Silicon Technology For Medical Application

A team of cardiologists, materials scientists, and bioengineers have created and tested a new type of implantable device for measuring the heart's electrical output that they say is a vast improvement over current devices. The new device represents the first use of flexible silicon technology for a medical application.

This technology may herald a new generation of active, flexible, implantable devices for applications in many areas of the body, commented Brian Litt, an associate professor of Neurology at the University Of Pennsylvania School Of Medicine and also an associate professor of Bioengineering in Penn's School of Engineering and Applied Science.

Implantable silicon-based devices have the potential to serve as tools for mapping and treating epileptic seizures, providing more precise control over deep brain stimulation, as well as other neurological applications, say Story Landis, PhD, director of the National Institute of Neurological Disorders and Stroke, which provided support for the study.

The new devices bring electronic circuits right to the tissue, rather than having them located remotely, inside a sealed can that is placed elsewhere in the body, such as under the collar bone or in the abdomen, explained Litt. This enables the devices to process signals right at the tissues, which allows them to have a much higher number of electrodes for sensing or stimulation than is currently possible in medical devices.

Now, for example, devices for mapping and eliminating life-threatening heart rhythms allow for up to 10 wires in a catheter that is moved in and around the heart, and is connected to rigid silicon circuits distant from the target tissue. This design limits the complexity and resolution of devices since the electronics cannot get wet or touch the target tissue.

The team tested the new devices - made of nanoscale, flexible ribbons of silicon embedded with 288 electrodes, forming a lattice-like array of hundreds of connections - on the heart of a porcine animal model. The tissue-hugging shape allows for measuring electrical activity with greater resolution in time and space. The new device can also operate when immersed in the body's salty fluids. The devices can collect large amounts of data from the body, at high speed. This allowed the researchers to map electrical activity on the heart of the large animal.

In this experiment, the researchers built a device to map waves of electrical activity in the heart of a large animal. The device uses the 288 contacts and more than 2,000 transistors spaced closely together, while standard clinical systems usually use about five to 10 contacts and no active transistors. High-density maps of electrical activity on the heart were recorded from the device, during both natural and paced beats.

Scientists are also planning to design advanced, intelligent pacemakers that can improve the pumping function of hearts weakened by heart attacks and other diseases. For each of these applications, the team is conducting experiments to test flexible devices in animals before starting human trials.

Another focus of ongoing work is to develop similar types of devices that are not only flexible, like a sheet of plastic, but fully stretchable, like a rubber band. The ability to fully conform and wrap around large areas of curved tissues will require stretch ability, as well as flexibility.

About Soft Interference Lithography (SIL)

Researchers at Northwestern University had developed a nano manufacturing technique (2007) which can be used to produce nanostructures measuring tens of square centimeters. This new technique, dubbed ‘soft interference lithography’ (SIL), can lead to nanomaterials with optical properties mimicking some metamaterials in the natural world such as peacock feathers and butterfly wings. As said the researchers, their SIL technique combines the ability of interference lithography to produce wafer-scale nanopatterns with the versatility of soft lithography and used it to create plasmonic metamaterials.

Here is how scientists described SIL. “The optical nanomaterials in this research are called ‘plasmonic metamaterials’ because their unique physical properties originate from shape and structure rather than material composition only. Two examples of metamaterials in the natural world are peacock feathers and butterfly wings. Their brightly colored patterns are due to structural variations at the hundreds of nanometers level, which cause them to absorb or reflect light. Through the development of a new nanomanufacturing technique, researchers succeeded in making gold films with virtually infinite arrays of perforations as small as 100 nanometers — 500-1000 times smaller than a human hair. On a magnified scale, these perforated gold films look like Swiss cheese except the perforations are well-ordered and can spread over macroscale distances. The researchers’ ability to make these optical metamaterials inexpensively and on large wafers or sheets is what sets this work apart from other techniques.”

In the research section of her site, Mrs. Odom describes plasmonic materials and their optical properties. “Plasmonics is an exciting and emerging area that uses metal nanostructures to manipulate light on the nanoscale. Depending on their size, shape, and materials properties, noble metal nanoparticles can scatter and absorb light to produce colors ranging from the ultra-violet to the near-infrared. In addition, significantly more light can be transmitted through metal films perforated with subwavelength hole arrays than is permitted by geometric optics, a phenomena known as enhanced optical transmission.”

