<a href="http://eas.caltech.edu/people/mgharib" target="_blank">Mory Gharib</a> (PhD &#39;83), the Hans W. Liepmann Professor of Aeronautics and Bioinspired Engineering in the Division of Engineering and Applied Science, and postdoctoral researcher Chris Roh (MS &#39;13, PhD &#39;17) studied Anisopteran dragonfly larvae, which live in water and both breathe and move by inhaling water, extracting oxygen from it, and then expelling the water back out through a tri-leaflet anal valve that is surprisingly similar in structure to tricuspid human heart valves.&nbsp;The larvae are able to control the retraction of each of the three leaves individually, and this, Gharib and Roh discovered, gives them fine control over the size and symmetry (or asymmetry) of the valve opening.&nbsp;&quot;The dragonfly larva is the only insect that uses jet propulsion to move and the only arthropod known to use reciprocal jetting&mdash;inhaling and exhaling through the same orifice&mdash;for underwater breathing,&quot; says Roh, the lead author of a paper on the larval jets that was published online by the journal Bioinspiration &amp; Biomimeticson May 30.&nbsp;To observe how the larvae directed the flow of water using the leaves on their anal valves, Gharib and Roh set up high-speed cameras around an aquarium filled with a colored dye and tethered 96 dragonfly larvae&mdash;one at a time&mdash;in front of the cameras using dental wax. They found that when the larvae retracted all three leaves, the water jet flows straight out, pushing the animals straight forward. Retracting just one or two leaves, on the other hand, results in an asymmetric flow, which the larvae use when breathing.&quot;The way the dragonfly larvae use their unique adaptation to control the jet direction has previously been overlooked,&quot; says Gharib, senior author of the paper. &quot;The asymmetry control by the larvae is an intriguing jet-vectoring mechanism, different from those of squids or salps that simply point their funnels or siphons in a desired direction.&quot;Like the anus of the dragonfly larvae, heart valves have two or three leaves (depending on the valve) that control the flow. Gharib and Roh intend to use what they have learned from the dragonflies to engineer a new prosthetic multi-leaf heart valve that can direct jets in specific directions that mimic natural blood flow emerging from the valve, which is never perfectly symmetric. Currently, the unnaturally symmetrical flow of blood emerging from prosthetic valves can cause blood clots to form or even be abrasive to the walls of blood vessels. To cope with this unintended side effect of prosthetic heart valves, patients typically must spend the rest of their lives taking blood-thinning medications.&nbsp;&quot;The current heart valve design is a one-size-fits-all, where no patient-specific design is considered, and this causes many post-transplant complications,&quot; Roh says. &quot;We believe that an intentionally off-centered opening of the heart valve to more closely match the patient&#39;s original blood flow will be an important design parameter that can be adjusted based on each patient&#39;s heart morphology.&quot;

Seen as a light-colored plume, water jets out from the back of a larval dragonfly. Credit: Chris Roh and Mory Gharib/Caltech

A new understanding of the mechanics of dragonfly larvae respiration and maneuvering could lead to the next generation of prosthetic heart valves, say Caltech engineers.

