A team from UCLA and SRI International have produced a durable material that can be used to develop flexible artificial muscles. Their new material and manufacturing process makes artificial muscles that are stronger and more flexible than their biological counterparts, and could lead to robots and wearable devices that copy natural motion.
An artificial muscle that enables work and can detect force and touch has long been investigated, but the required soft material would have to output mechanical energy and stay viable while undergoing high-strain conditions without losing form and strength even after repeated cycles. Although a range of materials have been assessed for this role, dielectric elastomers, lightweight materials with high elastic energy density, offer optimal flexibility and toughness. They are electroactive polymers that can be used as actuators, allowing machines to operate by transforming electric energy into mechanical work.
Although dielectric elastomers are usually made from acrylic or silicone, they need pre-stretching and lack flexibility. However, as reported in Science [Shi et al. Science (2022) DOI: 10.1126/science.abn0099], here commercially available chemicals and an ultraviolet light curing process was used to develop an improved acrylic-based material that is more pliable, tunable and simpler to scale without losing strength and endurance. Although acrylic acid allows more hydrogen bonds to form, making the material more movable, the crosslinking between polymer chains were adjusted to make the elastomers softer and more flexible.
This produced a thin, processable, high-performance dielectric elastomer film (PHDE), which was positioned between two electrodes to convert electrical energy into motion as an actuator. When multiple layers are combined, they become a miniature electric motor that can behave as muscle tissue and produce enough energy to power motion for small robots or sensors. Artificial muscles fitted with PHDE actuators can produce more force than biological muscles, as well as demonstrating three to 10 times more flexibility than natural muscles.
This new study involves a “dry” process where the films are layered and then UV-cured to harden, which enhances the actuator’s energy output to allow the device to support more complex movements. As corresponding author Qibing Pei points out: “This flexible, versatile and efficient actuator could open the gates for artificial muscles in new generations of robots, or in sensors and wearable tech that can more accurately mimic or even improve humanlike motion and capabilities”.
The process could also lead to new wearable and haptic technologies with a sense of touch, and the manufacturing process could also be applied to other soft thin-film materials for applications such as microfabrication, microfluidic technologies and tissue engineering.
“This flexible, versatile and efficient actuator could open the gates for artificial muscles in new generations of robots, or in sensors and wearable tech that can more accurately mimic or even improve humanlike motion and capabilities”Qibing Pei
A 4x5-inch film made of 10 layers of processable, high-performance dielectric elastomers (PHDE) stacked together with 20 actuators. Credit: Soft Materials Research Lab/UCLA