Rheological and structural properties of lecithin-based organogels

The objectives of this study were to develop lecithin-based organogels made of a biocompatible organic phase and to study the structural and rheological properties of organogels made with different organic phases. The materials used were soybean lecithin of >90% purity (phosphatidylcholine), distilled water and the following organic phases: isooctane (ISO), mineral oil (MO) and isopropylpalmitate (IPP). Phase diagrams for the PC/Water/ISO, PC/Water/ISO/MO (20:80 vo1/vo1), PC/Water/IPP,PC/Water/IPP/MO (50:50vo1/vo1 and 30:70vo1/vo1) and Pc/Water/MO systems were analysed using polarised light microscopy. A narrow region of organogel formation was observed in all systems at molar ratios of water to lecithin between values of 0.4 and 4, depending on the organic phase used. Small-angle X-ray diffraction studies for the PC/Water/ISO system revealed the existence of a highly ordered two-dimensional crystal lattice likely formed by the bundling of the cylindrical reverse micellar tubes. The results for the Pc/Water/IPP and PC/Water/MO systems indicated that there was not enough structural material in the organogels to observe any level of molecular organisation. In summary, this study demonstrated that it was possible to develop biocompatible lecithin-based organogels.