And she gives some additional details. “We focus primarily on the optical properties of two different but complementary systems that can control light on the nanometer scale: (i) metallic films of nanohole arrays and (ii) pyramidal nanoparticles. The former have properties dominated by SPPs, and the latter have properties dominated by LSPs. Such nanostructures are easily made by our innovative fabrication scheme, PEEL, for preparing large-area, free-standing films of nanoscale holes and particles. PEEL is a simple procedure which combines Phase-shifting photolithography, Etching, Electron-beam deposition, and Lift-off of the metal film.”

RAPID: A NEW NANOFABRICATION PROCESS

For exploring the full potentiality of nanotechnology and its sea like vast application in elctronics and hardware industry, the ability to create tiny patterns is important. They are extremely important for fabrication of computer chips and many other application. Yet, creating ever smaller features, through a widely-used process called photolithography, has required the use of ultraviolet light, which is difficult and expensive to work with. John Fourkas, Professor of Chemistry and Biochemistry in the University of Maryland College of Chemical and Life Sciences, and his research group have developed a new, table-top technique called RAPID (Resolution Augmentation through Photo-Induced Deactivation) lithography that makes it possible to create small features without the use of ultraviolet light. Photolithography uses light to deposit or remove material and create patterns on a surface. There is usually a direct relationship between the wavelength of light used and the feature size created. Therefore, nanofabrication has depended on short wavelength ultraviolet light to generate ever smaller features.

The RAPID lithography technique have been developed to create patterns twenty times smaller than the wavelength of light employed; by this process it streamlines the nanofabrication process. That’s how RAPID can be used in many applications in areas such as electronics, optics, and biomedical devices.

In this process, two laser lights of same color have been used for controlling the operation. First, short burst of light used to harden the material and secondly, a constant light source used to prevent it. The technique has been highly appreciated for its easiness to implement, as there is no need to control the timing between two different pulsed lasers.

Cold atoms could replace hot gallium in focused ion beams

Scientists at the National Institute of Standards and Technology (NIST) have developed a radical new method of focusing a stream of ions into a point as small as one nanometer (one billionth of a meter). Because of the versatility of their approach—it can be used with a wide range of ions tailored to the task at hand—it is expected to have broad application in nanotechnology both for carving smaller features on semiconductors than now are possible and for nondestructive imaging of nanoscale structures with finer resolution than currently possible with electron microscopes. Researchers and manufacturers routinely use intense, focused beams of ions to carve nanometer-sized features into a wide variety of targets. In principle, ion beams also could produce better images of nanoscale surface features than conventional electron microscopy. But the current technology for both applications is problematic. In the most widely used method, a metal-coated needle generates a narrowly focused beam of gallium ions. The high energies needed to focus gallium for milling tasks end up burying small amounts in the sample, contaminating the material. And because gallium ions are so heavy, if used to collect images they inadvertently damage the sample, blasting away some of its surface while it is being observed. Researchers have tried using other types of ions but were unable to produce the brightness or intensity necessary for the ion beam to cut into most materials.

The NIST team took a completely different approach to generating a focused ion beam that opens up the possibility for use of non-contaminating elements. Instead of starting with a sharp metal point, they generate a small "cloud" of atoms and then combine magnetic fields with laser light to trap and cool these atoms to extremely low temperatures. Another laser is used to ionize the atoms, and the charged particles are accelerated through a small hole to create a small but energetic beam of ions. Researchers have named the groundbreaking device "MOTIS," for Magneto-Optical Trap Ion Source.

Because the lasers cool the atoms to a very low temperature, they're not moving around in random directions very much. As a result, when ions are accelerated, they travel in a highly parallel beam, which is necessary for focusing them down to a very small spot, explains Jabez McClelland of the NIST Center for Nanoscale Science and Technology. The team was able to measure the tiny spread of the beam and show that it was indeed small enough to allow the beam to be focused to a spot size less than 1 nanometer. The initial demonstration used chromium atoms, establishing that other elements besides gallium can achieve the brightness and intensity to work as a focused ion beam .

