Featured Research

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A thinner, flatter lens

Curved lenses like those in cameras or telescopes are stacked to reduce distortions and clarify images. That’s why high-powered microscopes are so big and telephoto lenses so long. While lens technology has improved, it is still difficult to make a compact and thin lens.

But researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have demonstrated the first flat — or planar — lens that works highly efficiently within the visible spectrum of light, covering the whole range of colors from red to blue.

The lens can resolve nanoscale features separated by distances smaller than the wavelength of light. It uses an ultrathin array of tiny waveguides, known as a metasurface, which bends light as it passes through. The research is described in the journal Science.

Focusing Light

Light passing through the meta-lens is focused by millions of nanostructures. Courtesy of the Capasso Lab

“This technology is potentially revolutionary because it works in the visible spectrum, which means it has the capacity to replace lenses in all kinds of devices, from microscopes to cameras to displays and cell phones,” said Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering, the senior author of the paper. “In the near future, meta-lenses will be manufactured on a large scale at a small fraction of the cost of conventional lenses, using the foundries that mass-produce microprocessors and memory chips.”

“Correcting for chromatic spread over the visible spectrum in an efficient way, with a single flat optical element, was until now out of reach,” said Bernard Kress, partner optical architect at Microsoft, who was not part of the research. “The Capasso Group’s meta-lens developments enable the integration of broadband imaging systems in a very compact form, allowing for next generations of optical sub-systems addressing effectively stringent weight, size, power, and cost issues, such as the ones required for high performance AR/VR [augmented reality/virtual reality] wearable displays.”

In order to focus red, blue, and green light — light in the visible spectrum — the team needed a material that wouldn’t absorb or scatter light, said Rob Devlin, a graduate student in the Capasso Lab and co-author of the paper.

Meta-Lenses at Visible Wavelengths

The Capasso Group has developed a flat lens that works in visible light and can focus light as small as nature allows.

“We needed a material that would strongly confine light with a high refractive index,” he said. “And in order for this technology to be scalable, we needed a material already used in industry.”

The team used titanium dioxide, a material found in everything from paint to sunscreen, to create the nanoscale array of smooth and high-aspect ratio nanostructures that form the heart of the meta-lens.

“We wanted to design a single planar lens with a high numerical aperture, meaning it can focus light into a spot smaller than the wavelength,” said Mohammadreza Khorasaninejad, a postdoctoral fellow in the Capasso Lab and first author of the paper. “The more tightly you can focus light, the smaller your focal spot can be, which potentially enhances the resolution of the image.”

The team designed the array to resolve a structure smaller than a wavelength of light, around 400 nanometers across. At these scales, the meta-lens could provide better focus than a state-of-the art commercial lens.

Imaging of holographic eye

A hologram of an eye, about half a centimeter in diameter, is imaged by the meta-lens. Depending on the distance between the hologram and the meta-lens, the eye appears and disappears. Courtesy of the Capasso Lab

“Normal lenses have to be precisely polished by hand,” said co-author Wei Ting Chen, a postdoctoral fellow in the Capasso Lab. “Any kind of deviation in the curvature, any error during assembling makes the performance of the lens go way down. Our lens can be produced in a single step — one layer of lithography and you have a high-performance lens, with everything where you need it to be.”

“The amazing field of meta-materials brought up lots of new ideas, but few real-life applications have come so far,” said Vladimir M. Shalaev, professor of electrical and computer engineering at Purdue University, who was not involved in the research. “The Capasso Group with their technology-driven approach is making a difference in that regard. This new breakthrough solves one of the most basic and important challenges, making a visible-range meta-lens that satisfies the demands for high numerical aperture and high efficiency simultaneously, which is normally hard to achieve.”

One of the most exciting potential applications, said Khorasaninejad, is in wearable optics such as virtual reality and augmented reality.

“Any good imaging system right now is heavy because the thick lenses have to be stacked on top of each other. No one wants to wear a heavy helmet for a couple of hours,” he said. “This technique reduces weight and volume and shrinks lenses thinner than a sheet of paper. Imagine the possibilities for wearable optics, flexible contact lenses, or telescopes in space.”

The authors have filed patents and are actively pursuing commercial opportunities.

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Advance in high-pressure physics

Nearly a century after it was theorized, Harvard scientists report they have succeeded in creating the rarest material on the planet, which could eventually develop into one of its most valuable.

Thomas D. Cabot Professor of the Natural Sciences Isaac Silvera and postdoctoral fellow Ranga Dias have long sought the material, called atomic metallic hydrogen. In addition to helping scientists answer some fundamental questions about the nature of matter, the material is theorized to have a wide range of applications, including as a room-temperature superconductor. Their research is described in a paper published today in Science.

