Friday, 23 February 2018 17:02

Seeking materials that match the brain

Polina Anikeeva explores ways to make neural probes that are compatible with delicate biological tissues.
MIT Profile Anikeeva PRESS Web
Polina Anikeeva was born in St. Petersburg, Russia, then known as Leningrad, where two inspiring scientists helped propel her toward a career at MIT. She develops materials to help researchers probe the mysteries of the brain. Image, Bryce Vickmark.

Polina Anikeeva was born in Leningrad, USSR, but grew up in St. Petersburg, Russia; the city’s name reverted to its original form after the fall of the Soviet Union. While in school there, she encountered two inspiring scientists who helped propel her toward a career at MIT, where she now develops cutting-edge materials to help researchers probe the mysteries of the brain.

Anikeeva’s parents are both engineers, and she became interested very early on in figuring out how to make things that hadn’t been made before. She has pursued that passion through all her work — as the Class of 1942 Associate Professor in Materials Science and Engineering and in her other activities. She has been an active climber and runner (she ran her third Boston Marathon last year), and as an avid artist she occasionally creates paintings to illustrate her scientific research or help her students visualize scientific concepts. 

One of her earliest influences, she says, was Mikhail Georgievich Ivanov, the founder of a small math and science magnet school she attended in St. Petersburg, and her physics teacher there. “He was just a brilliant physics teacher and educated a lot of scientists who are now scattered across the world. He was a scientist himself and had worked in a research lab. But then he realized that his real passion and talent was educating kids,” she recalls.

She met her next significant mentor during her years as an undergraduate at the St. Petersburg State Polytechnic University, when she worked with Tatiana Birshtein, a professor of polymer physics at the Institute of Macromolecular Compounds of the Russian Academy of Sciences. “She was generous and adventurous enough to essentially get me a UROP position in her lab. And I had no idea how prominent she was, but as time went on it became clear that she’s actually one of the pioneers of polymer physics and went on to win the L’Oréal-UNESCO Award for Women in Science the same year as Millie Dresselhaus. ... So I got really lucky to work with someone of that stature very early on.”

From there, Anikeeva spent her senior year at the Swiss Federal Institute of Technology in Zurich and then went on to an internship at Los Alamos National Laboratory in New Mexico, where her work took a turn, introducing her to spectroscopy, nanomaterials, and quantum dot solar cells. As she was trying to decide between graduate programs in physics or chemistry, she met an intern from MIT’s Department of Materials Science and Engineering, and decided to try that as a way of combining those fields. She completed her doctorate at MIT in materials science and engineering, and last year earned tenure as an associate professor in that department. 

“It was very clear that I should go to MIT,” she says, “not because the faculty were really smart — faculty are pretty smart everywhere. It was because the students were really inspiring. They were really committed to their research but also had a really broad understanding of what is going on around them, from a research perspective and also from how it builds into the real world. … I wanted to be surrounded by really remarkable people.”

One of those people she met at MIT was to become her partner: a fellow faculty member, Warren Hoburg, who was in the aeronautics and astronautics department. While their relationship was very convenient with both of them working at MIT, she says, it suddenly became more complicated last year, when he was selected as part of NASA’s 2017 class of new astronauts. Now, “we’ll have to commute between Houston and Boston,” she says.

Soon after earning her PhD working with light-emitting quantum dots, Anikeeva determined that she was not interested in research aimed at making incremental improvements. “What I really wanted to do was not just improve devices that exist. I wanted to build devices that didn’t exist,” she says. She decided that biology was an area where a materials scientist could make significant contributions in developing new devices that could have a direct benefit for humanity.

Her first foray into moving from physics into biology produced an immediate surprise. The first time she felt a mouse brain, she was startled by its pudding-like consistency that was so different from the stiff, brittle materials she was used to handling in her work in optoelectronics. That immediately began a quest that has been a major theme of her research ever since: developing materials that can be used as probes to deliver stimuli deep into the brain and that are flexible enough to match the movements of the surrounding brain tissue without causing damage.

Already, she and her students have developed multipurpose fibers that can deliver electrical, optical, and chemical signals to individual neurons in the brain, while matching the stretchiness and flexibility of brain tissue. They have also developed similar flexible implantable fibers that can be implanted into the spinal cord. These devices can be used for basic research to analyze spinal neural pathways and responses in animals that are awake and active, whereas existing methods with stiff implants require the animals to be anesthetized and immobilized.

