Polymeric carriers, which physically entrap molecules ofinterest, and polymer conjugates, to which such molecules arechemically bound, play an important role in modern pharmaceuticaltechnology. The shared task of carriers and conjugatesis the targeted delivery of drugs to specific sites ofaction in the body. In the case of drug conjugates, inparticular, the increase of the molar mass leads to reducedkidney excretion and results in a prolonged blood circulationtime of the drug. Shielding of drug carriers and conjugates isrequired to avoid a fast recognition by the immune systemfollowed by rapid clearance from the body. The suppression ofnonspecific interactions with the body, that is, decreasedinteractions with blood components (opsonization) inducingactivation of the complement system, leads to a reducedblood clearance of drug carriers and conjugates, which isknown as the stealth effect. Drug-delivery vehicles can becoated with a hydrophilic polymer to allow both inhibition ofopsonization and enhancement of water solubility. Poly(ethyleneglycol) (PEG) is the most commonly applied non-ionichydrophilic polymer with stealth behavior. Furthermore,PEG reduces the tendency of particles to aggregate bysteric stabilization, thereby producing formulations withincreased stability during storage and application
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