Being the front line of a cell means that plasma membranes control what is allowed into the cell. Many of these mechanisms are not understood though. Why some molecules gain access to the cell while others do not? Pathogens such as viruses sometimes have protein coats that allow them access. The question becomes how do we insert our own nanoparticles. These require breaching into the cell membrane that do not happen naturally. Thus research is required to fully understand the cell membrane as well as study of the molecular mechanisms that drive the interactions between nanoparticles and membranes.