Since then, she has extended her research to include ways of stimulating localized brain areas without any invasive contact at all, using magnetic fields to activate nanoparticles injected into specific locations. The system could be used for brain research and potentially for disease treatment, Anikeeva says.

The work is constantly exciting, she says. “There’s really nothing like it, to see a neural interface experiment work, because it’s not like waiting for a gene to be expressed or for a tissue to change in some way. You know when neurons fire — you see it right away. And this is really very addictive. I think all my students, even though they’re all engineers working on materials or devices, they all essentially can’t wait to introduce their tools into the animal model or into the tissue model to see those neurons flash.”

Anikeeva sees a fertile future in this field in which she has already done groundbreaking work. “The nervous system is just really a huge [scientific] problem, and being able to develop tools to understand it and study it I think will be a task sufficient for a lifetime. That’s especially true if we start looking at not just the brain but also interactions between the brain and the peripheral nervous system, because it turns out we are wired to the max. Every single one of our organs is wired, and we have no idea of what that wiring is doing.”

“So I think taken all together,” she says, “there are many, many lifetimes of work in this field where a materials scientist can contribute.”back to newsletter

– David L. Chandler | MIT News Office
February 18, 2018

 

Thursday, 22 February 2018 14:44

Mapping photonic systems needs through 2035

AIM Photonics participants to take long view at Roadmap Meeting at MIT March 26-27, 2018.
AIM Photonics Academy Fall 2017 Web
Tom Marrapode, Director of Advanced Technology Development at Molex Optical Solutions Group, speaks about work on board-level optical interconnects at the AIM Photonics Academy fall 2017 meeting. Photo, Melissa Renzi, SUNY Polytechnic Institute.

Industry and academic leaders from across the country and around the world will gather at MIT on Monday and Tuesday, March 26-27, 2018, for the spring AIM Photonics Technical Roadmap Meeting, titled “Photonic Integration 2035: Economics, Technology and Manufacturing.”

This marks the 20th year that the Photonics Roadmap meetings have been held. Begun under the Microphotonics Center at MIT as gatherings of 50 experts, the Roadmap meetings have grown to more than 200 people representing the technology supply chain, from materials to systems to end-users.

“This is the premier gathering of leaders implementing photonics technology,” says Professor Lionel Kimerling, executive of AIM Photonics Academy, which is the MIT-based education and workforce development arm of AIM Photonics. AIM Photonics is one of 14 public-private manufacturing innovation institutes created as part of a federal initiative to revitalize American manufacturing.

Participants will “gauge the system requirements and technology needs to maintain the ongoing exponential product ramp in the field,” Kimerling says. The March meeting includes time for breakout groups that focus on different technology areas covered in the Roadmap, where companies that normally compete against one another can participate in productive pre-competitive discussions.

“I have been very engaged in AIM Photonics Academy’s Roadmap meetings and technical working groups,” said Yi Qian, vice president of product management at MRSI. “I want to be part of the discussion with some of the world’s top experts of where integrated photonics is headed.”

At the spring meeting, AIM Photonics Academy and the International Electronics Manufacturing Initiative (iNEMI) plan to incubate Application Interest Groups (AIGs) in sensors, data centers, analog RF signal applications, LIDAR and phased array imaging. These industry-led initiatives have the potential to turn into AIM Photonics-funded technical projects.

The Integrated Photonic Systems Roadmap (IPSR), which can be downloaded from the iNEMI and AIM Photonics Academy websites, is more than 400 pages long, and continues to be updated to include new chapters and findings. Close to 1,000 people from more than 300 organizations in 17 countries have participated in the creation of the Roadmap.

AIM Photonics Academy and iNEMI are also collaborating on a Roadmap workshop at the Optical Fiber Communication Conference March 12, 2018, in San Diego. At that conference, Kimerling and Director of Roadmapping Robert Pfahl will discuss grand challenges and key needs for commercially viable, high-volume manufacturing of photonic-enabled functionality.
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Julie Diop, Materials Research Laboratory, AIM Photonics Academy
February 26, 2018

AIM Photonics Smit Group DP Spring 2017 Web
Eindhoven University of Technology Professor Meint Smit speaks about “Photonic Integrated Circuits: How Foundries Transform Prototyping” during the spring 2017 AIM Photonics Roadmap meeting at MIT. Photo, Denis Paiste, MIT MRL

MIT researchers create predictable patterns from unpredictable carbon nanotubes.

