ABSTRACT
Following inhalation, nanoparticles must cross cellular barriers to enter the body further. In order for a substance to enter a cell’s interior, it must pass through the diffuse layer surrounding the cell and the plasma membrane which segregates the internal and external environments of a cell and regulates the entry and exit of substances into and out of the cell. The uptake of substances is accomplished via a variety of processes that can be described as active (energy dependent) or passive (energy independent). There are a number of clearly de†ned mechanisms for crossing the plasma membrane that include diffusion, facilitated diffusion, active transport, and endocytosis. Understanding the speci†c processes and physicochemical factors controlling the ability of nanoparticles to cross barriers, in particular epithelial cells, is key to understanding the intracellular fate as well as the potential for distribution of nanoparticles around the body.
