POLYHEDRAL NONIONIC SURFACTANT VESICLES

Large polyhedral (2-10 mu m) non-ionic surfactant vesicles (niosomes) formed from mixtures of a hexadecyl diglycerol ether (C(16)G(2)), a ch olesteryl poly-24-oxyethylene ether (solulan C24) and a low level of c holesterol are being investigated as slow-release systems for ophthalm ic, subcutaneous or intramuscular administration. The phase-diagram of this three-component system has been constructed and these polyhedral vesicles are found to be in the gel (L-beta) phase. Confocal laser-sc anning microscopy was used to confirm the complex morphology of these vesicles. The thermo-responsive nature of release of entrapped carboxy fluorescein and nicotinamide adenine dinucleotide has been studied; re lease is increased with increase in temperature (37 degrees C) even th ough the polyhedral vesicles still maintain their polyhedral shape at this temperature. The results indicate that the thermo-responsive feat ures of the niosomes are a result of reversible changes in bi-layer pe rmeability caused by temperature-mediated alteration in the membrane-p acking characteristics of the polyethoxylated cholesterol ether.