Integrating nanoscale fibers such as carbon nanotubes (CNTs) into commercial applications, from coatings for aircraft wings to heat sinks for mobile computing, requires them to be produced in large scale and at low cost. Chemical vapor deposition is a promising approach to manufacture CNTs in the needed scales, but it produces CNTs that are too sparse and compliant for most applications. Applying and evaporating a few drops of a liquid such as acetone to the CNTs is an easy, cost-effective method to more tightly pack them together and increase their stiffness, but until now, there was no way to forecast the geometry of these CNT cells.

MIT researchers have now developed a systematic method to predict the two-dimensional patterns CNT arrays form after they are packed together, or densified, by evaporating drops of either acetone or ethanol. CNT cell size and wall stiffness grow proportionally with cell height, they report in a Communication in the Feb. 14, 2018, issue of Physical Chemistry Chemical Physics [PCCP].

View the embedded image gallery online at:
https://mrl.mit.edu/index.php/tag/nanoscience#sigProId61dc469920

One way to think of this CNT behavior is to imagine how entangled fibers such as wet hair or spaghetti collectively reinforce each other. The larger this entangled region is, the higher its resistance to bending will be. Similarly, longer CNTs can better reinforce one another in a cell wall. The researchers also find that CNT binding strength to the base on which they are produced, in this case, silicon, makes an important contribution to predicting the cellular patterns that these CNTs will form.

“These findings are directly applicable to industry because when you use CVD, you get nanotubes that have curvature, randomness and are wavy, and there is a great need for a method that can easily mitigate these defects without breaking the bank,” AeroAstro Postdoc Itai Y. Stein [SM '13, PhD '16] says. Co-authors include materials science and engineering graduate student Ashley L. Kaiser, MechE Postdoc Kehang Cui, and senior author Brian L. Wardle, Professor of Aeronautics and Astronautics.

“From our previous work on aligned carbon nanotubes (CNTs) and their composites, we learned that more tightly packing the CNTs is a highly effective way to engineer their properties,” Wardle says. “The challenging part is to develop a facile way of doing this at scales that are relevant to commercial aircraft (100’s of meters), and the predictive capabilities that we developed here are a large step in that direction."

Detailed measurements

Carbon nanotubes are highly desirable because of their thermal, electrical, and mechanical properties, which are directionally dependent. Earlier work in Wardle’s lab demonstrated that waviness reduces the stiffness of CNT arrays by as little as 100 times, and up to 100,000 times. The technical term for this stiffness, or ability to bend without breaking, is elastic modulus. Carbon nanotubes are from 1,000 to 10,000 times longer than they are thick, so they deform principally along their length.

For an earlier Applied Physics Letters paper, Stein and colleagues used nanoindentation techniques to measure stiffness of aligned carbon nanotube arrays and found them to be 1,000 to 10,000 times less stiff than the theoretical stiffness of individual carbon nanotubes. Stein, Wardle and former visiting MIT graduate student Hülya Cebeci also developed a theoretical model explaining changes at different packing densities of the nanofibers. [Cebeci is now a professor of aerospace engineering at Istanbul Technical University.]

The new work shows that CNTs compacted by the capillary forces from first wetting them with acetone or ethanol and then evaporating the liquid also produces CNTs that are 100s to 1000s of times less stiff than expected by theoretical values. This capillary effect, known as elastocapillarity, is similar to a how a sponge often dries into a more compact shape after being wetted and then dried.

“Our findings all point to the fact that the CNT wall modulus is much lower than the normally assumed value for perfect CNTs because the underlying CNTs are not straight. Our calculations show that the CNT wall is at least two orders of magnitude less stiff than we expect for straight CNTs, so we can conclude that the CNTs must be wavy,” Stein says.

Heat adds strength

The researchers used a heating technique to increase the adhesion of their original, undensified CNT arrays to their silicon wafer substrate. CNTs densified after heat treatment were about four times harder to separate from the silicon base than untreated CNTs. Kaiser and Stein, who share first authorship of the paper, are currently developing an analytical model to describe this phenomenon and tune the adhesion force, which would further enable prediction and control of such structures.

