Nurmikko and Donoghue join U.S. BRAIN initiative

Neuroscientist John Donoghue and engineer Arto Nurmikko were on hand at the White House Tuesday morning, April 2, as President Barack Obama announced a new “Grand Challenge” initiative called BRAIN — Brain Research through Advancing Innovative Neurotechnologies. Donoghue, who directs the Brown Institute for Brain Science and is also a researcher at the Providence VA Medical Center, is part of a group

of scientists that has helped catalyze the idea of developing the tools and techniques needed to measure and sense brain activity at the scale of the neural networks that produce thoughts, behaviors, and (when they are not working properly) disease. Scientists today can study smaller scales of dozens of neurons with electrodes or very large-scale brain activity with MRI scans, but this crucial middle scale of thousands or millions of neurons is currently out of reach. Donoghue will serve on an advisory committee to National Institutes of Health Director Francis Collins to help shape the initiative’s development.

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Brown unveils novel wireless brain sensor

In a significant advance for brain-machine interfaces, engineers at Brown University have developed a novel wireless, broadband, rechargeable, fully implantable brain sensor that has performed well in animal models for more than a year. They describe the result in the Journal of Neural Engineering and at a conference this week.

PROVIDENCE, R.I. [Brown University] — A team of neuroengineers based at Brown University has developed a fully implantable and rechargeable wireless brain sensor capable of relaying real-time broadband signals from up to 100 neurons in freely moving subjects. Several copies of the novel low-power device, described in the Journal of Neural Engineering, have been performing well in animal models for more than year, a first in the brain-computer interface field. Brain-computer interfaces could help people with severe paralysis control devices with their thoughts.

Cortex communication
Engineers Arto Nurmikko and Ming Yin examine their
prototype wireless, broadband neural sensing device.
Credit: Fred Field for Brown University

Arto Nurmikko, professor of engineering at Brown University who oversaw the device’s invention, is presenting it this week at the 2013 International Workshop on Clinical Brain-Machine Interface Systems in Houston.

“This has features that are somewhat akin to a cell phone, except the conversation that is being sent out is the brain talking wirelessly,” Nurmikko said.

Neuroscientists can use such a device to observe, record, and analyze the signals emitted by scores of neurons in particular parts of the animal model’s brain.

Meanwhile, wired systems using similar implantable sensing electrodes are being investigated in brain-computer interface research to assess the feasibility of people with severe paralysis moving assistive devices like robotic arms or computer cursors by thinking about moving their arms and hands.

This wireless system addresses a major need for the next step in providing a practical brain-computer interface,” said neuroscientist John Donoghue, the Wriston Professor of Neuroscience at Brown University and director of the Brown Institute for Brain Science.

Tightly packed technology

David Borton
"The first fully implanted microsystem operated
wirelessly for more than 12 months in large animal
models - a milestone."

In the device, a pill-sized chip of electrodes implanted on the cortex sends signals through uniquely designed electrical connections into the device’s laser-welded, hermetically sealed titanium “can.” The can measures 2.2 inches (56 mm) long, 1.65 inches (42 mm) wide, and 0.35 inches (9 mm) thick. That small volume houses an entire signal processing system: a lithium ion battery, ultralow-power integrated circuits designed at Brown for signal processing and conversion, wireless radio and infrared transmitters, and a copper coil for recharging — a “brain radio.” All the wireless and charging signals pass through an electromagnetically transparent sapphire window.

In all, the device looks like a miniature sardine can with a porthole.

But what the team has packed inside makes it a major advance among brain-machine interfaces, said lead author David Borton, a former Brown graduate student and postdoctoral research associate who is now at Ecole Polytechnique Federale Lausanne in Switzerland.

“What makes the achievement discussed in this paper unique is how it integrated many individual innovations into a complete system with potential for neuroscientific gain greater than the sum of its parts,” Borton said. “Most importantly, we show the first fully implanted microsystem operated wirelessly for more than 12 months in large animal models — a milestone for potential [human] clinical translation.”

The device transmits data at 24 Mbps via 3.2 and 3.8 Ghz microwave frequencies to an external receiver. After a two-hour charge, delivered wirelessly through the scalp via induction, it can operate for more than six hours.

“The device uses less than 100 milliwatts of power, a key figure of merit,” Nurmikko said.

