Science claims that such a natural material as silk made by spiders has a very great strength. Before studying what it is made of, let me run through the theory of tissue strength in general. There are several properties defining strength parameters:
- Toughness. This is potency what fabric contains until it breaks bearing all the possible loading it gets.
- Tensile strength. It means maximum stretching property.
- Stiffness. Materials are apt to curve under pressure. Stiffness shows resistance to such deformations and is measured with the Young’s modulus.
Have a look at the table below. Caerostris darwini is one kind of spiders known as a Darwin spider. It is clearly visible what place its net has in comparison to other stuff and that it is much tougher than steel! But keep in mind, it is not stronger, but tougher than steel.
It is important to understand that the term «strength» is implied actually to indicate how much weight one can put on some material, for instance, on a cable. As for spider’s net the most curious parameter is toughness meaning power with what the net can be hit without damaging it.
Without any additional knowledge one can suppose that the spider’s net is homogenous and uniform. From the outside this is really so, but if to consider its chemical components it is clearly noticeable that there are not even two different kinds of silk in it. As researches show spiders spin up to 7 various types of silk!
Principal types of silk are flagelliform, aggregate and dragline which is the toughest one.
This is dragline silk that allows a spider to hang upside down from the tree. The diameter is about the tenth part of a human’s hair. Even if it is twisted it remains strong and that is a very unbelievable thing.
Another kind of silk, flagelliform, is produced by a spider to catch a prey. It is obvious that a prey is trying to get out of a trap, so the silk should possess the best characteristics to keep the prey inside. Therefore, this silk is really flexible (it can be elongated for 30 times more!) and is not afraid of deformations. Flagelliform silk serves as a large place to be able to grab insects.
For the net to be sticky a spider makes aggregate silk which contains sugars. Separately the sugar molecules are weak in their connection, but together silk stickiness become enormous.
Now it is time to mention the structural elements of spider’s silk. The main component is protein which is called spidroin. All the protein has common pattern of initial structure, it means there are plenty of them and they are steadily repeated. The components that are non-repetitive vary dapending on spider kinds.
The silk protein is made up of aminoacids — alanine and glycine. Their peculiarity of attaching to each other side-by-side is known as beta-sheet. These molecule arrangement form a special structure resembling some kind of a matrix joined together with helices (turns and spirals). Such a complex order gives the silk its phenomenal stength. Moreover, other compounds as pigments, lipids and sugars constitute an additional protective layer.
Scientists discovered that it is possible to harvest spider silk, i.e. to milk a spider. Thus, researches are trying to replicate spider’s silk, but stil there is no much success.
I suggest you to watch this small video how spider’s silk is extracted in the lab.
Every time I look around I have many questions about how our nature function. Discover the world with me!