“This is the Holy Grail of high-pressure physics,” Silvera said of the quest to find the material. “It’s the first-ever sample of metallic hydrogen on Earth, so when you’re looking at it, you’re looking at something that’s never existed before.”

In their experiments, Silvera and Dias squeezed a tiny hydrogen sample at 495 gigapascal (GPa), or more than 71.7 million pounds per square inch, which is greater than the pressure at the center of the Earth. At such extreme pressures, Silvera explained, solid molecular hydrogen, which consists of molecules on the lattice sites of the solid, breaks down, and the tightly bound molecules dissociate to transforms into atomic hydrogen, which is a metal.

While the work creates an important window into understanding the general properties of hydrogen, it also offers tantalizing hints at potentially revolutionary new materials.

“One prediction that’s very important is metallic hydrogen is predicted to be meta-stable,” Silvera said. “That means if you take the pressure off, it will stay metallic, similar to the way diamonds form from graphite under intense heat and pressure, but remain diamonds when that pressure and heat are removed.”

Understanding whether the material is stable is important, Silvera said, because predictions suggest metallic hydrogen could act as a superconductor at room temperatures.

“As much as 15 percent of energy is lost to dissipation during transmission,” he said, “so if you could make wires from this material and use them in the electrical grid, it could change that story.”

A room temperature superconductor, Dias said, could change our transportation system, making magnetic levitation of high-speed trains possible, as well as making electric cars more efficient and improving the performance of many electronic devices. The material could also provide major improvements in energy production and storage. Because superconductors have zero resistance, superconducting coils could be used to store excess energy, which could then be used whenever it is needed.

Metallic hydrogen could also play a key role in helping humans explore the far reaches of space, as a more powerful rocket propellant.

Microscopic images of the stages in the creation of atomic molecular hydrogen: Transparent molecular hydrogen (left) under about 200 gigapascals (GPa) of pressure, which becomes black molecular hydrogen, and finally reflective atomic metallic hydrogen at 495 GPa. Courtesy of Isaac Silvera
Microscopic images of the stages in the creation of atomic molecular hydrogen: Transparent molecular hydrogen (left) at about 200 GPa, which is converted into black molecular hydrogen, and finally reflective atomic metallic hydrogen at 495 GPa. Courtesy of Isaac Silvera

“It takes a tremendous amount of energy to make metallic hydrogen,” Silvera explained. “And if you convert it back to molecular hydrogen, all that energy is released, so that would make it the most powerful rocket propellant known to man, and could revolutionize rocketry.”

The most powerful fuels in use today are characterized by a “specific impulse” (a measure, in seconds, of how fast a propellant is fired from the back of a rocket) of 450 seconds. The specific impulse for metallic hydrogen, by comparison, is theorized to be 1,700 seconds.

“That would easily allow you to explore the outer planets,” Silvera said. “We would be able to put rockets into orbit with only one stage, versus two, and could send up larger payloads, so it could be very important.”

In their experiments, Silvera and Dias turned to one of the hardest materials on Earth, diamond. But rather than natural diamond, Silvera and Dias used two small pieces of carefully polished synthetic diamond and treated them to make them even tougher. Then they mounted them opposite each other in a device known as a diamond anvil cell.

“Diamonds are polished with diamond powder, and that can gouge out carbon from the surface,” Silvera said. “When we looked at the diamond using atomic force microscopy, we found defects, which could cause it to weaken and break.”

The solution, he said, was to use a reactive ion etching process to shave a tiny layer — just five microns thick, or about a tenth the thickness of a human hair — from the diamond’s surface. The diamond was then coated with a thin layer of alumina to prevent the hydrogen from diffusing into the crystal structure and embrittling it.

After more than four decades of work on metallic hydrogen, and nearly a century after it was first theorized, it was thrilling to see the results, Silvera said.

“It was really exciting,” he said. “Ranga was running the experiment, and we thought we might get there, but when he called me and said, ‘The sample is shining,’ I went running down there, and it was metallic hydrogen.”

“I immediately said we have to make the measurements to confirm it, so we rearranged the lab … and that’s what we did.”

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Soft robot helps the heart beat

Harvard University and Boston Children’s Hospital researchers have developed a customizable soft robot that fits around the heart and helps it beat, potentially opening new treatment options for people suffering from heart failure.

