Introduction

Researchers are always looking for and trying to develop new materials that are stronger, or lighter, or tougher than materials currently in use. One such material has been found, not in the laboratory, but in nature. That material is spider silk obtained from spiders. Spider silk is also known as gossamer. Spider silk is an extremely strong material and is on a weight basis stronger than steel. It has been suggested that a pencil-thick strand of silk could stop a Boeing 747 in flight.

The silk is used by the spider for a lot of different uses. Constructing their webs, the production of egg sacs, wrapping in their prey, as a lifeline when jumping, or dropping to escape, for transferring semen from the abdomen to the male palp, in drag lines marked with pheromones, as a shelter in which it can retreat.

Silk is for more than 50% a polymerized protein called fibroin with a molecular weight of 200,000 - 300,000. When looking at silk at a molecular scale one can see that the protein strands are regularly orientated.

Properties

Physical properties

  1. Length: Continuous

  2. Fineness: It is finer than human hair (most threads are a few microns in diameter)

  3. Strength: Spider silk is incredibly tough and is stronger by weight than steel. Quantitatively, spider silk is five times stronger than steel of the same diameter. It has been suggested that a Boeing 747 could be stopped in flight by a single pencil-width strand and spider silk is almost as strong as Kevlar, the toughest man-made polymer. The strength of a biological material like spider silk lies in the specific geometric configuration of structural proteins, which have small clusters of weak hydrogen bonds that work cooperatively to resist force and dissipate energy, researchers in Civil and Environmental Engineering have revealed.

This structure makes the lightweight natural material as strong as steel, even though the "glue" of hydrogen bonds that hold spider silk together at the molecular level is 100 to 1,000 times weaker than the powerful glue of steel's metallic bonds or even Kevlar's covalent bonds. It is simple to see why spider silk is of such interest to materials chemists since new ultra-strong fibers based on the silk could be developed.

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The authors are associated with the Department of Textile Technology, Shri Vaishnav Institute of Technology and Science