Stealth effect/properties

PLGA microspheres can be prepared in rather narrow size ranges from 0.2 /mi up to > 100 /mi. The preparation, properties and degradation of these polymers have been discussed extensively in Chapter 4 (see Section 4.5.1). PLGA microspheres can now be prepared with surface oriented PEG-chains which improves in vivo circulation time ( stealth-effects ). 

Gnanou, Taton et al. have reported a series of dendrimer-hke PEOs with an increasing structural complexity (Figure 27.7). In this case, the advantages of the dendritic stracture (multivalency and shape persistence) were combined with the specific properties of PEO, namely stealth effect, biocompatibihty, nontoxidty, low immunogenicity, and antigenicity. 

The specific applications require different bulk and surface properties of liposomes. Among others, for example, the unique properties of stealth, targeted, and cationic liposomes could be achieved by surface modification. Figure 1 illustrates examples of liposomal surface modifications for such specific applications. The goals of these surface modifications are (1) to increase liposome longevity and stability in the circulation, (2) to change liposome biodistribution, (3) to achieve targeting effect, and (4) to impart to liposomes some unusual properties such as pH or thermal sensitivity. 

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