Some lizards can walk on water, others can walk up walls. It’s hard to tell from the photo whether this gecko is walking on the floor, up a vertical surface, or upside down across the ceiling. And from its point of view, it probably doesn’t make much difference. Geckos’ amazing adhesive feet work by creating van der Waals interactions – attractive forces at the molecular level – between the vast number of microscopic protrusions on their feet and the surfaces they walk on.
The bottom of a gecko’s foot is structured hierarchically with each square millimetre of its plate-like lamellae covered by many thousands of tiny bristles, called stelae, each of which is in turn tipped with up to 1000 even tinier filaments known as spatulae. To give an idea of just how tiny we’re talking, each stela is about 5 micrometres in diameter – or roughly a quarter the width of a human hair – and each spatula is 0.2 micrometres long – or just under the wavelength of visible light.
The secrets of a gecko’s foot are still being uncovered. Until recently, for example, capillary action was thought to have played a role and that levels of humidity were a factor. Unsurprisingly, scientists are also keen to construct artificial sticky pads based on gecko mechanics that might give a new generation of robots the edge over their grounded peers. In the words of Dr. Emmet Brown, “Roads? Where we’re going, we don’t need roads.”
(And, for the record, that gecko at the top is walking up a wall.)
Image: Douglas Heaven