Used in liposome and nanoparticle formulations to enhance stability and prolong circulation time in the body. Its polyethylene glycol (PEG) chain creates a hydrophilic stealth layer that reduces recognition by the immune system, making it ideal for drug delivery systems, especially in cancer therapies and targeted treatments. Commonly found in lipid nanoparticles (LNPs) for mRNA delivery, including vaccines. Also helps improve solubility and reduce aggregation of lipid-based carriers.