Liposomes sonication

We reported (35) on a fluorescence test of the relative effectiveness of antioxidants in oxidizing soy lecithin liposomes (sonicated microdispersions). 

Surfactants having two alkyl chains can pack in a similar manner to the phospholipids (see Box 6.4 for examples). Vesicle formation by the dialkyldimethylammonium cationic surfactants has been studied extensively. As with liposomes, sonication of the turbid solution formed when the surfactant is dispersed in water leads ultimately to the formation of optically transparent solutions which may contain single-compartment vesicles. For example, sonication of dioctadecyldimethyl-ammonium chloride for 30 s gives a turbid solution containing bilayer vesicles of 250-450 nm diameter, while sonication for 15 min produces a clear solution containing monolayer vesicles of diameter 100-150 nm. The main use of such systems has been as membrane models rather than as drug delivery vehicles because of the toxicity of ionic surfactants. 

Phospholipid molecules form bilayer films or membranes about 5 nm in thickness as illustrated in Fig. XV-10. Vesicles or liposomes are closed bilayer shells in the 100-1000-nm size range formed on sonication of bilayer forming amphiphiles. Vesicles find use as controlled release and delivery vehicles in cosmetic lotions, agrochemicals, and, potentially, drugs. The advances in cryoelec-tron microscopy (see Section VIII-2A) in recent years have aided their characterization [70-72]. Additional light and x-ray scattering measurements reveal bilayer thickness and phase transitions [70, 71]. Differential thermal analysis... 

In water, a particle of lecithin exhibits myelin growth, ie, cylindrical sheets that are formed by bdayers and are separated by water which may break up into liposomes (vesicles with a single bilayer of Hpid enclosing an aqueous space). PhosphoHpids more generally form multilamellar vesicles (MLV) (5). These usually are converted to unilamellar vesicles (ULV) upon treatment, eg, sonication. Like other antipolar, surface-active agents, the phosphoHpids are... 

Batzri, S., and Korn, E. D. (1973). Single bilayer liposomes prepared without sonication, Biochim. Biophys. Acta, 298, 1015-1019. 

Pilot study of amphotericin B entrapped in sonicated liposomes in cancer patients with fungal infections, Eur. J. Cancer cun. Oncol., 24, 527-538. 

Artificial membrane systems can be prepared by appropriate techniques. These systems generally consist of mixtures of one or more phospholipids of natural or synthetic origin that can be treated (eg, by using mild sonication) to form spherical vesicles in which the lipids form a bilayer. Such vesicles, surrounded by a lipid bilayer, are termed liposomes. 

Liposomes have been, and continue to be, of considerable interest in drug-delivery systems. A schematic diagram of their production is shown in Fig. 10. Liposomes are normally composed of phospholipids that spontaneously form multilamellar, concentric, bilayer vesicles, with layers of aqueous media separating the lipid layers. These systems, commonly referred to as multilamellar vesicles (MLVs), have diameters in the range of 15 pm. Sonication of MLVs... 

The second model of a biological membrane is the liposome (lipid vesicle), formed by dispersing a lipid in an aqueous solution by sonication. In this way, small liposomes with a single BLM are formed (Fig. 6.11), with a diameter of about 50 nm. Electrochemical measurements cannot be carried out directly on liposomes because of their small dimensions. After addition of a lipid-soluble ion (such as the tetraphenylphosphonium ion) to the bathing solution, however, its distribution between this solution and the liposome is measured, yielding the membrane potential according to Eq. 

The binding of carotenoids within the lipid membranes has two important aspects the incorporation rate into the lipid phase and the carotenoid-lipid miscibility or rather pigment solubility in the lipid matrix. The actual incorporation rates of carotenoids into model lipid membranes depend on several factors, such as, the kind of lipid used to form the membranes, the identity of the carotenoid to be incorporated, initial carotenoid concentration, temperature of the experiment, and to a lesser extent, the technique applied to form model lipid membranes (planar lipid bilayers, liposomes obtained by vortexing, sonication, or extrusion, etc.). For example, the presence of 5 mol% of carotenoid with respect to DPPC, during the formation of multilamellar liposomes, resulted in incorporation of only 72% of the pigment, in the case of zeaxanthin, and 52% in the case of (1-carotene (Socaciu et al., 2000). A decrease in the fluidity of the liposome membranes, by addition of other... 

Construct a liposome by dissolving the desired lipids in chloroform to homogenize fully the mixture, drying them to remove solvent, and using any established method of forming bilayer vesicles in aqueous solution (i.e., sonication see Section 1, this chapter). 

Pick, U. (1981) Liposomes with a large trapping capacity prepared by freezing and thawing of sonicated phospholipid mixtures. Arch. Biochem. Biophys. 212, 186. 

The sensors discussed so far are based on ligands covalently bound to the polymer backbone. Other methods of detection - often referred to as mix and detect methods - work by simple noncovalent incorporation of the polymer with the ligand of interest. Reichert et al. generated liposomes of polydiacetylene with sialic acid for the same purpose of detection as Charych s surface-bound polymers, but realized that covalent functionalization of the polymer was not necessary [17]. Through simple mixing of the lipid-bound sialic acid with the polymer before sonication and liposome formation, they were able to form a functional colorimetric recognition system (Fig. 8). 

The extraliposomal ammonium ion concentration [(NH4)jJ yj ] was measured as ammonia with the ammonia electrode at pH 13.5. Under these conditions, all ammonium ions are converted to ammonia and no leakage of intraliposomal ammonium ion occurred during the measurement. For measurements of total ammonium ion plus ammonia present in both intraliposome aqueous phase and external medium ammonia [(NH4)jJ g4i y +(NH4)Jpg j ] the liposomes were sonicated under acidic conditions (pH 1.5-2.0) using the Transonic 460/H bath sonicator in sealed vials for 45 minutes. Then, in order to convert ammonium ion to ammonia, NaOH was added to bring the pH to... 

Liposomes (SUVs) were prepared by probe sonication according to standard procedures (31) in the presence of STPP. A mixture of lecithin, cholesterol, and STPP (PC/Ch/STPP = 65/15/20, molar ratio final total lipid 25 mg/ mL) was dissolved in chloroform followed by removal of the organic solvent using a rotary evaporator. After adding 5 mM HEPES (pH 7.4) to the dry lipid film, the sample was probe sonicated with a Sonic Dismembrator (Model 100, Fischer Scientific) at a power output of approximately 10 W for 30 minutes. To remove any titanium particles, which have been shed from the tip of the probe during sonication, the sample was centrifuged for 10 minutes at 3000 X g. The formed liposomes were separated from free, i.e., nonincorporated, STPP by gel filtration chromatography on a Sephadex G-15 column. 

Liposomes can be created by shaking or sonicating phospholipids in water. Low shear rates create multilamellar liposomes, which have many layers like an onion. Continued high-shear sonication tends to form smaller unilamellar liposomes. In this technique, the liposome contents are the same as the contents of the aqueous phase. Sonication is generally considered a gross method of preparation, and newer methods such as extrusion are employed to produce materials for human use. 

Liposomes (Fig. 8) are completely closed vesicular bilayer structures formed by exposing phosphoglycerides in water suspension to sonic oscil-... 

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