Used in drug delivery systems to improve the solubility and circulation time of therapeutic molecules. The mPEG-COOH is commonly conjugated to drugs, proteins, or nanoparticles through its carboxylic acid group, enabling controlled release and reduced immune recognition. It plays a key role in the development of PEGylated biopharmaceuticals, enhancing stability and bioavailability. Also utilized in creating hydrogels and surface coatings for medical devices due to its biocompatibility and anti-fouling properties. Widely applied in research and formulation of targeted therapies, including cancer treatments and diagnostic imaging agents.