Silk from milk? Method binds proteins into threads
By all appearances, cows have little in common with spiders. Yet despite the two species’ obvious differences, new research shows that ordinary milk can be used to spin artificial silk – a breakthrough that could open new doors for alternative plastics and regenerative medicine. Researchers from Sweden’s KTH Royal Institute of Technology and the German research center, DESY, recently reported they have spun strands of proteins derived from ordinary milk proteins, namely whey powder.
Just as in natural materials such as spider silk and muscle tissues, the building blocks of the experimental material are proteins. KTH researcher Christofer Lendel says that in principle any protein raw material could be used to make the artificial silk.
“This is, to our knowledge, the first time that one has managed to produce a cohesive thread of nanofibrils based on protein,” Lendel says. “The process is also completely free of nasty chemicals and solvents.”
Christofer Lendel is a researcher in the Department of Applied Physical Chemistry at KTH Royal Institute of Technology's School of Chemical Science and Engineering. In nature, building such structures is achieved by evolutionary optimised protein molecules and complex biological machinery. In the lab, Lendel says, the team used the inherent ability of protein molecules to spontaneously form orderly nanometer-sized fibers – or fibrils.
“These fibrils have shown impressive mechanical properties and virtually endless opportunities for functionalisation," Lendel says. The big challenge has been how to combine these building blocks in an orderly manner so that they form macroscopic materials.
“In addition to manufacturing the tiny fibers, we also managed to use a simplified apparatus for joining them to the micrometer thick threads,” he says. “This technique is reminiscent of how spiders produce their threads.
“The study also shows the potential for large scale production because we used a relatively impure raw materials and a simple process,” he says. The results of the researchers' experiments also revealed a surprise. It turned out that the ability of the threads to hold together is a balance between the orderly internal structure of nanofibrils and their flexibility when they form networks.
Lendel says that it was not surprising that proteins lacking a nanostructure could not be joined into a thread. Yet they were surprised that threads comprised of stiff fibrils with more impressive mechanical properties were weaker than those comprised of more flexible nanofibrils. “This could be an explanation for why no one managed to do this before,” he says.