Figure 5.

(a) SEM image of a “sharp” pillar with a diameter of 2 μm and a height of 2.5 μm. The inset highlights a cross section of the sharp edge, with an estimated radius of curvature of R_sharp ≈ 20 ± 5 nm (compare the approximating circle with the scale bar). (b) SEM image of a “smooth” pillar with a diameter of 2 μm and a height of 1 μm. The estimated radius of curvature is R_smooth ≈ 250 ± 20 nm. (c) Fluorescence image of cells cultured on sharp pillars fabricated with a spacing of 5 μm (green spots) and treated with both permeable calcein AM (green) and impermeable dye propidium iodide (red) administrated in solution. Most of the cells present green and red staining, with a permeability likelihood very close to 70%. (d) Corresponding fluorescence image of cells cultured on smooth pillars and treated with the same dyes. In this case, only a limited number of cells contain propidium iodide and are hence stained in red, meaning that the cell membrane is successfully permeabilized in a few cases (see S2 for more details). A specific red staining is probably due to the fraction of death cells and DNA dispersed in the cell culture.