Fabrication of vesicles from mixed cationic/anionic surfactants with additives

In this study, positively charged catanionic vesicles were fabricated from an ion pair amphiphile (IPA), hexadecyltrimethylammonium-dodecylsulfate (HTMA-DS), with the addition of a double-chained cationic surfactant, ditetradecyldimethylammonium bromide (DTDAB), and cholesterol by a mechanical dispersion process. The effects of the added cholesterol on physical stability of the catanionic vesicles were then investigated by size, zeta potential, and Fourier transform infrared (FTIR) analyses. The presence of cholesterol would increase the distance between the charged headgroups of vesicle-forming molecules and reduce the counterion binding ability onto the charged vesicle surfaces, leading to a more pronounced charge character of the catanionic vesicles. Furthermore, cholesterol-induced disorder was detected for the vesicular bilayers. The addition of cholesterol to the bilayer structures of HTMA-DS/DTDAB catanionic vesicles not only adjusted the intra-vesicular molecular packing but also enhanced the inter-vesicular electrostatic repulsion, resulting in enhanced physical stability for the vesicles.