JUNCTIONLESS TRANSISTORS!

From the early ages of transistors i.e. in 1940s when they were over 1 centimeter size to the modern age where transistors are less than 30 nanometers long – transistors are shrinking their size over three thousands times. The outcome is that more transistor based circuits are integrated into a single chip. But this development cannot continue for much longer. One of the increasingly difficult problems that chip designers are facing is that the high density of components packed on a chip makes interconnections increasingly difficult; and, as conventional chip structures continue to shrink, Moore's Law is on a collision course with the laws of physics.

All existing transistors are based on junctions – obtained by changing the polarity of silicon from positive to negative. It is a little bit like changing the color of silicon from black to white, explains Jean-Pierre Colinge, a professor at Tyndall National Institute, whose team has just reported a breakthrough in nanoelectronics by demonstrating the world's first junctionless transistor.

In modern transistors, a negative-positive-negative structure needs to be created, where the width of the positive region is only a few dozens of atoms wide.

In a junctionless gated transistor the doping concentration in the channel is identical to that in the source and drain. Because the gradient of the doping concentration between source and channel or drain and channel is zero, no diffusion can take place, which eliminates the need for costly ultrafast annealing techniques and allows one to fabricate devices with shorter channels.

The devices have full CMOS functionality, but they contain no junctions or doping gradients and are, therefore, much less sensitive to thermal budget issues than regular CMOS devices.

The key to fabricating a junctionless gated transistor is the formation of a semiconductor layer that is thin and narrow enough to allow for full depletion of carriers when the device is turned off. The semiconductor also needs to be heavily doped to allow for a reasonable amount of current flow when the device is turned on. Putting these two constraints together imposes the use of nanoscale dimensions and high doping concentrations.

The electrical current flows in this silicon nanowire, and the flow of current is perfectly controlled by a wedding ring structure that electrically squeezes the silicon wire. These structures are easy to fabricate even on a miniature scale which leads to the major breakthrough in potential cost reduction.

Germanium Nanoelectronics

In the world of miniaturization we are always thinking of faster and smaller things. The use of germanium instead of silicon as primary material of transistor would provide us smaller transistor chip which are faster than its previous counterparts.

During the production of transistor, foreign atoms such as phosphorus and boron are implanted into the semiconductor material so that it becomes partly conducting. But this production step damages the material; it must be repaired by subsequent annealing. As the phosphorus atoms are strongly redistributed within the material during annealing, it has not been possible to manufacture large scale integrated transistors using germanium.

Scientists of the research center Forschungszentrum Dresden-Rossendorf (FZD) surmount this problem with two novel techniques.

Germanium was the basic material of first-generation transistors before it was replaced by silicon at the end of the 1960s. This was due to the excellent electronic properties of the interface between the semiconductor silicon and its insulating and passivating oxide. However, this advantage cannot be utilized if transistor dimensions are further reduced since the oxide must then be replaced by so-called high-k dielectrics. This again stimulates science and industry to search for the most suitable basic material. Higher switching speeds could also be achieved using germanium and some other semiconductors.

By inserting foreign atoms the conductivity of semiconductors can be varied in a purposeful way. One possibility is ion implantation (ions are charged atoms) with subsequent heat treatment, which is called annealing. Annealing of the germanium crystal is necessary as the material is heavily damaged during implantation, and leads to the requested electronic properties. While these methods allow for the manufacturing of p-channel transistors (PMOS) according to future technology needs, it was not possible to produce corresponding n-channel transistors (NMOS) using germanium. This is due to the strong spatial redistribution (diffusion) of the phosphorus atoms which have to be used in manufacturing the n+ regions.

Physicists from the FZD applied a special annealing method that enables repairing the germanium crystal and yields good electrical properties without the diffusion of phosphorus atoms. The germanium samples were heated by short light pulses of only a few milliseconds. This period is sufficient in order to restore the crystal quality and to achieve electrical activation of phosphorus, but it is too short for the spatial redistribution of the phosphorus atoms. The light pulses were generated by the flash lamp equipment which was developed at the research center FZD. Analysis of the electrical and structural properties of the thin phosphorus-doped layers in germanium was performed in close collaboration with colleagues from the Belgian microelectronics center IMEC in Leuven and from the Fraunhofer-Center for Nanoelectronic Technologies (CNT) in Dresden.

