Liposomes freeze-drying method

Ultrasound-Responsive Liposomal Preparation by Freeze-Drying Method... 

Quantitative entrapment of vaccines into small (up to about 200 nm diameter) liposomes in the absence of microfluidization (which can damage DNA and other labile materials when extensive) can be carried out by a novel one-step method (7) as follows SUVs (e.g., cationic) prepared as in section Preparation of Small Unilamellar Vesicles are mixed with sucrose to give a range of sucrose-to-lipid weight/weight ratio of 1.0 to 5.0 and the appropriate amount of plasmid DNA (e.g., 10-500 pg) and/or protein (e.g., up to 1 mg). The mixture is then rapidly frozen and subjected to dehydration by freeze-drying, followed by rehydration as in section Preparation of Vaccine-Containing Dehydration-Rehydration Vesicles. ... 

The content of vaccine within the small liposomes is estimated as in the section Estimation of Vaccine Entrapment in Dehydration-Rehydration Vesicles Liposomes for both microfluidized and sucrose liposomes and expressed as percentage of DNA and/or protein in the mixture subjected to freeze drying as in the section Preparation of Vaccine-Containing Small Liposomes by the Sucrose Method in the case of sucrose small liposomes or in the original DRV preparation (obtained in the section Estimation of Vaccine Entrapment in DRV Liposomes ) for microfluidized liposomes. Vesicle size measurements are carried out by PCS as described elsewhere (6,8,17). Liposomes can also be subjected to microelectrophoresis in a Zetasizer to determine their zeta potential. This is often required to determine the net surface charge of DNA-containing cationic liposomes. 

Practically all available iodinated extracellular X-ray contrast agents have been encapsulated into liposomes using different lipids and methods of preparation. Table 1 gives a short and intentionally incomplete overview of some of the approaches. The first liposomal contrast agent preparation that was tested in humans contained diatrizoate [48]. The injected dose was up to 0.5 ml kg k The preparation was effective even in plain radiography where lesions down to 0.8-1.0 cm could be detected in patients. However, adverse events such as fever and hyperthermia, which occurred in 30% of the patients, limited further use. We have incorporated iopromide into MLVs that were prepared from phosphatidyl choline (PC), cholesterol and stearic acid at a molar ratio of 4 5 1 using the ethanol-evaporation technique [44]. The liposomes can be stored freeze-dried and they are reconstituted before use by... 

The advantages of this method are (i) it produces liposomes with high entrapment efLciency, (ii) the procedure s Lexibility may aid product stability as noted earlier, (iii) scale-up is possible, and (iv) the lyophile can be stored and rehydration can be done immediately before use. The drawbacks of the method are possible particle size instability of the liposome during the freeze-drying process and the high cost of the freeze-drying process. 

Ohsawa, T., Miura, H., and Harada, K. (1984). A novel method for preparing liposome with a high capacity to encapsulate proteinous drugs freeze-drying met6Mm. Parm. Bull., 32, 2442-2445. 

In mechanical dispersion, the lipids are dried down onto a solid support from organic solvents, followed by the dispersion of liposomes by adding the aqueous media through shaking. Other methods using mechanical dispersion techniques include freeze drying, pro-liposome preparation, hand shaking, and the non-shaken method (175). 

Lipids are mixed together and solvent is removed using freeze-drying. Then an aqueous solution is introduced and the hpid cake around the vessel wall is reconstituted. This method works best for manufacture of neutral liposomes, as the hydro-phobic lipids readily dissolve in solvents such as chloroform and are deposited dry on the wall of the rotavapor vessel. Then the material to be encapsulated is dissolved in an aqueous solution and the dry film on the vessel wall is hydrated with this solution. The exact steps involved in the preparation of hydrogenated soy phosphatidylcholine (PHSPC)- and cholesterol-containing vesicles at a molar ratio of 60 to 40% are as listed here ... 

There are countless fabrication techniques available for producing multifunctional nanoparticles. For liposomes, one such method is called the film hydration technique. In it, multilamellar liposomes are spontaneously formed after a dried lipid solution is exposed to an aqueous solution and mechanically agitated [23]. For unilamellar liposomes, the extrusion technique can be utilized in which multilamellar liposomes are extmded through a porous membrane in the presence of the drug and then undergo a freeze-thaw... 

There are many methods to prepare liposomes. This review will discuss only some of the commonly used methods. These include liposomes made by thin film hydration, reverse phase evaporation, freeze-drying, and proliposome methods. 

Zhang and Zhu [60] have combined two methods in preparing liposomes, by hydrating particulate-based proliposomes followed by freeze-drying. This approach has been reported to enhance the entrapment of amikacin compared to the same vesicles before freeze-drying or vesicles prepared by the thin film method. 

Zingel et al [141] prepared iopromide-carrying liposomes by lypophilisation. DSC and resistance temperature measurements were used to determine the maximum allowable temperature during primary drying. Melting was detected at -21 °C by DSC but conductivity changes down to -40°C were detected. The use of DSC and modulated methods of thermal analysis has been extended to freeze dried liposomal preparations [142,143]. 

One of the major drawbacks of liposomes is related to their preparation methods [3,4]. Liposomes for topical delivery are prepared by the same classic methods widely described in the literature for preparation of these vesicles. The majority of the liposome preparation methods are complicated multistep processes. These methods include hydration of a dry lipid film, emulsification, reverse phase evaporation, freeze thaw processes, and solvent injection. Liposome preparation is followed by homogenization and separation of unentrapped drug by centrifugation, gel filtration, or dialysis. These techniques suffer from one or more drawbacks such as the use of solvents (sometimes pharmaceutically unacceptable), an additional sizing process to control the size distribution of final products (sonication, extrusion), multiple-step entrapment procedure for preparing drug-containing liposomes, and the need for special equipment. 

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