“Many applications of vertically aligned carbon nanotubes (VACNTs), such as electrical interconnects, require much denser arrays of nanotubes than what is typically obtained for as-grown VACNTs synthesized by chemical vapor deposition (CVD),” says Mostafa Bedewy, assistant professor at the University of Pittsburgh, who was not involved in this work. “Hence, methods for post-growth densification, such as those based on leveraging elastocapillarity have previously been shown to create interesting densified CNT structures. However, there is still a need for a better quantitative understanding of the factors that govern cell formation in densified large-area arrays of VACNTs. The new study by the authors contributes to addressing this need by providing experimental results, coupled with modeling insights, correlating parameters such as VACNT height and VACNT-substrate adhesion to the resulting cellular morphology after densification.”

“There are still remaining questions about how the spatial variation of CNT density, tortuosity [twist], and diameter distribution across the VACNT height affects the capillary densification process, especially that vertical gradients of these features can be different when comparing two VACNT arrays having different heights,” Bedewy notes. “Further work incorporating spatial mapping of internal VACNT morphology would be illuminating, although it will be challenging as it requires combining a suite of characterization techniques.”

The variety of length scales and physical and chemical mechanisms present in carbon nanotubes and other nanoscale materials makes it easy to either oversimplify or to focus on the wrong mechanism, Stein cautions. “Our current predictive capabilities from this paper are very useful, because we give other researchers in the field a pragmatic solution for how they could at least get some predictability, so that they can accelerate their materials design process, and have a working prototype sooner,” Stein says. “In the meantime, while other groups can utilize this new information, which is the best we can do given our current data, we are going to work on collecting a richer dataset that will allow us to investigate the underlying mechanisms and thereby enable even better prediction in the future,” he adds.

Picturesque patterns

Graduate student Kaiser, who was a 2016 MIT Summer Scholar, analyzed the densified CNT arrays with scanning electron microscopy [SEM] in the MIT Materials Research Laboratory’s NSF-MRSEC supported Shared Experimental Facilities. While gently applying liquid to the CNT arrays in this study caused them to densify into predictable cells, vigorously immersing the CNTs in liquid imparts much stronger forces to them, forming randomly shaped CNT networks. “When we first started exploring densification methods, I found that this forceful technique densified our CNT arrays into highly unpredictable and interesting patterns. As seen optically and via SEM, these patterns often resembled animals, faces, and even a heart – it was a bit like searching for shapes in the clouds,” Kaiser says. A colorized version of her optical image showing a CNT heart is featured on the cover of the Feb. 14, 2018, print edition of Physical Chemistry Chemical Physics, which coincides with Valentine’s Day.

“I think there is an underlying beauty in this nanofiber self-assembly and densification process, in addition to its practical applications,” Kaiser adds. “The CNTs densify so easily and quickly into patterns after simply being wet by a liquid. Being able to accurately quantify this behavior is exciting, as it may enable the design and manufacture of scalable nanomaterials.”

The ultimate goal of this research is to be able to precisely predict the post-processing nanofiber pattern beforehand, Kaiser says. “When we have a specific end-goal structure in mind, such as this cellular pattern, we’d like to be able to accurately design its geometry based on our process,” Kaiser says. “With that capability, this liquid-based densification technique could be used to create large-scale nanofiber systems for a wide range of applications.”

This work made use of the MIT Materials Research Laboratory Shared Experimental Facilities, which are supported in part by the MRSEC Program of the National Science Foundation, and MIT Microsystems Technology Laboratories. This research was supported in part by Airbus, ANSYS, Embraer, Lockheed Martin, Saab AB, Saertex, and TohoTenax through MIT's Nano-Engineered Composite Aerospace Structures Consortium and by NASA through the Space Technology Research Institute for Ultra-Strong Composites by Computational Design.

Denis Paiste, Materials Research Laboratory
February 14, 2018
 

Wednesday, 07 February 2018 20:14

Microfluidics from LEGO bricks

MIT engineers have just introduced an element of fun into microfluidics.

Video, Melanie Gonick/MIT

The field of microfluidics involves minute devices that precisely manipulate fluids at submillimeter scales. Such devices typically take the form of flat, two-dimensional chips, etched with tiny channels and ports that are arranged to perform various operations, such as mixing, sorting, pumping, and storing fluids as they flow.

Now the MIT team, looking beyond such lab-on-a-chip designs, has found an alternative microfluidics platform in “interlocking, injection-molded blocks” — or, as most of us know them, LEGO bricks.

