Engineered brain tissue
Borrowing from microfabrication techniques used in the semiconductor industry, MIT and Harvard Medical School (HMS) engineers have developed what they say is a simple and inexpensive way to create three-dimensional brain tissues in a lab dish.

The technique yields tissue constructs that closely mimic the cellular composition of those in the living brain, the researchers said, which allows scientists to study how neurons form connections and to predict how cells from individual patients might respond to different drugs and paves the way for developing bioengineered implants to replace damaged tissue for organ systems.

Although researchers have had some success growing artificial tissues such as liver or kidney, the brain presents some unique challenges such as the spatial heterogeneity — there are so many kinds of cells, and they have intricate wiring.

Brain tissue includes many types of neurons, including inhibitory and excitatory neurons, as well as supportive cells such as glial cells. All of these cells occur at specific ratios and in specific locations. To mimic this architectural complexity in their engineered tissues, the researchers embedded a mixture of brain cells taken from the primary cortex of rats into sheets of hydrogel. They also included components of the extracellular matrix, which provides structural support and helps regulate cell behavior.

Those sheets were then stacked in layers, which can be sealed together using light to crosslink hydrogels. By covering layers of gels with plastic photomasks of varying shapes, the researchers could control how much of the gel was exposed to light, thus controlling the 3-D shape of the multilayer tissue construct.

This type of photolithography is also used to build integrated circuits onto semiconductors — a process that requires a photomask aligner machine, which costs tens of thousands of dollars. However, the team developed a much less expensive way to assemble tissues using masks made from sheets of plastic, similar to overhead transparencies, held in place with alignment pins.

The researchers believe this system is the first that includes all of the necessary features for building useful 3-D tissues: It is inexpensive, precise, and allows complex patterns to be generated. Many people could easily use this method for creating heterogeneous, complex gel structures.

Subatomic breakthrough for quantum computing
In what they say is a key step toward building a machine that promises to revolutionize computing, Princeton researchers have developed a method that they say could quickly and reliably transmit information through a computer using the power of subatomic particles. The finding could eventually allow engineers to build a working quantum computer. By using principles radically different from classical physics, quantum computers would allow mathematicians to solve problems impossible to approach with standard computers: factoring immense numbers, cracking codes or simulating molecular behavior.

Quantum computers take advantage of the strange behaviors of subatomic particles like electrons. By harnessing electrons as they spin, scientists could use the particles to form the basis for a new type of computing. The problem, though, is that these incredibly tiny electrons are hard to control. So far, scientists have only been able to harness extremely small numbers of them. But in a recent series of experiments, the Princeton team demonstrated a new approach that could eventually allow engineers to build quantum computers consisting of millions of quantum bits, or qubits.

The quest in quantum computing today is trying to build a larger system. To transfer information, the researchers used a stream of microwave photons to analyze a pair of electrons trapped in a tiny cage called a quantum dot. The “spin state” of the electrons — information about how they are spinning — serves as the qubit, a basic unit of information. The microwave stream allows the scientists to read that information.

Diamonds for nanomanufacturing
One of the most promising innovations of nanotechnology has been the ability to perform rapid nanofabrication using nanometer-scale tips and heating those tips can increase fabrication speeds. At the same time, high speed and high temperature have been known to blunt their atomically sharp points. However, research conducted by the University of Illinois, the University of Pennsylvania and Advanced Diamond Technologies has created a new type of nano-tip for thermal processing, made entirely made out of diamond.

Researchers have been imaging nanoscale objects with atomic force microscopes for two decades, which use nanometer-scale tips to feel the push and pull of individual atomic forces. Researchers have also been interested in using these tips to etch surfaces or deposit materials in nano-manufacturing processes, but one of the key challenges has been the reliability of the tips, especially with performing nano-writing on hard, semiconductor surfaces.

Using a process known as reactive ion etching, the researchers were able to create a new kind of diamond tip that is much more resistant to wear and heat than its silicon counterparts.

Images of the researchers' diamond tips compared to traditional silicon tips, before and after scanning for 1.2 meters. (Source: University of Pennsylvania)

The robustness of these diamond-based probes under such harsh conditions — high temperatures and stresses in an oxidizing environment — exceeds anything the researchers had seen with other atomic force microscope probes. Being able to heat the tips without their degrading opens up the possibility for using them in new manufacturing processes.

