Lipid particle sizing

In addition, to release lipids from source material, such as those in starch, fish meal, or milk, it might be necessary to treat the sample with an acid prior to lipid extraction (see Basic Protocol 4). In the case of milk, addition of ammonium hydroxide is necessary to dissolve casein prior to lipid extraction, which will release the lipids from its surrounding matrix (e.g., from the film surrounding the fat globules in milk). Furthermore, in certain cases, it is necessary to predry the sample in order to allow efficient and complete extraction of lipids. Particle size reduction is another factor that may improve lipid extraction efficacy. 

Ingold, K.U., Bowry, V.W., Stocker, R., and Walling, C., Autoxidation of lipids and antioxidation by alpha-tocopherol and ubiquinol in homogeneous solution and in aqueous dispersions of lipids unrecognized consequences of lipid particle size as exemplified by oxidation of human low density lipoprotein, Proc. Natl. Acad. Sci. U.S.A. 90 (1), 45-49, 1993. 

Perez-Gagd, M. B. Krochta, J. M. (2001). Lipid particle size effect on water vapor permeability and mechanical properties of whey protein/beeswax emulsion films. Journal of Agricultural and Food Chemistry, 49, 996-1002. 

Depending on the lipid concentration, vesicles with different particle sizes can be prepared (Kremer et al., 1977). At a low Upid concentration (3 mM), vesicles with a diameter of 30 nm are formed, whereas 110-nm vesicles are formed at higher concentrations... 

An alternative approach is the use of pH-sensitive fluorophores (Lichtenberg and Barenholz, lOSS). These probes are located at the lipid-water interface and their fluorescence behavior reflects the local surface pH, which is a function of the surface potential at the interface. This indirect approach allows the use of vesicles independent of their particle size. Recently, techniques to measure the C potential of Liposome dispersions on the basis of dynamic light scattering became commercially available (Muller et al., 1986). 

Heydenreich, A.V., Westmeier, R., Pedersen, N., Poulsen, H.S., and Kristensen, H.G., Preparation and purification of cationic solid lipid nanospheres effects on particle size, physical stability and cell toxicity, International Journal of Pharmaceutics, 2003, 254, 83-87. 

Silica gel G contains a binder, calcium sulphate, to help it to adhere to the plate, but silica gel H does not and is preferable for some lipid separations, particularly polar mixtures. Some commercially prepared plates contain an alternative organic binder that does not interfere in the same way as calcium sulphate but can present some difficulty with location methods, particularly charring. The degree of hydration of the adsorbent and the particle size will effect the separation and because these cannot be guaranteed, authentic standards should always be run at the same time as the samples. 

Shelf life of an LEH preparation is dependent on the change in particle size and oxidative damage to the lipid and hemoglobin upon storage. LEH tends to... 

The aim of the research carried out in our laboratory was to develop a lipid formulation that could be manufactured by a simple and reproducible procedure. In particular, we wanted to produce phospholipid-based particles with a high AmB loading coupled to a small particle size. 

Nomura T, et al. Effect of particle size and charge on the disposition of lipid carriers after intratumoral injection into tissue-isolated tumors. Pharm Res 1998 15 128. 

Mean particle size ranges 50 to 1000 mn. Depending on the type and concentration of the lipid, 0.5 to 5% emulsifier (surfactant) has to be added for physical stabilization. For dermal use, surfactants are very often poloxamer 188, polysorbate 80, lecithin, tyloxapol, polyglycerol methylglucose distearate (Tegocare 450), sodinm cocoamphoacetate (Miranol Ultra C32), or saccharose fatty acid ester. 

Lipid microparticles and nanopellets for oral use were first described by Speiser [11]. Nanopellets are prepared by dispersing melted lipids with high-speed mixers or via ultrasound techniques. Lipospheres developed by Domb are also prepared from dispersed lipids by stirring and sonication [12]. These preparations may contain a high degree of microparticles, which thus excludes an intravenous injection. For other routes of application (e.g., peroral administration), these microparticles might not be a serious problem. Furthermore, the dispersions may be contaminated by metal shed. With optimized conditions, however, mean particles sizes of 1(X) to 200 nm are possible [13]. 

In addition to particle size, the degree of crystallinity and the modification of the lipid are of relevance for drug incorporation and release. Lipid crystallization and a change of the modification can be delayed with very small particles and in the presence of emulsifiers [20,21]. 

The generally low lipid content and the poor viscosity of lipid nanodispersions make these preparations, as they are, less suitable for dermal drug application. The handling of the preparation by the patient is improved by SLN incorporation into ointments, creams, and gels. Alternatively, ready-to-use preparations may be obtained by one-step production, increasing the lipid phase to at least 30%. However, increasing the lipid frequently results in an unwanted increase in particle size. Surprisingly, it has been found that very concentrated (30 to 40%) semisolid cetyl palmitate formulations preserve the colloidal particle size [10]. 

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