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There is a scene in the film “Spider-Man 2” where Spider-Man prevents a train full of people from crashing by holding it back with about 10 sets of spider silk ropes each less than half an inch thick. It turns out the scene isn’t just fantasy.

“We calculated roughly how thick the fibers were, how many of them he had attached to the walls, how much the locomotive and people weighed, and how fast it appeared to be going,” says Randy Lewis, a professor of biology and biological engineering at Utah State University. “Spider-Man would have been able to stop that train,” says Lewis, a molecular biologist, materials scientist, and chemist who for 25 years has been striving to synthesize spider silk.

Despite being a protein, spider silk is by weight five times stronger than steel and three times tougher than Kevlar, a p-aramid fiber from DuPont. Strength is defined as the weight a material can bear, and toughness is the amount of kinetic energy it can absorb without breaking. The silk’s primary structure is its amino acid sequence, mainly consisting of repeated glycine and alanine blocks.

Potential applications include cables and bulletproof vests. Spider silk’s antimicrobial properties make it suitable for wound patches. Because the silk is not rejected by the human body, it can be used to manufacture artificial tendons or to coat implants. And its thermal conductivity is similar to that of copper but its mass density is one-seventh of copper’s, making it a potential heat management material.

However, gathering the silk from farm-raised spiders, which are territorial and cannibalistic, is not an option. Firms attempting to make spider silk synthetically have copied relevant genes from spiders and inserted them into organisms, such as Escherichia coli, that can express the protein. The protein, though, is complex, and producing silk that is as strong as nature’s has proven elusive.

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