Encapsulation hydrophilic molecules

Cohen-Sela, E. Chorny, M. Koroukhov, N. Danenherg, H.D. Golomb, G. A new double emulsion solvent diffusion technique for encapsulating hydrophilic molecules in PLGA nanoparticles. J. Contr. Release 2009,133 (2), 90-95. 

In addition to the hydrophobic interaction mentioned above to encapsulate guest molecules, other types of nonspecific interactions have also been explored to enhance binding. For example, block copolymer micelles based on PEO as hydrophilic segments and poly(/3-benzyl L-aspartate) as hydrophobic blocks have used to encapsulate doxombicin. The encapsulation efficiency of doxombicin, an aromatic anticancer drug molecule, has been found to be significantly higher. This observation has been attributed to the tt-tt interaction between the anthracycUne moiety of doxorubicin and the benzyl group of poly(/3-benzyl L-aspartate) (Cammas-Marion et al. 1999). 

The dialysis method is well suited for the encapsulation of lipophilic drugs. The liposomes prepared by this method are usually homogeneous in size with good reproducibility, and the encapsulation condition is mild compared with other methods. The drawbacks include (i) low entrapment efLciency for hydrophilic molecules, (ii) the complete removal of residual detergent is impossible, (iii) the procedure is lengthy, and (iv) scale-up is difLcult. 

Liposomes are predominantly used as carriers for hydrophilic molecules that are encapsulated within the aqueous inner volume which is confined by the lipid bilayer. These molecules generally do not interact with the lipid moiety of the vesicle. Long circulating liposomes modified with poly (ethylene glycol) (PEG) and other formulations carrying encapsulated cytotoxic drugs such as doxoru-bicine, paclitaxel, vincristine, lurtotecan and others are clinically approved chemotherapeutic liposome formulations (1-5). 

Strong hydrophilic molecules such as the negatively charged bisphosphonate dichloromethylene-bisphosphonate (clodronate) and the positively charged diamidine propamidine can be solved in aqueous solutions in substantial concentrations. As a consequence such molecules can be encapsulated in multilamellar liposomes with a high efficacy (3). Once encapsulated, they cannot easily escape from the liposomes, since they are unable to cross their... 

Liposomes are phospholipid vesicles composed of lipid bilayers enclosing an aqueous compartment. Hydrophilic molecules can be encapsulated in the aqueous spaces, and lipophilic molecules can be incorporated into the lipid bilayers. Liposomes, in addition to their use as artificial membrane systems, are used for the selective delivery of antioxidants and other therapeutic dmgs to different tissues in sufficient concentrations to be effective in ameliorating tissue injuries (Stone et al., 2002). Antioxidant liposomes containing combinations of water- and lipid-soluble antioxidants may provide a unique therapeutic strategy for mustard gas exposure because (1) the antioxidants are nontoxic and could, therefore, be used at the earliest stages of exposure (2) the liposomes themselves are composed of nontoxic, biodegradable, and reusable phospholipids ... 

The ability to encapsulate large aqueous volumes and consequently whatever is dissolved in it is one prerogative of polymersomes and represents their most promising ability. Nevertheless, while for hydrophobic and amphiphilic molecules the encapsulation process is more or less straightforward, the complex kinetics of polymersomes formations hampers the encapsulation of hydrophilic molecules. Clearly the most important parameter to consider in encapsulating water-soluble molecules is the polymersome membrane permeability. Early work carried out by Discher and co-workers [6] showed that the water permeability of PEO-PEE polymersomes was established by measuring the reduction in polymersome swelling as a function... 

Polymersomes are, like any other vesicular structure, able to encapsulate hydrophilic, hydrophobic and amphiphilic molecules, but unlike other vesicular structure, their macromolecular nature makes them stronger and more stable with the intrinsic responsiveness of polymers. All these properties make polymersomes one of the most interesting supramolecular structures with potential applications in drug... 

Liposomes aid in formulation because they are powerful in solubilizing nonwater-soluble compounds, enhancing their bioavailability. Furthermore, liposomes entrap hydrophilic molecules into their interior, and hydrophobic molecules into their lipophilic membrane, encapsulating various nutritional molecules. The first example of liposomes in foods is human milk, which has been... 

This versatile modifiable property allows liposomes to encapsulate functional molecules in the interior, inserted in the bilayer or attached on the bilayer membrane surface. Hence, they have been considered for application in multifunctional platforms, that is, therapy and imaging. They protect the amphiphilic, hydrophobic, and hydrophilic therapeutic agents against various threats that lead to their immediate dilution and degradation. 

More importantly, the vesicular structure appeared to transform into a micellar structure with the decrease of pH. The effect of pH on the aggregation behavior was investigated with 24 by DLS measurements. The small drop of pH induces a dramatic decrease of the aggregate size, from 36 nm in diameter at pH 7 to 6 nm at pH 5, while maintaining a narrow size distribution. Therefore, one can envision that the vesicles formed by 24 encapsulate hydrophilic guest molecules within their interior at neutral... 

The particular three-dimensional CD structure with its hydrophilic surface and apolar cavity, impacts water solubility and the ability to partially or totally encapsulate hydrophobic molecules of appropriated size and shape in aqueous solution as well as in solid-state through the formation of a reversible host-guest complex (Fig. 2.3) [2]. 

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