To prove its robustness, the researchers scanned the 10-nanometer diamond tip over a surface for a distance of more than 1.2 meters and showed that it experienced essentially no wear over that distance. The scan distance is equal to 100 million times the size of the tip, which is equivalent of a person walking around the circumference of the earth four times, and doing so with no measurable wear.

The researchers believe that the new tip’s durability combined with the multifunctionality of a thermal probe will open up new applications for atomic force microscopes.

–Ann Steffora Mutschler

Dissolving electronics
With the potential to introduce new design paradigms for medical implants, environmental monitors and consumer devices, researchers at the University of Illinois, in collaboration with Tufts University and Northwestern University, have demonstrated a new type of biodegradable electronics technology they call “transient electronics.”

John A. Rogers, the Lee J. Flory-Founder Professor of Engineering at the U. of I., who led the multidisciplinary research team said, “From the earliest days of the electronics industry, a key design goal has been to build devices that last forever – with completely stable performance. But if you think about the opposite possibility – devices that are engineered to physically disappear in a controlled and programmed manner – then other, completely different kinds of application opportunities open up.”

Three application areas appear particularly promising.  First are medical implants that perform important diagnostic or therapeutic functions for a useful amount of time and then simply dissolve and resorb in the body. Second are environmental monitors, such as wireless sensors that are dispersed after a chemical spill, that degrade over time to eliminate any ecological impact. Third are consumer electronic systems or sub-components that are compostable, to reduce electronic waste streams generated by devices that are frequently upgraded, such as cellphones or other portable devices.

The researcher pointed out that transient electronic systems harness and extend various techniques that the Rogers’ group has developed over the years for making tiny, yet high performance electronic systems out of ultra-thin sheets of silicon. In transient applications, the sheets are so thin that they completely dissolve in a few days when immersed in biofluids. Together with soluble conductors and dielectrics, based on magnesium and magnesium oxide, these materials provide a complete palette for a wide range of electronic components, sensors, wireless transmission systems and more.

A biodegradable integrated circuit during dissolution in water. (Source: Beckman Institute, University of Illinois and Tufts University)

The team has already built transient transistors, diodes, wireless power coils, temperature and strain sensors, photodetectors, solar cells, radio oscillators and antennas, and even simple digital cameras. All of the materials are biocompatible and they can dissolve in even minute volumes of water.

Carbon nanotube Fresnel lenses
Opening up new possibilities in designing highly flexible and efficient interconnection networks with massive parallelism, a team of researchers at the University of Cambridge has fabricated carbon nanotube Fresnel lenses.

The first Fresnel lens was installed in 1823 in the Cordouan lighthouse, where its beam was visible for 32 km. Since then, this lens design has been used in lighthouses, traffic lights, automobile headlights, magnifying glasses, cameras, and more. Compared to a conventional lens design of comparable aperture and focal length, a Fresnel lens requires less mass and volume, allowing it to be thinner and flatter, capturing more oblique light from a light source.

However, reflections from the opaque zones in a Fresnel lens can degrade the focusing and lensing properties but the Cambridge researchers overcame this limitation by using the darkest man-made material ever — low-density, vertically aligned carbon nanotube arrays.

Carbon nanotube Fresnel lens (Source: University of Cambridge)

Potential applications include efficient focusing, deflecting and collimating tasks in optical sensor systems, optical computers, optical data transfer, optical communication, and even integration into 2D source arrays for neural network architectures.

–Ann Steffora Mutschler

Turning Graphene Off, On
With the possibility of enabling the production of microarrays of sensors to detect trace biological or chemical materials, experiments conducted at MIT showed that a one-atom-thick material called graphene — a form of pure carbon whose atoms are joined in a chicken-wire-like lattice — behaved quite differently depending on the nature of material it’s wrapped around.

When sheets of graphene are placed on substrates made of different materials, fundamental properties such as how the graphene conducts electricity and how it interacts chemically with other materials can be drastically different, depending on the nature of the underlying material. The researchers were surprised to discover this altered behavior as they had expected it to behave like graphite, whose structure is essentially multiple layers of graphene piled on top of each other.

But its behavior turned out to be quite different. Due to its extreme thinness, in practice graphene is almost always placed on top of some other material for support. When that material underneath is silicon dioxide, a standard material used in electronics, the graphene can readily become functionalized when exposed to certain chemicals. But when graphene sits on boron nitride, it hardly reacts at all to the same chemicals. Therefore, graphene’s ability to form chemical bonds can be turned off and on based on what’s underneath.

