Reproducing the properties of cobwebs could create a material of unparalleled strength. Now researchers have began to understand the secrets of their construction.
Spider webs have fascinated researchers for many years. Their strength and flexibility are unsurpassed in the animal world and, at equal weight, these fibers would be five times stronger than steel.
Many would like to use this material for a variety of industrial purposes, from clothing to building construction. However, the creation of a “synthetic canvas” has remained a challenge, and what has been recreated in the laboratory so far has struggled to match the quality of the original silk.
Researchers returned to square one and observed closely one of the most venomous spiders in North America: the brown recluse. This work has produced the most detailed images to date of the composition of a spider web and could facilitate its manufacture in the laboratory.
Shy but venomous
The “brown recluse” is a species that is found mainly in the southern United States, but can exceptionally be found in Canada .
She usually lives alone in piles of firewood or in a wet basement and only goes out at night. It looks like some spiders commonly found in our homes, but is distinguished by its number of eyes (limited to six instead of eight), its powerful venom, containing enzymes capable of causing tissue necrosis at the site bite, and its web.
It is this last element that has attracted the attention of researchers. Unlike the webs of other species of spiders, which produce rather cylindrical fibers, the canvas of brown recluses is formed of totally flat filaments. This ribbon-shaped structure helps the spider make his canvas at ground level. The researchers were interested because it is very easy to observe under the microscope.
The strength in the number
To better understand the composition of this spider’s silk filaments, each fiber of which is already 1000 times smaller than a human hair, the researchers used an atomic force microscope. These devices use lasers and an ultra-sensitive tip to model surfaces at the nanometer scale, a unit equivalent to one billionth of a meter.
At this scale, researchers have noted that each fiber itself is made up of thousands of even smaller fibers, which can be just 20 nanometers wide, about 50 times smaller than a bacterium.
Each of these nanofibers is 50 times longer than it is wide. They are not twisted or braided as would be ropes, but rather simply arranged in parallel. Although the forces uniting each fiber to one another are relatively weak, it is the collective arrangement that gives the silk thread its strength.
The idea that spider silk threads are composed of nanofibers is not new, but so far these have only been observed on the surface and no one has been able to verify whether silk in its together possessed such a structure.
The thin threads typical of the brown recluse allowed researchers to dive into the heart of the material and capture unprecedented images.
Added to this is a feature unique to the brown recluse: she wraps her canvas on itself at regular intervals, in a style that could be likened to the twisted cables that connected the fixed phones to their handsets. These spirals allow the fabric to stretch and withstand more tension before yielding.
Researchers now want to confirm their model with the canvases of other species of spiders and hope to better understand how to reproduce one of the most resistant materials in the natural world.