Structural aspects of a self-emulsifying multifunctional amphiphilic excipient: Part II. The case of Cremophor EL

Abstract Lipids and lipid-based excipients, such as Cremophor EL used in this study, play an important role in improving the solubility of poorly soluble drugs and drug candidates. The use of such excipients in self-emulsifying formulations has been widely reported in the literature. In the current study, we report the micellar behavior of Cremophor EL at several concentrations (above the critical micelle concentration) and temperatures using small-angle neutron scattering. For all conditions, Cremophor EL formed core-shell spherical micelles with an overall radius of ∼50 A, a hydrophobic core radius of ∼25 A, and a shell thickness of ∼23 A with a polydispersity of ∼25%. The thickness of the shell (equivalent to the polymer length in the brush regime), and consequently of the overall micelle, was found to increase with increasing temperature. This study will aid our understanding of how drugs could interact with lipid excipients and how such drug-excipient mixtures behave during manufacture, storage, and after administration.