Nanotech Viagra patch

Sildenafil citrate, commonly known as Viagra, is currently the first choice drug for erectile dysfunction but despite its success oral delivery of the drug is hampered by numerous side effects, the long delay before it starts working and the short amount of time it lasts. Researchers in Egypt think they may have a solution via nanotechnology.

Writing in the International Journal of Nanotechnology, the team describes tests on different formulations for sildenafil citrate transdermal nanocarriers as the delivery agent on human skin rather than the user having to swallow a pill. The benefits of such nanocarriers are that the drug gets into the bloodstream through the skin much more quickly than having to be ingested. Moreover, 70% of an oral dose of sildenafil citrate is wasted as it is metabolized by the liver without having any effect. Improved delivery via the transdermal route would avoid several side-effects as well as making onset of activity much quicker.

Pharmaceutical scientist Yosra S.R. Elnaggar of Alexandria University and professors there and at Alexandria and Pharos University, explain how previous attempts to create a Viagra transdermal application have been hampered by the properties of the drug itself. The drug has low oil and water solubility and is loathe to cross membranes, such as human skin, because of this. However, it is possible to encapsulate the drug in nanoemulsion based systems that can cross membranes readily. As such, the team has investigated two types of nanocarriers made using fat-like lipid molecules – the first made by forming an emulsion with the drug using a surfactant compound to allow the lipid molecules and drug to mix, much as soap will emulsify oil and water. The second option is a self-emulsifying nanocarrier that has its own inbuilt surfactant.

The team demonstrated in the laboratory that both formulations would have benefits for oral drug delivery, whereas only the nano-emulsion, rather than the self-emulsifying formulation, shows promise for a Viagra patch, in other words.

Elnaggar, Y., Massik, M., & Abdallah, O. (2011). Sildenafil citrate nanoemulsion vs. self-nanoemulsifying delivery systems: rational development and transdermal permeation International Journal of Nanotechnology, 8 (8/9) DOI: 10.1504/IJNT.2011.041443

Tubes in space

Carbon nanotubes form in space but use a metal-free chemistry until now unavailable to chemists on Earth. The discovery is a surprising outcome of laboratory experiments designed by Joseph Nuth at NASA’s Goddard Space Flight Center, in Greenbelt, Maryland, and his colleagues. They were hoping to understand how carbon atoms are recycled in stellar nurseries, the regions of space where stars and planets are born, but the finding could have applications in nanotechnology, as well as help explain some characteristics of supernovae.

Writing in the journal Astrophys J Lett, Nuth and colleagues explain how astrochemistry makes carbon nanotubes without requiring a metal catalyst. Nanotubes are produced, they say, when graphite dust particles are exposed to a mixture of carbon monoxide and hydrogen gases, conditions that exist in interstellar space.

The finding corroborates the discovery of graphite whiskers, bigger than nano nanotubes, in three meteorites. The meteoric discovery hinted at why some supernovae appear dimmer and farther away than they ought to be based on calculations using current models. Nuth’s approach is a variation of a well-established way to produce gasoline or other liquid fuels from coal. It’s known as Fischer-Tropsch synthesis, and researchers suspect that it could have produced at least some of the simple carbon-based compounds in the early solar system. Nuth proposes that the nanotubes yielded by such reactions could be the key to the recycling of the carbon that gets released when carbon-rich grains are destroyed by supernova explosions.

Stellar Nursery
A stellar nursery could be home to carbon nanotube factories (Credit: NASA, http://apod.nasa.gov/apod/ap021102.html)

The structure of the carbon nanotubes produced by Nuth and colleagues was determined by materials scientist Yuki Kimura, of Tohoku University, Japan, using transmission electron microscopy. He observed particles on which the original smooth graphite gradually morphed into an unstructured region and finally to an area rich in tangled hair-like masses. A closer look with an even more powerful microscope showed that these tendrils were in fact cup-stacked carbon nanotubes, resembling a stack of disposable drinking cups with the bottoms removed. If further testing indicates that the new method is suitable for materials-science applications, it could supplement, or even replace, the familiar way of making nanotubes, explains Kimura.

Researchers might also now evaluate whether graphite whiskers absorb light. A positive result would lend credence to the proposition that the presence of these molecules in space affects the observations of some supernovae.

LINKS

Astrophys J Lett, 2010, 710, L98-L101

http://dx.doi.org/10.1088/2041-8205/710/1/L98

Non-carbon nanotubes

Carbon nanotubes rose to prominence on the back of the buckyball chemistry revolution in the 1990s and are now emerging from prototype applications across academic and industrial laboratories. They have potential in microelectronic circuits, novel sensor devices, special light conductors, and light-emitting nanotubes for display technology.

Indeed, applications as diverse as medical technology, for fibres with ultrahigh tensile strength, in hydrogen storage, for rechargeable batteries, in catalysis, and in nanotechnology are being developed. There are even applications for antifouling coatings for ships.

With this in mind, chemists in Germany who work with inorganic materials have now developed an approach to synthesising tin sulfide nanotubes which could expand the nanotube concept much further still and open up yet more avenues for applications. After all, carbon does not have a monopoly on nanotubes. Early in the development of tubular fullerene structures, inorganic chemists opted to make their nanotubes from metals and non-carbon atoms: tungsten sulfide, nickel chloride, vanadium sulfide, titanium sulfide, and indium sulfide. Many others have been produced.

Wolfgang Tremel and colleagues, Aswani Yella, Martin Panthoefer, Helen Annal Therese, Enrico Mugnaioli, Ute Kolb, of the Johannes Gutenberg-Universitaet in Mainz, Germany, have now developed a new process for the production of tin sulfide nanotubes, which they report in the Wiley journal Angewandte Chemie, the researchers found they could “grow” tin sulfide nanotubes from a drop of metal using a bismuth catalyst.

The team were faced with one of the fundamental problems of synthesising sulfidic nanotubes in that they require a high temperature to force the planar layers of material to bend and fuse into tubular structures. For tin sulfide, the situation is complicated still further by an unstable intermediate that is almost impossible to trap because it decomposes at a lower temperature.

The researchers used a different approach. First, they employed a vapour-liquid-solid (VLS) process, a technique borrowed from semiconductor scientists for producing nanowires as opposed to nanotubes. The process involved mixing bismuth metal powder with minute flakes of tin sulfide and heating this mixture in a tube furnace under a stream of the relatively unreactive noble gas argon. The product of the reaction forms a deposit at the cooler end of the tube.

The team explains that tiny droplets on the nanometre scale are form within the oven. These nanodroplets act as local points of contact for the tin so that the reactants become concentrated within the metal droplet and nanotubes can then grow from these seeds.

“In this process, the metal drop is obtained as a sphere at the end of the tube, and the nanotubes grow out of the sphere like a hair out of a follicle,” explains Tremel. “Catalysis by the metal droplet makes growth possible at low temperatures.”

The team has successfully grown nanotubes comprising multiple layers of tin sulfide with few defects. The nanotubes have diameters of between 30 and 40 nanometres and are 100 to 500 nm in length.

Tin sulfide nanotubes grow from droplets (Credit: Tremel et al/Wiley-VCH)

Angewandte Chemie, in press

Group of Prof. Dr. Wolfgang Tremel