We wear clothes made from unusual things all the time -- you even start to wonder what a "normal" material would be. From plant fibers to plastic to stuff produced by worms, there's no shortage of raw materials that can be used to make clothes. But researchers are constantly looking for others, with potentially even better properties.
An unusual idea is muscles -- or muscle fibers, to be more precise. It sounds a bit odd, but according to a new study, it could be more resilient than Kevlar, at a price that is competitive with other materials? Oh, and it's also more eco-friendly, and no animals are harmed in the process.
Cheap, durable, scalable
A belt made from muscle sounds like something straight out of a horror movie, but thanks to the work of researchers at Washington University in St. Louis, it may become real in the not too distant future. The team used microbes to polymerize proteins which were then spun into fibers (somewhat like how silkworms produce silk, but using microbes instead of worms).
The microbes can be engineered to tweak the properties of the protein, and in this case, researchers designed fibers that can endure a lot of energy before breaking.
"Its production can be cheap and scalable. It may enable many applications that people had previously thought about, but with natural muscle fibers," said Fuzhong Zhang, professor in the Department of Energy, Environmental & Chemical Engineering, and one of the study authors.
No actual animal tissues are needed for the process. Instead, the process starts from a protein called titin, which grants muscles passive elasticity. Adult humans have about 0.5 kg of titin in their bodies.
Titin was desirable because of its molecular size. "It's the largest known protein in nature," said Cameron Sargent, a Ph.D. student in the Division of Biological and Biomedical Sciences and a first author on the paper. This makes it very resilient but raises some challenges in producing it.
As weird as it may sound, the idea is not new. In fact, researchers have been toying with the idea of using muscle protein as fibers for a long time -- but gathering them from animals is unethical and challenging in many ways. So they looked for another idea.
"We wondered, 'Why don't we just directly make synthetic muscles?'" Zhang said. "But we're not going to harvest them from animals, we'll use microbes to do it."
Getting bacteria to produce large proteins is very hard. So instead, the researchers engineered bacteria to piece together smaller parts of the protein into an ultra-sturdy structure. They ended up with a protein with a high molecular weight and about 50 times larger than the average bacterial protein. Then, they used a wet-spinning process, converting the proteins into fibers about 10 times thinner than a human hair.
They opted for a fiber that is especially strong, but the process could be tweaked for any desired property. You could make clothes that are softer or dry quicker, the process can be scaled in any desired direction.
"The beauty of the system is that it's really a platform that can be applied anywhere," Sargent said. "We can take proteins from different natural contexts, then put them into this platform for polymerization and create larger, longer proteins for various material applications with a greater sustainability."
Furthermore, because the fibers are almost indistinguishable from natural muscle, they can also be used in medical procedures, for instance for sutures and stitching up wounds. Unlike other synthetic polymers, this is also biodegradable and less polluting to the environment.
"By harnessing the biosynthetic power of microbes, this work has produced a novel high-performance material that recaptures not only the most desirable mechanical properties of natural muscle fibers (i.e., high damping capacity and rapid mechanical recovery) but also high strength and toughness, higher even than that of many manmade and natural high-performance fiber," the researchers conclude.
So, would you wear clothes made from muscle?
The research has been published in Nature Communications.