Poly PEG or PEG polymer is a synthetic, hydrophilic, biocompatible polymer with widespread use in biomedical and other applications. PEGs are water soluble, non-toxic, FDA-approved, generally nonimmunogenic, and are frequently used in many biomedical applications including bioconjugation, drug delivery, surface functionalization, and tissue engineering. Bioconjugation with PEG (also known as PEGylation) is the covalent conjugation of drug targets such as peptides, proteins, or oligonucleotides with PEG for the optimization of pharmacokinetic properties. Linear PEGs are commonly used for PEGylation, bioconjugation, and crosslinking. Multi-arm PEGs (4-,6-,8-arm) can be crosslinked into hydrogels and scaffolds for drug delivery or tissue engineering. Y-shaped PEGs are typically used for PEGylation, as the branched structure may improve stability in vivo.