Polyhedral Non-ionic Surfactant Vesicles

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Abstract
Large polyhedral (2–10 μm) non‐ionic surfactant vesicles (niosomes) formed from mixtures of a hexadecyl diglycerol ether (C16G2), a cholesteryl poly‐24‐oxyethylene ether (solulan C24) and a low level of cholesterol are being investigated as slow‐release systems for ophthalmic, 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 (Lβ) phase. Confocal laser‐scanning microscopy was used to confirm the complex morphology of these vesicles. The thermo‐responsive nature of release of entrapped carboxyfluorescein and nicotinamide adenine dinucleotide has been studied; release is increased with increase in temperature (37°C) even though the polyhedral vesicles still maintain their polyhedral shape at this temperature. The results indicate that the thermo‐responsive features of the niosomes are a result of reversible changes in bi‐layer permeability caused by temperature‐mediated alteration in the membrane‐packing characteristics of the polyethoxylated cholesterol ether.