In vitro in vivo characterisation of polyhedral niosomes

Non-ionic surfactant vesicles (niosomes) formed by a hexadecyl diglycerol ether (C(16)G(2)) and a series of poly-oxyethylene alkyl ethers exhibit a variety of shapes dependant on their membrane composition. These surfactants form with an equimolar amount of cholesterol a mixture of largely spherical and tubular niosomes. In the absence of cholesterol, they form faceted polyhedral structures. The physicochemical and biological differences between polyhedral and spherical/tubular niosomes were studied. Polyhedral niosomes undergo a reversible shape transformation into spherical structures on heating above their phase transition temperature (T-m). The viscosity of polyhedral niosomes at room temperature is higher than their spherical counterparts due to their faceted and relatively rigid shape, and is more dependant on temperature due to shape transformation. At room temperature, polyhedral niosomes possess more rigid gel phase membranes and are less osmotically sensitive; however, they are more permeable because of a lack of or low levels of cholesterol in their membranes. Polyhedral niosomes loaded with luteinising hormone releasing hormone (LHRH), nonetheless, slow the release of drug compared to solution, albeit to a small extent. (C) 1999 Elsevier Science B.V. All rights reserved.