Different particulate systems--bypass the biological barriers?

The human body has adapted to defend against the aggressive biological or chemical agents. As a result, the defence mechanisms of the human body became barriers for the drug delivery. Theoretically, any problem that prevents a drug from reaching its site of action is considered to be a barrier to drug delivery. The aim of this article is to discuss the possibility of three types of nanocarriers (nanoparticles, liposomes, and solid lipid nanoparticles) to help the drugs to pass some important biological barriers (blood-brain barriers, skin, eye, and tumors) using different strategies/designs of drug delivery systems.