Muscles have inspired design since ancient times and even today’s top engineers turn to the fibrous tissue to inform their inventions. The problem is, many artificial muscle materials are either too expensive or too fragile for most practical applications.
That might change thanks to a new design by Massachusetts Institute of Technology researchers, whose relatively simple and inexpensive solution is to selectively heat nylon fibers.
While in the early stages of his Ph.D., doctoral candidate Seyed Mirvakili and his colleagues first discovered that, when twisted into a coil, nylon filaments can be used as artificial linear muscles. Although these twisted filaments could extend and retract further than natural muscles, the nylon couldn’t bend and recover like fingers do, so Mirvakili looked for a solution and found it while working under MIT’s Ian Hunter.
Nylon behaves strangely when heated — it shrinks in length but grows in width. Mirvakili and Hunter realized heating just one side of the filament causes that side to contract faster than the other, causing the entire strand to bend.
The stages of the nylon filament’s fabrication, from left to right: Standard, rounded fishing line. Compressed fishing line. Mask added to the middle of the filament. Filament coated in conductive ink. Mask removed so the conductive ink is only on the sides
Felice Frankel and Seyed Mohammad Mirvakili
But getting the nylon to behave in intended ways required the researchers to redesign fishing line, pressing its rounded shape into a rectangle. Luckily, the fishing line was easy to acquire. “Nylon is cheap and abundant,” Mirvakili told Digital Trends.
After forming the nylon into its desired shape, the researchers tested various heat sources and angles, prompting the filament into sophisticated motions like figure eights. As any angler knows, nylon is tough. Mirvakili and Hunter showed their filament could perform sufficiently through at least 100,000 bending cycles .
Nylon-based artificial muscles may have application for things like robotics, biomedical devices, toys, and form-fitting clothing. “In general, anywhere that muscle-like motion such as bending is needed, nylon artificial muscle can be useful,” Mirvakili said.
A paper detailing their design was published recently in the journal Advanced Materials.