Artificial Spider Silk: Tougher Than It Looks

Spider webs may look delicate, but their strength and toughness are exceptional.

Who likes spiders? Does anyone? In any case, these fascinating and useful creatures have something to offer to biotech industry and to us, consumers. Manmade spider silk is a natural polymer with many applications. And why would anyone want to produce spider silk? This recent article in Chemical & Engineering News explains:

[S]pider silk is by weight five times stronger than steel and three times tougher than Kevlar, a p-aramid fiber from DuPont. Strength is defined as the weight a material can bear, and toughness is the amount of kinetic energy it can absorb without breaking. The silk’s primary structure is its amino acid sequence, mainly consisting of repeated glycine and alanine blocks.

Potential applications include cables and bulletproof vests. Spider silk’s antimicrobial properties make it suitable for wound patches. Because the silk is not rejected by the human body, it can be used to manufacture artificial tendons or to coat implants. And its thermal conductivity is similar to that of copper but its mass density is one-seventh of copper’s, making it a potential heat management material.

Range of Properties

Let’s take a closer look at what is spider silk in nature. It is a tough protein fiber, spun (or rather stretched) on demand from a liquid silk precursor in special glands. The process is initiated by it being pulled away from the body. Spiders have a rather efficient method for this: They fall and use their weight to pull the silk fiber. Spiders can make several types of silk with different properties, depending on the need, be it capturing prey or building a web.

The properties of spider silks come from their unique compositions. They consist mostly of protein, with blocks of highly repetitive glycine and alanine amino acids, so in essence they are block co-polymers. Alanine blocks are mostly crystalline, or highly ordered microstructures, while glycine blocks compose the semi-amorphous and more flexible part of a fiber. The fibers also contain pyrrolidine, certain inorganic salts to maintain the pH, and additional sugars, lipids, and pigments on the surface.

The mechanical properties of spider silk are outstanding, combining high tensile strength and elasticity. Studies by a team of MIT scientists showed that it is a material with nonlinear stress response, i.e., if you keep pulling on a spider silk thread, it is initially stiff, then stretchy, then stiff again, and this makes the web very robust — any damage inflicted on it is highly localized with the rest of the web remaining functional, a property that would be valuable in many applications, including military, aerospace, and construction (think earthquake-resistant buildings)!

Artificial Silk

With all these wonderful properties, the competitive quest to make artificial spider silk has been going on for many years. And the winners are … several small companies:

  • AMSilk from Germany is producing spider silk protein using genetically engineered E. coli, a common and easy-to-handle bacteria. The process is now capable of making 20 different grades of silk protein. The protein is purified and made into beads, fibers, films and nonwoven materials, with high tensile strength and selective biodegradability. The hydrophilic, biocompatible and bactericidal spider silk can be a key component in a variety of medical products. AMSilk products include fibers, implant coatings, functional cosmetics, wound care, skin barrier, and surgical products.
  • Korea Advanced Institute of Science & Technology (South Korea) is using E.coli to produce spider silk fiber stronger than Kevlar.
  • Spiber, a Japanese company, is also using expression of spider silk protein from E. coli, and is almost ready to produce fibers and films, with a pilot facility planned for 2015.
  • Kraig Biocraft Laboratories, a company in Michigan, is producing spider silk using transgenic silkworms, which make hybrid spider-silkworm silk. The company has just started commercial production of Monster Silk ™ fibers.
  • Araknitek, a Utah State University “spin-out” company, is using different methods of producing spider silk, including E. coli, silkworms, transgenic alfalfa, and goats, which produce milk that contains spider silk protein. The company is building a pilot facility and plans to produce fiber with tensile strength and tenacity comparable to Kevlar, and twice as elastic as nylon.

While polymer fibers are used to mimic nature, natural polymers, such as spider silk can offer unique solutions to many mechanical and technical problems, and you need not go far for inspiration … it’s in your backyard!

Image by Dwight Sipler
Source: “Spider Silk Poised For Commercial Entry,” by Alex Scott, Chemical and Engineering News, Volume 92 Issue 9, pp. 24-27, cen.acs.org, March 3, 2014.
Source: “How Spider Webs Achieve Their Strength,” by David L. Chandler, MIT News Office, web.mit.edu, February 2, 2012.
Source: AMSilk, amsilk.com.
Source: Araknitek, araknitek.com.
Source: Spiber, spiber.jp/en.
Source: Kraig Biocraft Laboratories, kraiglabs.com.