UCLA scientists develop durable material for flexible artificial muscles

Materials scientists from the University of California, Los Angeles (UCLA) and colleagues from the nonprofit science research institute SRI International have developed a new material and manufacturing process to create artificial muscles that are stronger and more flexible than their biological counterparts.

“Creating an artificial muscle to enable labor and sense force and touch has been one of the great challenges in science and engineering,” said Qibing Pei, professor of materials science and engineering at the ‘UCLA Samueli School of Engineering and corresponding author of a study recently published in Science.

For a flexible material to be used as an artificial muscle, it must be able to produce mechanical energy and remain viable under high stress conditions, which means that it does not easily lose its shape and strength. after repeated work cycles. While many materials have been considered candidates for fabricating artificial muscles, dielectric elastomers (DE) – lightweight materials with high elastic energy density – have attracted particular interest due to their flexibility and toughness. optimal.

Dielectric elastomers are electroactive polymers, which are natural or synthetic substances composed of large molecules that can change size or shape when stimulated by an electric field. They can be used as actuators, allowing machines to operate by transforming electrical energy into mechanical work.

Most dielectric elastomers are acrylic or silicone, but both materials have drawbacks. While traditional acrylic EDs can achieve high actuation stress, they require pre-stretching and lack flexibility. Silicones are easier to manufacture, but they cannot withstand high stresses.

Using commercially available chemicals and employing an ultraviolet (UV) light curing process, the UCLA-led research team has created an improved acrylic-based material that is more flexible, tunable and easier to scale without losing strength and endurance. While the acrylic acid allows more hydrogen bonds to form, making the material more mobile, the researchers also tuned the cross-linking between the polymer chains, allowing the elastomers to be softer and more flexible. The resulting thin, transformable, high performance dielectric elastomeric film, or PHDE, is then sandwiched between two electrodes to convert electrical energy into motion as an actuator.

Each PHDE film is as thin and light as a human hair, about 35 micrometers thick, and when multiple layers are stacked together, they become a miniature electric motor that can act like muscle tissue and generate enough energy to power the movement of small robots or sensors. The researchers made stacks of PHDE films varying from four to 50 layers.

“This flexible, versatile and efficient actuator could open the doors to artificial muscles in new generations of robots, or in sensors and wearable technologies that can more accurately mimic or even improve human movements and abilities,” Pei said.

Artificial muscles fitted with PHDE actuators can generate more megapascals of force than biological muscles and they also exhibit three to 10 times more flexibility than natural muscles.

Multi-layered flexible films are generally manufactured via a “wet” process which involves the deposition and curing of liquid resin. But this process can result in uneven layers, making an actuator poorly performing. For this reason, so far many actuators have only been successful with single-layer DE films.

The UCLA research involves a “dry” process in which the films are layered using a blade, then UV-cured to harden, making the layers uniform. This increases the energy output of the actuator so that the device can support more complex movements.

The simplified process, coupled with the flexible and durable nature of PHDE, allows for the fabrication of new flexible actuators that can bend to jump, like spider legs, or coil and rotate. The researchers also demonstrated the ability of the PHDE actuator to launch a pea-sized ball 20 times heavier than PHDE films. The actuator can also expand and contract like a diaphragm when a voltage is turned on and off, providing insight into how artificial muscles could be used in the future.

This breakthrough could lead to soft robots with improved mobility and endurance, and new wearable and haptic technologies with a sense of touch. The manufacturing process could also be applied to other flexible thin-film materials for applications such as microfluidic technologies, tissue engineering or microfabrication.

Other study authors from UCLA’s Department of Materials Science and Engineering include Ye Shi, Erin Askounis, Roshan Plamthottam, Zihang Peng, Kareem Youssef, and Junhong Pu, all current or former members of the Materials Research Lab. Pei’s Soft Materials at UCLA. Shi, Askounis and Plamthottam are co-lead authors of the study. The authors from SRI International are Tom Libby and Ron Pelrine.

– This press release was provided by the University of California – Los Angeles

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