Spider Silk: The Holy Grail

Spider silk is a protein spun by spiders, and these tiny creatures use their silk to make webs and other structures, which may be used to catch other animals or serve as nests or cocoons to protect spider offspring.

Spider silks are incredibly elastic and can stretch or behave like a spring depending on their amino acid content. Spider silks are made from proteins, and biochemists have recently discovered that the silk’s performance is determined by the protein’s amino acid content.

By example, spider silks with high proline content behave like elastic rubber bands, while spider silks with low proline content behave like stretchy springs. Proline is an amino acid; one of 20 DNA-encoded amino acids.

Remarkably, spider silk is stronger than steel or nylon, and more elastic than Kevlar. Because of these unique properties, it is considered the “holy grail” of materials used in corresponding industrial applications.

Scientist John Gosline, fascinated by spider silks and their remarkable toughness, says if we are to learn how to manufacture the silk, we have to understand the relationship between the components and the resultant mechanical properties.

Science Behind Spiders

Spider silk is a uniquely strong material. The tensile strength is comparable to that of high-grade steel, but about half as strong as aramid filaments, like Twaron or Kevlar. Spider silk is about a fifth the density of steel. A strand long enough to circle the Earth would weigh less than 500 grams.

Spider silk also is very ductile. It is able to stretch up to nearly 1.5 times its static length without breaking. It also has a very high toughness and equals that of commercial polyaramid (aromatic nylon) filaments, the benchmark of modern polymer fiber technology. It also holds its strength below -40⁰C.

The strongest spider silk known to mankind is produced by the species Darwin’s bark spider (Caerostris darwin). Darwini silk is more than twice as tough as any previously described silk, and over 10 times stronger than DuPont’s Kevlar.

Sorting Silk Types

Various spider species have different glands to produce silk exhibiting unique properties.

These can include housing, web construction, defense, capturing and detaining prey, egg protection, and mobility (for instance, gossamer for ballooning and strands to let the spider drop down on as they are extruded).

Different specialized silks have evolved with properties suitable for different uses. For example, Argiope argentata has five different types of silk, each for a specific purpose.

Strength In Structure

Inside a typical fiber there are crystalline regions separated by amorphous linkages.

Spider silk is composed of complex protein molecules. This, along with the isolation stemming from the spider’s predatory nature, is making the study and replication of the substance quite challenging.

Because of the repetitive nature of the DNA encoding of silk protein, it is difficult to determine its sequence. To date, silk-producing sequences have been decoded for just 14 species of spider.

In 2005, independent researchers at the universities of Wyoming, the Pacific, California at Riverside, and Shinshu uncovered the molecular structure of the gene for the protein that various female spider species use to make silken egg cases.

Potential Benefits Abound

WMB believes that by understanding the subtle molecular structure of the proteins and crystalline layers, scientists are closer than ever to replicating spider silk’s unique properties.

Materials such as spider silk can propel many industries into a unique and enviable position. Applications may range from military to industrial, and even medical to help position the inventors for success.

From some of the world’s smallest creatures can spring the largest innovations.

 TechMan