Environmental Scanning Electron Microscope Imaging of Vesicle Systems
The structural characteristics of liposomes have been widely investigated and there is certainly a strong understanding of their morphological characteristics. Imaging of these systems, using techniques such as freeze-fracturing methods, transmission electron microscopy, and cryo-electron imaging, has allowed us to appreciate their bilayer structures and factors that influence this. However, there are a few methods that study these systems in their natural hydrated state; commonly, the liposomes are visualized after drying, staining and/or fixation of the vesicles. Environmental scanning electron microscopy (ESEM) offers the ability to image a liposome in its hydrated state without the need for prior sample preparation. We were the first to use ESEM to study the liposomes and niosomes, and have been able to dynamically follow the hydration of lipid films and changes in liposome suspensions as water condenses onto, or evaporates from, the sample in real-time. This provides an insight into the resistance of liposomes to coalescence during dehydration, thereby providing an alternative assay for liposome formulation and stability.
Key wordsLiposomes Surfactant vesicles Niosomes Non-ionic surfactant vesicles Lipoplexes ESEM analysis
The authors gratefully acknowledge the financial support rendered: during the time of this work, Afzal Mohammed’s research was supported by Pfizer Global Research and The School of Life and Health Sciences, Aston University; Anil Vangala was awarded an Aston Scholarship; Daniel Kirby was funded by the European Commission (contract no. LSHP-CT-2003-503367), Habib Ali and Sarah McNeil were both funded through EPSRC Case awards, with additional support from Lipoxen Technologies Ltd for Sarah McNeil.
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