The soft robotic sleeve twists and compresses in synch with a beating heart, augmenting cardiovascular functions weakened by heart failure. Unlike currently available devices that assist heart function, Harvard’s soft robotic sleeve does not directly contact blood. This reduces the risk of clotting and eliminates the need for a patient to take potentially dangerous blood thinner medications. The device may one day be able to bridge a patient to transplant or help in cardiac rehabilitation and recovery.

“This research demonstrates that the growing field of soft robotics can be applied to clinical needs and potentially reduce the burden of heart disease and improve the quality of life for patients,” said Ellen T. Roche, the paper’s first author and a former Ph.D. student at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and Wyss Institute of Biologically Inspired Engineering. Roche is currently a postdoctoral fellow at the National University of Ireland.

The research, published in Science Translational Medicine, was a collaboration between SEAS, the Wyss Institute, and Boston Children’s Hospital.

“This work represents an exciting proof-of-concept result for this soft robot, demonstrating that it can safely interact with soft tissue and lead to improvements in cardiac function. We envision many other future applications where such devices can delivery mechanotherapy both inside and outside of the body,” said Conor Walsh, senior author of the paper, John L. Loeb Associate Professor of Engineering and Applied Sciences at SEAS, and core faculty member at the Wyss Institute.

Heart failure affects 41 million people worldwide. Today, some of the treatment options are mechanical pumps called ventricular assist devices (VADs), which pump blood from the ventricles into the aorta, and heart transplants. While VADs are continuously improving, patients are still at high risk for blood clots and stroke.

To create an entirely new device that doesn’t come into contact with blood, Harvard researchers took inspiration from the heart itself. The thin silicone sleeve uses soft pneumatic actuators placed around the heart to mimic the outer muscle layers of the mammalian heart. The actuators twist and compress the sleeve in a motion similar to the beating heart.

The device is tethered to an external pump, which uses air to power the soft actuators.

The sleeve can be customized for each patient, said Roche. If a patient has more weakness on the left side of the heart, for example, the actuators can be tuned to give more assistance there. The pressure of the actuators can also increase or decrease over time, as the patient’s condition evolves.

The sleeve is attached to the heart using a combination of a suction device, sutures, and a gel interface to help with friction between the device and the heart.

In vivo demonstration of cardiac assist

The SEAS and Wyss engineers worked with surgeons at Boston Children’s Hospital to develop the device and determine the best ways to implant and test it on animal models.

“The cardiac field had turned away from idea of developing heart compression instead of blood-pumping VADs due to technological limitations, but now with advancements in soft robotics it’s time to turn back,” said Frank Pigula, a cardiothoracic surgeon and co-corresponding author on the study, who was formerly clinical director of pediatric cardiac surgery at Boston Children’s Hospital and is now a faculty member at the University of Louisville and division chief of pediatric cardiac surgery at Norton Children’s Hospital. “Most people with heart failure do still have some function left; one day the robotic sleeve may help their heart work well enough that their quality of life can be restored.”

More research needs to be done before the sleeve can be implanted in humans, but the research is an important first step toward an implantable soft robot that can augment organ function.

Harvard’s Office of Technology Development has filed a patent application and is actively pursuing commercialization opportunities.

“This research is really significant at the moment because more and more people are surviving heart attacks and ending up with heart failure,” said Roche. “Soft robotic devices are ideally suited to interact with soft tissue and give assistance that can help with augmentation of function, and potentially even healing and recovery.”

The research was co-authored by Markus A. Horvath, Isaac Wamala, Ali Alazmani, Sang-Eun Song, William Whyte, Zurab Machaidze, Christopher J. Payne, James Weaver, Gregory Fishbein, Joseph Kuebler, Nikolay V.Vasilyev, and David J. Mooney.

It was supported by a Translational Research Program grant from Boston Children’s Hospital, a Director’s Challenge Cross-Platform grant from the Wyss Institute for Biologically Inspired Engineering, Harvard School of Engineering and Applied Sciences, and the Science Foundation Ireland.

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Strengthening ties among women in physics

hen Margaret Morris looks around her physics class, sometimes she is the only woman there.

Morris, a senior at Brandeis University, is living the reality for physics in the United States. At a time when women make up the majority of the country’s college students, their numbers still trail male peers in certain fields. And in some disciplines, like physics, women remain a small minority.

Last weekend, 250 physics majors gathered at Harvard to take a collective step toward a new reality.

The Conference for Undergraduate Women in Physics included lab tours, lectures, personal stories, and practical discussions about research, graduate school applications, how to deal with discrimination and implicit bias, and finding mentors.

