Invisibility cloaks one step closer

Scientists have for the first time engineered 3-D materials that can reverse the natural direction of visible and near-infrared light, a development that could help form the basis for higher resolution optical imaging, nanocircuits for high-powered computers, and, to the delight of science-fiction and fantasy buffs, cloaking devices that could render objects invisible to the human eye.

Two breakthroughs in the development of metamaterials - composite materials with extraordinary capabilities to bend electromagnetic waves - are reported separately this week.

Applications for a metamaterial entail altering how light normally behaves. In the case of invisibility cloaks or shields, the material would need to curve light waves completely around the object like a river flowing around a rock. For optical microscopes to discern individual, living viruses or DNA molecules, the resolution of the microscope must be smaller than the wavelength of light.

The common thread in such metamaterials is negative refraction. In contrast, all materials found in nature have a positive refractive index, a measure of how much electromagnetic waves are bent when moving from one medium to another.

In a classic illustration of how refraction works, the submerged part of a pole inserted into water will appear as if it is bent up towards the water's surface. If water exhibited negative refraction, the submerged portion of the pole would instead appear to jut out from the water's surface. Or, to give another example, a fish swimming underwater would instead appear to be moving in the air above the water's surface.

Other research teams have previously developed metamaterials that function at optical frequencies, but those 2-D materials have been limited to a single monolayer of artificial atoms whose light-bending properties cannot be defined. Thicker, 3-D metamaterials with negative refraction have only been reported at longer microwave wavelengths.

"What we have done is take two very different approaches to the challenge of creating bulk metamaterials that can exhibit negative refraction in optical frequencies," said Xiang Zhang, professor at UC Berkeley's Nanoscale Science and Engineering Center, funded by the National Science Foundation (NSF), and head of the research teams that developed the two new metamaterials. "Both bring us a major step closer to the development of practical applications for metamaterials."

Zhang is also a faculty scientist in the Material Sciences Division at the Lawrence Berkeley National Laboratory.

Humans view the world through the narrow band of electromagnetic radiation known as visible light, with wavelengths ranging from 400 nanometers (violet and purple light), to 700 nanometers (deep red light). Infrared light wavelengths are longer, measuring from about 750 nanometers to 1 millimeter. (A human hair is about 100,000 nanometers in diameter.)

For a metamaterial to achieve negative refraction, its structural array must be smaller than the electromagnetic wavelength being used. Not surprisingly, there has been more success in manipulating wavelengths in the longer microwave band, which can measure 1 millimeter up to 30 centimeters long.

In the Nature paper, the UC Berkeley researchers stacked together alternating layers of silver and non-conducting magnesium fluoride, and cut nanoscale-sized fishnet patterns into the layers to create a bulk optical metamaterial. At wavelengths as short as 1500 nanometers, the near-infrared light range, researchers measured a negative index of refraction.

each pair of conducting and non-conducting layers forms a circuit, or current loop. Stacking the alternating layers together creates a series of circuits that respond together in opposition to that of the magnetic field from the incoming light.

Valentine also noted that both materials achieve negative refraction while minimizing the amount of energy that is absorbed or "lost" as light passes through them. In the case of the "fishnet" material described in Nature, the strongly interacting nanocircuits allow the light to pass through the material and expend less energy moving through the metal layers.

"Natural materials do not respond to the magnetic field of light, but the metamaterial we created here does," said Valentine. "It is the first bulk material that can be described as having optical magnetism, so both the electrical and magnetic fields in a light wave move backward in the material."

The metamaterial described in the Science paper takes another approach to the goal of bending light backwards. It is composed of silver nanowires grown inside porous aluminum oxide. Although the structure is about 10 times thinner than a piece of paper - a wayward sneeze could blow it away - it is considered a bulk metamaterial because it is more than 10 times the size of a wavelength of light.

The authors of the Science paper observed negative refraction from red light wavelengths as short as 660 nanometers. It is the first demonstration of bulk media bending visible light backwards.

"The geometry of the vertical nanowires, which were equidistant and parallel to each other, were designed to only respond to the electrical field in light waves," said Jie Yao, a student in UC Berkeley's Graduate Program in Applied Science and Technology and co-lead author of the study in Science. "The magnetic field, which oscillates at a perpendicular angle to the electrical field in a light wave, is essentially blind to the upright nanowires, a feature which significantly reduces energy loss."

