Showing Spotlights 1769 - 1776 of 2275 in category All (newest first):
Since their discovery in 1961, liposomes - nanoscale vesicles composed of phospholipids - have been developed as nano-vectors that are used for a variety of biomedical applications including diagnostic imaging, gene therapy, biosensing and targeted drug delivery. In fact, the FDA-approved drugs Ambisome, Doxil and DaunoXome all contain liposomal formulations. Such liposomes are typically comprised of glycerol-based phospholipids that contain a hydrophilic (water-soluble) head-group and one or two hydrophobic (water-insoluble) hydrocarbon chains of varying length. In aqueous solution, these phospholipids self-assemble into a lipid bilayer, with the hydrophilic lipid groups oriented toward the aqueous solution and the hydrophobic groups protected in the bilayer's interior. The bilayers form spherical vesicles that are used to carry drugs and diagnostic imaging agents to sites of interest within the body. The hollow interior of the vesicles is hydrophilic and can easily encapsulate a variety of hydrophilic drugs or imaging agent molecules, which are then released from the liposomes in a controlled fashion. But what about hydrophobic molecules - those that aren't water-soluble and therefore aren't easily encapsulated within the interior of traditional phospholipid liposomes? Many beneficial, yet water-insoluble drugs do exist, but the current methods used to administer to these drugs to patients, such as dissolving them in alcohols, castor oil or other hydrophobic liquids for injection, can cause patients much discomfort or other side effects. For these reasons, the development of a nano-vector with a hydrophobic interior - one that could successfully encapsulate and release hydrophobic molecules - is of great interest to the nanomedicine community.
Mar 3rd, 2008
Since their discovery, the single-walled carbon nanotube (SWCNT) has evolved into one of the most intensively studied materials. A SWCNT can be regarded as a monolayer of a graphene sheet rolled up to form a seamless cylinder with axial symmetry and in general exhibiting a spiral conformation called chirality. Chirality is defined by a single vector called the chiral vector (n,m). This chiral vector is dependent on the orientation of the tube axis with respect to the hexagonal lattice. SWCNTs with different chiral vectors have dissimilar properties such as optical activity, mechanical strength and electrical conductivity. An obvious question that has been around since their discovery, but so far has not been satisfactorily answered, is how small the smallest SWCNT is. Theoretical calculations predict that the smallest diameter for a stable SWCNT is around 0.4 nm, and there are three possible structures that correspond with this value - chiral vectors (5,0), (3,3) or (4,2). Many efforts have been made to produce the smallest SWCNT and identify its atomic structure, but the techniques used were not accurate enough. Consequently, until now, the diameter and structure of the smallest possible carbon nanotube have remained in doubt. Not anymore, though. Researchers in Japan, affiliated with Sumio Iijima, the discoverer of carbon nanotubes, have successfully synthesized the smallest SWCNTs with a diameter of 0.4 nm by thermal decomposition of ferrocene molecules inside commercial-grade SWCNTs with a diameter of 1.1 nm. Apart from the scientific aspects of these findings, using the inner space of a carbon nanotube as a reaction cell appears to be an intriguing approach to fabricating new structures which would be unstable on their own.
Feb 29th, 2008
When two surfaces approach each other in air, they attract. A phenomenon that is explained by van der Waals forces that affect molecules' interaction. Without these - very weak - intermolecular forces, life as we know it would be impossible. They are responsible for a number of properties of molecular compounds, including crystal structures, condensing, melting and boiling points, surface tension, and densities. Intermolecular forces form molecules like enzymes, proteins, and DNA into the shapes required for biological activity. Van der Waals forces can also be repulsive, for instance when two surfaces approach each other in liquid: the same force which causes attraction in air (and which is responsible for so called stiction and adhesion) can be made repulsive by choosing the right combination of surface materials and intervening liquid. This force has the characteristic that it increases very rapidly with very small changes in separation when the surfaces are close to each other. Researchers now have shown that if repulsive van der Waals forces exist between two surfaces prior to their contact then friction is essentially precluded and supersliding is achieved. This opens the possibility that, in certain material systems, the controlled use of repulsive van der Waals forces could be a way to reduce, if not eliminate, friction.
Feb 28th, 2008
The process of bringing a major new drug to market, from discovery to marketing, takes about 10-12 years and costs an average of $500-$800 million in industrialized countries. And still, most drugs fail before they even make it to market. About 80 percent of drugs never make it through their clinical trials. Of the medications that actually enter consumer use, an average of just 60 percent provide therapeutic benefits to patients. For a pharmaceutical company the results of the process designing new drugs leads to a library of novel compounds that are created with a specific goal, a given set of criteria. Often these criteria include the selectivity for a particular known receptor. A new drug treatment can be discovered by testing those drugs on other receptors by trial and error. Since this is a very expensive approach, pharma companies have developed sophisticated computer models that help reduce the risk and uncertainty inherent in the drug-development process. Here, one starts with a computer model of the structure of a receptor and a drug. The goal is to predict by simulation how a drug will dock (interact with a receptor), or how the receptor will fold. Drug design based on mathematical models will also become a massive task within the emerging field of nanomedicine. Although nanotechnology offers great visions of improved, personalized treatment of disease, at the same time it renders the problem of selecting the candidates for biological testing astronomically more complex. The new notion of 'design maps' for nanovectors - similar to the concept of the periodic table for chemical elements - could provide guidance for the development of optimized injectable nanocarriers through mathematical modeling.