Margaret Morris, senior at Brandeis University, listens to a presentation in the Aziz Lab during a tour through the labs of the Harvard Science Center organized for the Conference for Undergraduate Women in Physics (CUWiP). Photo by Silvia Mazzocchin
Margaret Morris, a senior at Brandeis University, listens to a presentation at the Conference for Undergraduate Women in Physics. Morris was one of 250 physics majors in attendance. Photo by Silvia Mazzocchin

Organizer Anne Hebert, a Harvard grad student, said the conference was designed to connect participants with a support network that will help them move ahead in the field.

“As an undergraduate, obviously I noticed there weren’t many girls around,” Hebert said. “Every girl in physics has a moment when they turn their head and realize they’re the only girl in the room.”

One of her fellow organizers, Ellen Klein, a Harvard doctoral student, said that as an undergrad at Yale University, she felt supported by faculty members and never experienced blatant gender discrimination. But she has noticed that there have been fewer women as she’s advanced through different academic levels.

A detail in one of the labs of the Harvard Science Center. Photo by Silvia Mazzocchin
Ellen Klein (not pictured), a Harvard Graduate School of Arts and Sciences doctoral student, said she’s noticed fewer women as she’s advanced through different academic levels. Photo by Silvia Mazzocchin

Delilah Gates, also an organizing committee member and Harvard doctoral student, agreed with Klein and Hebert that bias, though often subtle, is still a problem. All three have heard male classmates joke about women and understood in a visceral way that, though real progress has been made, plenty of work remains.

A quantum leap for women

Gates added that as a black woman, she felt a lot of pressure in college to show that her opportunities weren’t handed to her because of race, leaving her temporarily conflicted about applying to graduate school.

“In college, I kind of didn’t anticipate it. I was struck by the pressure I felt because of being an African-American woman and [proving] that no one was handing it to me because I check off a diversity box,” Gates said.

The campus conference, organized through the American Physical Society, was one of 10 that took place across the United States and Canada and the first to be hosted by Harvard.

Suela Restelica, sophomore at Orange County Community College, observes some of the equipments in one of the labs of Applied Physics, during a tour through the labs of the Harvard Science Center organized for the Conference for Undergraduate Women in Physics (CUWiP). Photo by Silvia Mazzocchin
Suela Restelica, a sophomore at Orange County Community College in New York state, joined her fellow physics majors. Photo by Silvia Mazzocchin

Some 1,500 women attended a session somewhere, Hebert said. A workshop titled SPIN UP, for Supporting Inclusion for Underrepresented Peoples, preceded the Harvard conference. The event was aimed at other underrepresented groups in the field, including minorities, students with disabilities, and students from low-income families.

Physics helps solve problems facing humanity, said Masahiro Morii, chair of Harvard’s Physics Department, which provided logistical support for the student-run conference. And, though women make up half the population, they still make up less than 25 percent of physics graduate students.

“Until it’s 50 percent, we’re still wasting a lot of talent that’s out there,” Morii said.

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Seeking a breakthrough on catalysts

They have been a fundamental part of modern industry for more than a century, but the development of new catalysts to speed chemical processes has remained frustratingly hit-or-miss.

Now, a group of Harvard researchers is approaching the problem in an entirely new way.

Working with colleagues at several national laboratories and other partnering institutions, researchers at the Department of Energy-funded Energy Frontier Research Center’s Integrated Mesoscale Architectures for Sustainable Catalysis(IMASC) at Harvard are combining tightly-controlled experimental conditions and computational tools to develop novel methods for developing catalysts and new ways to understand the process of catalysis.

Led by Cynthia Friend, the Theodore William Richards Professor of Chemistry and Professor of Materials Science and director of the Rowland Institute, the IMASC researchers have gained new insight into exactly how catalysis works — findings that could play an important role in the design and development of more energy-efficient catalysts. The work is described in a Dec. 19 paper published in Nature Materials.

“This is really a paradigm shift in catalyst discovery,” Challa S.S.R. Kumar, the program’s managing director, said. “For 100 years or more, this was a trial-and-error process. In recent years, people are striving for a more systematic approach. Our center, through synergistic collaboration between the investigators from the partnering institutions, is establishing new principles for understanding catalytic reactions under very tightly controlled conditions, with computational modeling. These principles are used to develop catalysts that work under real-world conditions.”

With those principles in mind, researchers are currently exploring the use of nanoporous silver-gold alloys as improved catalysts.

“These catalyst materials are designed based on our model systems,” Kumar said.

