Researchers Combine Artificial Eye and Artificial Muscle
Inspired by the human eye, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed an adaptive metalens that is essentially a flat, electronically controlled artificial eye. The adaptive metalens simultaneously controls for three of the major contributors to blurry images: focus, astigmatism, and image shift.[+MORE]
Inspired by the human eye, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed an adaptive metalens that is essentially a flat, electronically controlled artificial eye. The adaptive metalens simultaneously controls for three of the major contributors to blurry images: focus, astigmatism, and image shift.
The research is published in Science Advances.
“This research combines breakthroughs in artificial muscle technology with metalens technology to create a tunable metalens that can change its focus in real time, just like the human eye,” said Alan She, an SEAS graduate student at the Graduate School of Arts and Sciences, and first author of the paper. “We go one step further to build the capability of dynamically correcting for aberrations such as astigmatism and image shift, which the human eye cannot naturally do.”
“This demonstrates the feasibility of embedded optical zoom and autofocus for a wide range of applications, including cell phone cameras, eyeglasses, and virtual and augmented reality hardware,” said Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS and senior author of the paper. “It also shows the possibility of future optical microscopes, which operate fully electronically and can correct many aberrations simultaneously.”
The Harvard Office of Technology Development has protected the intellectual property relating to this project and is exploring commercialization opportunities.
To build the artificial eye, the researchers first needed to scale up the metalens.
Metalenses focus light and eliminate spherical aberrations through a dense pattern of nanostructures, each smaller than a wavelength of light. Earlier metalenses were about the size of a single piece of glitter.
“Because the nanostructures are so small, the density of information in each lens is incredibly high,” said She. “If you go from a 100 micron-size lens to a centimeter-size lens, you will have increased the information required to describe the lens by 10,000. Whenever we tried to scale up the lens, the file size of the design alone would balloon up to gigabytes or even terabytes.”
To solve this problem, the researchers developed a new algorithm to shrink the file size to make the metalens compatible with the technology currently used to fabricate integrated circuits. In a paper recently published in Optics Express, the researchers demonstrated the design and fabrication of metalenses of up to centimeters or more in diameter.
“This research provides the possibility of unifying two industries, semiconductor manufacturing and lens-making, whereby the same technology used to make computer chips will be used to make metasurface-based optical components, such as lenses,” said Capasso.
Discovery should lead the way to lighter, less-bulky cameras, telescopes, and cellphones, SEAS researchers say
Next, the researchers needed to adhere the large metalens to an artificial muscle without compromising its ability to focus light. In the human eye, the lens is surrounded by ciliary muscle, which stretches or compresses the lens, changing its shape to adjust its focal length. Capasso and his team collaborated with David Clarke, Extended Tarr Family Professor of Materials at SEAS and a pioneer in the field of engineering applications of dielectric elastomer actuators, also known as artificial muscles.
The researchers chose a thin, transparent dielectic elastomer with low loss — meaning light travels through the material with little scattering — to attach to the lens. To do so, they needed to develop a platform to transfer and adhere the lens to the soft surface.
“Elastomers are so different in almost every way from semiconductors that the challenge has been how to marry their attributes to create a novel multifunctional device and, especially, how to devise a manufacturing route,” said Clarke. “As someone who worked on one of the first scanning electron microscopes (SEMs) in the mid-1960s, it is exhilarating to be a part of creating an optical microscope with the capabilities of an SEM, such as real-time aberration control.”
The elastomer is controlled by applying voltage. As it stretches, the position of nanopillars on the surface of the lens shift. The metalens can be tuned by controlling both the position of the pillars in relation to their neighbors and the total displacement of the structures. The researchers also demonstrated that the lens can simultaneously focus, control aberrations caused by astigmatisms, and perform image shift.
Together, the lens and muscle are only 30 microns thick.
“All optical systems with multiple components — from cameras to microscopes and telescopes — have slight misalignments or mechanical stresses on their components, depending on the way they were built and their current environment, that will always cause small amounts of astigmatism and other aberrations, which could be corrected by an adaptive optical element,” said She. “Because the adaptive metalens is flat, you can correct those aberrations and integrate different optical capabilities onto a single plane of control.”
Next, the researchers aim to further improve the functionality of the lens and decrease the voltage required to control it.
To read the full story visit the Harvard Gazette website.[+MORE]
Metalenses — flat surfaces that use nanostructures to focus light — have promised to revolutionize optics by replacing the bulky, curved lenses currently used in optical devices with a simple, flat surface, but previously metalenses had been limited in the spectrum of light they could focus well. Now a team of researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) has developed the first single lens that can focus the entire visible spectrum — including white light — in the same spot and in high resolution, a feat previously achieved only by stacking multiple conventional lenses.
The research is published in Nature Nanotechnology.
Focusing the entire visible spectrum and white light — all the colors of the spectrum — is so challenging because each wavelength moves through materials at different speeds. Red wavelengths, for example, move through glass faster than the blue, so the two colors will reach the same location at different times, resulting in different foci. This creates image distortions known as chromatic aberrations.
Cameras and optical instruments use multiple curved lenses of different thicknesses and materials to correct these aberrations, which, of course, adds to a device’s bulk.
“Metalenses have advantages over traditional lenses,” said Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS and senior author of the research. “Metalenses are thin, easy to fabricate, and cost effective. This breakthrough extends those advantages across the whole visible range of light. This is the next big step.”
Harvard’s Office of Technology Development (OTD) has protected the intellectual property relating to this project and is exploring commercialization opportunities.
The metalenses Capasso and his team developed use arrays of titanium dioxide nanofins to equally focus wavelengths of light and eliminate chromatic aberration. Previous research demonstrated that different wavelengths of light could be focused, but at different distances, by optimizing the shape, width, distance, and height of the nanofins. In this latest design, the researchers created units of paired nanofins that control the speed of different wavelengths of light simultaneously. The paired nanofins also control the refractive index on the meta-surface, and are tuned to result in different time delays for the light passing through different fins, ensuring that all wavelengths reach the focal spot at the same time.
“One of the biggest challenges in designing an achromatic broadband lens is making sure that the outgoing wavelengths from all the different points of the metalens arrive at the focal point at the same time,” said Wei-Ting Chen, a postdoctoral fellow at SEAS and first author of the paper. “By combining two nanofins into one element, we can tune the speed of light in the nanostructured material, to ensure that all wavelengths in the visible are focused in the same spot, using a single metalens. This dramatically reduces thickness and design complexity compared to composite standard achromatic lenses.”
“Using our achromatic lens, we are able to perform high-quality, white-light imaging. This brings us one step closer to the goal of incorporating them into common optical devices such as cameras,” said Alexander Zhu, co-author of the study.
Next, the researchers aim to scale up the lens, to about 1 cm in diameter. This would open a whole host of new possibilities, such as applications in virtual and augmented reality.
To read the full story visit the Harvard Gazette website.[+MORE]
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.
“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
“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.
“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.[+MORE]
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.
“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.”[+MORE]
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.
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.[+MORE]
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.
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.
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.
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.
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.[+MORE]
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.”
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.”[+MORE]
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.
“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.[+MORE]