Liposome size determination

FIGURE 1 Effect of (sequential) extrusion of MLV dispersions through polycarbonate membrane filters (Unipore) with pore sizes of 1.0, 0.6, 0.4, 0.2, and 0.1 ym on the mean liposome diameter. DXR-containing MLV (phosphatidylcholine/phosphatidylserine/ cholesterol 10 1 4) mean diameter of nonextruded dispersion about 2 ym pH 4. Mean particle size determined by dynamic Light scattering (Nanosizer, Coulter Electronics). (From Crommelin and Storm, 1987.)... 

Liposome size can range from around 20 nm to around 50 pm. To a certain extent, the mean diameter and distribution of the diameters can be controlled by sizing procedures after the formation of the initial liposome dispersion or by a careful selection of the preparation conditions (cf. Sec. II). Several techniques can be used to determine mean particle size and particle size distribution (Groves, 1984). 

G-50 column and eluted in 2-(N-Morpholino) ethansulfonic acid hydrate (MES)/N-(2-Hydroxyethyl)piperazine-N-(2-ethane-sulfonic acid) (HEPES) buffer pH 7.2 (50 mM MES, 50 mM HEPES, 75mM NaCl) to remove unencapsulated BPs. Several formulations with different sizes were obtained (0.6, 0.4, 0.2, and 0.1 pm). Liposome size and morphology was determined by dynamic light scattering and cryo-TEM microscopy (Fig. 1). 

The mean sizes obtained were 500 150, 350 77, 192 25, and 100 16, for 0.6, 0.4, 0.2, and 0.1pm liposomes, respectively. Drug concentration was determined by spectrophotometric assay of chromophoric complex between the BP and copper (II) ions (63) or by high performance liquid chromatography (HPLC) (64). Lipid concentration was determined by Bartlett method (65). Stability of the liposomes was determined by examining drug leakage. Then 400 pL of liposomal formulations were centrifuged... 

For water-soluble agents, the encapsulation efficiency and thus the internal volume of vesicles which determines the amount of encapsulated material, is a very important factor with regard to the in vitro efficacy. It depends on the liposome size, lipid composition and lamellarity. When the number of liposomes delivered has to be known, the enumeration of the suspension can be performed by multinuclear NMR and photon correlation spectroscopy (110)-... 

Liposome Size, Size Distribution and Zeta Potential Determination... 

Determine liposome size and size distribution by photon correlation spectroscopy (PCS) using a Zetasizer 3000HS. 

The deformability of elastic liposomes is determined by assessment of the extrusion of the suspension through a filter membrane of defined pore size (50 nm) under pressure (24, 31). The amount of liposome suspension extruded is measured and the liposome size and shape are determined as previously described. For each liposome suspension, the mean standard deviation of... 

Particle size, polydispersity index, and zeta potential measurements of mannosylated liposomes are determined by Zetasizer nano ZS-90. 

The size of the liposomes was determined by dynamic light scattering using a Sub-micron Particle Analyzer (Coulter, Hialeah, FI). 

After by diluting of dispersion to an appropriate volume with water, the cumulant particle size of liposomes was determined using a dynamic light scattering instrument as shown in Figs. 1 and 2. 

The basic characterization of the liposomes revolves around size determination, usually by DLS, and sample liposome concentration by phosphorous assay, neither of which will be described here. Indeed, the procedures of the DLS experiments highly depend on the type of apparatus used, while the Bartlett colorimetric assay of phosphorous content has frilly been described elsewhere (12-14). 

Tissue Disposition and Pharmacological Effects of Liposomes In Vivo -Since the initial publication of studies involving injection of liposome-entrapped substances In vivo,H 71.72 there has been an increasing number of studies on both the altered tissue distribution and also on the increased pharmacological efficacy of encapsulated agents. The subject has been reviewed recently.13 15,20, The most important points for future consideration include the permeability properties of liposomes in a physiological environment, their interaction with plasma components, the role of liposome size and chemistry in determining the rate of removal from the circulation and their tissue localization at the cellular level. 

Reliable lipid and protein analysis of the prepared antibody-liposome conjugate is essential for proper characterization and subsequent interpretation of results obtained in the application of the conjugates. In addition, we strongly advise that the liposome conjugate size be determined with a particle sizer, if one is available, since liposome size plays such an important role in the pharmacokinetics of the system in vivo. 

Modification with NGPE allows binding of several hundred protein molecules per 250 nm diameter liposome (44). Using 125I-labeled antibody, the efficacy of protein binding varied between 65 and 75% and did not depend on the presence of PEG-PE in the lipid mixture. The unbound antibody is separated on a Bio-Gel A15M column. Liposomes obtained are serially filtered through polycarbonate filters with pore sizes of 0.6,0.4, and 0.2 pm. The actual size (normally 160-190 nm) and distribution of the liposomes are determined with a particle size analyzer. 

Liposome Size Measurements. Sizes were determined at 25°C by quasielastic light scattering (QELS) with a fixed 90 scattering angle using a Brookhaven Instrument Corporation Particle Sizer Model BI-90 equipped with a He/Ne laser. In a typical measurement values were determined over 2000 cycles with a count rate of 50 kpcs. The software provided by... 

The size distribution of the liposomes is determined by dynamic light scattering (DLS) with a Dynapro apparatus (http //www.wyatt.com). DLS is a hydrodynamic method by which one determines the rate of diffusion of particles through the solvent. The hydrodynamic radius is defined as the radius of a theoretical hard sphere that diffuses with the same speed as the particle under examination. The measurement is performed at 25° and requires about 2 /ul of the extruded liposome suspension diluted in 18 /ul of liposome buffer (final lipid concentration in the range of 0.1 roM). Ten autocorrelation functions are sequentially measured, from which the size distribution of the liposome is determined using the Dynamics v5 software from Dynapro. A complete measurement takes a few minutes. Figure lA shows typical size distributions of extruded liposomes as determined by DLS. Figure IB shows how the actual hydrodynamic radius of the liposomes varies with the pore size of the polycarbonate filter. 

The type and size of the liposomes were determined using a JOEL ISM 5300 (Japan) scanning electron microscope and the program package OZARIA for visual information quantification. The samples of liposome dispersions for microscope observation were... 

Gangliosides were reconstituted in the liposomal membrane according to a method previously established [16,17]. Both the diameter and the size distribution of the liposomes were determined by the dynamic light scatter-... 

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