Fig. 5.

Model of interactions between N gecko spatulae of radius R_s, a spherical dirt particle of radius R_p, and a planar wall. Van der Waals interaction energies for the particle-spatula (W_ps) and particle-wall (W_pw) systems are shown. When N × W_ps = W_pw, equal energy is required to detach the particle from wall or N spatulae. Our results suggest that N is sufficiently great that self-cleaning results from energetic disequilibrium between the wall and the relatively few spatulae that can attach to a single particle.