The innovation of this nanowire material, researchers said, is that it finds a new way to bend light backwards without technically achieving a negative index of refraction. For there to be a negative index of refraction in a metamaterial, its values for permittivity - the ability to transmit an electric field - and permeability - how it responds to a magnetic field - must both be negative.

The benefits of having a true negative index of refraction, such as the one achieved by the fishnet metamaterial in the Nature paper, is that it can dramatically improve the performance of antennas by reducing interference. Negative index materials are also able to reverse the Doppler effect - the phenomenon used in police radar guns to monitor the speed of passing vehicles - so that the frequency of waves decreases instead of increases upon approach.

But for most of the applications touted for metamaterials, such as nanoscale optical imaging or cloaking devices, both the nanowire and fishnet metamaterials can potentially play a key role, the researchers said.

"What makes both these materials stand out is that they are able to function in a broad spectrum of optical wavelengths with lower energy loss," said Zhang. "We've also opened up a new approach to developing metamaterials by moving away from previous designs that were based upon the physics of resonance. Previous metamaterials in the optical range would need to vibrate at certain frequencies to achieve negative refraction, leading to strong energy absorption. Resonance is not a factor in both the nanowire and fishnet metamaterials."

While the researchers welcome these new developments in metamaterials at optical wavelengths, they also caution that they are still far off from invisibility cloaks and other applications that may capture the imagination. For instance, unlike the cloak made famous in the Harry Potter novels, the metamaterials described here are made of metal and are fragile. Developing a way to manufacture these materials on a large scale will also be a challenge, they said.

Nevertheless, the researchers said achieving negative refraction in an optical wavelength with bulk metamaterials is an important milestone in the quest for such devices.

Goodbye to batteries

If a machine in a factory goes on strike, it could be for any of a thousand reasons. Self-sufficient sensors that provide their own power supply will soon make these machines more robust.

When a factory machine breaks down, it’s hard to know what to do. Production often comes to a standstill until the error has finally been pinpointed – and that can take hours. The causes are legion; in many cases it is all due to a single interrupted contact. Consequently, many manufacturers have long been hoping for a technology that will work without vulnerable power and data cables. The idea is basically feasible, using small devices that harvest energy from their surroundings and provide their own power supply rather like a solar calculator. Experts speak of energy self-sufficient sensor-actuator systems. These high-tech components normally consist of a sensor, a processor and a radio module. They measure position, force or temperature and transmit the data instantaneously by radio. In this way, vital machine data reach the control center without using cables at all. Is the machine overheating? Is the drive shaft wearing out?

So far, however, there are hardly any off-the-shelf solutions with their own energy supply.

Damaged Brain Can Be Repaired

Brain injury in adults can cause irreparable, long-term physical and cognitive damage. However, motor and spatial functions can be recovered if undamaged neurons are stimulated to create new innervation. This type of innervation develops spontaneously after a brain injury in very young children.

Researchers had previously shown – based on injury to the neuronal pathway linking the stem to the cerebellum – it was possible to induce reinnervation in young adults similar to that observed in newborn infants. This repair was rendered possible by treating the damaged cerebellum with a peptide chain Derived Neurotrophic Factor which plays a role in the development and satisfactory functioning of this neuronal pathway.

In the present case, the researchers have extended the use of this model and showed that the terminals of new axons interact with the network of undamaged neuronal cells to restore their associated functions, such as synchronized movement and spatial orientation. These results demonstrate a correlation between an improvement in behavior and the degree of reinnervation in the cerebellum. Thus a small amount of correctly-targeted reinnervation makes it possible to recover fine functions such as motor and cognitive skills.

These results open promising new perspectives and make it possible to envisage using BDNF – already employed during clinical trials on the treatment of neurodegenerative conditions such as Parkinson's disease – to repair the human brain after a cerebral lesion.

Asthma and Smoker’s Lung

Dry airways may not only play a central role in the development of the in-herited lung disease cystic fibrosis, but also in much more common ac-quired chronic lung diseases such as asthma and smoker’s lung, the ciga-rette smoke-induced chronic obstructive pulmonary disease (COPD). This is the conclusion reached by scientists at Heidelberg University Hospital under the direction of Assistant Professor Dr. Marcus Mall from the Department of Pediatrics at Heidelberg University Hospital and Professor Dr. Richard Boucher of the University of North Carolina at Chapel Hill. In ani-mal studies, they found that insufficient hydration of the airway surfaces leads to pathologies typical of chronic obstructive lung diseases in humans.