To aid in the development of catalytic materials, Friend and colleagues from the Lawrence Berkeley, Brookhaven, and Lawrence Livermore national laboratories set out to observe the process of catalysis as it happens. Cutting-edge scientific tools yielded images of the atoms in the material and monitored how the composition of the catalyst surface changed. Microscopy facilities at the Center for Functional Nanomaterials at Brookhaven and the Advanced Light Source at Berkeley were essential for these experiments.

“We know we can design the catalysts and then transmit them to realistic conditions, but we didn’t know how the catalyst materials behave as catalysis is occurring,” Kumar said. “That’s a critical piece of information that has not been taken into consideration when designing new catalysts.

“What we have shown with this paper is that we now have the tools to investigate how catalysts dynamically change just before catalysis, during catalysis, and after catalysis,” he continued. “And these dynamic changes can be correlated to the activity and selectivity of the catalyst.”

Improving industrial chemical processes isn’t the only reason for developing new catalysts.

Nearly one-third of the world’s energy is devoted to the chemical industry, Kumar said, so finding ways to make those processes more efficient — either by speeding them up or by enabling them to take place at lower temperatures — could yield a significant environmental impact.

“There is a huge carbon footprint left by many of these chemical processes, some of which are more than 100 years old,” Kumar said. “If we can reduce the energy budget for those processes … it could have a tremendous impact on energy usage, and dramatically change that carbon footprint. And now we have the tools to do that.”

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Diamonds are a lab’s best friend

It’s one of the purest and most versatile materials in the world, with uses in everything from jewelry to industrial abrasives to quantum science. But a group of Harvard scientists has uncovered a new use for diamonds: tracking neural signals in the brain.

Using atomic-scale quantum defects in diamonds known as nitrogen-vacancy (NV) centers to detect the magnetic field generated by neural signals, scientists working in the lab of Ronald Walsworth, a faculty member in Harvard’s Center for Brain Science and Physics Department, demonstrated a noninvasive technique that can image the activity of neurons.

The work was described in a recent paper in the Proceedings of the National Academy of Sciences, and was performed in collaboration with Harvard faculty members Mikhail (Misha) Lukin and Hongkun Park.

“The idea of using NV centers for sensing neuron magnetic fields began with the initial work of Ron Walsworth and Misha Lukin about 10 years ago, but for a long time our back-of-the-envelope calculations made it seem that the fields would be too small to detect, and the technology wasn’t there yet,” said Jennifer Schloss, a Ph.D. student and co-author of the study.

“This paper is really the first step to show that measuring magnetic fields from individual neurons can be done in a scalable way,” said Ph.D. student and fellow co-author Matthew Turner. “We wanted to be able to model the signal characteristics, and say, based on theory, ‘This is what we expect to see.’ Our experimental results were consistent with these expectations. This predictive ability is important for understanding more complicated neuronal networks.”

At the heart of the system developed by Schloss and Turner, together with postdoctoral scientist John Barry, is a tiny — just 4-by-4 millimeters square and half a millimeter thick — wafer of diamond impregnated with trillions of NV centers.

The system works, Schloss and Turner explained, because the magnetic fields generated by signals traveling in a neuron interact with the electrons in the NV centers, subtly changing their quantum “spin” state. The diamond wafer is bathed in microwaves, which put the NV electrons in a mixture of two spin states. A neuron magnetic field then causes a change in the fraction of spins in one of the two states. Using a laser constrained to the diamond, the researchers can detect this fraction, reading out the neural signal as an optical image, without light entering the biological sample.

In addition to demonstrating that the system works for dissected neurons, Schloss, Turner, and Barry showed that NV sensors could be used to sense neural activity in live, intact marine worms.

“We realized we could just put the whole animal on the sensor and still detect the signal, so it’s completely noninvasive,” Turner said. “That’s one reason using magnetic fields offers an advantage over other methods. If you measure voltage- or light-based signals in traditional ways, biological tissue can distort those signals. With magnetic fields, though the signal gets smaller with stand-off distance, the information is preserved.”

Schloss, Turner, and Barry were also able to show that the neural signals traveled more slowly from the worm’s tail to its head than from head to tail, and their magnetic field measurements matched predictions of this difference in conduction velocity.

While the study proves that NV centers can be used to detect neural signals, Turner said the initial experiments were designed to tackle the most accessible approach to the problem, using robust neurons that produce especially large magnetic fields. The team is already working to further refine the system, with an eye toward improving its sensitivity and pursuing applications to frontier problems in neuroscience. To sense signals from smaller mammalian neurons, Schloss explained, they intend to implement a pulsed magnetometry scheme to realize up to 300 times better sensitivity per volume. The next step, said Turner, is implementing a high-resolution imaging system in hopes of producing real-time, optical images of neurons as they fire.