“LEGOs are fascinating examples of precision and modularity in everyday manufactured objects,” says Anastasios John Hart, associate professor of mechanical engineering at MIT. 

Indeed, LEGO bricks are manufactured so consistently that no matter where in the world they are found, any two bricks are guaranteed to line up and snap securely in place. Given this high degree of precision and consistency, the MIT researchers chose LEGO bricks as the basis for a new modular microfluidic design.

In a paper published in the journal Lab on a Chip, the team describes micromilling small channels into LEGOs and positioning the outlet of each “fluidic brick” to line up precisely with the inlet of another brick. The researchers then sealed the walls of each modified brick with an adhesive, enabling modular devices to be easily assembled and reconfigured.

Each brick can be designed with a particular pattern of channels to perform a specific task. The researchers have so far engineered bricks as fluid resistors and mixers, as well as droplet generators. Their fluidic bricks can be snapped together or taken apart, to form modular microfluidic devices that perform various biological operations, such as sorting cells, mixing fluids, and filtering out molecules of interest.

“You could then build a microfluidic system similarly to how you would build a LEGO castle — brick by brick,” says lead author Crystal Owens, a graduate student in MIT’s Department of Mechanical Engineering. “We hope in the future, others might use LEGO bricks to make a kit of microfluidic tools.”

Modular mechanics

Hart, who is also director of MIT’s Laboratory for Manufacturing and Productivity and the Mechanosynthesis Group, primarily focuses his research on new manufacturing processes, with applications ranging from nanomaterials to large-scale 3-D printing.

“Over the years, I’ve had peripheral exposure to the field of microfluidics and the fact that prototyping microfluidic devices is often a difficult, time-consuming, resource-intensive process,” Hart says.

Owens, who worked in a microfluidics lab as an undergraduate, had seen firsthand the painstaking efforts that went into engineering a lab on a chip. After joining Hart’s group, she was eager to find a way to simplify the design process.

Most microfluidic devices contain all the necessary channels and ports to perform multiple operations on one chip. Owens and Hart looked for ways to, in essence, explode this one-chip platform and make microfluidics modular, assigning a single operation to a single module or unit. A researcher could then mix and match microfluidic modules to perform various combinations and sequences of operations.

In casting around for ways to physically realize their modular design, Owens and Hart found the perfect template in LEGO bricks, which are about as long as a typical microfluidic chip.

“Because LEGOs are so inexpensive, widely accessible, and consistent in their size and repeatability of mounting, disassembly, and assembly, we asked whether LEGO bricks could be a way to create a toolkit of microfluidic or fluidic bricks,” Hart says.

Building from an idea

To answer this question, the team purchased a set of standard, off-the-shelf LEGO bricks and tried various ways to introduce microfluidic channels into each brick. The most successful method turned out to be micromilling, a well-established technique commonly used to drill extremely fine, submillimeter features into metals and other materials.

Owens used a desktop micromill to first mill a simple, 500-micron-wide channel into the side wall of a standard LEGO brick. She then taped a clear film over the wall to seal it and pumped fluid through the brick’s newly milled channel. She observed that the fluid successfully flowed through the channel, demonstrating the brick functioned as a flow resistor — a device that allows very small amounts of fluid to flow through.

Using this same technique, she fabricated a fluid mixer by milling a horizontal, Y-shaped channel, and sending a different fluid through each arm of the Y. Where the two arms met, the fluids successfully mixed. Owens also turned a LEGO brick into a drop generator by milling a T-shaped pattern into its wall. As she pumped fluid through one end of the T, she found that some of the liquid dropped down through the middle, forming a droplet as it exited the brick.

To demonstrate modularity, Owens built a prototype onto a standard LEGO baseplate consisting of several bricks, each designed to perform a different operation as fluid is pumped through. In addition to making the fluid mixer and droplet generator, she also outfitted a LEGO brick with a light sensor, precisely positioning the sensor to measure light as fluid passed through a channel at the same location.

Owens says the hardest part of the project was figuring out how to connect the bricks together, without fluid leaking out. While LEGO bricks are designed to snap securely in place, there is nevertheless a small gap between bricks, measuring between 100 and 500 microns. To seal this gap, Owens fabricated a small O-ring around each inlet and outlet in a brick.

