CAMBRIDGE, Mass. — As a cucumber plant grows, it sprouts tightly coiled tendrils that search out helps with a purpose to pull the plant upward. This ensures the plant receives as a lot daylight publicity as attainable. Now, researchers on the Massachusetts Institute of Know-how have discovered a solution to imitate this coiling-and-pulling mechanism to provide contracting fibers that could possibly be used as synthetic muscular tissues for robots, prosthetic limbs, or different mechanical and biomedical functions.
Whereas many alternative approaches have been used for creating artificial muscles, together with hydraulic methods, servo motors, shape-memory metals, and polymers that reply to stimuli, all of them have limitations, together with excessive weight or gradual response instances. The brand new fiber-based system, against this, is extraordinarily light-weight and might reply in a short time, the researchers say. The findings are being reported in the present day within the journal Science.
The brand new fibers have been developed by MIT postdoc Mehmet Kanik and graduate scholar Sirma Örgüç, working with professors Polina Anikeeva, Yoel Fink, Anantha Chandrakasan, and C. Cem Taşan. The group additionally included MIT graduate scholar Georgios Varnavides, postdoc Jinwoo Kim, and undergraduate college students Thomas Benavides, Dani Gonzalez, and Timothy Akintlio. They’ve used a fiber-drawing approach to mix two dissimilar polymers right into a single strand of fiber.
The important thing to the method is mating collectively two supplies which have very completely different thermal enlargement coefficients — that means they’ve completely different charges of enlargement when they’re heated. This is identical precept utilized in many thermostats, for instance, utilizing a bimetallic strip as a approach of measuring temperature. Because the joined materials heats up, the aspect that wishes to develop sooner is held again by the opposite materials. In consequence, the bonded materials curls up, bending towards the aspect that’s increasing extra slowly.
Utilizing two completely different polymers bonded collectively, a really stretchable cyclic copolymer elastomer and a a lot stiffer thermoplastic polyethylene, Kanik, Örgüç and colleagues produced a fiber that, when stretched out to a number of instances its unique size, naturally types itself into a good coil, similar to the tendrils that cucumbers produce.
Synthetic muscular tissues shock
However what occurred subsequent really got here as a shock when the researchers first skilled it. “There was loads of serendipity on this,” Anikeeva recalled.
As quickly as Kanik picked up the coiled fiber for the primary time, the heat of his hand alone triggered the fiber to curve up extra tightly. Following up on that remark, he discovered that even a small enhance in temperature might make the coil tighten up, producing a surprisingly sturdy pulling power. Then, as quickly because the temperature went again down, the fiber returned to its unique size.
In later testing, the group confirmed that this means of contracting and increasing could possibly be repeated 10,000 instances “and it was nonetheless going sturdy,” Anikeeva stated.
One of many causes for that longevity, she stated, is that “all the pieces is working beneath very reasonable circumstances,” together with low activation temperatures. Only a 1-degree Celsius enhance may be sufficient to begin the fiber contraction.
The fibers can span a variety of sizes, from just a few micrometers (millionths of a meter) to a couple millimeters (thousandths of a meter) in width, and might simply be manufactured in batches as much as a whole bunch of meters lengthy. Assessments have proven that a single fiber is able to lifting a great deal of as much as 650 instances its personal weight. For these experiments on particular person fibers, Örgüç and Kanik have developed devoted, miniaturized testing setups.
The diploma of tightening that happens when the fiber is heated may be “programmed” by figuring out how a lot of an preliminary stretch to present the fiber. This enables the fabric to be tuned to precisely the quantity of power wanted and the quantity of temperature change wanted to set off that power.
The fibers are made utilizing a fiber-drawing system, which makes it attainable to include different parts into the fiber itself. Fiber drawing is completed by creating an outsized model of the fabric, referred to as a preform, which is then heated to a selected temperature at which the fabric turns into viscous. It could possibly then be pulled, very like pulling taffy, to create a fiber that retains its inner construction however is a small fraction of the width of the preform.
For testing functions, the researchers coated the fibers with meshes of conductive nanowires. These meshes can be utilized as sensors to disclose the precise pressure skilled or exerted by the fiber. Sooner or later, these fibers might additionally embody heating parts corresponding to optical fibers or electrodes, offering a approach of heating it internally with out having to depend on any exterior warmth supply to activate the contraction of the “muscle.”
Such synthetic muscle fibers might discover makes use of as actuators in robotic arms, legs, or grippers, and in prosthetic limbs, the place their slight weight and quick response instances might present a major benefit.
Some prosthetic limbs in the present day can weigh as a lot as 30 kilos, with a lot of the load coming from actuators, which are sometimes pneumatic or hydraulic; lighter-weight actuators might thus make life a lot simpler for individuals who use prosthetics.
“Such fibers may also discover makes use of in tiny biomedical gadgets, corresponding to a medical robotic that works by going into an artery after which being activated,” Anikeeva stated. “We have now activation instances on the order of tens of milliseconds to seconds,” relying on the scale.
To offer better energy for lifting heavier hundreds, the fibers may be bundled collectively, a lot as muscle fibers are bundled within the physique. The group efficiently examined bundles of 100 fibers.
By way of the fiber-drawing course of, sensors may be included within the fibers to supply suggestions on circumstances they encounter, corresponding to in a prosthetic limb. Örgüç stated bundled muscle fibers with a closed-loop suggestions mechanism might discover functions in robotic methods the place automated and exact management are required.
Kanik stated that the probabilities for supplies of this sort are nearly limitless, as a result of nearly any mixture of two supplies with completely different thermal enlargement charges might work, leaving an enormous realm of attainable combos to discover. He added that this new discovering was like opening a brand new window, solely to see “a bunch of different home windows” ready to be opened.
“The energy of this work is coming from its simplicity,” he stated.
The work was supported by the Nationwide Institute of Neurological Issues and Stroke and the Nationwide Science Basis.
Editor’s notice: This text republished with permission from MIT Information.