Co-author Ming Yin, a Brown postdoctoral scholar and electrical engineer, said one of the major challenges that the team overcame in building the device was optimizing its performance given the requirements that the implant device be small, low-power and leak-proof, potentially for decades.

“We tried to make the best tradeoff between the critical specifications of the device, such as power consumption, noise performance, wireless bandwidth and operational range,” Yin said. “Another major challenge we encountered was to integrate and assemble all the electronics of the device into a miniaturized package that provides long-term hermeticity (water-proofing) and biocompatibility as well as transparency to the wireless data, power, and on-off switch signals.”

With early contributions by electrical engineer William Patterson at Brown, Yin helped to design the custom chips for converting neural signals into digital data. The conversion has to be done within the device, because brain signals are not produced in the ones and zeros of computer data.

Ample applications

The team worked closely with neurosurgeons to implant the device in three pigs and three rhesus macaque monkeys. The research in these six animals has been helping scientists better observe complex neural signals for as long as 16 months so far. In the new paper, the team shows some of the rich neural signals they have been able to record in the lab. Ultimately this could translate to significant advances that can also inform human neuroscience.

Current wired systems constrain the actions of research subjects, Nurmikko said. The value of wireless transmission is that it frees subjects to move however they intend, allowing them to produce a wider variety of more realistic behaviors. If neuroscientists want to observe the brain signals produced during some running or foraging behaviors, for instance, they can’t use a cabled sensor to study how neural circuits would form those plans for action and execution or strategize in decision making.

In the experiments in the new paper, the device is connected to one array of 100 cortical electrodes, the microscale individual neural listening posts, but the new device design allows for multiple arrays to be connected, Nurmikko said. That would allow scientists to observe ensembles of neurons in multiple related areas of a brain network.

The new wireless device is not approved for use in humans and is not used in clinical trials of brain-computer interfaces. It was designed, however, with that translational motivation.

“This was conceived very much in concert with the larger BrainGate* team, including neurosurgeons and neurologists giving us advice as to what were appropriate strategies for eventual clinical applications,” said Nurmikko, who is also affiliated with the Brown Institute for Brain Science.

Borton is now spearheading the development of a collaboration between EPFL and Brown to use a version of the device to study the role of the motor cortex in an animal model of Parkinson’s disease.

Meanwhile the Brown team is continuing work on advancing the device for even larger amounts of neural data transmission, reducing its size even further, and improving other aspects of the device’s safety and reliability so that it can someday be considered for clinical application in people with movement disabilities.

In addition to Nurmikko, Borton and Yin, the paper was also co-authored by Juan Aceros, an expert in mechanical engineering.

The National Institutes of Health/National Institute of Biomedical Imaging and Bioengineering and National Institute of Neurological Disorders and Stroke (Grant 1R01EB007401-01), with partial support from the National Science Foundation (Grants: 0937848) and the Defense Advanced Research Projects Agency (Contract: N66001-10-C-2010), funded the research.

*Caution: Investigational device. Limited by federal law to investigational use.

by David Orenstein

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Single nanomaterial yields many laser colors

Engineers at Brown University and QD Vision Inc. have created nanoscale single crystals that can produce the red, green, or blue laser light needed in digital displays. The size determines color, but all the pyramid-shaped quantum dots are made the same way of the same elements. In experiments, light amplification required much less power than previous attempts at the technology. The team’s prototypes are the first lasers of their kind.

PROVIDENCE, R.I. [Brown University] — Red, green, and blue lasers have become small and cheap enough to find their way into products ranging from BluRay DVD players to fancy pens, but each color is made with different semiconductor materials and by elaborate crystal growth processes. A new prototype technology demonstrates all three of those colors coming from one material. That could open the door to making products, such as high-performance digital displays, that employ a variety of laser colors all at once.

Vertical-cavity surface-emitting laser
Colloidal quantum dots — nanocrystals — can produce lasers of
many colors. Cuong Dang manipulates a green beam that pumps
the nanocrystals with energy, in this case producing red laser
light. Credit: Mike Cohea/Brown University

“Today in order to create a laser display with arbitrary colors, from white to shades of pink or teal, you’d need these three separate material systems to come together in the form of three distinct lasers that in no way shape or form would have anything in common,” said Arto Nurmikko, professor of engineering at Brown University and senior author of a paper describing the innovation in the journal Nature Nanotechnology. “Now enter a class of materials called semiconductor quantum dots.”