STRANGE CARBON NANOTUBES!

Carbon nanotubes (CNTs) are 'strange' nanostructures in a sense that they have both high mechanical strength and extreme flexibility. Deforming a carbon nanotube into any shape would not easily break the structure, and it recovers to original morphology in perfect manner. Researchers in China are exploiting this phenomenon by making CNT sponges consisting of a large amount of interconnected nanotubes, thus showing a combination of useful properties such as high porosity, super elasticity, robustness, and little weight (1% of water density).

The nanotube sponges not only show exciting properties as a porous material but they also are very promising to be used practically in a short time. The production method is simple and scalable, the cost is low, and the sponges can find immediate use in many fields related to water purification.

One of the researchers explains that the nanotube sponges are a completely new structure compared with artificial porous materials in several aspects. The sponge is built entirely with nanotubes through a random (yet desired) interconnection. With a high porosity of >99%, the sponge can be compressed to less than 10% of its original volume yet still recover perfectly. Usually, porous materials tend to become brittle at increasing porosity, thus obtaining a material with both high porosity and flexibility has been challenging.

Carbon nanotubes could take advantage of their high surface area and excellent mechanical strength and flexibility. The scientists synthesized the sponges by a chemical vapor deposition (CVD) process during which the CNTs (multi-walled nanotubes with diameters in the range of 30 to 50nm and lengths of tens to hundreds of micrometers,) self-assembled into a porous, interconnected, three-dimensional framework.

The growth process of the sponges is like a consecutive stacking and penetration of numerous CNT 'piles' into centimeter thickness, which is substantially different from aligned arrays where most of CNTs grow continuously from the bottom to top surface or thin sheets where CNTs were densified into a two-dimensional network during vacuum filtration.

According to the scientists, the CNT sponges are capable of absorbing a wide range of solvents and oils with excellent selectivity, recycle ability, and absorption capacities up to 180 times their own weight, two orders of magnitude higher than activated carbon.

The potential application areas for these sponges are vast. They could be used in large-area oil spill clean-ups, water purification and toxic gas filtration. In addition to environmental applications, the CNT sponges can find use as protective coating, thermal insulator, and high strength-to-weight composite. For example, the sponges can absorb mechanical energy during large-strain deformation, therefore resist foreign force or impact. Their high surface area and porosity are also useful for supporting fine catalyst particles in photo-catalytic devices and fuel cells.

NANOCOMPOSITES COULD CHANGE DIABETES TREATMENT

The people who are suffering from diabetes may soon be able to wear contact lenses that continuously alert them to variations in their glucose levels by changing colors. This facility reduces the need to routinely draw blood throughout the day.

The non-invasive technology, developed by Chemical and Biochemical Engineering professor Jin Zhang at The University of Western Ontario, uses extremely small nanoparticles embedded into the hydrogel lenses. These engineered nanoparticles react with glucose molecules found in tears, causing a chemical reaction that changes their color.

Zhang received $216,342 from the Canada Foundation for Innovation (CFI)  to further develop technologies using multifunctional nanocomposites.These technologies have vast potential applications beyond biomedical devices, including for food packaging. For example, nanocomposite films can prevent food spoilage by preventing oxygen, carbon dioxide and moisture from reaching fresh meats and other foods, or by measuring pathogenic contamination; others can make packaging increasingly biodegradable.

SURFACE TO TOUCH SCREEN: BY THIN FILMS.

DISPLAX, a Portugal-based company, promises to turn any surface — flat or curved — into a touch-sensitive display. The company has created a thinner-than-paper polymer film that can be stuck on glass, plastic or wood to turn it into an interactive input device.

It is extremely powerful, precise and versatile and film can be used on top of anything including OLED and LCD displays.

Human-computer interaction that goes beyond keyboards and mouse has become a hot new area of emerging technology. Since Apple popularized the swipe and pinch gestures with the iPhone, touch has become a new frontier in the way we interact with our devices.

