Formulation design, preparation and physicochemical characterizations of solid lipid nanoparticles containing a hydrophobic drug: Effects of process variables

This study aimed to prepare solid lipid nanoparticles (SLNs) of a hydrophobic drug, tretinoin, by emulsification-ultrasonication method. Solubility of tretinoin in the solid lipids was examined. Effects of process variables were investigated on particle size, polydispersity index (PI), zeta potential (ZP), drug encapsulation efficiency (EE), and drug loading (L) of the SLNs. Shape and surface morphology of the SLNs were investigated by cryogenic field emission scanning electron microscopy (cryo-FESEM). Complete encapsulation of drug in the nanoparticles was checked by cross-polarized light microscopy and differential scanning calorimetry (DSC). Crystallinity of the formulation was analyzed by DSC and powder X-ray diffraction (PXRD). In addition, drug release and stability studies were also performed. The results indicated that 10 mg tretinoin was soluble in 0.45 +/- 0.07 g Precirol (R) ATO5 and 0.36 +/- 0.06 g Compritol (R) 888ATO, respectively. Process variables exhibited significant influence in producing SLNs. SLNs with <120 nn size, <0.2 PI, >130I mV ZP, >75% EE, and similar to 0.8% L can be produced following the appropriate formulation conditions. Cryo-FESEM study showed spherical particles with smooth surface. Cross-polarized light microscopy study revealed that drug crystals in the external aqueous phase were absent when the SLNs were prepared at <= 0.05% drug concentration. DSC and PXRD studies indicated complete drug encapsulation within the nanoparticle matrix as amorphous form. The drug release study demonstrated sustained/prolonged drug release from the SLNs. Furthermore, tretinoin-loaded SLNs were stable for 3 months at 4 degrees C. Hence, the developed SLNs can be used as drug carrier for sustained/prolonged drug release and/or to improve oral absorption/bioavailability. (C) 2011 Elsevier B.V. All rights reserved.