The materials in prototype lasers described in the paper are nanometer-sized semiconductor particles called colloidal quantum dots or nanocrystals with an inner core of cadmium and selenium alloy and a coating of zinc, cadmium, and sulfur alloy and a proprietary organic molecular glue. Chemists at QD Vision of Lexington, Mass., synthesize the nanocrystals using a wet chemistry process that allows them to precisely vary the nanocrystal size by varying the production time. Size is all that needs to change to produce different laser light colors: 4.2 nanometer cores produce red light, 3.2 nanometer ones emit green light and 2.5 nanometer ones shine blue. Different sizes would produce other colors along the spectrum.

The cladding and the nanocrystal structure are critical advances beyond previous attempts to make lasers with colloidal quantum dots, said lead author Cuong Dang, a senior research associate and nanophotonics laboratory manager in Nurmikko’s group at Brown. Because of their improved quantum mechanical and electrical performance, he said, the coated pyramids require 10 times less pulsed energy or 1,000 times less power to produce laser light than previous attempts at the technology.

Quantum nail polish
When chemists at QDVision brew a batch of colloidal quantum dots for Brown-designed specifications, Dang and Nurmikko get a vial of a viscous liquid that Nurmikko said somewhat resembles nail polish. To make a laser, Dang coats a square of glass — or a variety of other shapes — with the liquid. When the liquid evaporates, what’s left on the glass are several densely packed solid, highly ordered layers of the nanocrystals. By sandwiching that glass between two specially prepared mirrors, Dang creates one of the most challenging laser structures, called a vertical-cavity surface-emitting laser. The Brown-led team was the first to make a working VCSEL with colloidal quantum dots.

The nanocrystals’ outer coating alloy of zinc, cadmium, sulfur and that molecular glue is important because it reduces an excited electronic state requirement for lasing and protects the nanocrystals from a kind of crosstalk that makes it hard to produce laser light, Nurmikko said. Every batch of colloidal quantum dots has a few defective ones, but normally just a few are enough to interfere with light amplification.

Faced with a high excited electronic state requirement and destructive crosstalk in a densely packed layer, previous groups have needed to pump their dots with a lot of power to push them past a higher threshold for producing light amplification, a core element of any laser. Pumping them intensely, however, gives rise to another problem: an excess of excited electronic states called excitons. When there are too many of these excitons among the quantum dots, energy that could be producing light is instead more likely to be lost as heat, mostly through a phenomenon known as the Auger process.

The nanocrystals’ structure and outer cladding reduces destructive crosstalk and lowers the energy needed to get the quantum dots to shine. That reduces the energy required to pump the quantum dot laser and significantly reduces the likelihood of exceeding the level of excitons at which the Auger process drains energy away. In addition, a benefit of the new approach’s structure is that the dots can act more quickly, releasing light before Auger process can get started, even in the rare cases when it still does start.

“We have managed to show that it’s possible to create not only light, but laser light,” Nurmikko said. “In principle, we now have some benefits: using the same chemistry for all colors, producing lasers in a very inexpensive way, relatively speaking, and the ability to apply them to all kinds of surfaces regardless of shape. That makes possible all kinds of device configurations for the future.”

In addition to Nurmikko and Dang, another author at Brown is Joonhee Lee. QD Vision authors include Craig Breen, Jonathan Steckel, and Seth Coe-Sullivan, a company co-founder who studied engineering at Brown as an undergraduate.

The US. Department of Energy, the Air Force Office for Scientific Research, and the National Science Foundation supported the research. Dang is a Vietnam Education Foundation (VEF) Scholar.

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Research project aims at achieving a fundamental understanding of heat transfer at interfaces

Brown's Arto Nurmikko and Humphrey Maris are part of a multidisciplinary research effort that is helping to achieve a fundamental understanding of heat transfer at interfaces. A two-year-old Air Force Office of Scientific Research Multidisciplinary University Research Initiative effort involving the University of Michigan, Stanford University, Brown University, and the University of California at Santa Cruz is making great strides in achieving a fundamental understanding of heat transfer at interfaces.

