Polyethylene glycol (PEG) is a synthetic polymer composed of repeating ethylene glycol (-CH2-CH2-O-) units. It has low toxicity, is strongly hydrophilic and has a large exclusion volume in aqueous solution. The covalent attachment of PEG (PEGylation) is commonly used to modify a variety of proteins and drugs. PEGylation can offer several benefits including decreased immunogenicity, increased bioavailability, and optimized pharmacokinetics5.