With their eight hairy, scurrying legs, their fat bodies and sticky webs, spiders can be really creepy. But they have a skill that humans have long sought to replicate: they spin threads of silk with a tensile strength four times greater than that of steel. Webs are also three times more elastic than steel and resistant to heat, fungi and bacteria.
Physicians, in particular, are placing big hopes in spider silk. It is well tolerated by the human body, which can degrade it. In antiquity, spider webs were used to staunch blood from wounds.
Today, scientists and business enterprises around the world are experimenting with extracting the silk from spiders or synthesizing it. Last year, a German company, AMSilk, which is located near Munich, presented what it called the first scalable fibre with mechanical properties similar to those of natural spider silk.
"For a long time this was considered to be impossible," said Mathias Woker, chief operating officer at AMSilk.
Woker said it was difficult to gather silk threads directly from spiders themselves, which are territorial and cannibalistic. Keeping a "herd" of some spider species in a cage is no option.
"There'd be just one spider left at the end of every day," he said.
At Hanover Medical School (MHH), however, silk is actually harvested from spiders day by day. Staff have even given individual names such as Rosa and Dasha to their 150 spiders, which are about 5 centimetres in size, not including leg span and very peaceable.
The 150 golden orb weaver spiders are regularly rounded up to be "milked." While they are immobilized on a piece of foam material with gauze, the dangling dragline fibre from their abdomen is gently pulled and wound around a spindle.
"The spider uses the dragline to secure itself to a branch, for example," said Kerstin Reimers, head of the MHH's Laboratory of Experimental Plastic and Reconstructive Surgery.
"When you pull on it, you simulate the spider falling," and more fibre is expelled automatically.
"The spider can't control it."
MHH researchers take an average of about 200 metres of silk per spider during each milking. "You could probably take 500 metres, but we don't," Reimers said, explaining that the procedure was strenuous for the spiders, which get restless after 10 minutes.
To refresh them afterwards, they are given water to drink and crickets to eat.
Physicians hope to use spider silk to help people with nerves severed in accidents or tumour operations. Biomatrices in which the nerves regenerate could be made of the silk.
"We've concluded pre-clinical testing," said Reimers, noting that the method had worked "excellently" in rat and sheep cell cultures. "We were able to bridge six centimetres in a sheep without supplementary treatment with the sheep's own cells."
A clinical study on humans is now planned. Researchers in Belgium and the Netherlands are taking a similar path, Reimers pointed out. The other alternative, synthesizing the silk, is being attempted in Japan, the United States, Sweden and Germany.
Spider silk is made of protein, and some researchers have experimented with genetically modified silkworms to produce it. Others have tried to cultivate it in goat udders.
AMSilk scientists use cultures of genetically modified E. coli bacteria to produce the proteins.
AMSilk makes a protein powder similar to spider silk, but is still a big step away from spinning the powder into thread. "We've found a way to make a fibre from the protein," remarked Woker.
The company distributes the protein for use in cosmetics since "it forms a nice film and can create a barrier to environmental influences," according to Woker.
Spider silk was once valued as a clothing fabric. In the 19th century, naturally gold-coloured garments were woven from the silk of golden orb weaver spiders. Louis XIV of France, known as the Sun King, is said to have had gloves made of the material.
Using a process revived from that era, a golden cape was painstakingly woven over four years from spider silk and put on display in 2012 at London's Victoria and Albert Museum.
Unlike AMSilk, the MHH researchers working with spiders directly on a daily basis have come to learn how they tick. "When you touch a spider you can see that it, too, immediately begins to clean the touched spot," Sarah Strauss, an MHH biologist, said in a report by the Bavarian Broadcasting Service. "Our skin is fatty and salty to the animals, it's sticky and presumbly extremely unpleasant. "Spiders probably feel the same about us as most people feel about them."