Smooth As Silk

The building southwest of Munich’s city limits may look like nothing special from the outside, but inside you can marvel at a fascinating process. A viscous mass is being extruded under pressure through 40 tiny holes in a faucet-sized nozzle into a flask full of transparent fluid. Suddenly, thin threads are forming and sinking to the bottom of the glass as if in slow motion. Only a few get to see this spectacle live. The two chemical engineers who are in attendance wear protective clothing while presenting the effect, which they call the “magic moment.”

What the employees in the spinning mill of the biotech company AMSilk in Planegg are demonstrating so vividly is otherwise done in secret. So just how the 40 filaments inside the machine are stretched up to 80 times their length and spun into a fine thread remains a secret.

“It’s the strongest natural protein in the world—the thread has a tensile strength two and a half times that of steel,” enthuses AMSilk CEO Ulrich Scherbel. “No wonder the Spiderman story fascinates people. However, for a long time no one had succeeded in producing significant quantities of spider silk from proteins.” AMSilk has—initially on a small scale in the laboratory, and now, together with Evonik, on an industrial scale.

There is a great deal of interest in this innovative material, and the customers who are already using it are well known worldwide. The fiber can be found in blouses from this year’s spring collection of the Parisian fashion group Balenciaga. It is used in watch straps for the luxury brand Omega.

And in 2022, AMSilk announced a collaboration with Mercedes-Benz. The interior of the Vision EQXX concept car now features door handles that contain silk fibers. Spider silk threads are now playing a role in more and more applications. Demand is increasing, and that is why Evonik and AMSilk expanded their existing cooperation—which had been in place since 2021—in the fall of last year.

The use of biotechnologically produced spider silk is conceivable in more than 20 sectors, for example in the cosmetics industry as a substitute for silicones in shampoos, in the health sector, and in agriculture. “We know, for example, that implants coated with spider silk are tolerated better by the body,” says AMSilk CEO Scherbel. “And if we coat plant seeds with it, their shelf life doubles.” AMSilk’s high-performance fiber was the first to be used in the textile industry as an alternative to natural silk and other materials. The industry urgently needs innovative solutions. According to the European Environment Agency, it is the third-largest cause of water pollution and land use. The EU’s plan to achieve a circular economy by 2050 is also clearly aimed at the textile industry.

The AMSilk material is more sustainable than many other textiles. Because the composition of the threads corresponds to that of their natural model, they are completely biodegradable—unlike polyester fibers, for example. Their production is better for both the climate and the environment than conventionally produced silk. This comes mainly from the cocoons of the caterpillars of the mulberry moth, which is native to China. Real spider silk, the model for the AMSilk product, can indeed be obtained from cultivated spiders and has been experimentally tried in silk production. However, the process is extremely labor-intensive, and the quantities produced are negligible.

According to AMSilk, the biotechnological production of spider silk requires 97 percent less water and 92 percent less land area than the laborious natural extraction and production of traditional mulberry silk, and the carbon footprint is around 81 percent smaller. In addition, the AMSilk process allows the production of silk thread in far greater quantities than nature can provide.

To make one kilo of silk with the help of mulberry silkworms, you need the cocoons of around 15,000 caterpillars. In just one working day, AMSilk’s technology produces a hundred times this amount of protein, which can be processed into almost as much fiber material. “The textile industry urgently needs sustainable solutions like these,” says CEO Scherbel.

At AMSilk, the source of the silk thread is not a spider but a microorganism. Ever since science has been able to precisely analyze and modify genes, it has been possible to turn such single-celled organisms into tiny factories. To do this, a segment of DNA containing the code for the desired molecule is introduced into the interior of the bacteria by means of electrical pulses. All that the genetically modified microorganisms then need to multiply and produce the silk protein in bulk is a lot of sugar, a supply of the right amino acids from Evonik’s own production, and optimal living conditions.

This is a fermentation process like those used for centuries to preserve food and produce beer and wine. For a long time it was not known that microorganisms play the decisive role in this process.

In the 19th century, the French biochemist Louis Pasteur was the first to show that bacteria are responsible for what is known as lactic acid fermentation. Modern precision fermentation with genetically modified microorganisms has been gaining momentum for around 40 years and is now an integral part of biotechnology. Forecasts predict average annual sales growth of 43 percent for fermentation-based products by 2030—to a market value of more than 35 billion US dollars.

However, getting genetically modified microorganisms to produce silk protein through fermentation sounds easier than it is—at least if you need large quantities, as AMSilk does. What works well in a two-liter tank in the laboratory does not necessarily work smoothly in a 50,000-liter tank. “Fermenting the protein in suitable yields and bringing it into large-scale production was a challenge,” reports AMSilk CEO Scherbel about the early days of the company, which was founded in 2008 as a spin-off from the Technical University of Munich.

