Homobifunctional polyethylene glycol refers to a PEG molecule with two identical reactive groups. This structure enables it to form crosslinks or connections with other molecules or materials, and is often used to construct multifunctional nanocarriers or crosslinked polymers. Oligopolyethylene glycol (such as PEG-2 and PEG-4) is mainly used as a solvent and permeation enhancer to promote the dissolution of active ingredients, improve stability and solubility, enhance the permeability and absorption of oral drugs, and thus improve bioavailability.