In the past, students have shown a touchscreen where pop-up buttons and keypads can dynamically appear and disappear. That facilitates the user to experience the physical feel of buttons on a touchscreen. In 2008, Microsoft offered Surface, a multitouch product that allows users to manipulate information using gesture recognition.

Displax’s films range from 3 inches to 120 inches diagonally.

Grids of nanowires are embedded in the thin polymer film that is just about 100 microns thick. A microcontroller processes the multiple input signals it receives from the grid. A finger or two placed on the screen causes an electrical disturbance. The microcontroller analyzes this to decode the location of each input on that grid. The film comes with its own firmware, driver — which connect via a USB connection — and a control panel for user calibration and settings.

Currently, it can detect up to 16 fingers on a 50-inch screen. And the projective capacitance technology that Displax uses is similar to that seen on the iPhone, so the responsiveness of the touch surface is great.

And if feeling around the screen isn’t enough, Displax allows users to interact with the screen by blowing on it. Displax says the technology can also be applied to standard LCD screens.

Displax’s versatility could make it valuable for a new generation of displays that are powering devices such as e-readers. For instance, at the Consumer Electronics Show last month, Pixel Qi showed low-power displays that can switch between an active color LCD mode and an e-reader-like, low-power black-and-white mode. Pixel Qi’s displays, along with other emerging display technologies from the likes of Qualcomm’s Mirasol and E Ink’s color screen are keenly awaited in new products because they promise to offer a good e-reader and a netbook in a single device.

But touch is a feature that is missing in these emerging displays. Displax could help solve that problem.

It is also more versatile than Microsoft Surface. The film is about 100 microns thick, while Surface is about 23 inches deep. Surface is not just another hardware solution, it includes integrated software applications and vision technology so it can respond to just the shape of the object.

Displax’s thin film offers a big breakthrough for display manufacturers because it they don’t have to make changes to their manufacturing process to use it. Displax says the first screens featuring its multitouch technology will start shipping in July.

NANOPARTICLE ORGANIC MEMORY FIELD-EFFECT TRANSISTOR

For the first time, CNRS (Centre National de la Recherche Scientifique; National Center for Scientific Research) and CEA researchers have developed a unique transistor that can simulate the main functionalities of a synapse.

This organic transistor, based on pentacene and gold nanoparticles and known as a NOMFET (Nanoparticle Organic Memory Field-Effect Transistor), has revolutionized modern computing world and inspired the researchers to create new generations of neuro-inspired computers, capable of responding in a manner similar to the nervous system.

In the development of new information processing strategies, one approach consists in mimicking the way biological systems such as neuron networks operate to produce electronic circuits with new features. In the nervous system, a synapse is the junction between two neurons, enabling the transmission of electric messages from one neuron to another and the adaptation of the message as a function of the nature of the incoming signal. For example, if the synapse receives very closely packed pulses of incoming signals, it will transmit a more intense action potential. Conversely, if the pulses are spaced farther apart, the action potential will be weaker. It is exactly the nature what researchers succeeded to have copied in the NOMFET.

A transistor, the basic building block of an electronic circuit, can be used as a simple switch - it can then transmit, or not, a signal - or instead offer numerous functionalities for example :amplification, modulation, encoding, etc.

The innovation of the NOMFET resides in the original combination of an organic transistor and gold nanoparticles. These encapsulated nanoparticles, fixed in the channel of the transistor and coated with pentacene, have a memory effect that allows them to transmit in a way a synapse does during the transmission of action potentials between two neurons. This property therefore makes the electronic component capable of evolving as a function of the system in which it is placed. Its performance is comparable to the seven CMOS transistors that have been needed until now to achieve this plasticity.

The devices produced have been optimized to nanometric sizes in order to be able to integrate them on a large scale. Neuro-inspired computers, produced using this technology, are capable of functions comparable to those of the human brain.

Unlike silicon computers, widely used in high performance computing, neuro-inspired computers can resolve much more complex problems, such as visual recognition.

NANOSCALE OPTICAL FIBERS FOR DETECTION OF BIOTERRORIST AGENTS

In an age when bacterial agents may be intentionally released as method of terrorist attack, there is an increased need for quick diagnostic methods that require limited resources and personnel. Thomas Inzana, the Tyler J. and Frances F. Young Chair of Bacteriology in the Virginia-Maryland Regional College of Veterinary Medicine at Virginia Tech, has been awarded a grant from the National Institutes of Health to develop such a diagnostic test.

