Login with your Social Account

Artificial “muscles” achieve powerful pulling force

Artificial “muscles” achieve powerful pulling force

As a cucumber plant grows, it sprouts tightly coiled tendrils that seek out supports in order to pull the plant upward. This ensures the plant receives as much sunlight exposure as possible. Now, researchers at MIT have found a way to imitate this coiling-and-pulling mechanism to produce contracting fibers that could be used as artificial muscles for robots, prosthetic limbs, or other mechanical and biomedical applications.

While many different approaches have been used for creating artificial muscles, including hydraulic systems, servo motors, shape-memory metals, and polymers that respond to stimuli, they all have limitations, including high weight or slow response times. The new fiber-based system, by contrast, is extremely lightweight and can respond very quickly, the researchers say. The findings are being reported today in the journal Science.

The new fibers were developed by MIT postdoc Mehmet Kanik and MIT graduate student Sirma Örgüç, working with professors Polina Anikeeva, Yoel Fink, Anantha Chandrakasan, and C. Cem Taşan, and five others, using a fiber-drawing technique to combine two dissimilar polymers into a single strand of fiber.

The key to the process is mating together two materials that have very different thermal expansion coefficients — meaning they have different rates of expansion when they are heated. This is the same principle used in many thermostats, for example, using a bimetallic strip as a way of measuring temperature. As the joined material heats up, the side that wants to expand faster is held back by the other material. As a result, the bonded material curls up, bending toward the side that is expanding more slowly.

Artificial muscles achieve powerful pulling force

Credit: Courtesy of the researchers

Using two different polymers bonded together, a very stretchable cyclic copolymer elastomer and a much stiffer thermoplastic polyethylene, Kanik, Örgüç and colleagues produced a fiber that, when stretched out to several times its original length, naturally forms itself into a tight coil, very similar to the tendrils that cucumbers produce. But what happened next actually came as a surprise when the researchers first experienced it. “There was a lot of serendipity in this,” Anikeeva recalls.

As soon as Kanik picked up the coiled fiber for the first time, the warmth of his hand alone caused the fiber to curl up more tightly. Following up on that observation, he found that even a small increase in temperature could make the coil tighten up, producing a surprisingly strong pulling force. Then, as soon as the temperature went back down, the fiber returned to its original length. In later testing, the team showed that this process of contracting and expanding could be repeated 10,000 times “and it was still going strong,” Anikeeva says.

Artificial muscles achieve powerful pulling force

Credit: Courtesy of the researchers

One of the reasons for that longevity, she says, is that “everything is operating under very moderate conditions,” including low activation temperatures. Just a 1-degree Celsius increase can be enough to start the fiber contraction.

The fibers can span a wide range of sizes, from a few micrometers (millionths of a meter) to a few millimeters (thousandths of a meter) in width, and can easily be manufactured in batches up to hundreds of meters long. Tests have shown that a single fiber is capable of lifting loads of up to 650 times its own weight. For these experiments on individual fibers, Örgüç and Kanik have developed dedicated, miniaturized testing setups.

Artificial muscles achieve powerful pulling force

Credit: Courtesy of the researchers

The degree of tightening that occurs when the fiber is heated can be “programmed” by determining how much of an initial stretch to give the fiber. This allows the material to be tuned to exactly the amount of force needed and the amount of temperature change needed to trigger that force.

The fibers are made using a fiber-drawing system, which makes it possible to incorporate other components into the fiber itself. Fiber drawing is done by creating an oversized version of the material, called a preform, which is then heated to a specific temperature at which the material becomes viscous. It can then be pulled, much like pulling taffy, to create a fiber that retains its internal structure but is a small fraction of the width of the preform.

For testing purposes, the researchers coated the fibers with meshes of conductive nanowires. These meshes can be used as sensors to reveal the exact tension experienced or exerted by the fiber. In the future, these fibers could also include heating elements such as optical fibers or electrodes, providing a way of heating it internally without having to rely on any outside heat source to activate the contraction of the “muscle.”

Such fibers could find uses as actuators in robotic arms, legs, or grippers, and in prosthetic limbs, where their slight weight and fast response times could provide a significant advantage.

Some prosthetic limbs today can weigh as much as 30 pounds, with much of the weight coming from actuators, which are often pneumatic or hydraulic; lighter-weight actuators could thus make life much easier for those who use prosthetics. Such fibers might also find uses in tiny biomedical devices, such as a medical robot that works by going into an artery and then being activated,” Anikeeva suggests. “We have activation times on the order of tens of milliseconds to seconds,” depending on the dimensions, she says.

To provide greater strength for lifting heavier loads, the fibers can be bundled together, much as muscle fibers are bundled in the body. The team successfully tested bundles of 100 fibers. Through the fiber drawing process, sensors could also be incorporated in the fibers to provide feedback on conditions they encounter, such as in a prosthetic limb. Örgüç says bundled muscle fibers with a closed-loop feedback mechanism could find applications in robotic systems where automated and precise control are required.

Kanik says that the possibilities for materials of this type are virtually limitless because almost any combination of two materials with different thermal expansion rates could work, leaving a vast realm of possible combinations to explore. He adds that this new finding was like opening a new window, only to see “a bunch of other windows” waiting to be opened.

“The strength of this work is coming from its simplicity,” he says.

The team also included MIT graduate student Georgios Varnavides, postdoc Jinwoo Kim, and undergraduate students Thomas Benavides, Dani Gonzalez, and Timothy Akintlio.

Materials provided by Massachusetts Institute of Technology

Brain computer interface schematic

Elon Musk announces updates on Neuralink to be declared soon

Elon Musk was asked for an update on Neuralink, the neuro-tech company he started in 2016, to which he replied with a tweet saying “Coming Soon.” Though started almost three years ago, there have not been any major announcements from the company. The company has been reported to developing implantable brain-computer interfaces(BCI) and is located at San Francisco, California.

Brain-computer interfaces provide a pathway for direct communication between an advanced brain and an external machine. Research on BCI first started in the 70s at the UCLA, after which it was offered a contract from DARPA. It primarily attempts to restore damaged hearing, eyesight and other motion activities with the help of advanced neuroprosthetics equipment. Neuroprosthetics such as cochlear implant have been widely used in people but they differ in some areas from BCI. While the neuroprosthetics make a connection of any part of the nervous system to a device, BCI attempts to connect the central nervous system( or brain) to a computer.

Neuralink primarily aims to manufacture devices which will help in treating severe brain diseases and brain damage that has been caused by a stroke. In the long run, it aims to make equipment for overall human enhancement.

The inspiration of this company came from a concept in science fiction named Neural Lace, which is in the fictional world created by author Iain M. Banks in his series of books The Culture. In the futuristic world of Culture, there are aliens, advanced beings, humanoids who live in places spread all over our galaxy, Milky Way.

Elon Musk has been quite vocal about the dangers which artificial intelligence pose to the human civilization and he has said that human beings have to augment their brains for survival in the coming times. According to Musk, if we do not develop we can be degraded to the position of servants in the world dominated by AI. So he feels that a solution can be adding an extra layer of AI to our brain.

Neuralink published a paper in 2015 describing a concept for the BCI. It explained the process of augmenting the human brain with a circuit. Charles Lieber, one of the co-authors of the paper from Harvard University mentioned how researchers are trying hard to minimize the differences that exist between electronic and neural circuits.

But the path is filled with dangers such as ethical mistakes, health side effects and scientists have warned that future advancements can result in manipulation of a person’s emotions, thoughts which is certainly not permissible.