Thus, these findings point to a new approach for the treatment of these diseases, which are listed by the World Health Organization WHO as the fourth leading cause of death worldwide. There are currently no causal therapies available for treating these diseases; only the symptoms such as shortness of breath and oxygen deficiency can be treated. The results of the study have now been published in the “American Journal of Respira-tory and Critical Care Medicine”.

Cystic fibrosis gene causes airways to dry out and thickens mucus

In the hereditary disease cystic fibrosis, which affects about 8,000 people in Germany (about 80,000 people in the Western world), a defective gene causes a change in the transport of salt and water across the mucosal sur-faces in the lungs, the intestine and other organs, and thus produce a change in the composition of the secretions.

Using a mouse model he developed, Dr. Mall succeeded in proving a direct relationship between the defective gene and development of lung disease – certain sodium channels on the surface of airway cells that are respon-sible for the resorption of salt and water are “hyperactive”. The cells ab-sorb too much fluid, causing the airway surfaces to dry out. This gives rise to thick “dry” mucus that cannot be cleared. As a consequence, the respi-ratory tract gets clogged with mucus – the lungs cannot be cleaned effec-tively of inhaled allergens, toxins and pathogens, giving rise to chronic pulmonary inflammation and respiratory insufficiency.

Dry airways lead to allergic inflammation, chronic bronchitis and emphysema

The research team from Heidelberg and the US has now for the first time studied the spontaneous course of lung disease caused by dehydration of airway surfaces in mice from birth to adulthood. “We found changes that are not only typical for cystic fibrosis, but also for other chronic obstructive lung diseases such as asthma, chronic bronchitis, and emphysema,” re-ports Dr. Mall, head of the Heidelberg Cystic Fibrosis Center and also head of a research program funded by a Marie Curie Excellence Grant from the European Union.

In young mice, overly dry airways lead to allergic airway inflammation - characterized by an increase in specific white blood cells, the eosinophils - typically seen in asthma, a disease that affects every tenth child in Ger-many. Subsequently, adult mice gradually develop chronic bronchitis (dominated by neutrophils), and emphysema, i.e. the destruction of the small alveoli in the lungs that are responsible for the exchange of oxygen between air and blood. These changes are typical for lung disease caused by exposure to cigarette smoke.

Improved hydration through sodium channel blockers?

The researchers conclude that dehydrated airway surfaces could play a key role in the development of chronic obstructive pulmonary disease in hu-mans. These results indicate that improving hydration of airway surfaces and thus mucus clearance of the lungs, for example by blocking the so-dium channels in the cells of the respiratory tract could be a successful strategy for treating chronic obstructive pulmonary diseases of different etiologies. The Heidelberg research team now wants to test the benefits of this new therapeutic approach in animals.

New snapshot of the universe

Deep in the bowels of the earth –100 metres below ground in Geneva, Switzerland – lies a supermachine of 27 km circumference called the Large Hadron Collider (LHC) that has been built to unlock the mysteries of the universe.

Claude Leroy, a Université de Montréal physics professor, was among the 2,500 scientists from 37 countries recruited to help design, test and build the ATLAS detector at the supermachine that will provide a new perspective into what occurred at the time of the Big Bang and immediately after. Designed for CERN, the European Organization for Nuclear Research, the ATLAS detector, the largest among the four detectors operating at the supermachine in question, is 46 metres in length, 25 metres in height and 7000 tonnes in weight – or the size of three football fields.

Prof. Leroy was responsible for the radiation and irradiation studies conducted to ensure the ATLAS detector will run smoothly. His investigations also led to the creation of MPX, a small device attached throughout the supermachine and ATLAS that uses pixel silicon detectors to perform real-time measurements of the spectral characteristics and composition of radiation inside and around the ATLAS detector. The small devices essentially capture images of what’s inside the detector and its environment, such neutrons and photons, a world-first.

