Knitted muscles could make clothes that help us move

Artificial, external muscles made of fabric could help people with impaired mobility.

Researchers have created muscle-like textiles that move in response to electrical signals, a technology that shows promise for future innovations in clothing and mobility assistance. Presented in Science Advances, the fabric is made from cellulose yarn and was knitted and woven into structures inspired by actual muscle fibers. In a process similar to dying, researchers then dipped the fabric in an electroactive material to make it move in response to low-voltage electrical signals.

Force measurement of the knitted textile. Credit: Thor Balkhed/Linköping University

The textile works by harnessing the properties that real muscles use to move our bodies. Though the process is different at a molecular level, many of the same mechanical principles apply. “Like a muscle, the actuation is triggered by an electrical potential, driven by a chemical reaction, and operated in an electrolyte,” says study author Edwin Jager, an applied physicist at Linköping University.

The knitted version of the textile is more flexible, while the woven version can exert more force. This is because the woven fibers, like those in our muscles, are coupled in parallel. “In this case, the extension of the fabric is the same as that of the individual threads. But what happens is that the force developed is much higher when the threads are connected in parallel in the weave,” explains Nils-Krister Persson of the Swedish School of Textiles at the University of Borås.

Among other applications in soft robotics, the researchers anticipate that muscle-like textiles can be sewn into clothing to help people with limited mobility. This would provide a more comfortable alternative to rigid exoskeleton devices driven by motors or pressurized air. “We envision that textile actuators can be integrated into a sleeve or something resembling running tights that can be worn—hidden—under your clothes,” says Jager.

Conceptual model of a textile exoskeleton with the textile actuator (black) on an elastic elbow sleeve (white). Credit: Thor Balkhed/Linköping University

Before you throw away your running tights, Jager cautions that getting to that point will require more work and refinements: “This is only a first demonstration, and there is still much to prove. We want to investigate the effect of different knitting and weaving patterns. With respect to the electroactive material, we want to have it operate in air; it currently requires an electrolyte.” For now, though, the researchers have demonstrated that the textile muscles do indeed work. They were able to move a LEGO lever arm, and lift a two-gram weight.

“I hope that this work will inspire others to look into the possibilities of textile technology,” says Jager. “My collaborators have taught me that textiles, ubiquitous as they are, can truly be high-tech technology.”

Featured image courtesy of Thor Balkhed/Linköping University