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Studies on polyhedral niosomes

Arunothayanun, Parinya.; (1998) Studies on polyhedral niosomes. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Niosomes prepared from non-ionic surfactants were studied and characterised with regard to their physicochemical and biological properties. Hexadecyl diglycerol ether (C16G2) and a series of poly(oxyethylene) alkyl ethers form, with an equimolar amount of cholesterol, a mixture of largely spherical and tubular niosomes. In the absence of cholesterol, they form polyhedral structures below their phase transition temperature (Tm) and they transform into spheres on heating above Tm. Various properties, namely vesicle shape, size, encapsulation efficiency, membrane permeability, thermal behaviour, viscosity, and osmotic activity were investigated using in addition, as a comparator, sorbitan monostearate (Span 60) niosomes. The role of membrane composition was in particular an issue. Rheological studies showed that viscosity of niosomes can be affected by a number of factors including vesicle shape. The values of intrinsic viscosity were used in attempt to predict the hydration and the volume fraction of the vesicle dispersions. Polyhedral niosomes formed by C16G2 are less osmotically active, and more permeable than their spherical/ tubular counterparts, formed with cholesterol. The release profiles of 5(6)-carboxyfluorescein from both types of niosomes are also different and can be affected by the content of the hydrophilic surfactant poly(24) oxyethylene cholesteryl ether (Solulan C24) in the membranes. The high encapsulation efficiency of luteinising hormone releasing hormone (LHRH) in C16G2 niosomes was achieved when these are prepared with the remote loading method (exploiting either pH or (NH4)2SO4 gradients). In vitro studies showed that spherical/ tubular C16G2 niosomes are more stable than their polyhedral counterparts in rat plasma and muscle homogenate. Following intramuscular injection in rats, 125I-LHRH solution was cleared from the site of injection within 2h, whilst both polyhedral and spherical/ tubular C16G2 niosomes act as a depot and release 125I-LHRH over 25 h and 49 h, respectively. Extrusion of single niosomes (4-40 μm in diameter) from glass capillaries (5 μm in diameter) was studied as a biomimetic approach for pulsatile delivery. This was simply achieved but when vesicle diameter was larger than the capillary diameter, the vesicles can be extruded into a variety of simple or complex structures, depending on their initial ultrastructure, possibly a reflection of the differences in membrane elasticity of the vesicle formulations.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Studies on polyhedral niosomes
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Health and environmental sciences; Niosomes; Polyhedral
URI: https://discovery.ucl.ac.uk/id/eprint/10105133
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