Rheological and Dielectric Characterization of Monoolein/Water Mesophases in the Presence of a Peptide Drug

Abstract

A series of glyceryl monoolein/water gel systems containing 10%, 22%, and 30% w/w water has been investigated using two complementary techniques, oscillatory rheology and dielectric analysis, in order to establish the utility of these two techniques in conjunction and to investigate the influence of the inclusion of a model peptide, cyclosporin A, on the properties of the gels. Oscillatory rheology was performed in two modes; frequency sweeps at 20, 37, and 70 degrees C and temperature sweeps from 20 to 70 degrees C. Dielectric spectroscopy was performed in the kHz to mHz frequency range over a temperature range of 20-70 degrees C. Both rheology and dielectric spectroscopy were able to identify structural changes in the systems analyzed, with the 10% and 30% (w/w) water sample showing typical features of the lamellar and cubic phase respectively at 20 degrees C, while the 22% (w/w) system showed intermediate behavior. The thermotropic phase transitions could be monitored using rheological temperature sweeps. Drug loading resulted in marked changes in rheological and dielectric response of the 10% w/w water system, causing a decrease in both elasticity and permittivity values, while a less marked effect was observed for the 22% and, in particular, the 30% w/w systems. The investigation has demonstrated that rheological and dielectric measurements yield distinct yet complementary information and that the inclusion of a model peptide may alter the properties of the gel, the extent of the effect being dependent on the phase composition of the system.