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Coatings & surface treatment The amazing spider-material


Medical devices might just be the beginning for spider silk. A recent application analysis in the journal e-Polymers suggests that it could be used in everything from parachutes to concrete. The authors divide the potential applications into five categories: ■Textiles: Spider silk is like silk, but better. Cloth made from spider silk is lightweight, resilient and breathable, as well as having strong water absorption and UV resistance capabilities. The authors believe that promoting spider silk- spinning technologies could revolutionise the clothing industry.


■Medical devices: The authors highlight spider silk’s biocompatibility and note that it is well-suited to be used in prosthetics, as well to support or even replace ligaments and skin.


■Military: Body armour and parachutes made from spider silk fibres should be able to achieve increased performance at less weight. Using cobweb structures can also help absorb impact forces and help improve the strength of the material for use in tanks, aircraft, satellites and the reinforced structures of military buildings.


■Materials: The strength of spider silk fibres should mean it could be used to replace the steel bars in concrete, greatly reducing the weight of buildings. As synthetic spider silk is resistant to humidity and cold, and will not rust, it is especially suitable for building bridges and other important infrastructure. Applying spider silk materials in the automotive industry could also help reduce vehicle weight, while improving tyre performance and chassis strength.


■Environmental protection: Spider silk-based nanocomposites are expected to replace some common plastics. Replacing plastic bags with bags made from spider silk proteins is a relatively quick and easy way of protecting the environment and reducing plastic waste.


Source: e-Polymers


Due to its microbe-free nature, spider silk can be used as a coating for medical implants to prevent infection and protect them from the immune system.


hypothesised that the shape of the silk fibres prevents bacteria from accessing nitrogen, which is necessary for their growth. To test the theory, the engineered spider silk was exposed to several species of biofilm-forming microbes, including superbug Staphylococcus aureus and fungal tyrant Candida albicans. The same experiment was performed on three other materials as controls – a silkworm protein, polycaprolactone plastic, and gelatine. Engineered spider silk emerged as the winner – it repelled the pathogens in all experiments, unlike the other materials.


Holding pattern


Atomic force microscopy helped explain why certain materials stave off bugs while others are quickly


colonised by them. “There are these hydrophobic islands within a hydrophilic surrounding,” explains Scheibel of the spider silk fibre. “But the distancing of these patches is too far off, so a tiny microbe can’t hold on to it.” In contrast, the other proteins tested have larger hydrophobic (water-repelling) regions, representing a more microbe-friendly surface. Therefore, it is the structure at the nanometre level that makes certain materials microbe-repellent, says Scheibel. He likens spider silk’s antimicrobial mechanism to a property exhibited by the lotus flower. The topography of this plant’s leaves causes water droplets to form spherical beads that simply bounce right off the surface.


The Bayreuth researchers have so far tested the microbe-repellent function on two types of engineered spider silk materials. One is a fine coating, just a few nanometres thick, which could be used on medical devices. AMSilk already has a breast implant coating that was originally marketed to camouflage the device, so it is not challenged by the patient’s immune system. “At the beginning, we didn’t know why the silk coating was so beneficial for breast implant patients,” says Scheibel. “Now we know it is microbe-free. With any implantation, if you can prevent biofilm formation, that helps a lot during the healing process because you don’t get local inflammation.” He hopes the material will soon be used for wound dressings, skin replacements and other medical implants. The second spider silk formation, a three- dimensional hydrogel scaffold, could help advance tissue engineering research – which Scheibel is particularly excited about. Most other microbe- repelling materials are so effective at booting out bacteria that they repel all cells, including human ones. This limits their usefulness in tissue engineering. To see if that would be the case with spider silk, the team added a cell-binding motif known to enhance cell attachment. When the hydrogel was incubated with a human and bacterial cell culture for ten days, the human cells attached but there was no microbial contamination. “The human cells win and bind to the scaffold, while the bacteria are just washed away,” Scheibel sums up. “That means it’s bioselective. It allows the good guys to grow and the bad guys are kicked off.” The next step for the Bayreuth team is to work out how to 3D print the spider silk scaffold with the human cells already attached to its surface. The resulting structure could help rebuild damaged heart muscle and possibly even replace whole organs in the future. “It’s like building a house with all the furniture and the people living in it at the same time,” Scheibel reveals, suggesting we could soon be more grateful to our eight-legged housemates than we ever thought possible. ●


110 Medical Device Developments / www.nsmedicaldevices.com


www.epo.org


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