Characterization of liposomes. The influence of extrusion of multilamellar vesicles through polycarbonate membranes on particle size, particle size distribution and number of bilayers (original) (raw)
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Analysis of the particle size distribution and internal volume of liposomal preparations
Journal of Pharmaceutical Sciences, 1993
0 In this work we studied the particle size distribution of three liposomal preparations by quasi-elastic light scattering spectroscopy. Sized unilamellar vesicles of small diameter (s-SUV) were prepared by ultrasonication and subsequent centfigation followed by extrusion through polycarbonate membranes of 0.5-pm pore size. Large unilamellar vesicles were obtained by reversed-phase evaporation (REV) and extrusion through polycarbonate filters with or without preliminary freezing-thawing cycles (VET, and VET,,, respectively). After preparation, REV were sized to small diameter REV (s-REV) by extrusion through 0.4-and 0.2-pm polycarbonate membranes. According to the results, the s-SUV preparations were made up of two subpopulations, the major of which consisted of vesicles that were 26 nm in mean diameter and accounted for 95% of the overall s-SUV population. The s-REV dispersions always resolved into two populations centered at 120 and 380 nm, the relative proportions of which depended on the pore size of the filters used. VET structures were composed of a single population of vesicles that were -100 nm in mean diameter. Cholesterol inclusion into the bilayer composition extended the distribution without altering its mean value. On the other hand, the internal volumes calculated from mean diameters or assuming a Gaussian distribution were inconsistent with experimental data obtained by usual techniques.
Preparation of liposomes of defined size distribution by extrusion through polycarbonate membranes
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1979
Liposomes of defined size and homogeneity have been prepared by sequential extrusion of the usual multilamellar vesicles through polycarbonate membranes. The process is easy, reproducible, produces no detectable degradation of the phospholipids, and can double the encapsulation efficiency of the liposome preparation. Multilamellar vesicles extruded by this technique are shown by both negative stain and freeze-fracture electron microscopy to have mean diameters approaching the pore diameter of the polycarbonate membrane through which they were extruded. When sequentially extruded down through a 0.2 pm membrane, the resulting vesicles exhibit a very homogeneous size distribution with a mean diameter of 0.27/lm while maintaining an acceptable level of encapsulation of the aqueous phase.
Effect of Lyophilization on the Size and Polydispersity of Unilamellar and Multilamellar Liposomes
Journal of Nanotechnology and Materials Science, 2016
With the emergence of drug delivery systems, liposome's attracted many attentions as drug and gene delivery vehicles. In this regard, long-term stability of liposomes becomes important in the clinical use of these particles and their success in the market of therapeutics. Lyophilisation is one of the most common methods for preservation of liposome nanoparticles. This process may change some key properties of particles such as size and polydispersity. Hence, in this article we investigated the effects of lyophilization process on these two parameters. A multilamellar liposomal formulation of DOTAP/DOPE/Cholesterol was fabricated through modified lipid film hydration method while extrusion was employed to obtain unilamellar ones. Lyophilization was performed in the presence of sucrose used as the cryoprotectant. The results show that after lyophilization, the mean particle size of both multilamellar and unilamellar vesicles had no significant change (p > 0.1) in contrast to poly dispersity index (p < 0.05
Dispersion of phospholipids in water, which spontaneously form a closed structure with environment bounded by phospholipids bilayer membranes, this vesicular system is called as liposome [1]. Liposomes are the small vesicle of spherical shape that can be produced from cholesterols, non sphingolipids, glycolipids, long chain fatty acids and even membrane proteins [2]. Liposomes are the drug carrier loaded with great variety of molecules such as small drug molecules, proteins, nucleotides and even plasmids. Liposomes were discovered about 40 years ago by A.D. biology, biochemistry and medicine today. In 1960s, liposome has been used as a carrier to transport a wide variety of compounds in its aqueous compartment. Liposome can be formulated and processed to di composition, charge and lamellarity. To date liposomal formulations of anti been commercialized [4]. The clinical potential of liposomes as a vehicle for replacement therapy in genetic deficiencies of lysosomal enzymes was first established in 1970s [5, 6]. Considerable progress was made during 1970s and 1980s in the field of liposome stability leading to long circulation times of liposomes after intravenous administration resulting in the improvement in doxorubicin had been formulated as liposome in 1980s to improve the therapeutic index. There are several mechanisms by which liposomes act within and outside the body which are as follows [7]: Liposomes are a novel drug delivery system (NDDS), in which the medication is encapsulated in a vesicle. It has been a study interest in the development of a NDDS. Liposomes are surfactants, sphingolipids, glycolipids, long chain fatty acids and even membrane proteins and drug molecules or it is also called vesicular system. It is differ in size, composition and charge. It is a drug carri variety of molecules such as small drug molecules, proteins, nucleotides and even plasmids. Few drugs are also formulated as liposomes to improve their therapeutic index. Consequently a number of vesicular drug delivery systems such as liposomes, niosomes, transfersomes, and pharmacosomes were developed. The focus of this review is to the various method of preparation, characterization of liposomes, advantages and brings out the application vesicular systems.
Biophysical Journal, 1997
Phospholipids with covalently attached poly(ethylene glycol) (PEG lipids) are commonly used for the preparation of long circulating liposomes. Although it is well known that lipid/PEG-lipid mixed micelles may form above a certain critical concentration of PEG-lipid, little is known about the effects of PEG-lipids on liposome structure and leakage at submicellar concentrations. In this study we have used cryogenic transmission electron microscopy to investigate the effect of PEG -PE on aggregate structure in preparations of liposomes with different membrane compositions. The results reveal a number of important aggregate structures not documented before. The micrographs show that enclosure of PEG-PE induces the formation of open bilayer discs at concentrations well below those where mixed micelles begin to form. The maximum concentration of PEG-lipid that may be incorporated without alteration of the liposome structure depends on the phospholipid chain length, whereas phospholipid saturation or the presence of cholesterol has little or no effect. The presence of cholesterol does, however, affect the shape of the mixed micelles formed at high concentrations of PEG-lipid. Threadlike micelles form in the absence of cholesterol but adapt a globular shape when cholesterol is present.
Asian Journal of Pharmaceutical Research and Development
Liposomes are sphere-shaped vesicles made up of one or more bilayers of phospholipids. The ability of delayed vesicles to transport medications, vaccines, diagnostic specialists, and other bioactive operators has accelerated development in the liposomal drug delivery system. The liposomal delivery system's pharmacyelements and pharmacokinetics properties have been altered, resulting in a higher therapeutic index and lower overall toxicity. There are many factors to consider, including size, size distribution, surface electrical potential, lamella count, and encapsulation efficacy. The use of surface modification in the development of liposomes with various mechanisms, kinetic properties, and biodistribution was discovered to be beneficial. Drug delivery, drug targeting, controlled release, and improved solubility have all been studied extensively with liposomes.
Structural Components of Liposomes and Characterization Tools
Liposomes are the artificially formulated spherical vesicles which are composed of lipid bilayer having encapsulation ability of both hydrophilic and lipophilic drugs in order to prevent them from degradation. The controlled and targeted release ability of liposomes makes them a unique drug delivery system. Liposomes are combination of phospholipids in an aqueous media resulting in bilayered structures. Liposomes can be characterized by various methods. Liposomes can be used in controlling and targeting drug delivery system. Liposomes have various therapeutic application including cancer, ocular, infectious diseases and also various applications in diagnostics, industrial and gene therapy. With the advancement of science and technology, liposomes will have a remarkable future in the pharmaceutical market.