The poster child for the nanotechnology revolution, the nanotube, is beginning to look a bit like the poster child of environmental contamination, asbestos. New research with mice suggests that certain nanotubes can cause potentially dangerous inflammation similar to that caused by asbestos, the culprit behind the worst occupational health disaster in United States history.
Discovered nearly 20 years ago, carbon nanotubes have been described as the wonder material of the 21st century. Light as plastic and stronger than steel, they are being developed for use in new drugs, advanced batteries, and futuristic electronics. But since their discovery, researchers have questioned whether nanotubes' shape might be a cause for concern. Long, multiwalled nanotubes (MWNTs), for example, which are formed from concentric layers of graphite, tend to have a rigid, needle-like shape that resembles that of asbestos fibers.
And asbestos is bad news. A family of naturally occurring mineral fibers, it was widely used in the late 19th and early 20th century for insulation, fire-resistant coatings, fireproof drywall, and even siding for houses and buildings. But by the 1950s and 1960s, it became clear that asbestos exposure could trigger lung disease and cancer. The fibers penetrate deep into the lungs, where their long, thin shape makes them hard to clear. Macrophages, cells that normally engulf and clear foreign substances in the body, can't surround asbestos fibers, as the tiny lances puncture the cells. This can set off a chronic inflammatory response that can lead to mesothelioma, a cancer of the protective lining that covers most of the body's internal organs.
Although previous studies had suggested that MWNTs can cause cancer in mice genetically predisposed to it, the nanotubes' effects on normal mice has not been studied as extensively. In the new study, Andrew Maynard, chief scientist at the Woodrow Wilson International Center for Scholars' Project on Emerging Nanotechnologies in Washington, D.C., teamed up with Ken Donaldson and colleagues at the University of Edinburgh, U.K., as well as team members from three other institutions in the United Kingdom to compare the effect of long and short MWNTs, injecting them into the lining of the abdominal cavity of normal mice. The researchers also injected floppier, single-walled nanotubes and asbestos fibers into other mice. Only the long, rigid MWNTs and asbestos fibers triggered a chronic inflammatory response, the researchers report online today in Nature Nanotechnology.
"This study is important in that it links multiwalled nanotubes to a disease of grave human consequence," says Kristen Kulinowski, executive director of the Center for Biological and Environmental Nanotechnology at Rice University in Houston, Texas. The new work does not prove that MWNTs cause cancer, Kulinowski says, "but it strongly suggests we better learn more." Maynard adds that the study also suggests that engineers may be able to avoid health risks by using either single-walled nanotubes or short MWNTs. He adds that the new work underscores the need to determine the potential health and environmental effects of nanoparticles before their use becomes widespread.