“We’re looking at imaging networks of neurons over long durations, up to days,” said Schloss. “We hope to use this to understand not just the physical connectivity between neurons, but the functional connectivity — how the signals actually propagate to inform how neural circuits operate over the long term.”

“No tool that exists today can tell us everything we want to know about neuronal activity or be applied to all systems of interest,” Turner said. “This quantum diamond technology lays out a new direction for addressing some of these challenges. Imaging neuron magnetic fields is a largely unexplored area due to previous technological limitations.”

The hope, Schloss said, is that the tool might one day find a home in the labs of biomedical researchers or anyone interested in understanding brain activity.

“We want to understand the brain from the single-neuron level all the way up, so we envision that this could become a tool useful both in biophysics labs and in medical studies,” she said. “It’s noninvasive and fast, and the optical readout could allow for a variety of applications, from studying neurodegenerative diseases to monitoring drug delivery in real time.”

Walsworth credits the leadership of Josh Sanes, the Paul J. Finnegan Family Director of the center, and Kenneth Blum, executive director, for enabling this biological application of quantum diamond technology. “Center for Brain Science leadership provided the essential lab space and a welcoming, interdisciplinary community,” he said. “This special environment allows physical scientists and engineers to translate quantum technology into neuroscience.”

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The first fully 3-D-printed heart-on-a-chip

arvard University researchers have made the first entirely 3-D-printed organ-on-a-chip with integrated sensing. Built by a fully automated, digital manufacturing procedure, the 3-D-printed heart-on-a-chip can be quickly fabricated and customized, allowing researchers to easily collect reliable data for short-term and long-term studies.

This new approach to manufacturing may one day allow researchers to rapidly design organs-on-chips, also known as microphysiological systems, that match the properties of a specific disease or even an individual patient’s cells.

The research is published in Nature Materials.

3-D-printed heart-on-a-chip

“This new programmable approach to building organs-on-chips not only allows us to easily change and customize the design of the system, but also drastically simplifies data acquisition,” said Johan Ulrik Lind, first author of the paper, postdoctoral fellow at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), and researcher at the Wyss Institute for Biologically Inspired Engineering at Harvard University.

Organs-on-chips mimic the structure and function of native tissue and have emerged as a promising alternative to traditional animal testing. However, the fabrication and data collection process for organs-on-chips is expensive and laborious. Currently, these devices are built in cleanrooms using a complex, multistep lithographic process, and collecting data requires microscopy or high-speed cameras.

“Our approach was to address these two challenges simultaneously via digital manufacturing,” said Travis Busbee, co-author of the paper and a graduate student in the lab of Jennifer Lewis, Hansjorg Wyss Professor of Biologically Inspired Engineering, core faculty member of the Wyss Institute, and co-author of the study. “By developing new printable inks for multimaterial 3-D printing, we were able to automate the fabrication process while increasing the complexity of the devices,” Busbee said.

The researchers developed six different inks that integrated soft strain sensors within the microarchitecture of the tissue. In a single, continuous procedure, the team 3-D-printed those materials into a cardiac microphysiological device — a heart on a chip — with integrated sensors.

“We are pushing the boundaries of three-dimensional printing by developing and integrating multiple functional materials within printed devices,” said Lewis. “This study is a powerful demonstration of how our platform can be used to create fully functional, instrumented chips for drug screening and disease modeling.”

The chip contains multiple wells, each with separate tissues and integrated sensors, allowing researchers to study many engineered cardiac tissues at once. To demonstrate the efficacy of the device, the team performed drug studies and longer-term studies of gradual changes in the contractile stress of engineered cardiac tissues, which can occur over the course of several weeks.

“Researchers are often left working in the dark when it comes to gradual changes that occur during cardiac tissue development and maturation because there has been a lack of easy, noninvasive ways to measure the tissue functional performance,” said Lind. “These integrated sensors allow researchers to continuously collect data while tissues mature and improve their contractility. Similarly, they will enable studies of gradual effects of chronic exposure to toxins.”

“Translating microphysiological devices into truly valuable platforms for studying human health and disease requires that we address both data acquisition and manufacturing of our devices,” said Kit Parker, Tarr Family Professor of Bioengineering and Applied Physics at SEAS, who co-authored the study. Parker is also a core faculty member of the Wyss Institute. “This work offers new potential solutions to both of these central challenges.”

To read the full story on the SEAS website.