“The O-ring fits into a small circle milled into the brick surface. It’s designed to stick out a certain amount, so when another brick is placed beside it, it compresses and creates a reliable fluid seal between the bricks. This works simply by placing one brick next to another,” Owens says. “My goal was to make it straightforward to use.”

View the embedded image gallery online at:
https://mrl.mit.edu/index.php/tag/nanoscience#sigProIdf24fc59c4a

“An easy way to build”

The researchers note just a couple drawbacks to their method. At the moment, they are able to fabricate channels that are tens of microns wide. However, some microfluidic operations require much smaller channels, which cannot be made using micromilling techniques. Also, as LEGO bricks are made from thermoplastics, they likely cannot withstand exposure to certain chemicals that are sometimes used in microfluidic systems.

“We’ve been experimenting with different coatings we could put on the surface to make LEGO bricks, as they are, compatible with different fluids,” Owens says. “LEGO-like bricks could also be made out of other materials, such as polymers with high temperature stability and chemical resistance.”

For now, a LEGO-based microfluidic device could be used to manipulate biological fluids and perform tasks such as sorting cells, filtering fluids, and encapsulating molecules in individual droplets. The team is currently designing a website that will contain information on how others can design their own fluidic bricks using standard LEGO pieces.

“Our method provides an accessible platform for prototyping microfluidic devices,” Hart says. “If the kind of device you want to make, and the materials you work with, are suitable for this kind of modular design, this is an easy way to build a microfluidic device for lab research.”

This research was supported in part by a National Science Foundation Graduate Research Fellowship, the MIT Mechanical Engineering Department Ascher H. Shapiro Fellowship, the MIT Lincoln Laboratory Advanced Concepts Committee, a 3M Faculty Award, and the National Science Foundation EAGER/Cybermanufacturing Program. 

Jennifer Chu | MIT News Office
January 30, 2018

Tuesday, 19 December 2017 14:36

Engineers create plants that glow

Illumination from nanobionic plants might one day replace some electrical lighting.

 

MIT Glowing Plants Web
Illumination of a book (“Paradise Lost,” by John Milton) with the nanobionic light-emitting plants (two 3.5-week-old watercress plants). The book and the light-emitting watercress plants were placed in front of a reflective paper to increase the influence from the light emitting plants to the book pages. Image, Seon-Yeong Kwak

Imagine that instead of switching on a lamp when it gets dark, you could read by the light of a glowing plant on your desk.

MIT engineers have taken a critical first step toward making that vision a reality. By embedding specialized nanoparticles into the leaves of a watercress plant, they induced the plants to give off dim light for nearly four hours. They believe that, with further optimization, such plants will one day be bright enough to illuminate a workspace.

“The vision is to make a plant that will function as a desk lamp — a lamp that you don’t have to plug in. The light is ultimately powered by the energy metabolism of the plant itself,” says Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT and the senior author of the study.

This technology could also be used to provide low-intensity indoor lighting, or to transform trees into self-powered streetlights, the researchers say. MIT postdoc Seon-Yeong Kwak is the lead author of the study, which appears in the journal Nano Letters.

Nanobionic plants

Plant nanobionics, a new research area pioneered by Strano’s lab, aims to give plants novel features by embedding them with different types of nanoparticles. The group’s goal is to engineer plants to take over many of the functions now performed by electrical devices. The researchers have previously designed plants that can detect explosives and communicate that information to a smartphone, as well as plants that can monitor drought conditions.

Lighting, which accounts for about 20 percent of worldwide energy consumption, seemed like a logical next target. “Plants can self-repair, they have their own energy, and they are already adapted to the outdoor environment,” Strano says. “We think this is an idea whose time has come. It’s a perfect problem for plant nanobionics.”

To create their glowing plants, the MIT team turned to luciferase, the enzyme that gives fireflies their glow. Luciferase acts on a molecule called luciferin, causing it to emit light. Another molecule called co-enzyme A helps the process along by removing a reaction byproduct that can inhibit luciferase activity.

The MIT team packaged each of these three components into a different type of nanoparticle carrier. The nanoparticles, which are all made of materials that the U.S. Food and Drug Administration classifies as “generally regarded as safe,” help each component get to the right part of the plant. They also prevent the components from reaching concentrations that could be toxic to the plants.

