Coatings & surface treatment
Opposite page: Thomas Scheibel, who was nominated for the European Inventor Award 2018 in the SMEs category.
Left: Artificial spider silk, created by Scheibel, which relies on E. coli reprogrammed/altered with the genes of the common European garden spider.
surveillance mechanisms. Instead, spider silk is essentially shrouded in an invisibility cloak that allows it to hide from the immune system. This property could be useful for implantable medical devices, which are often registered as foreign objects by the body, leading to scar formation, poor healing and discomfort for patients. If you coat the implant in spider silk, reasons Scheibel, the immune system won’t spot it and it won’t be rejected.
The Bayreuth team has recently discovered yet another advantageous quality of spider silk – it can repel microbes. This could have benefits for medical device implantation too, as it currently comes with a widely underestimated risk of infection. Over half of the nearly two million healthcare- associated infections reported by the Centers of Disease Control each year in the US are attributed to indwelling medical devices. Bacteria or fungi can thrive on an implant’s surface, grouping together to form an invisible biological barrier called a biofilm, which cannot easily be removed by antibiotics or cleaning agents. The microbes can then migrate into the adjacent body tissues, interfere with the healing process and cause life-threatening infections.
Smoothing silk
The sterile quality of spider webs isn’t an entirely new discovery. It has been speculated about since ancient times. “Two thousand years ago, people used spider webs as wound coverage devices,” says Scheibel. “They didn’t know why – they just knew it worked.” A more detailed understanding of the specific mechanism behind spider silk’s non-fouling effect was lacking until very recently. “It took us eight years to find out the reason spider webs are
Medical Device Developments /
www.nsmedicaldevices.com
microbe-free,” reveals Scheibel, noting that it seems counter-intuitive that cobwebs repel pathogens. Spider webs are composed of proteins, themselves made up of amino acids, which should be a valuable source of nutrition for microbes. To make matters more confusing, the surface of the web’s silk fibres consists of a mixture of proteins and lipids that vary depending on the species of arachnid and the environmental conditions under which the web is formed. This makes it difficult to study the way spider silk can inhibit bacterial or fungal infestation. It is also tricky to produce natural spider silk in the lab. Spiders only make a tiny amount of their robust thread. Luckily, Scheibel has a patented process for reproducing spider silk proteins without having to wrangle any of the pests themselves. It relies on E. coli bacteria that are genetically reprogrammed with genes from the common European garden spider. The modified bacteria are given a feed of beets and sugar cane, which they ferment to produce the raw material for spider silk. That’s just the first step. Spinning this product into the fibres spiders use to make webs is also challenging to replicate in the laboratory – each rope contains over 1,500 silk strands. It is another process that has taken years to perfect, but Scheibel now has a mechanical system that copies the way spiders extrude the thread for spinning their webs. When he finally cracked the technique, he co-founded start-up AMSilk in 2014, which produces spider silk in industrial quantities for various industries, including cosmetics and sportswear. Webs must ward off microbes in one of two ways, figured the researchers. Either the silk fibres themselves contain an antibiotic substance or the web’s molecular structure is the culprit. The team
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