Surface structural characteristics of some colloidal lipid systems used in pharmaceutics

Surface properties of solid lipid nanoparticles (SLN), nanostructured lipid carriers (NLC), and nanoemulsions (NE) are determinant to understand their structural characteristics and their behavior as drug delivery systems; however, there is still limited knowledge in this respect. As a contribution, this paper reports the study of some surface properties of these colloidal systems which were prepared with binary mixtures of trimyristin and medium-chain triglycerides (MCT) and stabilized with Poloxamer 188 (P188). Particle sizes and polydispersity indexes decrease in the order SLN>NLC>NE suggesting that the addition of MCT to trimyristin reduces the particle asymmetry. ζ potentials range from −6 mV to −10 mV and the P188 layer is ∼20 nm; thus, steric stabilization seems to predominate. The amount of P188 on the surface of the drops in the NE was less than that on the surface of the particles in the SLN and NLC and decreases as the proportion of MCT decreases. Finally, depending on the physical state of the lipid matrix, hydrophobic molecules could be adsorbed on the particle surface and located at the interface between the particle and the P188 layer or absorbed inside the matrix.