"We aim to accomplish this by applying state-of-the-art techniques from several disciplines to arrive at a set of design rules for engineering interfaces with desired thermal properties," said Dr. Kevin Pipe, a professor of Mechanical Engineering at the University of Michigan who is leading the project.

Heat transfer is important to the performance, power requirements, and reliability of many military and commercial systems including thermoelectric refrigerators, waste heat recovery systems, heat sinks, power electronics, thermal barrier coatings, and thermal interface materials.

"Recent advances in nanoscience have enabled the precise control of interface physical and chemical structure, but the fundamental physics that link this nanoscale structure with thermal transport is not yet well developed, inhibiting the engineering of interfaces with radically enhanced thermal properties," said Pipe.

Interfaces can decrease a composite material's thermal conductivity by scattering the acoustic waves that are the primary carriers of heat in solids.

"This scattering process gives each interface a thermal resistance," said Pipe.

The researchers have made a number of achievements during the first two years of their research effort, including the development of a high-speed thermal imaging system and a technique to measure the propagation of phonons, the elementary packets of vibrational energy that carry heat, with high signal-to-noise ratio. Using ultrafast laser systems that emit laser pulses less than 50 femtoseconds in duration, Pipe's team creates high-frequency acoustic waves at the surface of a material and in a process similar to medical ultrasound imaging measures how these waves scatter off of buried interface structures.

"In one of our measurements," said Pipe, "we use picosecond x-ray pulses to look directly at atomic motion near an interface as heat flows across it."

By applying precise nanofabrication techniques to create interfaces with known atomic structure, the researchers are able to link measured heat transfer properties with the predictions of atomistic simulations to yield further understanding of the fundamental processes involved.

"By advancing the state-of-the-art in these techniques, we aim to fully characterize an interface and achieve a complete understanding of what controls the flow of heat across it," said Pipe.

"The Michigan MURI led by Professor Kevin Pipe is making extraordinary breakthroughs to understand nano-scale thermal transport by precisely tailoring interfaces using advanced processing techniques and innovative experimental laser based methods to delineate phonon modes participating in the heat transport," said Dr. Kumar V. Jata, Thermal Sciences, AFOSR, Arlington, Va. and Materials Science, Asian Office of Aerospace Research and Development, Tokyo, Japan. "In the past we never paid attention to the interfaces and considered them as either perfect or imperfect, one or the other."

Collaborating investigators on the project include Professors John Kieffer, Rachel Goldman, Roberto Merlin, and Max Shtein,University of Michigan; Profs. Humphrey Maris and Arto Nurmikko, Brown University; Prof. David Reis (Stanford University; and Prof. Ali Shakouri University of California at Santa Cruz.

Source: Air Force Office of Scientific Research

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Professor Nurmikko collaborates on $14.9 million DARPA grant

Researchers at Brown University and Stanford University have launched a $14.9 million project geared to developing new brain micro-implants that can both sense the brain’s electrical signals and deliver optogenetic lightpulses to neural tissue.

The project, funded by a two-year Defense Advanced Research Projects Agency (DARPA) grant, is being led by Krishna Shenoy, a Stanford researcher, and Arto Nurmikko, a professor of electrical engineering and physics at Brown.

For more information visit the Providence Business News.

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Nurmikko elected to Finnish Academy of Science and Letters

Professor Arto Nurmikko was recently elected to the Finnish Academy of Science and Letters. The Finnish Academy of Science and Letters is the largest general scientific and academic society in Finland. It is a learned society covering the full range of academic disciplines which is devoted to the promotion of scientific and scholarly research and serves as a bond uniting researchers engaged in these activities at the highest level. It functions as a traditional learned society in the sense that its membership is limited and it selects its new members on their academic and scientific merits. For more information on the Academy: http://www.acadsci.fi/frontpage.htm

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Collaborative project highlighted in premier neuroscience journal

The February issue of the journal Neuron features a cover story highlighting the joint work between Professors Arto Nurmikko and Barry Connors. Neuron is a premier journal in Neuroscience.

This is another illustration of the collaboration between Engineering and Biology and Medicine here at Brown. Arto Nurmikko's group has successfully led the initiative to bring the ‘optogenetics’ methodology to Brown.

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