Polymers liposome modification with

Several of these problems can be solved by polyplex modification with polyethylene glycol (PEG). PEGylation has been broadly explored for surface shielding ( stealthing ) of many liposomal and nanoparticulate carriers. In the case of cationic polymers, Plank et al. [62] demonstrated that complement activation can be reduced when the polymers are PEGylated. Such a modification can be... 

A novel approach to the development of an extremely sensitive biosensor has been published by Durst et al. [34]. They used an electrode modified with an ion-exchange polymer in conjunction with complement or surfactant lysis of marker loaded liposomes. lon-ex-change preconcentration of the ferrocyanide marker ions makes a signal enhancement of two to three orders of magnitude possible. The modification of the electrode also protects it from sample-constituent fouling. 

Another method to improve the incorporation of bioactive polymers into the cells is the grafting of hydrophobic groups on the polymer, which improves the affinity for the cell membrane. Maleic copolymers are good candidates for such modifications, the anhydride cycle being easily reacted with hydrophobic amines. Poly(MA-St), poly(MA-CDA) and poly(maleic anhydride-alt-3,4-dihydroxyphenylprop-l-ene) modified with alkyl amines or aniline were proved to perturb the liposome membrane and to interact with epithelial cells or DMSO-differentiated HL-60 cells [48-50]. As a result, the biological activity, evaluated by the ability to simulate the release of superoxide anion by the cells, was enhanced when the polymer was modified with hydrophobic units [49]. 

In addition, the modification with thermosensitive polymers can provide liposomes with a temperature-sensitive surface property the liposome surface is covered with a layer of the hydrated polymer chains below the LCST. However, the dehydrated polymer chains shrink efficiently and are adsorbed on the liposome surface above this temperature. 

The most versatile method to prepare such hollow capsules is self-assembly [203-205, 214, 215]. Owing to their amphiphilic nature and molecular geometry, lipid-based amphiphiles can aggregate into spherical closed bilayer structures in water so-called liposomes. It is quite reasonable that the hollow sphere structure of liposomes makes them suitable as precursors for the preparation of more functional capsules via modification of the surfaces with polymers and ligand molecules [205, 216, 217]. Indeed, numerous studies based on liposomes in this context have been performed [205, 209, 213]. 

In spite of these formidable challenges, the attractiveness of oral route has fueled the exploration of an incredibly diverse set of strategies to deliver proteins and peptides and the subject has been exhaustively reviewed. The various approaches include permeation enhancers, enzyme inhibitors, mucoadhesives, multifunctional matrices that simultaneously incorporate the above strategies, enteric coatings that offer protection from the acidic environment of the stomach, encapsulation (liposomes, microspheres, and nanoparticles), pH-sensitive polymers, microemulsions, carriers (delivery agents), and protein modification either to simply enhance permeability or to exploit specific transporters. While proof-of-concept has been demonstrated with most of these delivery systems in animal... 

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