biomimetics

Robots perform many tasks that humans can&rsquo;t or don&#39;t want to perform, getting around on intricately designed wheels and limbs. If they tip over, however, they are rendered almost useless. A team of University of Illinois mechanical engineers and entomologists are looking to click beetles, who can right themselves without the use of their legs, to solve this robotics challenge.The researchers presented their findings at Living Machines 2017: The 6th International Conference on Biomimetic and Biohybrid Systems at Stanford University, and later won second place in a student and faculty research competition at the international BIOMinnovate Challenge, in Paris, France &ndash; a research expo that showcases biologically-inspired design in engineering, medicine and architecture.<iframe src="https://www.youtube.com/embed/9ozz2jRfBUk?&wmode=opaque" allowfullscreen="" class="fr-draggable" style="width: 766px; height: 406px;" frameborder="0"></iframe> &ldquo;This idea came to life when a group of insect physiology students decided to take a closer look at what makes click beetles jump as part of a class project,&rdquo; said <a href="https://www.life.illinois.edu/entomology/index.html" target="_blank">department of entomology</a> research scientist and study co-author <a href="https://www.life.illinois.edu/entomology/faculty/alleyne.html" target="_blank">Marianne Alleyne.</a>The beetles have a unique hinge-like mechanism between their heads and abdomens that makes a clicking sound when initiated and allows them to flip into the air and back onto their feet when they are knocked over, Alleyne said.&ldquo;Very little research had been performed on these beetles, and I thought this legless jumping mechanism would be a perfect candidate for further exploration in the field of bioinspiration,&rdquo; said Alleyne, who teaches a bioinspiration design course with <a href="https://mechanical.illinois.edu/" target="_blank">mechanical science and engineering</a> professor, co-author and lead investigator <a href="https://mechanical.illinois.edu/directory/faculty/awissa" target="_blank">Aimy Wissa</a>.The researchers looked at several species of click beetles, ranging in size from a few just few millimeters to several centimeters in length.&ldquo;Each insect goes through an assembly line of analyses that involve basic characterization, high-speed filming to observe the jump and measurements in the <a href="https://publish.illinois.edu/tribology/" target="_blank">Materials Tribiology Lab</a> with co-author and mechanical science and engineering professor <a href="http://mechanical.illinois.edu/directory/profile/acd" target="_blank">Alison Dunn</a>, to determine how much force it takes to overcome the friction of the hinge within an individual beetles jumping mechanism,&rdquo; Wissa said. &ldquo;We observe, model and validate each stage of the jump with the hopes that we can later integrate them into a self-righting robot.&rdquo;<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1568998642025-118939.jpg" style="width: 766px;" class="fr-fic fr-dib">The University of Illinois click beetle robotics team. Front row, from left: Professor Aimy Wissa, Aidan Garrett, Luis Urrutia, Ophelia Bolmin and professor Alison Dunn. Back row, from left: Isandro Malik, Xander Hazel, Robert Chapa, Harmen Alleyne, Chengfang Duan and research scientist Marianne Alleyne. Garrett, Malik and H. Alleyne are University of Illinois Laboratory High School students. Photo by L. Brian StaufferThe group has already built several prototypes of a hinge-like, spring-loaded device that will eventually be incorporated into a robot, the researchers said.&ldquo;This study is a two-way street &ndash; engineers are informing the biologists and vice versa,&rdquo; Wissa said. &ldquo;We look forward to seeing where this research will take us and are very proud of the attention it received at the BIOMinnovate Challenge expo.&rdquo;

Click beetles can jump without the aid of their limbs when they are tipped onto their backsides. A team of University of Illinois researchers are examining this mechanism to engineer self-righting robots.  Photo by L. Brian Stauffer

Robots perform many tasks that humans can’t or don't want to perform, getting around on intricately designed wheels and limbs. If they tip over, however, they are rendered almost useless.

