MTI created artificial muscle fibers from nylon

Artificial muscles are materials that can contract and contract like muscle fibers. They can be used in many areas: from components of robotics to the automotive industry and the aviation industry. Researchers at the Massachusetts Institute of Technology have said that they have developed the simplest and cheapest system to create such "muscles."

The key component from which MIT scientists have made artificial muscle fibers is inexpensive and widespread nylon fibers. A new approach to the use of this material is to form and heat the fibers in a certain way.
')

Previously, researchers developed the principle of using twisted spirals of nylon threads to simulate the progressive work of muscles. They showed that in a specific size and weight, such devices could expand and contract, store and release more energy than natural muscles. But to repeat the bending movements of the fingers and limbs of a person is a more difficult task. According to the MIT researchers, no one has yet managed to solve this problem simply and cheaply.

There are materials that can be used to reproduce bending movements in biomedical devices or tactile displays. But most often these materials are “exotic” and expensive, they are difficult to produce. For example, carbon nanotube threads are durable material that can withstand more than a million compression cycles, but still too expensive for widespread use. Alloys with shape memory effect provide a strong tension, but withstand only 1000 cycles.

The new system uses cheap material and a simple manufacturing process. Nylon maintains a sufficient number of cycles due to the method of forming nylon fibers. Some materials from polymer fibers, including nylon, have an unusual property: when heated, they decrease in length, but expand in diameter. Some scientists have used this property to create linear actuator devices. But in order to transform linear translational movements into bends, devices are needed, such as a mechanical block or a winding drum. This adds complexity and costs. The MIT team was going to use the force of motion directly without additional mechanical parts.

Linear drives made from polymeric materials have one major drawback: to cause a reduction, the material must be cooled. The cooling rate may be a limiting factor. However, scientists realized that this disadvantage could be an advantage. Selective heating of one side of the fiber causes it to shrink faster than heat reaches the opposite side. Thus, the thread may deviate to the side. According to PhD Seyed Mirvakili, the lead author of the study, it was necessary to achieve a combination of two properties: high voltage (contraction tension) and low thermal conductivity.

To make this system work effectively as an artificial muscle, fiber sections must be carefully processed. To change the cross-section from round to rectangular or square, the team seemed to “flatten” them. Then the scientists heated one side, which caused the fiber to bend. Changing the direction of heating caused the fiber to perform more complex movements. In laboratory tests, the team used this heating method to force the fibers to perform circular motions and “eights”. According to scientists, the fibers can move along more complex trajectories.

An electric resistive heater, chemical reactions or a laser beam that is emitted on a filament will be suitable as a heat source. In some experiments, the researchers applied a special electrically conductive paint to the fibers and held it in one place using binder resins. Under voltage, only the part of the fiber coated with paint was heated. When heated on one side, the fiber could deviate to the side. If you heat it from the opposite, the thread returns to its original position.

Studies have shown that the material can withstand at least 100 thousand cycles of bends and can shrink and relax up to 17 times per second. According to Jan Hunter, one of the authors of the study, such fibers are suitable for the production of clothing that will shrink in order to adapt to the contours of the human body. Then manufacturers could cut the size bar, increasing comfort and simplifying fit. It is possible to make shoes from bending fibers, which will sit exactly on the leg, and its rigidity and shape will be adjusted with each step.

The system can be used to produce self-adjusting catheters and other biomedical devices. In the long run, you can create mechanical systems, such as exterior panels for cars. Fiber panels adjust aerodynamic shape to adapt to changes in speed and wind. Or they can be used as automatic “tracking systems” for solar cells. They would use excess heat to control the direction of the batteries toward the sun.

Scientific work published in Advanced Materials magazine November 23, 2016
DOI: 10.1002 / adma.201604734