The potential medical applications of nanotechnology are by the use of human-engineered devices. These can interact with biological processes in sophisticated ways by the creation of a "smart drug". Smart drug is a nano-scale device designed to perform a particular medical task such as destroying cancer cells, cleaning out clogged arteries or to construct needed proteins or mimicking anti-bodies. Researchers have shown that spheres harbor drugs in their inner core and contain an outer shell made of a material called polyethylene glycol. This shell of polyethylene glycol latches onto the membranes of cancer cells, allowing fluorescent probes mimicking cancer drugs to enter the cancer cells. Drug enters tumor cells and the micelles break down in the blood before they have a chance to deliver the drug to cancer cells. visit http://nano.cancer.gov/ for further information.