Click beetles inspire design of self-righting robots

Compression therapy is a standard form of treatment for patients who suffer from venous ulcers and other conditions in which veins struggle to return blood from the lower extremities. Compression stockings and bandages, wrapped tightly around the affected limb, can help to stimulate blood flow. But there is currently no clear way to gauge whether a bandage is applying an optimal pressure for a given condition.Now engineers at MIT have developed pressure-sensing photonic fibers that they have woven into a typical compression bandage. As the bandage is stretched, the fibers change color. Using a color chart, a caregiver can stretch a bandage until it matches the color for a desired pressure, before, say, wrapping it around a patient&rsquo;s leg.The photonic fibers can then serve as a continuous pressure sensor &mdash; if their color changes, caregivers or patients can use the color chart to determine whether and to what degree the bandage needs loosening or tightening.&ldquo;Getting the pressure right is critical in treating many medical conditions including venous ulcers, which affect several hundred thousand patients in the U.S. each year,&rdquo; says Mathias Kolle, assistant professor of mechanical engineering at MIT. &ldquo;These fibers can provide information about the pressure that the bandage exerts. We can design them so that for a specific desired pressure, the fibers reflect an easily distinguished color.&rdquo;Kolle and his colleagues have published their results in the journal Advanced Healthcare Materials. Co-authors from MIT include first author Joseph Sandt, Marie Moudio, and Christian Argenti, along with J. Kenji Clark of the Univeristy of Tokyo, James Hardin of the United States Air Force Research Laboratory, Matthew Carty of Brigham and Women&rsquo;s Hospital-Harvard Medical School, and Jennifer Lewis of Harvard University.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1568994301001-single-fiber-stretch.gif" style="width: 766px;" class="fr-fic fr-dib">Natural inspirationThe color of the photonic fibers arises not from any intrinsic pigmentation, but from their carefully designed structural configuration. Each fiber is about 10 times the diameter of a human hair. The researchers fabricated the fiber from ultrathin layers of transparent rubber materials, which they rolled up to create a jelly-roll-type structure. Each layer within the roll is only a few hundred nanometers thick.In this rolled-up configuration, light reflects off each interface between individual layers. With enough layers of consistent thickness, these reflections interact to strengthen some colors in the visible spectrum, for instance red, while diminishing the brightness of other colors. This makes the fiber appear a certain color, depending on the thickness of the layers within the fiber.&ldquo;Structural color is really neat, because you can get brighter, stronger colors than with inks or dyes just by using particular arrangements of transparent materials,&rdquo; Sandt says. &ldquo;These colors persist as long as the structure is maintained.&rdquo;The fibers&rsquo; design relies upon an optical phenomenon known as &ldquo;interference,&rdquo; in which light, reflected from a periodic stack of thin, transparent layers, can produce vibrant colors that depend on the stack&rsquo;s geometric parameters and material composition. Optical interference is what produces colorful swirls in oily puddles and soap bubbles. It&rsquo;s also what gives peacocks and butterflies their dazzling, shifting shades, as their feathers and wings are made from similarly periodic structures.&ldquo;My interest has always been in taking interesting structural elements that lie at the origin of nature&rsquo;s most dazzling light manipulation strategies, to try recreating and employing them in useful applications,&rdquo; Kolle says.