Before I begin telling you about this fascinating new
glue (adhesive), there's a thing or two you need to know about the animal that inspired it all, the
gecko. Geckos are small lizards that have the ability to run up walls and scurry across ceilings with the help of tiny rows of hairs on their feet known as
setae. Setae generate a multitude of weak attractions (called
Van der Waals forces) between molecules on the two surfaces that add up to a secure foothold. Unlike glue or tape, a gecko’s sticky feet attach and detach effortlessly, which made it a perfect case study for engineers to model.
To create their artificial gecko adhesive, a Stanford team of scientists started by making silicone micro-wedges, which imitated gecko hair. They assembled these into 24 stamp-sized tiles, each of which contained hundreds of thousands of micro wedges. The team then connected the tiles to springs with tendon-like strings and attached them on an octagonal-shaped plate. Unlike gecko skin, the springs apply the same force to the tiles after they are stretched beyond a certain threshold, thus distributing loads evenly among the tiles. This allowed the assembled patch to offer similar adhesive strength for sizes from a square millimeter to a human hand. Even if an individual tile peels off, the weight it carries is transferred to tiles with the lightest loads, where the springs haven't stretched past the threshold, so that the overall system remains sticky.
The only downfall to this invention boils down to scaling: The stickiness diminishes when the size of the adhesive exceeds a few square centimeters, severely limiting its practical applications. Even the gecko hasn’t solved this problem, according to its inventors. In theory, each gecko hair is so sticky that the animal, which has about 6.5 million setae, should be able to hold up a 130-kilogram linebacker. In reality, a gecko can lift only 2 kilograms with its front feet.
Source: https://geckskin.umass.edu
