The gecko walks on ceilings without a drop of glue
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A gecko can run upside down along a smooth pane of glass without ever letting go, yet its feet produce nothing sticky. How does it hold on, and why do its toes stay clean?
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The answer lies in millions of microscopic hairs, called setae, covering each toe. Each seta branches into billions of nanoscale tips ending in tiny plates known as spatulae.
The spatulae do not work by suction or glue. They rely on van der Waals forces, molecular attractions that act only over very short distances. Experiments in 2002 provided direct evidence for this. A single seta supported about 200 µN in one measurement, and about 40 µN in another on MEMS surfaces, so the force depends on the conditions of measurement.
The most striking part is the cleaning. Before each step, the gecko peels its toe pads from front to back, pulling the setae off one by one. In living geckos, a dirty foot regained about 80% of its grip within four steps, with no grooming and no secretion.
