*3.2.3 Poly(ethylene glycol)*

Polyethylene glycol (PEG) is also the most widely used "stealth" polymer in drug delivery. It is approved by the US FDA and considered to be safe. Coating of nanocapsules with PEG generates a hydration layer due to its hydrophilic nature and forms a steric barrier. This steric hindrance effect helps the nanocapsules to avoid interactions with neighboring capsules and blood components like immunogenic cells [11]. PEG coating on nanocapsules shields it from aggregation, opsonization, and phagocytosis by reticuloendothelial system. The lack of immunogenicity confers PEG-coated nanocapsules with prolonged systemic circulation time which in turn leads to enhance absorption due to enhanced permeation and retention effect. PEGylation has become a mainstay in fabrication of drug-delivery systems that require high doses of toxic drugs with prolonged duration of action.