Feb 27th, 2008
Transparent electrical conductors pervade modern electronic devices, providing a critical component of digital cameras and video recorders, solar cells, lasers, optical communication devices, and solid-state lighting. Given the advantageous electrical properties of carbon nanotubes (CNTs), researchers already have used CNTs to impart electrical conductivity to polymeric thin films and coatings while maintaining excellent optical transparency. While this was done initially with complex lithography processes and sophisticated deposition facilities, advances in nanotube chemistry have enabled both the dissolution and dispersion of CNTs in various solvents. This has led to new alternatives for fabricating CNT patterns by simply dispensing/printing the dissolved/dispersed particles on substrates. Most methods of fabricating CNT transparent conductive film, such as vacuum filtering, laser printing, dip coating, spray coating and contact printing, require two fabrication steps to achieve the patterns. The first is to fabricate the film over all the area of the substrate. The second is to make the pattern by chemical etching or pattern transfer. In contrast, a direct printing approach has the merits of forgoing complex and expensive equipment, reducing the fabrication processes, saving the amount of material used, and removing chemical exposure in the processes. The use of off-the-shelf inkjet printers for printing patterns of carbon nanotubes on paper and plastic surfaces has been previously reported. These first inkjet demonstrations were done with multi-walled CNTs but now researchers in South Korea have managed to print pure single-walled CNTs based inkjet patterns.
Feb 26th, 2008
Adhesive tapes are ubiquitous in our lives, whether it's on the back of a yellow sticky note, the tape that closes baby diapers, masking connectors on printed circuit boards, or surgical tape in hospitals. Most adhesive tape will stick to a wide variety of surfaces - provided that they are clean and dry. Adhesive tapes are made up of two components: a carrier which is usually paper or plastic, and an adhesive which is either water or solvent based. Many modern adhesive tapes use pressure sensitive adhesives. When you apply pressure to the tape with your finger, a strong adhesive bond is formed. Most tapes have poor ageing properties and will deteriorate quickly: with time, after several uses, or as the sticky side becomes dirty, they lose their adhesive ability. As we have reported previously, scientists are very interested in exploring the secret of the gecko's adhesive properties and to use this knowledge to create superior man-made adhesives. But it's not just the stickiness that intrigues researchers: because geckos are able to walk across a dusty or dirty surface and then scale a vertical wall without problems, their feet must also possess some kind of self-cleaning ability. Scientists have now managed to mimic the remarkable self-cleaning abilities of the gecko, as well as lotus leaves, and incorporate this ability into the design of a self-cleaning, carbon nanotube based adhesive material.
Feb 25th, 2008
Only 30% of all freshwater on the planet is not locked up in ice caps or glaciers (not for much longer, though). Of that, some 20% is in areas too remote for humans to access and of the remaining 80% about three-quarters comes at the wrong time and place - in monsoons and floods - and is not always captured for use by people. The remainder is less than 0.08 of 1% of the total water on the planet. Expressed another way, if all the earth's freshwater were stored in a 5-liter container, available fresh water would not quite fill a teaspoon. The problem is that we don't manage this teaspoon very well. Currently, 600 million people face water scarcity. Depending on future rates of population growth, between 2.7 billion and 3.2 billion people may be living in either water-scarce or water-stressed conditions by 2025. Freshwater looks like it will become the oil of the 21st century - scarce, expensive and the reason for armed conflicts. While in our previous article we have only talked about nanotechnology and water in general terms, a new paper gives us the opportunity to look in more detail at the role that nanotechnology could play in resolving issues relating to water shortage and water quality. This review highlights the uses of nanotechnology in areas relevant to water purification, including separation and reactive media for water filtration, as well as nanomaterials and nanoparticles for use in water bioremediation and disinfection.
Feb 22nd, 2008
There has been quite a buzz about graphene, a single atomic layer thick, plane of carbon atoms arranged in a honeycomb lattice. Discovered only in 2004, graphene exhibits many exotic properties and currently is considered the most exciting new material system among nanotechnology researchers. This rising star in material science exhibits remarkable electronic properties that qualify it for applications in future optoelectronic devices. In a first experimental study of the thermal conductivity of single-layer graphene, researchers found that on top of many unique electronic properties, graphene also is an extraordinary good heat conductor. Measurements revealed that graphene's near room temperature thermal conductivity, which is in the range from 3500-5300 W/mK, is much higher than that of diamond, the best bulk crystal heat conductor. It appears that the thermal conductivity of graphene is larger than conventionally accepted experimental values reported for individual suspended carbon nanotubes (CNTs) and corresponds to the upper bound of the highest values reported for single-wall CNT bundles. The superb thermal conduction property of graphene is beneficial for its proposed electronic applications and establishes graphene as an excellent material for thermal management also in optoelectronics, photonics and bioengineering.
Feb 21st, 2008