Liposomes physical properties

The behavior of liposomes in vivo can be influenced to a considerable extent by varying chemical composition and physical properties. Parameters affecting rate of clearance from the blood and tissue distribution include size, composition, dose, and surface characteristics (e.g., charge, hydrophobicity, presence of homing devices such as antibodies). 

Woodle MC, Newman MS, Cohen JA. Sterically stabilized liposomes physical and biological properties. J Drug Target 1994 2 397. 

Going back to the physical properties, it should be mentioned that vesicles can be seen as a microphase, which can undergo temperature-induced phase transitions. Thus, liposomes can pass from amore ordered state at low temperature (the so-called... 

The physical properties of diacetylene-containing phospholipid liposomes (25) have been investigated by D. Chapman 102 103 104> by means of UV/VIS and 13C-NMR spectroscopy. They found that short linear segments of polymer are interconnected through the glycerol backbone of the lipid in identical-chain phosphatidyl cholines, but the molecular weights of the polymers are still unknown. 

Since liposomes have an aqueous interior, they are also termed as nanovesicles or nanocapsules. On the other hand, nanoparticulates with a solid matrix-type interior represent another type of drug carrier called nanospheres.27 Compared with liposomes, the solid interior of nanospheres generally offers a lower drug-loading capacity but at the same time provides some unique physical properties that can be advantageous in certain applications. 

The hydrophobic lipid anchors can be either fatty chains (e.g. derived from oleic or myristic acid) or a cholesterol group. Lipid anchors help in forming liposomes (or micellar structures) and determine the physical properties of a lipid bilayer, such as membrane rigidity and rate of lipid exchange between lipid... 

Liposomes occur in nature, but can also be easily synthesized in the laboratory. Depending on the preparation method used, whioh influenoes their size — in relation to the number of bilayer shells — and physical properties, liposomes are olassified as small unilamellar vesicles (SUVs, 25-50 nm), large unilamellar vesioles (LUVs, 100 nm to 1 pm), giant unilamellar vesicles (GUVs, 1.0-200 pm) multilamellar vesioles (MLVs, 0.1-15 pm), and multi-vesicular vesicles (MWs, 1.6-10.5 pm) the last consists of several small vesicles. Bicelles, which contain surfactant molecules in the lipid bilayer, constitute a special type of liposome. 

Higgins J, Hodges NA, Olliff CJ, Phillips AJ. A comparative investigation of glycinebetaine and dimethylsulphoxide as liposome cryoprotectants. J Pharm Pharmacol 1987 39 577-582. MacGregor WS. The chemical and physical properties of DMSO. 

Synthetic phospholipids are commercially available and they contain polar heads occurring in nature and and the same type of fatty acid in both, 9 -l and sn-2 sites. The acyl chains may be mainly myristoyl (C14 0), palmitoyl (C16 0), olcoyl (C16 l) or stearoyl (C18 0) residues. The physicochemical characteristics of the lipidic bilayers that are prepared from synthetic phospholipids are well defined. The lipid composition influences many physical properties of model membranes and it has been shown that single synthetic lipids or mixtures of short and long fatty acid chains can produce stable lipidic bilayers and liposomes. 

It is important to know the position of drug in the liposomes, i.e., whether the drug is entrapped in the liposome aqueous core or intercalated within the membrane because in the later case it can cause marked changes in the physical properties of the liposome membranes. Polar drugs are released from the liposomes when the bilayer membrane is breached, whereas nonpolar drugs remain affiliated with the liposomes unless there is a gross disruption of the membrane structure. In the case of chloroquine it resides in the internal aqueous phase rather than the lipid bilayer. 

Although liposome and GNP systems are similar in many aspects, the important differences are explained by their respective physical properties. Cycloaddition is a novel generic chemical tool for the facile in situ surface modification of liposomes. Fluorescence resonance energy transfer was used to demonstrate that the reaction takes place at the surface and a colorimetric assay was developed to follow the reaction in time without the need for any equipment... 

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