This occurs because the material is so thin that the way it reacts is strongly affected by the electrical fields of atoms in the material beneath it. This means that it is possible to create devices with a micropatterned substrate — made up of some silicon dioxide regions and some coated with boron nitride — covered with a layer of graphene whose chemical behavior will then vary according to the hidden patterning.

The researchers said graphene ultimately could even become a protective coating for many materials. For example, the one-atom-thick material, when bonded to copper, completely eliminates that metal’s tendency to oxidize, which produces the characteristic blue-green surface of copper roofs, effectively turning off the corrosion completely with just the whisper of a coating.

DNA-directed Gold Nanoparticle Shapes
With potential impacts in bio-nanotechnology and applications in our everyday lives such as catalysis, sensing, imaging and medicine, University of Illinois researchers have found that DNA’s code can similarly shape metallic structures just as DNA holds the genetic code for all sorts of biological molecules and traits.

The team, led by Yi Lu, the Schenck Professor of Chemistry at the U. of I., found that DNA segments could direct the shape of gold nanoparticles, which are tiny gold crystals that have many applications in medicine, electronics and catalysis. 
“DNA-encoded nanoparticle synthesis can provide us a facile but novel way to produce nanoparticles with predictable shape and properties,” Lu said.

Gold nanoparticles have wide applications in both biology and materials science thanks to their unique physicochemical properties. Properties of a gold nanoparticle are largely determined by its shape and size, so it is critical to be able to tailor the properties of a nanoparticle for a specific application.

–Ann Steffora Mutschler

How Nanotubes Bend, Break

Researchers at Rice University have discovered that even though carbon nanotubes are 100 times stronger than steel and weighs one-sixth as much, they can be snapped like twigs by a tiny air bubble.

“We find that the old saying ‘I will break but not bend’ does not hold at the micro- and nanoscale,” said Rice engineering researcher Matteo Pasquali, the lead scientist on a new study that appears this month in the Proceedings of the National Academy of Sciences.

This work is key for researchers who want to make and study long nanotubes and shows how the ultrasonic vibrations used to separate and prepare nanotubes in the lab are a detriment to long nanotubes.

“We found that long and short nanotubes behave very differently when they are sonicated,” said Pasquali, professor of chemical and biomolecular engineering and of chemistry at Rice. “Shorter nanotubes get stretched while longer nanotubes bend. Both mechanisms can lead to breaking.”

Nanotubes can be used in paintable batteries and sensors, to diagnose and treat disease, and for next-generation power cables in electrical grids. Many of the optical and material properties of nanotubes were discovered at Rice’s Smalley Institute for Nanoscale Science and Technology, and the first large-scale production method for making single-wall nanotubes was discovered at Rice by the institute’s namesake, the late Richard Smalley.

The mechanism by which carbon nanotubes break or bend under the influence of bubbles during sonication is the topic of a new paper led by researchers at Rice University. The team found that short nanotubes are drawn end-first into collapsing bubbles, stretching them, while longer ones are more prone to breakage. (Source: Pasquali Lab/Rice University)

Sharpen Microscope Probe, Improve Resolution

A simple, new improvement to an essential microscope component could greatly improve imaging for researchers who study the very small, from cells to computer chips, according to Joseph Lyding, a professor of electrical and computer engineering at the University of Illinois, who led a group that developed a new microscope probe-sharpening technique.

Labs can spend hundreds of thousands of dollars on an elegant instrument – for example, a scanning tunneling microscope (STM) or an atomic force microscope (AFM) – yet the quality of the data depends on the probe. Probes can degrade rapidly with use, wearing down and losing resolution. In such cases, the researcher then has to stop the scan and replace the tip.

“To put it in perspective, if you had an expensive racecar but you put bicycle tires on it, it wouldn’t be a very good car,” Lyding said. To shape tips, researchers shoot a stream of ions at the tip. The material sputters off as the ions collide with the tip, whittling away the probe. One day in the lab, after yet another tip failure, Lyding had the simple, novel idea of applying a matching voltage to the tip to deflect the incoming ions. When a voltage is applied to a sharp object, the electrical field gets stronger as the point narrows. Therefore, ions approaching the sharpest part of the electrified tip are deflected the most and causing the ions to remove the material around that sharp part, not on the sharp part itself, and that makes it sharper.

