Scientists have developed a type of artificial muscle for soft robots that requires no rigid components and can be used in wearable devices, soft grippers and surgical tools.
Artificial muscles that move soft robots, called actuators, tend to rely on hydraulics or pneumatics, which are slow to respond and difficult to store.
Dielectric elastomers, soft materials that have good insulating properties, offer an alternative to pneumatic actuators but they currently require complex and inefficient circuitry to deliver high voltage as well as rigid components to maintain their form - both of which defeat the purpose of a soft robot.
Researchers at the Harvard John A Paulson School of Engineering and Applied Sciences (SEAS) have developed a dielectric elastomer with a broad range of motion that requires relatively low voltage and no rigid components.
"Until now, the electric fields required to power actuators in soft robots has been too high," said Mishu Duduta, a graduate student at SEAS.
"This research solves a lot of the challenges in soft actuation by reducing actuation voltage and increasing energy density, while eliminating rigid components," Duduta said.
Researchers combined two known materials that worked well individually - an elastomer that eliminated the need for rigid components and an electrode of carbon nanotubes.
The complementary properties of these two materials enabled the new device to outperform standard dielectric elastomer actuators.
The team fabricated the elastomers one on top of the other, creating a multilayer sandwich of elastomer, electrode, elastomer, electrode and so on. In this way, each electrode gets double usage, powering the elastomer above and below.
"The voltage required to actuate dielectric elastomers is directly related to the thickness of the material, so you have to make your dielectric elastomer as thin as possible," said Duduta.
"But really thin elastomers are flimsy and can't produce force. A multilayer elastomer is much more robust and can actually provide significant force," he said.
"The significance of this work is that the combination of materials and processing enables two of the current technical limitations of dielectric elastomers - the need for high voltage and pre-stretch - to be overcome," said David Clarke, professor at SEAS.
This type of actuator may be used in everything from wearable devices to soft grippers, laparoscopic surgical tools, entirely soft robots or artificial muscles in more complex robotics.
"This breakthrough in electrically-controlled soft actuators brings us much closer to muscle-like performance in an engineered system and opens the door for countless applications in soft robotics," said Robert Wood, professor at SEAS.
The research appears in the journal Advanced Materials.