The researchers used silica nanoparticles about 10 nanometers in diameter to carry luciferase, and they used slightly larger particles of the polymers PLGA and chitosan to carry luciferin and coenzyme A, respectively. To get the particles into plant leaves, the researchers first suspended the particles in a solution. Plants were immersed in the solution and then exposed to high pressure, allowing the particles to enter the leaves through tiny pores called stomata.

Particles releasing luciferin and coenzyme A were designed to accumulate in the extracellular space of the mesophyll, an inner layer of the leaf, while the smaller particles carrying luciferase enter the cells that make up the mesophyll. The PLGA particles gradually release luciferin, which then enters the plant cells, where luciferase performs the chemical reaction that makes luciferin glow.

Video: Melanie Gonick/MIT

The researchers’ early efforts at the start of the project yielded plants that could glow for about 45 minutes, which they have since improved to 3.5 hours. The light generated by one 10-centimeter watercress seedling is currently about one-thousandth of the amount needed to read by, but the researchers believe they can boost the light emitted, as well as the duration of light, by further optimizing the concentration and release rates of the components.

Plant transformation

Previous efforts to create light-emitting plants have relied on genetically engineering plants to express the gene for luciferase, but this is a laborious process that yields extremely dim light. Those studies were performed on tobacco plants and Arabidopsis thaliana, which are commonly used for plant genetic studies. However, the method developed by Strano’s lab could be used on any type of plant. So far, they have demonstrated it with arugula, kale, and spinach, in addition to watercress.

For future versions of this technology, the researchers hope to develop a way to paint or spray the nanoparticles onto plant leaves, which could make it possible to transform trees and other large plants into light sources.

“Our target is to perform one treatment when the plant is a seedling or a mature plant, and have it last for the lifetime of the plant,” Strano says. “Our work very seriously opens up the doorway to streetlamps that are nothing but treated trees, and to indirect lighting around homes.”

The researchers have also demonstrated that they can turn the light off by adding nanoparticles carrying a luciferase inhibitor. This could enable them to eventually create plants that shut off their light emission in response to environmental conditions such as sunlight, the researchers say.

The research was funded by the U.S. Department of Energy.

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Anne Trafton | MIT News Office 
December 12, 2017

 

Wednesday, 01 November 2017 17:43

A magical dimension

Engineering at the nanoscale opens new doors to control optical, electronic and magnetic behaviors of materials and enable new multi-functional devices

Materials Day Panel 9584 DP Web
MIT MRL External Advisory Board Chair Julia Phillips [far left] moderated the Materials Day Symposium panel on “Frontiers in Materials Research.” She was joined by [from second left] Professors Karen Gleason, Caroline Ross, Timothy Swager, and Vladimir Bulović. The session was held Wednesday, Oct. 11, 2017.

Newly discovered optical, electronic and magnetic behaviors at the nanoscale, multifunctional devices that integrate with living systems, and the predictive power of machine learning are driving innovations in materials science, a panel of MIT professors told the MIT Materials Research Laboratory [MRL] Materials Day Symposium.

“The development of new material sets is a key to the launch of new physical technologies,” Professor Vladimir Bulović, founding director of MIT.nano, said. “Once we get down to the nanoscale, we can start inducing quantum phenomena that were never quite accessible. So that scale between 1 nanometer, the typical size of a molecule, and on the order of, let’s say, 20 nanometers, that’s a magical dimension, where you can fine tune your optical, electronic and magnetic properties.”

Professor Caroline Ross, Associate Head of the Department of Materials Science and Engineering, cited a trend of harnessing nature to self assemble complex structures. “As we want to make things smaller and smaller, we need to have nature helping out,” she said. Ross noted progress on a range of new multi-functional materials that use, for example, extremely low voltage levels  to control magnetism or that use strain to control electronic properties. “All of these can enable new kinds of devices from those materials, so you can imagine devices which are smart that can have memory or logic functions, that can have analog instead of just digital type of behavior, that can work together to make smart circuits. … The difficulties of integrating those types of materials will be well paid for by the new sorts of functionality we can get from the devices we make.”

MIT MRL External Advisory Board Chair Julia Phillips moderated the Materials Day Symposium panel on Wednesday, Oct. 11, 2017. Phillips is a former Sandia National Laboratories executive.

Professor Timothy Swager, Director of the Deshpande Center, said the expectation that new medical devices, for example, are compatible with our bodies demands different requirements than previous generations of electronics. “Thinking about how we interface complex dynamic chemically reactive systems with a material is really a very important area that, I think, will continue to be of importance and many good discoveries are going to come about as result of the interest in that area,” he said.