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The first autonomous, entirely soft robot

A team of Harvard University researchers with expertise in 3-D printing, mechanical engineering, and microfluidics has demonstrated the first autonomous, untethered, entirely soft robot. This small, 3-D-printed robot — nicknamed the “octobot” — could pave the way for a new generation of such machines.

Soft robotics could help revolutionize how humans interact with machines. But researchers have struggled to build entirely compliant robots. Electric power and control systems — such as batteries and circuit boards — are rigid, and until now soft-bodied robots have been either tethered to an off-board system or rigged with hard components.

Robert Wood, the Charles River Professor of Engineering and Applied Sciences, and Jennifer A. Lewis, the Hansjorg Wyss Professor of Biologically Inspired Engineering at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), led the research. Lewis and Wood are also core faculty members of the Wyss Institute for Biologically Inspired Engineering at Harvard University.

“One longstanding vision for the field of soft robotics has been to create robots that are entirely soft, but the struggle has always been in replacing rigid components like batteries and electronic controls with analogous soft systems and then putting it all together,” said Wood. “This research demonstrates that we can easily manufacture the key components of a simple, entirely soft robot, which lays the foundation for more complex designs.”

Introducing the Octobot

The research is described in the journal Nature.

“Through our hybrid assembly approach, we were able to 3-D print each of the functional components required within the soft robot body, including the fuel storage, power, and actuation, in a rapid manner,” said Lewis. “The octobot is a simple embodiment designed to demonstrate our integrated design and additive fabrication strategy for embedding autonomous functionality.”

Octopuses have long been a source of inspiration in soft robotics. These curious creatures can perform incredible feats of strength and dexterity with no internal skeleton.

Harvard’s octobot is pneumatic-based, and so is powered by gas under pressure. A reaction inside the bot transforms a small amount of liquid fuel (hydrogen peroxide) into a large amount of gas, which flows into the octobot’s arms and inflates them like balloons.

And now, the hopping robot

“Fuel sources for soft robots have always relied on some type of rigid components,” said Michael Wehner, a postdoctoral fellow in the Wood lab and co-first author of the paper. “The wonderful thing about hydrogen peroxide is that a simple reaction between the chemical and a catalyst — in this case platinum — allows us to replace rigid power sources.”

To control the reaction, the team used a microfluidic logic circuit based on pioneering work by co-author and chemist George Whitesides, the Woodford L. and Ann A. Flowers University Professor and a core faculty member of the Wyss. The circuit, a soft analog of a simple electronic oscillator, controls when hydrogen peroxide decomposes to gas in the octobot.

Powering the Octobot: A chemical reaction

“The entire system is simple to fabricate. By combining three fabrication methods — soft lithography, molding, and 3-D printing — we can quickly manufacture these devices,” said Ryan Truby, a graduate student in the Lewis lab and co-first author of the paper.

The simplicity of the assembly process paves the way for designs of greater complexity. Next, the Harvard team hopes to design an octobot that can crawl, swim, and interact with its environment.

“This research is a proof of concept,” Truby said. “We hope that our approach for creating autonomous soft robots inspires roboticists, material scientists, and researchers focused on advanced manufacturing.”

The paper was co-authored by Daniel Fitzgerald of the Wyss Institute and Bobak Mosadegh of Cornell University. The research was supported by the National Science Foundation through the Materials Research Science and Engineering Center at Harvard and by the Wyss Institute.

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Toward a better screen

Harvard University researchers have designed more than 1,000 new blue-light-emitting molecules for organic light-emitting diodes (OLEDs) that could dramatically improve displays for televisions, phones, tablets, and more.

OLED screens use organic molecules that emit light when an electric current is applied. Unlike the ubiquitous liquid crystal displays (LCDs), OLED screens don’t require a backlight, meaning the display can be as thin and flexible as a sheet of plastic. Individual pixels can be switched on or off, dramatically improving the screen’s color contrast and energy consumption. OLEDs are already replacing LCDs in high-end consumer devices, but a lack of stable and efficient blue materials has made them less competitive in large displays such as televisions.

The interdisciplinary team of Harvard researchers, in collaboration with Massachusetts Institute of Technology (MIT) and Samsung, developed a large-scale, computer-driven screening process called the Molecular Space Shuttle that incorporates theoretical and experimental chemistry, machine learning, and cheminformatics to quickly identify new OLED molecules that perform as well as, or better than, industry standards.

“People once believed that this family of organic light-emitting molecules was restricted to a small region of molecular space,” said Alán Aspuru-Guzik, professor of chemistry and chemical biology, who led the research. “But by developing a sophisticated molecular builder, using state-of-the art machine learning, and drawing on the expertise of experimentalists, we discovered a large set of high-performing blue OLED materials.”