He and his co-investigators, James “Randy” Heflin, a professor in the Department of Physics in the university’s College of Science, and Abey Bandera, a research assistant professor in the veterinary college, are working to develop nanoscale optical fiber biosensor tests, or assays, for detection of Francisella tularensis, Burkholderia mallei, and B. pseudomallei.

Currently, testing involves either the use of cultures in Biosecurity Level-3(BSL-3) laboratories, or since facilities do not have BSL-3 capabilities -- serology or antibody-based testing. Both require extensive materials and training, and the results can take days or weeks.

“This assay will be rugged, portable, inexpensive, and rapid,” said Inzana, who is also the associate vice president for research programs at the university. All of these are critical to minimizing the affect on an intentionally introduced biological weapon.

The increased speed of detection allowed by this new, optical fiber assay will also increase the speed of treatment for those affected, according to Inzana.

The optical fiber is coated with antibodies or DNA that will bind to antigens or DNA in the specimen. When this happens, the light that normally passes through the fiber will be decreased, indicating the presence of a biological agent.

According to Inzana, there are advantages and disadvantages to both. Antigens are more abundant and closer to the surface of the agent, but aren’t always very specific. DNA, however, is very specific, but is less plentiful and resides deep within the cell.

NEW METHOD PRESENTED FOR SYNTHESIS & GROWTH OF CARBON NANOTUBES

Researchers at the Plasma Physics Research Center of Iran's Islamic Azad University devised a new method to improve the synthesis and growth of carbon nanotubes. Carbon nanotubes synthesized in this new way can be used in manufacturing electron emitters and solid devices with high thermal conductivity.

Since 1991, along with the discovery of carbon nanotubes, researchers have always attempted to optimize their production and to utilize them in different industries. Majid Mojtahedzadeh Larijani, one of the researchers, undertook this study with the aim of synthesizing carbon nanotubes by a novel method, which is the growth on the beds with catalytic base by means of ionic bombardment.

The bed used in this study was steel. First in the process, sub-layer underwent surface was treated by argon ionic bombardment at different ion energies and doses. Then by Chemical Vapor Deposition method carbon nanotube growth on bombarded samples using hydrogen and steel gases was accomplished.

The results showed that ion energy and dose in which sub-layer surface turns into fine grains are very appropriate for the growth of dense and adhesive carbon nanotubes. These nanotubes could be applied for manufacturing electron emitters and solid devices with high thermal conductivity in electronics industry.

PARTICLE LENGTH CONTROLS THE TOXICITY AND BIOACTIVITY OF TITANIUM DIOXIDE NANOMATERIAL

Titanium dioxide (TiO2) nanomaterials have considerable beneficial applications varying from additives in paint, paper, plastics and cosmetics to uses in photocatalysts, solar cells and medical materials and devices. It has been established for many years that pigment-grade TiO2 (200 nm sphere) is relatively inert when internalized into a biological model system (in vivo or in vitro).

For this reason, TiO2 nanomaterials are an attractive alternative in applications where biological exposures will occur. Unfortunately, metal oxides on the nanoscale (one dimension <100 nm) may or may not exhibit the same toxic potential as the original material. A further complicating issue is the effect of modifying or engineering of the nanomaterial to be structurally and geometrically different from the original material. TiO2 nanospheres, short (<5 µm) and long (>15 µm) nanobelts were synthesized, characterized and tested for biological activity using primary murine alveolar macrophages and in vivo in mice. This study demonstrates that alteration of anatase TiO2 nanomaterial into a fibre structure of greater than 15 µm creates a highly toxic particle and initiates an inflammatory response by alveolar macrophages.

These fibre-shaped nanomaterials induced inflammasome activation and release of inflammatory cytokines through a cathepsin B-mediated mechanism. Consequently, long TiO2 nanobelts interact with lung macrophages in a manner very similar to asbestos or silica.

These observations suggest that any modification of a nanomaterial, resulting in a wire, fibre, belt or tube, be tested for pathogenic potential.