Evonik’s experience as a production partner therefore comes in handy: The chemical company’s biotech hub has specialized in the industrial fermentation of bioproducts for animal feed, cosmetics, and medicine for many years. An Evonik plant was the first to produce large quantities of silk protein.

Scherbel has to smile when he thinks back to the start of the collaboration: “It quickly became clear that although we at AMSilk know a lot about how our product behaves in the laboratory, we knew about as much about fermentation on an industrial scale as we do about rocket science. The experts at Evonik always believed in the silk protein and contributed their knowledge so that we were finally able to make the process industrially viable.”

If you want to see this for yourself, you should drive 750 kilometers east from Scherbel’s office in Bavaria, into the heart of Slovakia, where the village of Slovenská Ľupča lies at the foot of the Low Tatras in the shadow of a castle. The Evonik Fermas chemical plant is an important employer for the people who live here, and an internationally significant production site for the biotechnology industry. A total of 23 tanks, each with a capacity of 50 cubic meters, are located in the huge fermentation hall, in which pumps and motors hum sonorously, warm temperatures prevail even in winter, and it smells like a bakery.

Yellow lines mark the safe routes. Safety goggles, ear muffs, and safety shoes are mandatory for everyone here. In the control center, specialists work in shifts around the clock to monitor the fermentation process, checking parameters such as pressure, pH, temperature, and sugar content. Directly in front of it is a truck-high tank reserved for AMSilk alone. Inside it, billions of microorganisms produce silk protein.

The process, which was developed in the Munich laboratory, was transferred to an industrial scale here in 2020. Since then, it has been continuously optimized to produce even larger quantities, reports Richard Vereš, Head of Technology and Process Development at Evonik Fermas.

“Here, we start with individual laboratory experiments to familiarize ourselves with a new product. Then we start the upscaling process.” Evonik sometimes advises the customer to adapt the genetic make-up of the bacteria, the ingredients or the sequence of the isolation steps for industrial production. It can take weeks or even months to produce a protein in a large tank with the same quality as in the laboratory.

The biggest challenge in the production of silk protein is to isolate and purify the target molecules from the bacterial solution—only then can they be spun into a thread later on. To ensure the necessary quality, AMSilk’s and Evonik’s experts have developed a multi-stage process.

“The silk protein required some technical changes in our plant,” says Vereš. “For example, we needed new specialized equipment for cell disruption.” This unit is located in a container outside the hall and is responsible for a decisive step in the separation process: It breaks open the bacterial cells, causing them to release the protein. The solution is then centrifuged several times until only spider silk protein remains. During processing, the mixture undergoes several clarification and concentration stages, gradually transitioning into a more refined and concentrated protein solution. After the water has been evaporated in a drying unit, what remains is protein powder, which is delivered to the spinning mill in 20-kilogram barrels.

The fact that Evonik purchased new equipment specifically for AMSilk doubled the capacity and significantly improved the efficiency of the process.

Tim Pohlmann and Ronald Mathä accompanied this process. The two men, a chemist and a biotechnologist, regularly travel to Slovenská Ľupča from Germany. They handle contract manufacturing in the field of microbial fermentation. They enable customers to manufacture their products economically at Evonik and open doors to global partners for startups. “We look forward to continuing on this path with AMSilk and further improving the process,” says Pohlmann, for whom close cooperation between both partners is essential. “Evonik ensures transparency and whenever challenges arise, we solve them as a team.” This works so well that the capacity of the plant in Slovenská Ľupča, which runs on green electricity, has quadrupled since the start of production in 2023—several tons of silk protein are now produced in Slovakia every month.

But how is this powder turned into a high-tensile thread that could later be used in a silk blouse, a watch strap or a car door handle? As soon as the barrels arrive at the AMSilk pilot spinning mill near Munich, the protein is first gradually stirred into a solvent. The powder must not be allowed to form clumps or the proteins in the honey-like liquid will never line up to form a stable thread, preventing that “magic moment.” A lot can go wrong, from cultivation to spinning, but the process now runs smoothly. The machine in the inconspicuous building reliably pulls a silvery spider thread out of the solution around the clock and wraps it around bobbin after bobbin.

Depending on customer requirements and the intended use, AMSilk is now able to produce thinner or thicker threads. All of them are as light as a feather, very resilient, less sticky—and yet close to nature’s model. “I’m certain that we will become one of the leading suppliers of high-performance fibers,” says Scherbel enthusiastically. “Great things can happen when the innovative strength of new companies like AMSilk meets the expertise of experienced industrial partners like Evonik.” The feeling of magic, for example, when a viscous mass becomes a delicate, silvery thread.