For its size, spider silk is stronger than steel, extraordinarily lightweight and stretchy. Now scientists are learning how spiders produce it.
Spiders store silk proteins, called spidroins, in their glands. But how they converted these soluble, gel-like proteins into a solid state has been a mystery.
Researchers from Sweden report that the change to solid is brought about by a change in pH that occurs as the proteins travel through the glands. The findings appear in the journal PLOS Biology.
The change from the neutral 7.6 to an acidic 5.7 pH, is set off by an enzyme called carbonic anhydrase. It creates an acidic environment by converting carbon dioxide and water to bicarbonate and hydrogen ions.
“Going from this soluble state is very important because, otherwise, the silk gland would get clogged,” said an author of the study, Dr. Jan Johansson, a medical biochemist at the Swedish University of Agricultural Sciences.
Anna Rising, a veterinary scientist at the university, hopes to mimic the silk. “If we could produce large amounts at a low price, there’s no limit to what it could be used for.”
Gecko feet are sticky and fast
What gives geckos the remarkable ability to run upside down across ceilings and stop short on smooth vertical surfaces? You could call it “the hierarchy of hairs.”
Geckos make use of a relatively weak intermolecular force that exists between atoms known as van der Waals force.
The sole of a gecko foot is covered in tiny folds of skin. Those folds are in turn covered in tiny hairs that branch, and then branch again until the tips of the hairs, called seta, are just a few nanometers across.
The structure provides millions of tiny locations where that weak molecular force can be activated so that, amplified millions of times, it becomes strong enough to allow a gecko to hang from a ceiling.
Perhaps even more amazing is that despite their hyper-sticky feet, geckos move fast, running at speeds of up to 20 body lengths per second. That means the bottom of a gecko’s foot has to be able to unstick to surfaces just as efficiently as it sticks to them.
In a paper in the Journal of Applied Physics, researchers at Oregon State University showed that the seta on gecko feet are not just plentiful and minuscule, but also flexible, curved and at a 60-degree angle.
For a gecko to stick on a ceiling or a wall, it pulls the hairs on the sole of its foot sideways just a bit, and because of the angle of the hairs (and how many of them there are), it provides enough force to support weight. But, when the gecko wants to move its foot, all it does is lift straight up, and it pulls away immediately with little extra energy expended.
“The angle allows it to turn the stickiness on and off,” said Alex Greaney, an assistant professor at the Oregon State University College of Engineering and lead author of the paper.
Greaney is interested in creating synthetic adhesives that mimic the gecko’s feet.