta -polymorph after crystallization. Conclusions. Drug incorporation may significantly alter important physicochemical parameters of solid lipid nanoparticles. Slow release of ubidecarenone may only be possible for the fraction of drug which is tightly bound to the matrix while the liquid fraction should be rapidly released.