Cholesterol is a waxy, fat-like substance that's found in all cells, and it strengthens lipid bilayer packing, resulting in decreased fluidity and reduced permeability in vesicle-mediated drug delivery systems.
Cholesterol can also attach to polyPEG to create a lipophilic lipid PEG derivative. The polymer derivatives can be used to make targeted liposomes to improve circulation time for encapsulated drugs/therapeutic agents.