Scaling up spider silk for human limb-sized artificial muscles could be problematic, says Brent Opell, a professor at Virginia Tech. A single thread of drag line spider silk is very narrow, about five microns in diameter, and has a high surface area that lets it quickly absorb large amounts of water to quickly contract.
Stacking multiple fibers next to each other will likely slow the diffusion of water through the fiber and slow the speed of contraction.
While there are still multiple issues that still need to be resolved before any actual device using spider silk as an artificial muscle is built, the idea does have its merits, especially when compared to other artificial muscles out there, says Adam Summers, a professor at the University of Washington.
"Spider silk is a remarkably long-lived polymer that would last for tens of thousands of cycles," said Summers.
Other artificial muscles exist that are superior to spider silk in terms of speed or amount of contraction, says Summers, but often require high amounts of electricity or toxic chemicals for activation and break down after a couple hundred cycles.