Characterization of the effects of drug addition on the structure of glyceryl monoolein/water gel systems using low frequency dielectric spectroscopy

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Abstract
The influence of propantheline bromide incorporation on the phase structure of glyceryl monoolein/water systems has been investigated using low-frequency dielectric spectroscopy over a frequency range of 10(-2) to 10(6) Hz at 20 degrees C. The responses of glyceryl monoolein systems composed of 10% and 30% w/w were measured and the spectra modeled using an equivalent circuit based on the Maxwell-Wagner theory.1,2 Marked changes in the dielectric responses of the systems were noted on addition of the propantheline bromide at concentrations up to 10% w/w. For the lamellar (10% w/w water) glyceryl monoolein systems, an increase in the imaginary permitivity was seen, corresponding to an increase in conductivity due to the presence of additional ionic species within the system. Evidence was also obtained for the incorporation of the drug directly into the lipid bilayers, particularly at higher concentrations (10% drug) at which dielectric behavior corresponding to bilayer disruption was seen. Incorporation of 3% and 5% w/w drug into the cubic phase systems (30% w/w water) resulted in a change to the lamellar phase. However, circuit modeling indicated that the system formed structures which showed features of both the lamellar and cubic phases at 3% w/w drug loadings. The study has therefore demonstrated that dielectric analysis may provide a novel means of studying the effects of drug incorporation on the phase behavior of complex gel systems.