Liposomes particle charge

Characterizing the resultant complex for the amount of protein per liposome is somewhat more difficult than in other protein conjugation applications. The protein-liposome composition is highly dependent on the size of each liposomal particle, the amount of protein charged to the reaction, and the mole quantity of reactive lipid present in the bilayer construction. An approach to solving this problem is presented by Hutchinson et al. (1989). In analyzing at least 17 different protein-liposome preparations, the ratio of proteindipid content (pg protein/pg lipid) in most of the complexes ranged from a low of about 4 to as much as 675. In some instances, however, up to 6,000 molecules of a particular protein could be incorporated into each liposome. 

MakCay, A. J., Deen, D. F., and Szoka, F. C., Jr. (2005), Distribution in brain of liposomes after convection enhanced delivery modulation by particle charge, particle diameter, and presence of steric coating, Brain Res., 1035,139-153. 

Solvent system Particle size Liposomes (type, charge)... 

Juliano, R. L., and Stamp, D. (1975). Effect of particle size and charge on the clearance rates of liposomes and liposome encapsulated drugs, Biochlm. Biophys. Res. Commun.. 63, 651-658. 

Few systems allow for the incorporation measurements of PEG-lipids into lipopiexes. First of all, because the nonincorporated PEG-lipid should be removed from the liposome PEG mixture, prior to determination of the associated PEG concentration, it is not always easy for positively charged particles. They glue to the exclusion membrane used to eliminate the free PEG-lipid and do not easily ultracentrifuge if highly charged. Membrane exclusion is, however, facilitated by the presence of PEG-lipid, as compared to free lipopiexes. 

The top-down approach involves size reduction by the application of three main types of force — compression, impact and shear. In the case of colloids, the small entities produced are subsequently kinetically stabilized against coalescence with the assistance of ingredients such as emulsifiers and stabilizers (Dickinson, 2003a). In this approach the ultimate particle size is dependent on factors such as the number of passes through the device (microfluidization), the time of emulsification (ultrasonics), the energy dissipation rate (homogenization pressure or shear-rate), the type and pore size of any membranes, the concentrations of emulsifiers and stabilizers, the dispersed phase volume fraction, the charge on the particles, and so on. To date, the top-down approach is the one that has been mainly involved in commercial scale production of nanomaterials. For example, the approach has been used to produce submicron liposomes for the delivery of ferrous sulfate, ascorbic acid, and other poorly absorbed hydrophilic compounds (Vuillemard, 1991 ... 

In conclusion, we have designed a synthetic vesicular DNA carrier that physically and functionally mimics an enveloped virus particle. To achieve an acceptable degree of encapsulation within the vesicle, we use a process that is essentially inverse to the preparation of cationic lipid-DNA complexes. A suitable DNA condensing agent is introduced that, at a certain critical concentration, conveys a weak net cationic charge to the condensed DNA that then interacts spontaneously with a liposome containing one or more anionic components. These DNA formulations behave distinctly different from classic cationic liposome DNA complexes in vitro in as much as they have been shown to be nontoxic, to display a traditional linear dose response, and to be serum-insensitive. 

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