Entrapment solution

Gregoriadis, G. (1988a). Fate of injected liposomes Observations on entrapped solute retention, vesicle clearance and tissue distribution in vivo, in Liposomes as Drug Carriers Recent Trends and Progress (G. Gregoriadis, ed.), John Wiley and Sons, Chichester, pp. 3-18. 

Another mechanism for modulated drug release is local pH-induced surface erosion of interpolymer complex gels with entrapped solutes, as shown in... 

Gregoriadis, G., and Senior J. (1980) The phospholipid component of small unilamellar liposomes controls the rate of clearance of entrapped solutes from the circulation. FEBS Lett. 119, 43—46. 

There are several other ways to entrap solutes inside the liposomes, and the entrapping efficiency depends on the structure of liposomes (small unilamellar, large unilamellar, multilamellar, vesicles, etc.) and from the technique for liposome preparation (Roseman etal., 1978 Cullis etal., 1987 Walde and Ishikawa, 2001). 

The rate of liposome accumulation in alveolar type-II cells is dependent on lipid composition. It is therefore possible to select liposome compositions displaying minimal interaction with these cells and thereby function as controlled-release systems for entrapped solutes. For example, liposomes composed of dipalmitoylphosphatidylcholine and cholesterol and containing entrapped sodium cromoglycate will provide sustained delivery of the drag for over 24 hours. Conversely other liposome compositions could be utilized for enhanced epithelial interaction and transport of the drug (e g. cationic lipids for the cellular delivery of the CFTR gene). 

External polymers can also be employed to control leakage of entrapped solutes. Adsorption of the hydrophobic polyelectrolyte poly(2-ethylacrylic acid) on phosphatidylcholine membranes causes the disruption of vesicle membranes (Figure 4.32) with small changes in pH (7.4—>6.5). The surface polyelectrolyte undergoes a well-defined conformational transition from an... 

In order to use the DRV liposomes, and/or measure the entrapment or encapsulation efficiency (or yield) they should first be separated or purified from not entrapped solute. Depending on the MW of the entrapped solute and on the final size of the DRV liposomes this can be done by centrifugation or size exclusion chromatography). 

For the formation of DRV liposomes entrapping solutes that are not sensitive to the conditions used for MLV and/or SUV preparation, it is possible to prepare drug containing liposomes in the initial step of DRV formation. This is particularly important if amphiphilic/lipophilic or in general substances with low aqueous solubility are to be entrapped. However, when there is interest to have a method that can be easily up-scaled for large batch manufacturing, this approach can be problematic. 

Our interest is in using giant vesicles as microcompartments and as models for precursors to cells. To entrap solute molecules microinjection is used because this technique is mild and allows the controlled encapsulation of the solute molecules into a target giant vesicle [7]. 

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