<img src="blob:https://www.wevolver.com/6c22c5d1-56bb-4ed0-a5ce-9b2933c079ca" style="width: 766px;" class="fr-fic fr-dib">A multilayered approachThe team&rsquo;s approach combines known optical design concepts with soft materials, to create dynamic photonic materials.While a postdoc at Harvard in the group of Professor Joanna Aizenberg, Kolle was inspired by the work of Pete Vukusic, professor of biophotonics at the University of Exeter in the U.K., on&nbsp;Margaritaria nobilis,&nbsp;a tropical plant that produces extremely shiny blue berries. The fruits&rsquo; skin is made up of cells with a periodic cellulose structure, through which light can reflect to give the fruit its signature metallic blue color.Together, Kolle and Vukusic sought ways to translate the fruit&rsquo;s photonic architecture into a useful synthetic material. Ultimately, they fashioned multilayered fibers from stretchable materials, and assumed that stretching the fibers would change the individual layers&rsquo; thicknesses, enabling them to tune the fibers&rsquo; color. The results of these first efforts were published in&nbsp;Advanced Materials in 2013.When Kolle joined the MIT faculty in the same year, he and his group, including Sandt, improved on the photonic fiber&rsquo;s design and fabrication. In their current form, the fibers are made from layers of commonly used and widely available transparent rubbers, wrapped around highly stretchable fiber cores. Sandt fabricated each layer using spin-coating, a technique in which a rubber, dissolved into solution, is poured onto a spinning wheel. Excess material is flung off the wheel, leaving a thin, uniform coating, the thickness of which can be determined by the wheel&rsquo;s speed.For fiber fabrication, Sandt formed these two layers on top of a water-soluble film on a silicon wafer. He then submerged the wafer, with all three layers, in water to dissolve the water-soluble layer, leaving the two rubbery layers floating on the water&rsquo;s surface. Finally, he carefully rolled the two transparent layers around a black rubber fiber, to produce the final colorful photonic fiber.&shy;&shy;Reflecting pressureThe team can tune the thickness of the fibers&rsquo; layers to produce any desired color tuning, using standard optical modeling approaches customized for their fiber design.&ldquo;If you want a fiber to go from yellow to green, or blue, we can say, &lsquo;This is how we have to lay out the fiber to give us this kind of [color] trajectory,&rsquo;&rdquo; Kolle says. &ldquo;This is powerful because you might want to have something that reflects red to show a dangerously high strain, or green for &lsquo;ok.&rsquo; We have that capacity.&rdquo;The team fabricated color-changing fibers with a tailored, strain-dependent color variation using the theoretical model, and then stitched them along the length of a conventional compression bandage, which they previously characterized to determine the pressure that the bandage generates when it&rsquo;s stretched by a certain amount.The team used the relationship between bandage stretch and pressure, and the correlation between fiber color and strain, to draw up a color chart, matching a fiber&rsquo;s color (produced by a certain amount of stretching) to the pressure that is generated by the bandage.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1568995401582-MIT-Bandage-Pressure-02.jpg" style="width: 766px;" class="fr-fic fr-dib">As the bandage is stretched, the fibers change color. Courtesy of the researchersTo test the bandage&rsquo;s effectiveness, Sandt and Moudio enlisted over a dozen student volunteers, who worked in pairs to apply three different compression bandages to each other&rsquo;s legs: a plain bandage, a bandage threaded with photonic fibers, and a commercially-available bandage printed with rectangular patterns. This bandage is designed so that when it is applying an optimal pressure, users should see that the rectangles become squares.Overall, the bandage woven with photonic fibers gave the clearest pressure feedback. Students were able to interpret the color of the fibers, and based on the color chart, apply a corresponding optimal pressure more accurately than either of the other bandages.The researchers are now looking for ways to scale up the fiber fabrication process. Currently, they are able to make fibers that are several inches long. Ideally, they would like to produce meters or even kilometers of such fibers at a time.&ldquo;Currently, the fibers are costly, mostly because of the labor that goes into making them,&rdquo; Kolle says. &ldquo;The materials themselves are not worth much. If we could reel out kilometers of these fibers with relatively little work, then they would be dirt cheap.&rdquo;Then, such fibers could be threaded into bandages, along with textiles such as athletic apparel and shoes as color indicators for, say, muscle strain during workouts. Kolle envisions that they may also be used as remotely readable strain gauges for infrastructure and machinery.&ldquo;Of course, they could also be a scientific tool that could be used in a broader context, which we want to explore,&rdquo; Kolle says.