Associate Provost and Professor Karen Gleason spoke of the growing influence of machine learning on materials advances and the potential for one-dimensional and two-dimensional materials to provide better computers and memory storage. “It’s going be incredible for materials discovery as we learn how to use machine learning to predict what materials are optimal, but there’s also a credible place for materials in making this technology grow. Now computational power and memory and databases have gotten large enough that the predictive power is actually great.”

“The biggest component is you need the data so you need all of these sensors for accurate positioning, for detection of gases, for health. People want wearables,” Gleason said. “So I think this is an enormous field with tremendous impact in many different ways that materials can play.”

Bulović said while it takes a lot of perseverance to implement a new idea on the nanoscale, “It’s important to highlight that the invention of an idea happens in a moment, that eureka moment, but to actually scale that idea up so a million people can hold it in their hands, that takes a decade sometimes, especially if it’s in the materials space. Recognition of that is important in order to support the evolution of the new ideas.”

The annual Materials Day Symposium was hosted for the first time by the MIT Materials Research Laboratory, which formed from the merger of the Materials Processing Center and the Center for Materials Science and Engineering, effective Oct. 1, 2017. The MIT MRL will work hand-in-hand with MIT.nano, the central research facility being built in the heart of the MIT campus due to open in June 2018. MIT will receive a $2.5 million gift from the Arnold and Mabel Beckman Foundation to help develop a state-of-the-art cryo-electron microscopy (cryo-EM) center to be housed at the MIT.nano facility.

“I don’t think we can underestimate the value of the tool sets in providing us the direction to what we need to do to advance life as we know it,” Bulović said. “I get struck by the example of DNA … It took 80-plus years to obtain the first inkling that there was something twisted inside our cells. Then we debated for another decade, is this thing really a twisted molecule inside our cells. If you add it all up, 80, 90 years of debate. Today that’s reduced to a couple of hours of work by one graduate student who can take a cell, pull out a nucleus, put it under a scanning tunneling microscope or cryo electron microscope and see a twisted molecule we call DNA now.”

Swager noted that biologists also will use MIT.nano. “They are going to be using the cryo-EM in the basement, so nano is not only for engineers and molecule builders. … I think that’s going to be really exciting and where that fusion leads us, who knows.”

Moderator Phillips asked the panelists what tool sets that would like to see in MIT.nano. Gleason said she would like to see chemical vapor deposition for thin polymer films. Ross said that MIT needs to be at the forefront for materials characterization tools. “We need to have the best tools to do the best work,” Ross said. She would like to see MIT.nano get the best possible electron microscope and advanced deposition tools for oxide molecular beam epitaxy and building up complex materials layer by layer. Swager said it is important for the shared facility to house tools for rapid prototyping and fabrication of devices.back to newsletter

Denis Paiste, Materials Research Laboratory
November 27, 2017

Related: Poster Highlights

Interdisciplinary materials science model offers key to progress

Monday, 23 October 2017 15:07

A new approach to ultrafast light pulses

Unusual fluorescent materials could be used for rapid light-based communications systems.

MIT FastLight Emit 1 Daily
In this image, light strikes a molecular lattice deposited on a metal substrate. The molecules can quickly exchange energy with the metal below, a mechanism that leads to a much faster response time for the emission of fluorescent light from the lattice. Courtesy of the researchers

Two-dimensional materials called molecular aggregates are very effective light emitters that work on a different principle than typical organic light-emitting diodes (OLEDs) or quantum dots. But their potential as components for new kinds of optoelectronic devices has been limited by their relatively slow response time. Now, researchers at MIT, the University of California at Berkeley, and Northeastern University have found a way to overcome that limitation, potentially opening up a variety of applications for these materials.

The findings are described in the journal Proceedings of the National Academy of Sciences, in a paper by MIT associate professor of mechanical engineering Nicholas X. Fang, postdocs Qing Hu and Dafei Jin, and five others.

The key to enhancing the response time of these 2-D molecular aggregates (2DMA), Fang and his team found, is to couple that material with a thin layer of a metal such as silver. The interaction between the 2DMA and the metal that is just a few nanometers away boosts the speed of the material’s light pulses more than tenfold. 

Read more at the MIT News Office.

David L. Chandler | MIT News Office
Sept. 18, 2017