Dragonfly Larvae Inspire New Designs for Prosthetic Heart Valves

Implantation of a stent-like flow diverter can offer one option for less invasive treatment of brain aneurysms &ndash; bulges in blood vessels &ndash; but the procedure requires frequent monitoring while the vessels heal. Now, a multi-university research team has demonstrated proof-of-concept for a highly flexible and stretchable sensor that could be integrated with the flow diverter to monitor hemodynamics in a blood vessel without costly diagnostic procedures.The sensor, which uses capacitance changes to measure blood flow, could reduce the need for testing to monitor the flow through the diverter. Researchers, led by Georgia Tech, have shown that the sensor accurately measures fluid flow in animal blood vessels in vitro, and are working on the next challenge: wireless operation that could allow in vivo testing.&nbsp;<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1571290181747-sensor_9577.jpg" style="width: 766px;" class="fr-fic fr-dib">Woon-Hong Yeo, an assistant professor in Georgia Tech&rsquo;s George W. Woodruff School of Mechanical Engineering and Wallace H. Coulter Department of Biomedical Engineering, holds a flow sensor on a stent backbone. (Credit: John Toon, Georgia Tech)&nbsp;The research was reported July 18 in the journal ACS Nano and was supported by multiple grants from Georgia Tech&rsquo;s Institute for Electronics and Nanotechnology, the University of Pittsburgh and the Korea Institute of Materials Science.&nbsp;&ldquo;The nanostructured sensor system could provide advantages for patients, including a less invasive aneurysm treatment and an active monitoring capability,&rdquo; said&nbsp;<a href="http://www.me.gatech.edu/faculty/yeo" target="_blank">Woon-Hong Yeo</a>, an assistant professor in Georgia Tech&rsquo;s&nbsp;<a href="http://www.me.gatech.edu/" target="_blank">George W. Woodruff School of Mechanical Engineering</a> and&nbsp;<a href="http://www.bme.gatech.edu/" target="_blank">Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University</a>. &ldquo;The integrated system could provide active monitoring of hemodynamics after surgery, allowing the doctor to follow up with quantitative measurement of how well the flow diverter is working in the treatment.&rdquo;Cerebral aneurysms occur in up to five percent of the population, with each aneurysm carrying a one percent risk per year of rupturing, noted Youngjae Chun, an associate professor in the Swanson School of Engineering at the University of Pittsburgh. Aneurysm rupture will cause death in up to half of affected patients.&nbsp;Endovascular therapy using platinum coils to fill the aneurysm sac has become the standard of care for most aneurysms, but recently a new endovascular approach &ndash; a flow diverter &ndash; has been developed to treat cerebral aneurysms. Flow diversion involves placing a porous stent across the neck of an aneurysm to redirect flow away from the sac, generating local blood clots within the sac.&ldquo;We have developed a highly stretchable, hyper-elastic flow diverter using a highly-porous thin film nitinol,&rdquo; Chun explained. &ldquo;None of the existing flow diverters, however, provide quantitative, real-time monitoring of hemodynamics within the sac of cerebral aneurysm. Through the collaboration with Dr. Yeo&#39;s group at Georgia Tech, we have developed a smart flow-diverter system that can actively monitor the flow alterations during and after surgery.&rdquo; &nbsp;Repairing the damaged artery takes months or even years, during which the flow diverter must be monitored using MRI and angiogram technology, which is costly and involves injection of a magnetic dye into the blood stream. Yeo and his colleagues hope their sensor could provide simpler monitoring in a doctor&rsquo;s office using a wireless inductive coil to send electromagnetic energy through the sensor. By measuring how the energy&rsquo;s resonant frequency changes as it passes through the sensor, the system could measure blood flow changes into the sac.&ldquo;We are trying to develop a batteryless, wireless device that is extremely stretchable and flexible that can be miniaturized enough to be routed through the tiny and complex blood vessels of the brain and then deployed without damage,&rdquo; said Yeo. &ldquo;It&rsquo;s a very challenging to insert such electronic system into the brain&rsquo;s narrow and contoured blood vessels.&rdquo;<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1571290214140-sensor_0903.jpg" style="width: 753px;" class="fr-fic fr-dib">With gloved fingers for scale, a proof-of-concept flow sensor is shown here on a stent backbone. (Credit: Woon-Hong Yeo, Georgia Tech) The sensor uses a micro-membrane made of two metal layers surrounding a dielectric material, and wraps around the flow diverter. The device is just a few hundred nanometers thick, and is produced using nanofabrication and material transfer printing techniques, encapsulated in a soft elastomeric material.&ldquo;The membrane is deflected by the flow through the diverter, and depending on the strength of the flow, the velocity difference, the amount of deflection changes,&rdquo; Yeo explained. &ldquo;We measure the amount of deflection based on the capacitance change, because the capacitance is inversely proportional to the distance between two metal layers.&rdquo;Because the brain&rsquo;s blood vessels are so small, the flow diverters can be no more than five to ten millimeters long and a few millimeters in diameter. That rules out the use of conventional sensors with rigid and bulky electronic circuits.&ldquo;Putting functional materials and circuits into something that size is pretty much impossible right now,&rdquo; Yeo said. &ldquo;What we are doing is very challenging based on conventional materials and design strategies.&rdquo;The researchers tested three materials for their sensors: gold, magnesium and the nickel-titanium alloy known as nitinol. All can be safely used in the body, but magnesium offers the potential to be dissolved into the bloodstream after it is no longer needed.The proof-of-principle sensor was connected to a guide wire in the in vitro testing, but Yeo and his colleagues are now working on a wireless version that could be implanted in a living animal model. While implantable sensors are being used clinically to monitor abdominal blood vessels, application in the brain creates significant challenges.&ldquo;The sensor has to be completely compressed for placement, so it must be capable of stretching 300 or 400 percent,&rdquo; said Yeo. &ldquo;The sensor structure has to be able to endure that kind of handling while being conformable and bending to fit inside the blood vessel.&rdquo;

A proof-of-concept flow sensor is shown here on a stent backbone. (Credit: John Toon, Georgia Tech)

Implantation of a stent-like flow diverter can offer one option for less invasive treatment of brain aneurysms – bulges in blood vessels – but the procedure requires frequent monitoring while the vessels heal.

Integrated Sensor Could Monitor Brain Aneurysm Treatment

3D printed tracheal splints are shown around a model of a patient’s trachea. The splints are designed to be absorbed into the body, allowing for expansion of the trachea and bronchus. (Credit: Rob Felt, Georgia Tech)

Children’s Healthcare of Atlanta has performed Georgia’s first-ever procedure to place 3D-printed tracheal splints in a pediatric patient.

3D-Printed Tracheal Splints Used in Groundbreaking Pediatric Surgery

Rear view of the ankle-assisting exosuits with its soft robotic elements and the cable that transfers mechanical power from actuators operated from the hip to the ankle join. (Image courtesy of the Rolex Awards/Fred Merz)

A soft wearable robotic suit promotes normal walking in stroke patients, opening new approaches to gait re-training and rehabilitation

Post-stroke patients reach terra firma with exosuit technology

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

healthcare

Latest Posts

Dragonfly Larvae Inspire New Designs for Prosthetic Heart Valves

Integrated Sensor Could Monitor Brain Aneurysm Treatment

3D-Printed Tracheal Splints Used in Groundbreaking Pediatric Surgery

Post-stroke patients reach terra firma with exosuit technology

Engineers design color-changing compression bandage