In vitro release behavior of SLN, NLC, and NE: An explanation based on the particle structure and carried molecule location

Studying the in vitro release behavior of active pharmaceutical ingredients incorporated into colloidal lipid systems is paramount in predicting their in vivo performance. As a contribution in this regard, this paper reports the relationship between the in vitro release behavior and the structure of solid lipid nanoparticles (SLN), nanostructured lipid carriers (NLC), and nanoemulsions (NE) containing methyl and propylparaben. These colloidal systems are prepared from binary mixtures of trimyristin (MMM) and medium-chain triglycerides (MCT), stabilized with poloxamer 188, using the emulsification-diffusion technique. The structure of the colloidal lipid systems is investigated by differential scanning calorimetry, X-ray diffraction, and Raman spectroscopy. The release behavior depends on the type of nanoparticle dispersion, the physical state of the lipid matrix, the location of the paraben molecule into the particle, and the distribution coefficient and solubility of parabens in the matrix components. Binary mixtures of MMM and MCT lead to the formation of biphasic structures wherein a separated liquid phase of MCT + MMM could locate on the surface of the β -trimyristin crystals. The parabens molecules could be in an amorphous or solubilized state in the interface between the β -trimyristin crystals and the stabilizing agent layer or dissolved in the MCT + MMM liquid phase.