PEG-coated long-circulating drug carriers

To overcome the stabhity problems, another approach in designing PEG-coated long-circulating carriers is the grafting or the adsorption of 

Surface modification by polymer adsorption is an alternative to surface modification by polymer grafting. For example, polystyrene nanospheres coated by Poloxamer or Poloxamine (Ilium and Davis, 1983 Muller, 1991) or poly(methyl methacrylate) colloidal carriers coated by Poloxamer (Trds-ter and Kreuter, 1988) circulate longer in blood. This family of surfactants consist of poly(propylene glycol) (PPG) blocks, which adsorb on the hydrophobic polystyrene surface, and of more hydrophilic PEG blocks, which stick out of the surface in aqueous solutions and prevent opsonin adsorption. In spite of the increase in blood circulation time, particle coating by polymer adsorption was found to have several drawbacks (Petrak, 1993)  

PEG-COATED BIODEGRADABLE NANOSPHERES POTENTIAL LONG-CIRCULATING DRUG CARRIERS 

F urel. SchematicrepresentationofPEG-coatednaQospheres.Thecoatingsterichindrance should avoid blood protein (P) adsorption on the particle core, formed in a hydrophobic hiodegradahlepolymerR (PLA, PLGA,PCL, or PSA), (a) Nanosphere prepared from diblock PEG-R pol mer (h) nanosphere prepared from mrjltihlock PEG -R polymer. 

To prepare PEG-coated nanospheres as depicted in Fig. 1, first, amphiphilic bioerodible polymers (symbolized as PEG R), composed of a PEG block and a hydrophobic biodegradable block (R = PLA or PLGA), were synthesized. PEG-coated nanospheres were then formed by taking advantage of the different solubdities of R and PEG in aqueous and organic solutions (Spenlehauer et al., 1992 Grefet al., 1993a). Nanospheres were also formed with diblock PEG poly(E-caprolactone) (PEG PCL) and PEG-poly(sebacic acid) (PEG PSA) (Peracchia et al, 1996). 

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