Spider silk

Observations of male spiders producing silk during sexual interactions are common across widespread taxa.

On a secondary level, the short side-chained alanine is mainly found in the crystalline domains (beta sheets) of the nanofibril.

Glycine is mostly found in the so-called amorphous matrix consisting of helical and beta turn structures.

[5][6] The interplay between the hard crystalline segments and the strained elastic semi-amorphous regions gives spider silk its extraordinary properties.

This enables a silk fibre to absorb a large amount of energy before breaking (toughness, the area under a stress-strain curve).

The variability of spider silk fibre mechanical properties is related to their degree of molecular alignment.

Unlike steel or Kevlar which are stiff, spider silk is ductile and elastic, having lower Young's modulus.

[23] According to Spider Silkome Database, Clubiona vigil silk has the highest tensile strength.

The combination of strength and ductility gives dragline silks a high toughness (or work to fracture), which "equals that of commercial polyaramid (aromatic nylon) filaments, which themselves are benchmarks of modern polymer fibre technology".

[17] When exposed to water, dragline silks undergo supercontraction, shrinking up to 50% in length and behaving like a weak rubber under tension.

[17] Many hypotheses have attempted to explain its use in nature, most popularly to re-tension webs built in the night using the morning dew.

[31] The pyriform threads polymerise under ambient conditions, become functional immediately, and are usable indefinitely, remaining biodegradable, versatile and compatible with other materials in the environment.

It is pulled on demand from a precursor out of specialised glands,[41] rather than continuously grown like plant cell walls.

Silk production is a pultrusion,[42] similar to extrusion, with the subtlety that the force is induced by pulling at the finished fibre rather than squeezing it out of a reservoir.

As an example of a complex spinning field, the spinneret apparatus of an adult Araneus diadematus (garden cross spider) consists of many glands shown below.

Spider silks with comparatively simple molecular structure need complex ducts to be able to form an effective fibre.

[80][81] Microfluidics have the advantage of being controllable and able to test spin small volumes of unspun fibre,[82][83] but setup and development costs are high.

[citation needed] Silk can be formed into other shapes and sizes such as spherical capsules for drug delivery, cell scaffolds and wound healing, textiles, cosmetics, coatings, and many others.

[85][86] Spider silk proteins can self-assemble on superhydrophobic surfaces into nanowires, as well as micron-sized circular sheets.

[86] Recombinant spider silk proteins can self-assemble at the liquid-air interface of a standing solution to form protein-permeable, strong and flexible nanomembranes that support cell proliferation.

[88] Replicating the complex conditions required to produce comparable fibres has challenged research and early-stage manufacturing.

[121] The development of methods to mass-produce spider silk led to the manufacturing of military, medical, and consumer goods, such as ballistic armour, athletic footwear, personal care products, breast implant and catheter coatings, mechanical insulin pumps, fashion clothing, and outerwear.

[122] Eighty-two people worked for four years to collect over one million golden orb spiders and extract silk from them.

[124] Peasants in the southern Carpathian Mountains used to cut up tubes built by Atypus and cover wounds with the inner lining.

[129] In 2011, silk fibres were used to generate fine diffraction patterns over N-slit interferometric signals used in optical communications.

[131] Silk has been used to suspend inertial confinement fusion targets during laser ignition, as it remains considerably elastic and has a high energy to break at temperatures as low as 10–20 K. In addition, it is made from "light" atomic number elements that emit no x-rays during irradiation that could preheat the target, limiting the pressure differential required for fusion.