Living cells aren't self-sufficient; they need to interact with their environment in order to survive. But these interactions are extensively controlled by the barrier called the cell membrane, a dynamic entity made up of lipids and proteins. Molecules are constantly passing in and out of the cell through the semi-permeable cell membrane, their movement often orchestrated by different forces and membrane components. This was the level of understanding of this barrier's structure and function, posited by the 'fluid mosaic' model developed by Singer and Nicholson in 1972. Little was known then about minute details of the driving forces at the nano scale.