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Artificial Muscles Constructed From Wax-Filled Nanotech Yarn

Artificial muscles made from nanotech yarns and infused with paraffin wax can lift more than 100,000 times their own weight and generate 85 times more mechanical power than the same size natural muscle, according to scientists at The University of Texas at Dallas and their international team from Australia, China, South Korea, Canada and Brazil.

UT Dallas researchers have made artificial muscles from carbon nanotube yarns that have been infiltrated with paraffin wax and twisted until coils form along their length. The diameter of this coiled yarn is about twice the width of a human hair.
Credit: UT Dallas

The yarns are made up of carbon nanotubes, knitted together like strands of rope, to form a composite structure. Each carbon nanotube strand is 10,000 times smaller than the diameter of a human hair, yet has a tensile strength a hundred times that of steel – even stronger than spider silk.

“The artificial muscles that we’ve developed can provide large, ultrafast contractions to lift weights that are 200 times heavier than possible for a natural muscle of the same size,” said Dr. Ray Baughman, team leader, Robert A. Welch Professor of Chemistry and director of the Alan G. MacDiarmid NanoTech Institute at UT Dallas. “While we are excited about near-term applications possibilities, these artificial muscles are presently unsuitable for directly replacing muscles in the human body.”

So, they are not suitable for use in prosthetic devices that are implanted. The reason being of course, the paraffin wax component, which would leak into surrounding organic tissues, causing significant damage. However, there is nothing stopping them being used in the external parts of a prosthetic. So, a prosthetic arm say, connects to the body as normal, anchored into the bone or soft tissues. The electrodes tap into adjacent nerve bundles for control signals, and, anchored on the metallic superstructure, these artificial muscles serve as the actuators, delivering pound-for-pound, far more strength than a human muscle could ever manage.

In fact, that is exactly what the team have in mind. One of their ideal applications is muscles in robotics, and, if you take away the controlling implanted electrodes and anchoring spike, that is exactly what a full limb replacement prosthetic is: a robotic arm or leg.

“Because of their simplicity and high performance, these yarn muscles could be used for such diverse applications as robots, catheters for minimally invasive surgery, micromotors, mixers for microfluidic circuits, tunable optical systems, microvalves, positioners and even toys,” Baughman said.

Including times for both actuation and reversal of actuation, the researchers demonstrated a contractile power density of 4.2 kW/kg, which is four times the power-to-weight ratio of common internal combustion engines.

To achieve these results, the guest-filled carbon nanotube muscles were highly twisted to produce coiling, as with the coiling of a rubber band of a rubber-band-powered model airplane.
When free to rotate, a wax-filled yarn untwists as it is heated electrically or by a pulse of light. This rotation reverses when heating is stopped and the yarn cools. Such torsional action of the yarn can rotate an attached paddle to an average speed of 11,500 revolutions per minute for more than 2 million reversible cycles. Pound-per-pound, the generated torque is slightly higher than that obtained for large electric motors, Baughman said.
Because the yarn muscles can be twisted together and are able to be woven, sewn, braided and knotted, they might eventually be deployed in a variety of self-powered intelligent materials and textiles. For example, changes in environmental temperature or the presence of chemical agents can change guest volume; such actuation could change textile porosity to provide thermal comfort or chemical protection. Such yarn muscles also might be used to regulate a flow valve in response to detected chemicals, or adjust window blind opening in response to ambient temperature.

Heating the yarn in inert atmosphere from room temperature to about 2,500 degrees Celsius provided more than 7 percent contraction when lifting heavy loads, indicating that these muscles can be deployed to temperatures 1,000 C above the melting point of steel, where no other high-work-capacity actuator can survive.

“This greatly amplified thermal expansion for the coiled yarns indicates that they can be used as intelligent materials for temperature regulation between 50 C below zero and 2,500 C,” said Dr. Márcio Lima, a research associate in the NanoTech Institute at UT Dallas who was co-lead author of the Science paper with graduate student Na Li of Nankai University and the NanoTech Institute.

“The remarkable performance of our yarn muscle and our present ability to fabricate kilometre yarns suggest the feasibility of early commercialization as small actuators comprising centimetre yarn length,” Baughman said. “The more difficult challenge is in upscaling our single-yarn actuators to large actuators in which hundreds or thousands of individual yarn muscles operate in parallel.”


Wax-Filled Nanotech Yarn Behaves Like Super-Strong Muscle

Electrically, Chemically, and Photonically Powered Torsional and Tensile Actuation of Hybrid Carbon Nanotube Yarn Muscles (Paper)

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