PEG (polyethylene glycol) is a high-molecular-weight polymer composed of repeating ethylene glycol units [-CH2-CH2-O-], known for its high water solubility and biocompatibility. Its molecular weight can range widely, from a few hundred to several hundred thousand Daltons, and variations in molecular weight result in differences in physical properties such as viscosity and solubility. PEG molecules can have a linear or branched structure, typically terminating with hydroxyl groups (-OH), but these can be chemically modified into other functional groups (e.g., amino, carboxyl) to suit various application needs. PEG is widely used in pharmaceuticals, biotechnology, and chemical industries, for example, as a carrier in drug delivery systems, a protein modifier, and a lubricant. Its non-toxic, non-immunogenic, and protein-resistant properties make it a crucial material in biomedical research.