  A very common strategy to penetrate the cell membrane and access the internal
compartment, consists of using sharp tips or nano needles. However recent
experiments of cell penetration by atomic force microscopy tips show, contrary
to expectations, a weak dependence of penetration force on the curvature of the
tip. Using molecular dynamics simulations and analytical arguments, here we
show that membrane disruption can be driven either by elastic or entropic
forces depending on the membrane size. Our findings have potentially relevant
implications in tissue engineering and drug delivery, as they help assessing
the effectiveness of the most common membranes penetration methods.
