Although silk and the closely related spider silk, consist merely of proteins, they are materials with unparalleled properties. Silk is strong and breathable, and soft to the skin as no man-made material could achieve so far. Spider silk is much tougher, even to the extent that it would make excellent bulletproof vests. Researchers have now succeeded in producing genetically engineered silk, a miracle of precision. Several companies will introduce these materials on the market soon.
Silk consists of two elements, so we learn from professor Jan van Hest of Eindhoven Technical University. Part of the protein molecules fold in crystalline areas, the other part has a more random structure. The first domain is characterized by repetitions of oligo-alanines (8 to 10 alanines in a row), that lend themselves to be folded to a beta sheet structure, and subsequently to a crystal. This is the element that lends strength to the material. The random element readily absorbs energy, this is the area that lends to silk its toughness. In the past years, says Van Hest, researchers have made much progress, using modified microorganisms, in the development of commercial artificial silk products; these very much resemble natural silk. Progress has been made both in artificial silk design and in processing. But artificial silk will feel stiff competition from synthetic nylons with comparable properties, says Jan van Hest. They might even never be able to compete on price with them. But then artificial silk can probably always find a market because of appearance and quality.
A miraculous material
One of the companies that is about to commercialize genetically engineered silk is AMSilk from Bavaria, Germany. AMSilk set the first steps on the path towards artificial silk some ten years ago. In 2011, they developed their first proof of concept filament. In 2013, the process was improved to such an extent that they could present their first commercial filament, called Biosteel®. In 2014, they built a pilot plant in Planegg in the outskirts of Munich. Since 2015, they produce customer- and project-driven fibres with established proven parameters. They target high-performance applications like apparel, footwear, automotive parts, home and interior design, and technical and medical textiles. Prototype footwear from this material has been made by Adidas. Customers in the luxury and high fashion industry also discuss projects applying Biosteel®. This material is superior to most artificial yarns both in its high skin sensation and in its biodegradability. AMSilk also uses the material in skin care products, also with superior properties. Nail polish with Biosteel® for instance produces a breathable layer, whereas traditional nail polish produces a solid layer.
Spider silk might even be more miraculous than common silk. It is claimed to be 340 times stronger than steel; we are also told that a net woven from spider silk threads 1 cm thick would be able to stop a Boeing 747 in full flight. One of the companies that develops artificial spider silk is Spiber, a Japanese company. As they say on their website, ‘we have designed and synthesized over 600 types of original proteins, carefully analysing their material properties to accumulate a massive amount of data. In the near future, proteins will widely be used as a basic industrial material, just as metals, glass, and plastics are used today.’ But in order for Spiber to deliver its genetically engineered silk to the market, they have to conquer a formidable cost barrier. They claim that they have essentially done this: ‘compared to when we started in 2008, we have dramatically increased productivity and decreased costs, bringing us to a place where large scale adoption of protein materials is finally becoming a reality.’ The initial market for their genetically engineered silk is outdoor apparel. Together with The North Face, Spiber developed a new parka made from artificial spider silk. They called this historic prototype the MOON PARKA™. It is designed to endure the harsh conditions and intense cold of the South Pole. The outer material is the natural web colour of the Golden Orb spider, dubbed by the makers ‘Moon Gold’. The prototype was displayed in 2016 in the Toyota Municipal Museum of Art in Aichi, Japan.
Genetically engineered silk from the old workhorse
Whereas the two companies discussed so far use fermentation technology to produce genetically engineered silk, the American company Kraig Biocraft Laboratories uses the old workhorse, the silkworm. They introduced spider genes into the silkworm in order to arrive at products much like spider silk. They claim their genetically engineered silk to have superior properties, for instance for bulletproof vests. They managed to secure a $ 1 million contract from the US Army that allows them to prove they’re right. Kraig Labs are confident that their product is the most cost-effective one on the market, based on two factors. First, with their silkworms they can tap directly into an established industry. ‘Silkworms,’ so they write, ‘have a proven industrial scale production record, producing approximately $ 5 billion worth of normal raw silk per year. Our technology simply harnesses that production capacity by introducing a genetically engineered silkworm that produces a genetically engineered silk instead of common silk.’ The second factor is that their competitors, after a fermentation processes on the basis of modified yeasts or bacteria, still have to purify the fibroin. And after purification, this has to be ‘wet-spun’ to produce usable fibres. Wet-spinning, says Kraig Labs, is a process that often requires the use of chemicals like dimethyl sulfoxide, or DMSO, which has to be handled with great care. In nature, the silkworm itself takes care of these processes.
Spider silk cannot be produced by setting up spider farms, as spiders are cannibalistic. Letting silkworms produce spider silk is an elegant way to circumvent this problem. The ultimate resource of the company’s genetically engineered silk are the mulberry trees on which the silkworms feed; they require little maintenance and help in reducing soil erosion. Applications of this silk include use as structural material and for any application in which light weight and high strength are required. Kraig believe that spider silk is in some ways so superior to the materials currently available in the marketplace, that an expansion of demand and market opportunities will follow spider silk’s commercial introduction.
So to all likeliness, we will hear much more about this miracle of precision technology, genetically engineered silk.