Phospholipid-PEG-Biotin (MW 5000), a derivative of phospholipid PEG, serves to modify the surfaces of liposomes, cells, and pancreatic islets for cell transplantation. This compound incorporates a phospholipid (a lipid featuring a hydrophilic "head" and two hydrophobic "tails"), PEG (a hydrophilic, water-soluble polymer with low toxicity), and Biotin (an enzyme co-factor useful for protein labeling) [1].