Penetration mechanism of cells by vertical nanostructures

Cell penetration by high aspect-ratio vertical nanostructures such as nanowires and nanopillars provides a powerful method for accessing the cell interior for delivery and sensing. However, there is a lack of studies on the understanding of the mechanism of cell membrane penetration and how design nanostructures to optimize the efficiency of penetration remains unclear. Here, we propose an analytical model to elucidate the mechanism of cells penetration by analyzing the free-energy change of cells adhered to the nanostructures surface. Furthermore, we provide a simple method to evaluate the crossover radius or density for cell membrane penetration. By introducing a dimensionless parameter, i.e., adhesion area factor, we investigated the effects of the radius and distribution densities of nanostructures on cell membrane penetration which is determined by the competition between adhesion energy and deformation energy. Besides, a diagram of the distribution of cell penetration and no penetration is obtained. From the cell penetration diagram, one can determine easily and intuitively the relations of cell penetration state with the radius and distribution densities of nanostructures. Our theoretical results seem to show broad agreement with experimental observations, which implies that these studies would provide useful guidance to the design of nanopatterned surfaces for biomedical applications.