He also participated in physics studies that targeted the production of heavy leptons, excited leptons, quarks and supersymmetry, in particular the study of neutralinos as dark matter candidates. Prof. Leroy’s experiments were critical in ensuring the viability of the ATLAS detector at the core of the supermachine, which is the world’s biggest particles physics detector. Indeed, before the LHC can be started up, some 38,000 tons of equipment of the supermachine must be cooled down to minus 456 degrees Fahrenheit for the magnets to operate in a superconducting state. This will be achieved by using liquid helium for magnet. Parts of the ATLAS calorimeters use liquid argon cooled at minus 312 degrees Fahrenheit. “The radiation field produced by the operation of the machine and ATLAS is stronger than a nuclear reactor, so it is vital that its design master all aspects of physics,” said Prof. Leroy.

Supermachine’s Big Bang

The LHC will recreate conditions akin to the Big Bang – which many scientists believe gave birth to the universe – by colliding two beams of particles at close to the speed of light. Since it is estimated that only 4 percent of the universe has been charted, the supermachine will help answer the following questions in physics when it is turned on in summer

Use of powerful anticoagulants to prevent pulmonary embolism may actually lead to more deaths after surgery

Anticoagulants are routinely prescribed before and after total hip and knee replacement operations to reduce the risk of thrombosis, and death from pulmonary embolism in particular, as recommended by the Chest Physicians Consensus Statement. During the last decades, deaths from pulmonary embolism have fallen significantly due to a combination of advancements in anesthesia, better surgical techniques and care pre- and post-surgery, as well as a better understanding of how thrombosis develops as a result of surgery. In light of these developments, Sharock and his team looked at whether the prescription of potent anticoagulants by surgeons who perform joint replacement operations is still warranted, as these drugs also have side effects.

The authors reviewed 20 studies among a total of just over 28,000 patients undergoing joint replacement surgery who were prescribed medication to reduce the risk of thrombosis. They compared the total number of deaths and cases of non-fatal pulmonary embolism between three frequently used prevention protocols worldwide. Patients in group A received potent anticoagulants such as low molecular weight heparin; those in group B received local spinal or epidural anesthesia, pneumatic compression and aspirin; patients in group C were prescribed slow-acting oral anticoagulants such as warfarin.

The lowest number of deaths occurred in patients in group B. Patients in groups A and C were more than twice as likely to have died as those in group B. There was no difference in the number of deaths between groups A and C. Patients in group A were also at 60-70% greater risk of non-fatal pulmonary embolism than those in group B, indicating that pulmonary embolism occurs despite the use of powerful anticoagulants.

Sharock and colleagues conclude that “the American College of Chest Physicians should reconsider their guidelines to reflect the fact that pulmonary embolism occurs despite the use of potent anticoagulants and may, in fact, expose patients to increased mortality after surgery.” In their view, the current recommendations often result in physicians feeling compelled to prescribe these anticoagulants to avoid potential litigation when, in reality, these drugs could be doing more harm than good.

Umbilical cord blood cell therapy in an animal model of Alzheimer's disease

Following a series of low-dose infusions of human umbilical cord blood cells into mice with Alzheimer’s-like disease, the amount of amyloid-ß and ß-amyloid plaques—hallmarks of Alzheimer’s pathology in the brain—was markedly reduced. Amyloid-ß induces an inflammatory response in the brain associated with the interaction of CD40 and CD40L, two pro-inflammatory molecules.

Human umbilical cord blood cell therapy was associated with suppression of CD40-CD40L activity, suggesting that this therapeutic approach modulates the activity of the immune system, offering the potential to target the pathogenic inflammatory response that may contribute to a variety of degenerative conditions, including Alzheimer’s disease.

Jun Tan, PhD, MD, and colleagues from USF (Tampa), Yale University (New Haven, CT), Cedars-Sinai Medical Center (Los Angeles, CA), Saneron CCEL Therapeutics (Tampa, FL), and Saitama Medical School (Japan), concluded that human umbilical cord blood cell-induced disruption of the CD40-CD40L interaction may alleviate the key pathologic changes in the brain associated with Alzheimer’s disease in a report entitled, “Peripherally administered human umbilical cord blood cells reduce parenchymal and vascular beta-amyloid deposits in Alzheimer mice.”

“Previously, challenging observations have reported phenomena suggesting the non-hematologic therapeutic potential of blood stem cells. What is novel about this paper is its application to Alzheimer’s disease, and a significant advance in characterizing the ameliorative mechanism of action” says Graham C. Parker, PhD, Editor-in-Chief of Stem Cells and Development, and a research professor in The Carman and Ann Adams Department of Pediatrics, Wayne State University School of Medicine, Children's Hospital of Michigan.