The research is described in the current issue of Nature Materials.

The biggest challenge in manufacturing affordable OLEDs is emission of the color blue. Like LCDs, OLEDs rely on green, red, and blue sub-pixels to produce every color on screen. But it has been difficult to find organic molecules that efficiently emit blue light. To improve efficiency, OLED producers have created organometallic molecules with expensive transition metals such as iridium to enhance the molecule through phosphorescence. This solution is expensive and it has yet to achieve a stable blue color.

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Aspuru-Guzik and his team sought to replace these organometallic systems with entirely organic molecules.

The team began by building libraries of more than 1.6 million candidate molecules. Then, to narrow the field, researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), led by Ryan Adams, assistant professor of computer science, developed new machine-learning algorithms to predict which molecules were likely to have good outcomes, and prioritize those to be virtually tested. This effectively reduced the computational cost of the search by at least a factor of 10.

“This was a natural collaboration between chemistry and machine learning,” said David Duvenaud, a postdoctoral fellow in the Adams lab and co-author of the paper. “Since the early stages of our chemical design process starts with millions of possible candidates, there’s no way for a human to evaluate and prioritize all of them. So, we used neural networks to quickly prioritize the candidates based on all the molecules already evaluated.”

“Machine-learning tools are really coming of age and starting to see applications in a lot of scientific domains,” said Adams. “This collaboration was a wonderful opportunity to push the state of the art in computer science, while also developing completely new materials with many practical applications. It was incredibly rewarding to see these designs go from machine-learning predictions to devices that you can hold in your hand.”

“We were able to model these molecules in a way that was really predictive,” said Rafael Gómez-Bombarelli, a postdoctoral fellow in the Aspuru-Guzik lab and first author of the paper. “We could predict the color and the brightness of the molecules from a simple quantum chemical calculation and about 12 hours of computing per molecule. We were charting chemical space and finding the frontier of what a molecule can do by running virtual experiments.”

“Molecules are like athletes,” Aspuru-Guzik said. “It’s easy to find a runner, it’s easy to find a swimmer, it’s easy to find a cyclist, but it’s hard to find all three. Our molecules have to be triathletes. They have to be blue, stable, and bright.”

Still, finding these super molecules takes more than computing power — it takes human intuition, said Tim Hirzel, a senior software engineer in the Department of Chemistry and Chemical Biology and co-author of the paper.

To help bridge the gap between theoretical modeling and experimental practice, Hirzel and the team built a Web application for collaborators to explore the results of more than half a million quantum chemistry simulations.

Every month, Gómez-Bombarelli and Jorge Aguilera-Iparraguirre, another co-author and postdoctoral fellow in the Aspuru-Guzik lab, selected the most promising molecules and used their software to create “baseball cards,” profiles containing important information about each molecule. This process identified 2,500 molecules worth a closer look. The team’s experimental collaborators at Samsung and MIT then voted on which molecules were most promising for application. The team nicknamed the voting tool “molecular Tinder” after the popular online dating app.

“We facilitated the social aspect of the science in a very deliberate way,” said Hirzel.

“The computer models do a lot, but the spark of genius is still coming from people,” said Gómez-Bombarelli.

“The success of this effort stems from its multidisciplinary nature,” said Aspuru-Guzik. “Our collaborators at MIT and Samsung provided critical feedback regarding the requirements for the molecular structures.”

“The high-throughput screening technique pioneered by the Harvard team significantly reduced the need for synthesis, experimental characterization, and optimization,” said Marc Baldo, professor of electrical engineering and computer science at MIT and co-author of the paper. “It shows the industry how to advance OLED technology faster and more efficiently.”

After this accelerated design cycle, the team was left with hundreds of molecules that perform as well as, if not better than, state-of-the-art metal-free OLEDs. Applications of this type of molecular screening also extend far beyond OLEDs.

“This research is an intermediate stop in a trajectory toward more and more advanced organic molecules that could be used in flow batteries, solar cells, organic lasers, and more,” said Aspuru-Guzik. “The future of accelerated molecular design is really, really exciting.”

In addition to the authors mentioned, the manuscript was co-authored by Dougal Maclaurin, Martin A. Blood-Forsythe, Hyun Sik Chae, Markus Einzinger, Dong-Gwang Ha, Tony Wu, Georgios Markopoulos, Soonok Jeon, Hosuk Kang, Hiroshi Miyazaki, Masaki Numata, Sunghan Kim, Wenliang Huang, and Seong Ik Hong.

The research was supported by the Samsung Advanced Institute of Technology.

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