Super strong rayon? It’s so metal.
Putting a metal bath on regenerated silkworm silk can make the threads both strong and stiff, scientists report Oct. 6 in Material. Some threads were up to 70 percent stronger than silk spun by spiders, the team found.
The project is the latest in a decades-long effort to create fibers as strong, light and biodegradable as spider silk. If scientists could mass-produce such material, potential uses range from biomedicine to sports. Sutures, artificial ligaments and tendons — even sports equipment could improve the arachnoid.
“If you have a climbing rope that weighs half what it normally does and still has the same mechanical properties, then obviously you’re going to be a happy climber,” says Randy Lewis, a silk scientist at Utah State University in Logan who was not involved. in the study.
Finding enough silk material to make these super strong products was a big hurdle. Silk from silkworms is simple to harvest, but not as strong. And spider silk, the gold standard for hand strength and toughness, is not easy to collect. “Unlike silkworms, spiders cannot be domesticated due to their territorial and aggressive nature,” write study co-author Zhi Lin, a structural biologist at Tianjin University in China, and colleagues.
Scientists around the world have attempted to spin robust strands in the lab using silkworm cocoons as a starting point. The first step is to remove the sticky outer coating of the silk. Scientists can do this by boiling the fibers in a chemical bath, but that can be like taking an ax to silk proteins. If the proteins become too damaged, it’s difficult for scientists to restore them to high-quality clones, says Chris Holland, a materials scientist at the University of Sheffield in England who was not involved in the study.
Lin’s team tried gentler approaches, one of which used lower temperatures and a papaya enzyme to help break down the silk coating. This gentle method seemed to work. “They don’t have little pieces of silk protein,” says Lewis. “That’s huge because the longer the proteins that remain, the stronger the fibers will be.”
After some processing steps, the researchers squeezed the resulting silk slime through a tiny tube, much like brushing out toothpaste. Then, they bathed the extruded silk in a solution containing zinc and iron ions, eventually stretching the threads like taffy to make long, thin fibers. The immersion of the metal could be why some of the yarns were so strong — Lin’s team detected zinc ions in the final fibers. But Holland and Lewis aren’t so sure.
The team’s real innovation may be that they “managed to unlock the silk in a less damaging way,” says Holland. Louis agrees. “In my mind,” he says, “this is a major step forward.”