Advances in soft robotics over the past decade have made it possible to go from rigid, jerky machines to flexible, bendable forms that can both mimic living organisms, and interact with them more naturally. The increased flexibility provided by the use of softer materials, however, has come at the cost of reduced strength and resiliency.
But that's changing with the use of origami-inspired artificial muscles, which allow soft robots to lift objects up to 1,000 times their own weight. The muscles also generate about six times more force per unit area than mammalian skeletal muscle, and are incredibly lightweight.
"It's like giving these robots superpowers," says Daniela Rus, Ph.D., director of MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL) and one of the senior authors of a study on the subject, published in Proceedings of the National Academy of Sciences (PNAS).
"Artificial muscle-like actuators are one of the most important grand challenges in all of engineering," adds Rob Wood, Ph.D., a corresponding author of the paper and founding core faculty member of the Wyss Institute at Harvard. "Now that we have created actuators with properties similar to natural muscle, we can imagine building almost any robot for almost any task."
Each artificial muscle consists of an inner "skeleton" that can be made of various materials, folded into a pattern. It is surrounded by air or fluid and sealed inside a plastic or textile bag that serves as the "skin." Tension can then be created by applying a vacuum to the inside of the bag, which drives muscle motion in a way that is determined entirely by the shape and composition of the skeleton.
The muscles' vacuum power means that they are safer than most other artificial muscles currently being tested. They can also be integrated into closer-fitting robots on the human body. And they're programmable, as postdoctoral fellow and first author Shuguang Li, Ph.D. explains: "Designing how the skeleton folds defines how the whole structure moves."
Using materials ranging from metal springs to packing foam to sheets of plastic, the team constructed dozens of muscles. They also experimented with different skeleton shapes to create muscles that can contract down to 10 percent of their original size, lift a delicate flower off the ground or twist into a coil. Additionally, a single muscle can be constructed within 10 minutes, using materials that cost less than $1.
"In addition to their muscle-like properties, these soft actuators are highly scalable. We have built them at sizes ranging from a few millimeters up to a meter, and their performance holds up across the board," Wood says. This could translate to numerous applications at multiple scales: miniature surgical devices, wearable robotic exoskeletons, transformable architecture, deep-sea manipulators for research or construction and large deployable structures for space exploration.
"The possibilities really are limitless," says Rus.