In a laboratory at Hanover Medical School in Germany, scientists are exploring how silk from spiders can be used to treat wounds and repair torn tendons and nerves. Recently, they succeeded in bridging a 6-centimeter (2.4-inch) tibial nerve defect with spider silk in a large animal model. The nerves regenerated in just ten months.
“We have been investigating the uses of spider silk in surgical applications such as sutures and nets and as a means to stimulate nerve and skin healing,” said Kerstin Reimers, a biological professor in Hanover’s Department of Plastic, Hand and Reconstructive Surgery. “Spider silk is stronger than nylon, but it is also of low immunogenicity and has a remarkable effect on the healing process.”
Tougher gram for gram than steel and Kevlar and more elastic than rubber, spider silk is also antimicrobial, biocompatible and completely biodegradable. These properties - plus many more - have helped to make spider silk one of the hottest fields in material research, being tested for medical and military applications including bulletproof armor, and for industrial uses such as high-strength cables, thin films and coatings.
“There are numerous types of spider silks, and many of them are strong, stretchy and durable,” said Cheryl Hayashi, a professor of biology at the USA’s University of California, Riverside, who has been studying the genetics of spider silks for more than two decades. “The combination of these attributes makes these silks amazingly tough, especially considering that silk is nearly weightless. Silks can be used by themselves to make superb filaments and yarns, and they can be blended with other materials for all sorts of medical, industrial and consumer applications.”
The biggest hurdle is producing the material in sufficient volumes. Unlike silkworms, spiders are cannibalistic and cannot be raised in concentrated colonies. Their silk output also is low. For example, it took eight years and more than 1 million Madagascar Golden Orb spiders to produce enough silk for a 2-meter (6.5-foot) shawl and cape displayed at London’s Victoria and Albert museum in 2012.
Hanover Medical School breeds its own spiders, extracting silk threads in a painstaking process. A single spider can provide up to 200 meters (656 feet) of silk in a single thread, but not enough for commercial applications. Therefore, scientists have been exploring ways of producing synthetic spider silk, bypassing the need for actual spiders.
A GENE-SEQUENCE BREAKTHROUGH
Randy Lewis, who joined the Synthetic Bioproducts Center at Utah State University (USA) in 2011, is a pioneer in synthetic spider-silk production. When investigating spider-silk gene sequences, he succeeded in isolating the gene that produces spider-silk proteins. While a professor of molecular biology at the University of Wyoming (USA), Lewis transferred the gene to other organisms, including transgenic goats that produce spider-silk proteins in their milk. When extracted from the milk and spun, these proteins yield a fiber that contains some of natural spider silk’s properties.
“Spider silk is stronger than nylon, but it is also of low immunogenicity and has a remarkable effect on the healing process.”KERSTIN REIMERS
PROFESSOR, DEPARTMENT OF PLASTIC, HAND AND RECONSTRUCTIVE SURGERY, HANOVER MEDICAL SCHOOL
Lewis and his team also are exploring methods for producing silk proteins from bacteria. In 2014, they achieved two breakthroughs. “The first is that we have achieved a four- to six-fold increase in the amount of bacteria that we are able to produce in a fermentation vessel,” Lewis said. “The second is that we’ve been able to quadruple the amount of protein that each bacterium produces. As a result, we’re seeing an increase in our production capacity of at least a factor of ten.”
SILK FROM FERMENTED BACTERIA
Spiber – a company spun off from Japan’s Keio University – has produced Qmonos, a material created from synthetic fibroin, a class of proteins that form natural silks, including spider and silkworm silk. Qmonos is created with a microbial fermentation process, can be fabricated into fibers, films, gels, sponges and powders, and is being developed for applications in the automotive, aerospace and medical industries.
“Spiber has designed and synthesized over 400 variations of Qmonos to date,” said Kenji Higashi, the company’s head of marketing. “In November 2013, we launched the first prototype production plant to test and tune our production process, and we expect the first industrial Qmonos products to enter the global market within the next few years.”
“Silks can be used by themselves to make superb filaments and yarns, and they can be blended with other materials for all sorts of medical, industrial and consumer applications.”Cheryl Hayashi
professor of biology, University of California, Riverside
German firm AMSilk, meanwhile, has completed pre-clinical testing of its proprietary silicone implant coating made from recombinant spider-silk proteins. In March 2013, it announced that it had developed a proprietary process for producing spider-silk fibers on an industrial scale. Since November 2013, AMSilk has sold its spider-silk proteins to the cosmetics industry.
“Of all the many applications for spider silk, the spinning of a viable commercial fiber has always been technically the most challenging,” said Lin Römer, AMSilk’s managing director and head of scientific and technical development. “With the current process, we have shown that a commercial spider-silk fiber is possible.”
Another spider-silk frontrunner is US-based Kraig Biocraft Laboratories of Lansing, Michigan. Its transgenic silkworms can produce a number of spider-silk proteins and manage the hard task of assembling those proteins into strong fibers. The company is already working with US-based protective-materials manufacturer Warwick Mills to jointly develop textile products from synthetic spider silk.
Working with Dr. Malcolm Fraser, a professor of molecular biology and genetics at the University of Notre Dame in Indiana (USA), Thompson used a gene-splicing technique to create his spider-silk silkworms. In 2010, he hatched the first batch of “Monster Silk” silkworms, which produce a hybrid spider/silkworm silk. Since then, Thompson’s team has focused on preparing for commercial production and creating new silk fibers with different properties.
“Since we launched our commercial program in October 2013, we’ve already managed to double the amount of silk we’re producing,” Thompson said. “Our near-term goal is tapping into the textile market. The silk industry alone is worth around US$5 billion a year. Regular silk usually costs US$100 per kilogram, and we have a super silk that can be produced at the same price.”
BETTER THAN THE REAL THING?
To date, no one has produced a synthetic silk that matches all the properties of natural spider silk. But they are getting close. “Right now, our best fibers are equivalent to Kevlar, but about half as good as natural spider silk,” Utah State’s Lewis said. Spiber is also optimistic. “Some of our Qmonos variations are outperforming natural spider silks in terms of toughness,” Higashi said. “As we invent new Qmonos designs every day, we expect to achieve even better properties.”
Thompson predicts that Kraig Biocraft is not far away from producing synthetic spider silk with properties equal to the real thing. In fact, he believes Kraig’s synthetics have the potential to outperform natural spider silk.
“We’re at a point now where we can theoretically take a gene sequence and plug a different protein into it to add a new property to the silk,” Thompson said. “For example, we could potentially create a silk with antibiotic properties. Nature is the inspiration for everything we are doing, but it’s not the limit.” ◆