Researchers at the MIT Media Lab and Politecnico di Bari have built artificial muscle fibers that contract like the real thing, and don’t need the noisy hydraulic hardware that has held soft robotics back. The work appears in Science Robotics.
The fibers are called electrofluidic muscles. They pair a thin McKibben actuator, a fluid-driven soft tube that contracts under pressure, with a miniature solid-state pump built on electrohydrodynamic principles. The pump sits inside the system. There is no external reservoir, no servo motor, and no tether.
Most fluidic actuators need bulky off-board pumps, which makes them hard to fit inside a prosthetic limb or a wearable exoskeleton. Each pump weighs just a few grams, and everything is sealed in a closed loop about the thickness of a toothpick. The team has cleared a path for prosthetics and humanoid robots to shed their motor boxes and distribute muscle mass along the limb itself, closer to how biology already does it.
The real work is done by paired fibers. PhD candidate Ozgun Kilic Afsar and co-author Vito Cacucciolo arranged the muscles in antagonistic configurations. One contracts while the other stretches, the same way a biceps works against a triceps. A fiber pump between the two shuttles dielectric fluid back and forth under an electric field.
“This is very much reminiscent of how biological muscles are configured and organized,” Afsar said. The antagonistic pairing also solved a practical headache, removing the need for an open fluid reservoir, which had kept earlier EHD pumps stuck in the lab.
Demonstrations were specific. A fast lever launched objects in 0.2 seconds. A bundled configuration lifted 4 kilograms (about 8.8 lb). A woven biceps-triceps pair bent a robotic arm while staying soft enough to shake a human hand. Response speed and peak contraction can be tuned by changing the ratio of pumps to actuators, or by adjusting a pre-set “bias” pressure that stops vapor bubbles from forming at the pump inlet.
Herbert Shea of EPFL, who was not involved in the study, called the absence of moving parts in the pump “a major advantage for prosthetic devices and assistive clothing.” For wearables that sit against the body all day, silence and softness are what move a lab demo toward something a person could comfortably wear to work.
Article & Image Source: MIT News
