The Nano Raceby Bill Chameides | November 3rd, 2009
posted by Erica Rowell (Editor)
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The race between finding new applications for nanoparticles and determining if they are safe is still very much in question.
You know the expression “in the first place do no harm?” One of the fundamental principles all medical students are taught. You might think that when it comes to the environment, chemical manufacturers and regulators might abide by the same motto: before taking a new chemical to market, make sure it does no harm — also known as the precautionary principle [pdf].
In the United States, however, we typically exercise precaution, but not on behalf of the environment and public but rather on behalf of the manufacturers who, though required to report data related to a product’s potential health and environmental impacts, are unregulated until specific impacts are documented. In some cases this can be like closing the barn door after the toxic horse has already bolted. Take for example ozone-destroying Freons, numerous pesticides, or gasoline additives such as MTBE [pdf].
Nanoparticles Are a Case in Point
Quantum mechanics is one of the great intellectual achievements of the 20th century. It predicts that, contrary to common sense, the properties and behavior of the world change as one explores it on very, very small spatial scales.
Take carbon. In our everyday life we know it as a diamond or the graphite in your pencil or as a black glob of soot. But now take a bit of that graphite or diamond or soot and grind it down to a smaller and smaller size. For a while all you get is a smaller and smaller piece of carbon.
But then at some point, usually when the particle has been ground down to a size of about 100 nanometers (one nanometer is one billionth of a meter), that tiny piece of carbon becomes a nanoparticle, an entity with properties completely different from the regular old carbon particle.
Now, here’s a quiz: which is stronger, steel or carbon? The answer: it depends. Tennis-racket manufacturers have taken advantage of the strength and weight properties of carbon nanotubes to formulate lightweight rackets that are stronger than steel.
Nano Potential: Technological Breakthroughs or Dangerous Mischief Makers?
Nanoparticles could turn out to be our century’s technological breakthrough, the stuff that changes life for the better — for example by providing the material that makes solar power economical or electrical wires resistance-less.
While the world awaits major breakthroughs, other, more esoteric and even quotidian applications have been identified and sent to market. Nanoparticles abound in cosmetics, sunscreens, and clothes.
This is great — I love not having to iron my shirts. But there may be a problem. While a chemical like carbon in its normal shape and size may be harmless, that same carbon in the form of a nanoparticle may not be. Because they are so tiny, nanoparticles can get to places in our bodies that ordinary particles can’t, and when they get there, they may do some mischief.
And thus we have our race between finding new applications and finding if they’re safe. Here’s an update from the racetrack.
Carbon Nanotubes Not So Great for Mice
Carbon nanotubes are made of carbon and shaped like a tube — long and thin. Because this is similar to the shape of asbestos, which is known to cause mesothelioma or lung cancer, Jessica Ryman-Rasmussen of North Carolina State University and co-authors wondered whether carbon nanotubes might lead to similar diseases. And so they exposed mice to inhalable nanotubes and analyzed their lung tissue. Their results, reported in Nature Nanotechnology, appear to confirm that carbon nanotubes do penetrate the lungs’ membrane lining, causing inflammation and lesions.
The authors conclude that while the results are suggestive, the question of whether carbon nanotubes cause pulmonary disease in humans “is not known,” but they recommend “precautions” for handlers of carbon nanotubes who are most likely to inhale the stuff.
I wonder if some more basic precaution is also needed to delay the penetration of carbon nanotubes into our consumer products and buildings to make sure that these tiny particles don’t become the asbestos of the 21st century.
Nano Tech to Break the De-Icing Ice?
On the other side of the coin nano research is full speed ahead. One recent development might break the ice of, well, breaking the ice. Or more technically it might help prevent ice from forming in the first place.
Ice is a pain, no argument. Ice on your windshield means getting out the scraper for a full-frontal attack in frigid temperatures (and maybe making you late for that early morning meeting); ice on the sidewalk could mean a broken elbow (here’s to you, Madame Secretary); ice on a jet can lead to long delays on the tarmac; and ice on the road, a fatal accident.
De-icers are the weapons we use in the battle against ice. A popular, regular-sized weapon uses coatings made of a class of chemical called superhydrophobes. What are those? Well, do you remember Old Yeller? The hero dog got rabies, a condition also known as “hydrophobia” because infected individuals show a fear of water. In chemistry hydrophobic materials ”hate” or, a little less anthropomorphically, reject water. Superhydrophobic materials really, really reject water.
Superhydrophobic coatings are effective against ice because they prevent water molecules from binding to their surface, and if they can’t bind there, the water molecules can’t coalesce to form ice.
But there’s always room for a better de-icer and nanotechnology might help lead the way. Liangliang Cao of the University of Pittsburgh and co-authors report in the journal Langmuir that just such a de-icing breakthrough may be forthcoming by tuning the size of particles used in superhydrophobic surface coatings. Put differently, what’s important is not just the coating’s chemical properties but also its surface morphology.
In one experiment, for example, the authors found that varying the size of the nanoparticles in (changing the surface roughness of) the superhydrophobic coatings also changed the efficacy of their de-icing properties. (See a demonstration of a de-icing experiment using a 50-nanometer nanoparticle coating here.)
Stay tuned. Could be, in a few years, we will all be walking on a bed of ice-free nanoparticles — is that what they meant by walking in a winter wonderland? Hopefully we won’t have to hold our breath as we stroll though that brave new wonderland.filed under: faculty, health, Planetary Watch, policy
and: carbon, nanotechnology, precautionary principle, research