A traditionally etched tungsten STM probe, sharpened to a 1-nanometer point after bombarding it with ions. (Source: University of Illinois)

To keep the probe tips from wearing down just as quickly as other probes, a coating of hafnium diboride was applied.

–Ann Steffora Mutschler

How Heat Flows
Through a combination of atomic-scale materials design and ultrafast measurements, researchers at the University of Illinois have revealed new insights about how heat flows across an interface between two materials. This is important because improved control of heat exchange is a key element to enhancing the performance of current technologies such as ICs and combustion engines as well as emerging technologies such as thermoelectric devices, which harvest renewable energy from waste heat. Achieving control, however, is hampered by an incomplete understanding of how heat is conducted through and between materials. The researchers demonstrated that a single layer of atoms could disrupt or enhance heat flow across an interface.

Through atomic-scale manipulation, researchers at the University of Illinois have demonstrated that a single layer of atoms can disrupt or enhance heat flow across an interface. (Source: University of Illinois)

David Cahill, a Willett Professor and the head of materials science and engineering at Illinois and co-author of the paper said, “Heat travels through electrically insulating material via ‘phonons,’ which are collective vibrations of atoms that travel like waves through a material. Compared to our knowledge of how electricity and light travel through materials, scientists’ knowledge of heat flow is rather rudimentary.”

One reason such knowledge remains elusive is the difficulty of accurately measuring temperatures, especially at small-length scales and over short time periods – the parameters that many micro- and nano-devices operate under. 

Over the past decade, Cahill’s group has refined a measurement technique using very short laser pulses, lasting only one trillionth of a second, to probe heat flow accurately with nanometer-depth resolution. He teamed with Paul Braun, the Racheff Professor of Materials Science and Engineering at the University of Illinois and a leader in nanoscale materials synthesis, to apply the technique to understanding how atomic-scale features affect heat transport.

Braun said the experiments used a ‘molecular sandwich’ that allowed them to manipulate and study the effect that chemistry at the interface has on heat flow, at an atomic scale.  The researchers assembled their molecular sandwich by first depositing a single layer of molecules on a quartz surface. Next, through a technique known as transfer-printing, they placed a very thin gold film on top of these molecules. Then they applied a heat pulse to the gold layer and measured how it traveled through the sandwich to the quartz at the bottom. 

By adjusting just the composition of the molecules in contact with the gold layer, the group observed a change in heat transfer depending on how strongly the molecule bonded to the gold. They demonstrated that stronger bonding produced a twofold increase in heat flow.

The Illinois group is already working toward a deeper fundamental understanding of heat transfer by refining measurement methods for quantifying interfacial bonding stiffness, as well as investigating temperature dependence, which will reveal a better fundamental picture of how the changes in interface chemistry are disrupting or enhancing the flow of heat across the interface.

Growing Computer Components From Scratch
Researchers at the University of Leeds have used a type of bacterium which ‘eats’ iron to create a surface of magnets, similar to those found in traditional hard drives and wiring and creates tiny magnets within itself as it ingests the iron. The team has also begun to understand how the proteins inside these bacteria collect, shape and position these “nanomagnets” inside their cells and can now replicate this behavior outside the bacteria. The research team hopes to develop a bottom up approach to creating cheaper, more environmentally friendly electronic devices.

Dr. Sarah Staniland from the University of Leed’s School of Physics and Astronomy, who led the project as part of a longstanding collaboration with the Tokyo University of Agriculture and Technology said, “We are quickly reaching the limits of traditional electronic manufacturing as computer components get smaller. The machines we’ve traditionally used to build them are clumsy at such small scales. Nature has provided us with the perfect tool to circumvent this problem.”

The magnetic array was created by Leeds PhD student Johanna Galloway using a protein that creates perfect nanocrystals of magnetite inside the bacterium Magnetospirilllum magneticum. Using a process akin to potato-printing on a much smaller scale, the protein was attached to a gold surface in a checkerboard pattern and placed in a solution containing iron. At a temperature of 80°C, similarly-sized crystals of magnetite form on the sections of the surface covered by the protein and the team are currently working to reduce the size of these islands of magnets in order to make arrays of single nanomagnets. They also plan to vary the magnetic materials that this protein can control. These next steps would allow each of these nanomagnets to hold one bit of information allowing the construction of better hard drives.