Engineers at MIT have developed pressure-sensing photonic fibers that they have woven into a typical compression bandage  Courtesy of the researchers

Bandage is threaded with photonic fibers that change color to signal pressure level.

Engineers design color-changing compression bandage

The work blurs the boundary between materials and robots. In the self-propelled devices, the material itself makes the machine function. "Our examples show that we can use structured materials that deform in response to environmental cues, to control and propel robots," says Daraio, professor of mechanical engineering and applied physics in Caltech's Division of Engineering and Applied Science, and corresponding author of a paper unveiling the robots that appears in the Proceedings of the National Academy of Sciences&nbsp;on May 15.The new propulsion system relies on strips of a flexible polymer that is curled when cold and stretches out when warm. The polymer is positioned to activate a switch inside the robot's body, that is in turn attached to a paddle that rows it forward like a rowboat.The switch is made from a bistable element, which is a component that can be stable in two distinct geometries. In this case, it is built from strips of an elastic material that, when pushed on by the polymer, snaps from one position to another.<iframe src="https://www.youtube.com/embed/tBxb1A6boTI?&amp;wmode=opaque" allowfullscreen="" class="fr-draggable" style="width: 767px; height: 439px;" frameborder="0"></iframe>When the cold robot is placed in warm water, the polymer stretches out, activates the switch, and the resulting sudden release of energy paddles the robot forward. The polymer strips can also be "tuned" to give specific responses at different times: that is, a thicker strip will take longer to warm up, stretch out, and ultimately activate its paddle than a thinner strip. This tunability allows the team to design robots capable of turning and moving at different speeds.The research builds on previous work by Daraio and Dennis Kochmann, professor of aerospace at Caltech. They used chains of <a href="http://www.caltech.edu/news/utility-instability-51629" target="_blank">bistable elements to transmit signals and build computer-like logic gates</a>.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1564499883153-Screenshot_2019-07-30+Harnessing+bistability+for+directional+propulsion+of+soft%2C+untethered+robots+-+5698+full+pdf%281%29.png" style="width: 766px;" class="fr-fic fr-dib">In the latest iteration of the design, Daraio's team and collaborators were able to link up the polymer elements and switches in such a way to make a four-paddled robot propel itself forward, drop off a small payload (in this case, a token with a Caltech seal emblazoned on it), and then paddle backward.&nbsp;"Combining simple motions together, we were able to embed programming into the material to carry out a sequence of complex behaviors," says Caltech postdoctoral scholar Osama R. Bilal, co-first author of the PNASpaper. In the future, more functionalities and responsivities can be added, for example using polymers that respond to other environmental cues, like pH or salinity. Future versions of the robots could contain chemical spills or, on a smaller scale, deliver drugs, the researchers say.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1564499825448-1.jpg" style="width: 766px;" class="fr-fic fr-dib">Currently, when the bistable elements snap and release their energy, they must be manually reset in order to work again. Next, the team plans to explore ways to redesign the bistable elements so that they are self-resetting when water temperature shifts again—making them potentially capable of swimming on indefinitely, so long as water temperature keeps fluctuating.The PNAS&nbsp;paper is titled <a href="http://resolver.caltech.edu/CaltechAUTHORS:20180515-101708023" target="_blank">"Harnessing bistability for directional propulsion of soft, untethered robots."</a> Daraio and Bilal collaborated with Tian Chen and Kristina Shea from ETH in Zurich. This research was supported by the Army Research Office and an ETH postdoctoral fellowship to Bilal.

 An artist's rendering of the new design for a robot that uses material deformation to propel itself through water. 

Engineers have developed robots capable of self-propulsion without using any motors, servos, or power supply. Instead, these first-of-their-kind devices paddle through water as the material they are constructed from deforms with temperature changes.

Self propelling robots

The android called Kannon Mindar. Photo by Richard Atrero de Guzman 

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