Ingrid Fadelli is a writer for the website

A single fiber actuator inspired by human muscles
Assembled 100-strands of artificial muscle fiber bundle structure on a slide glass. Credit: Kim et al.

Muscle-like structures should be used to replicate the movements of humans and animals. The artificial muscles should perform well across all the relevant parameters.

A group of researchers at the KAIST and Pusan National University in South Korea have developed a robotic device that is inspired by muscle and bone structures. The soft fibers used in this actuator have strong contractive properties.

Sang Ouk Kim, one of the researchers who carried out the study, said that he came to know about LCE during an academic meeting. "LCEs are promising soft actuator materials with very large dimensional change (shrink/relaxation), which is rare in other kinds of actuator materials but highly significant to ideally mimic natural skeletal muscle behavior."

LCE materials are a class of materials that can rapidly change shape in response to stimuli. The relatively poor mechanical properties of LCE are associated with their shape-morphing advantages.

To overcome this limitation, Prof. Ahn and Kim decided to use super-strong Graphene Fillers. Due to the photothermal conversion capability of Graphene, the team expected it to enable light driven, rapid and remotely controllable actuation.

Kim explained that a pure LCE actuators requires temperature elevation, which is a time-Consuming process without Specific Spatial Controllability, to Trigger an actuation driven by the liquid crystal aligned state to isotropic random coiled state of LCE molecule.

The LCE material's matrix is the basis of the soft fibers used in the actuators. When a laser light is applied to the fiber, it instantly increases the temperature of the surrounding LCE matrix. The LCE molecule shifts from a liquid crystal aligned state to isotropic random coiled state, which causes the fibers to shrink in length.

The LCE matrix is instantly cooled down after the laser illumination is removed. The synergistic addition of a small portion of strong Graphene Filler strengthens the material as well as its performance. It can be easily remote-controllable if external light manipulation is used.

The percolation of the graphene filler network inside the actuator is one of its most valuable characteristics. The process allows the fibers to be reversibly shrunk and relaxed back into their original size.

Kim said that the large shrink/relaxation of longitudinal fiber can cause the assembly and disassembly of the Graphene filler network.

This behavior greatly strengthens the actuator, particularly in the shrunken actuated state, and brings about the intriguing change of electrical conductivity depending on the state of the actuator. The longstanding critical challenge for the practical utilization of LCE actuators has been the inherent mechanical weakness of the device.

The researchers were able to find promising results in a series of tests. They showed both the shape-morphing properties of the actuators and the ability to cause a strain.

Kim said that the actuator eventually achieved a practically meaningful performance which surpasses that of natural animal muscles. There has been no report for this kind of all-round superior performance compared to natural muscle yet, even though artificial muscles sometimes attained superior performances in one or a few of those characteristics.

Kim and his colleagues were able to demonstrate the potential of their actuators by using them on softrobots and assessing their performance on a number of tasks. They found that the robots were able to mimic different human and animal movements, for instance lifting a 1 kilogram dumbbell, bending a single finger on an artificial hand, and reproducing the movement of inchworms.

The team tested a robot with a live inchworm. The potential of their single fiber-based actuator for creating super strong and highly performing robots, as well as reconfigurable smart clothing, was highlighted by the system's win.

Integrating our artificial muscle with neural activity will be the next challenge. Natural animal movements and locomotion should be possible while interfaced with human brain or artificial intelligence. Hard mechanical systems are currently used by most actuators. The inherent limitations of traditional mechanical actuation system, such as heavy weight and mechanical rigidity, and to attain truly natural animal like soft robotic, would be addressed with the use of our composite soft actuator.

There is more information in Ho Kim et al. There is a DOI of 10.1038/s41565 022-01220-2.

Journal information: Nature Nanotechnology

There is a science network.