Galloway explained that using today’s top-down method that sculpts tiny magnets out of a big magnet it is increasingly difficult to produce the small magnets of the same size and shape which are needed to store data but with this new method the proteins do all the hard work; they gather the iron, create the most magnetic compound, and arrange it into regularly-sized cubes.

Forget computer viruses - magnet-making bacteria could be used to build tomorrow’s computers with larger hard drives and speedier connections. (Source: University of Leeds)

A different protein was used to create tiny electrical wires by Dr Masayoshi Tanaka, during a secondment to Leeds from Tokyo University of Agriculture and Technology: these ‘nanowires’ are made of ‘quantum dots’ – particles of copper indium sulphide and zinc sulphide which glow and conduct electricity – and are encased by fat molecules, or lipids. The magnetic bacteria contain a protein that moulds mini compartments for the nanomagnets to be formed in using the cell membrane lipids. Dr. Tanaka used a similar protein to make tubes of fat containing quantum dots – biological-based wiring.

“It is possible to tune these biological wires to have a particular electrical resistance. In the future, they could be grown connected to other components as part of an entirely biological computer,” said Dr Tanaka.

The research group and the team at Tokyo University of Agriculture and Technology plan to examine the biological processes behind the behavior of these proteins in order to develop a toolkit of proteins and chemicals that could be used to grow computer components from scratch.

—Ann Steffora Mutschler

By John Blyler
Both the sensor and wireless market continue to be strong growth areas in the electronics industry, especially the mobile segment. This growth is attributed in large measure to the cost-effective availability of sensors based on microelectromechanical systems (MEMS) and RF components.

Sensors and wireless technology always have been important subsystems in the design of most mobile electronics. Today, however, these technologies have become so pervasive as to define what is meant by “a system.”

Mobile electronics—from smartphones and tablets to smart robots—are no longer distinguished by their processors or RTOSes, but by the type of sensors and wireless features that they support.

To get a sense of the changes taking way, consider the Segway. When first introduced, the Segway was a marvel of balance and control. Digital signal processors, microcontrollers, sensors and motors keep the personal transport upright during motion. Gyroscopes and level-detecting sensors—mainly accelerometers—detect shifts in passenger weight to both control the speed and direction of the Segway.

Thanks to the area, power and performance scaling achieved by the semiconductor industry, today’s Segway has found many new applications. The smaller size of high-performance and ultra-low-power electronics and motors has made Segway technology ideal for the robotics industry.

So affordable have these constituent subsystems become that Segway-like robots are being used in engineering course at institutions like the University of Illinois. The Segbot is part of several inverted pendulum projects in the U of I Control Systems Labs. Like their big brothers, these miniature robots use MEMS-based accelerometers and rate gyroscopes to determine and maintain balance of the device. The sensors give the robot its amazing stability. As with it big brethren, the Segbot relies on TI DSPs embedded in a microcontroller to perform the necessary the necessary positioning and balancing algorithms.

The basic design of these robotic systems is not new; nor is the use of sensors to control the motion or position of the robots. What are new are the tiny sizes, ultra-low power and fast performance of today’s sensors and associated signal conditioning components.

Aside from new technology in the control system, there other new features that have become synonymous with mobile systems is the wireless connection. For example, the Segbot is remotely controlled by a wireless watch – namely, the Texas Instruments’ eZ430-Chronos Wireless Watch Development Tool. The watch is basically a motion-sensitive microcontroller development platform that uses a USB interface for coding and debugging of the embedded target system. Once programmed, a user moves his/her watch arm in various positions to control the Segbot. (Youtube video: “Segbot controlled with TI’s Chronos watch at ESC2011“)

Gesturing is a growing type of user interface, especially in the consumer market. Many applications are being developed for gesture-based interfaces that rely on camera and video systems (See Qualcomm Recognizes Importance of Gesture IP ). These applications, like the U of I Segbot, require high-performance DSPs to process sensor and video stream data. Unlike camera-based system, the Segbot requires only arm motions to wirelessly control motions on the target platform. The user can literally control the direction of the robot with a wave of their arm.

Yesterday’s vernacular of hardware and software has given way to a more functionally-based discussion. Systems designers should take note that it will be difficult to develop future electronics devices that don’t contain an array of sensors and wireless interfaces.