Artificial muscles bloom, dance and wave

Wearing a flower brooch that flowers before your eyes sounds like magic. KAIST researchers concretized this concept with robotic muscles.

Researchers have developed an ultra-thin artificial muscle for soft robotics. The progress, recently reported in the newspaper Robotic science, has been demonstrated with a floral brooch in bloom, dancing butterflies and leaves of trees floating on a kinetic work.

The robotic equivalent of a muscle able to move is called an actuator. The actuator expands, contracts or rotates like muscle fibers using a stimulus such as electricity. Engineers around the world are striving to develop more dynamic actuators that can react quickly, bend without breaking, and are very durable. The flexible and robotic muscles could have a wide variety of applications, from portable electronic devices to advanced prostheses.

The team at the Functionally Antagonistic Nanotechnology Research Center at KAIST's Creative Research Initiative has developed a very thin, responsive, flexible and durable artificial muscle. The actuator looks like a thin strip of paper about an inch long. They used a special type of material called MXene, which is a class of compounds that have thick layers of only a few atoms.

Their selected MXene material (Ti₃C₂T_X) consists of thin layers of titanium compounds and carbon. This was not flexible in itself; sheets of material become detached from the actuator when they are folded in a loop. This changed when the MXene was "ionically crosslinked" – linked by an ionic bond – to a synthetic polymer. The combination of materials has made the actuator flexible, while maintaining strength and conductivity, which is essential for motions driven by electricity.

Their particular combination has performed better than others. Their actuator reacted very quickly to the low voltage and lasted more than five hours without interruption.

To prove the tiny operation of robotic muscle, the team has incorporated the actuator to the sartorial art: an origami-inspired brooch mimics the way a narcissus flower unfolds its petals when A small amount of electricity is applied. They also designed robotic butterflies that move their wings up and down and floated the leaves of a tree sculpture.

"Portable robotics and kinetic art show how robotic muscles can have great fun applications," said He-Kwon Oh, lead paper author and professor of mechanical engineering. "It also shows the enormous potential of small artificial muscles for a variety of uses, such as haptic feedback systems and active biomedical devices."

The team then plans to investigate more practical applications of MXene-based software actuators and other MXene 2D nanomaterial engineering applications.