<Li> Tethered Bilayer Lipid Membranes (t - BLM) </Li> <Li> Droplet Interface Bilayers (DIBs) </Li> <P> To date, the most successful commercial application of lipid bilayers has been the use of liposomes for drug delivery, especially for cancer treatment . (Note - the term "liposome" is in essence synonymous with "vesicle" except that vesicle is a general term for the structure whereas liposome refers to only artificial not natural vesicles) The basic idea of liposomal drug delivery is that the drug is encapsulated in solution inside the liposome then injected into the patient . These drug - loaded liposomes travel through the system until they bind at the target site and rupture, releasing the drug . In theory, liposomes should make an ideal drug delivery system since they can isolate nearly any hydrophilic drug, can be grafted with molecules to target specific tissues and can be relatively non-toxic since the body possesses biochemical pathways for degrading lipids . </P> <P> The first generation of drug delivery liposomes had a simple lipid composition and suffered from several limitations . Circulation in the bloodstream was extremely limited due to both renal clearing and phagocytosis . Refinement of the lipid composition to tune fluidity, surface charge density, and surface hydration resulted in vesicles that adsorb fewer proteins from serum and thus are less readily recognized by the immune system . The most significant advance in this area was the grafting of polyethylene glycol (PEG) onto the liposome surface to produce "stealth" vesicles, which circulate over long times without immune or renal clearing . </P>

What is the function of the lipid bilayer in a cell membrane check all that apply