The twin toxics: nanotubes and asbestos

Sales of carbon nanotubes could reach $2 billion annually within the next 4 years, according to forecasting firms, but a new study suggests caution and more research on human exposure and health impacts.
Like other nanomaterials, tiny but strong-as-steel nanotubes are touted as this century's wonder materials. Researchers and manufacturers expect these nanomaterials to usher in a new era of drugs, high-efficiency batteries, and exciting electronics. But scientists fear that the nanotubes' striking resemblance to asbestos also implies a likelihood of asbestos-like impacts on humans. A new study published in Nature Nanotechnology on May 20 proves these fears to be well founded. It shows that the materials can induce lung cancer in mice.

In the study, Ken Donaldson of the University of Edinburgh (U.K.) and his colleagues exposed the lungs of mice to 50 micrograms of multiwalled carbon nanotubes by injecting the nanotubes into the mice's abdominal cavities. The effects—inflamed mesothelium (a membrane that lines lung tissue) and development of lesions—were similar to those of mesothelioma, a known health hazard caused by inhaling asbestos over an extended period of time.

The study "really confirms that the fiber hypothesis applies to carbon nanotubes," says coauthor Andrew Maynard of the Woodrow Wilson International Center for Scholars Project on Emerging Nanotechology. According to this hypothesis, fibers that are long, thin, straight, and durable have similar effects on the body, regardless of whether they are made of asbestos or carbon atoms, Maynard adds.

The results provide evidence of potential harm if people are exposed to carbon nanotubes in sufficient quantities. But the study cannot say whether people will be exposed and, if so, under what conditions. "That's one of the big unknowns here that's really got to be addressed as fast as possible," says Maynard. Still, the results show the need for more research on exposure scenarios, the health effects of nanomaterials, and guidelines from

New nano-structured materials

It has been known for the last few years that man made synthetic polymeric materials have the potential to grow and multiply human cells. 'About 10 years ago, scientists discovered the important influence that nano-structures had on the way a line of cells would develop. It was the beginning of an entire new scientific field, somewhere between medicine and nanotechnology,' says Professor Johannes Heitz, Senior Research Associate at the University of Linz, Austria and main coordinator of the ModPolEUV project.

In the case of human skin cells, re-implantation of the tissue can be performed once a sufficient amount of skin is obtained, by growing it on a polymeric material surface.

However, in many cases, imperfections in the material structure can make the process relatively long and sometimes inefficient, with cells developing erratically.

The team of Austrian, Czech and Polish scientists involved in the research project managed to develop a new and simple way to create nano-structured materials that would allow a better development of human cells.

The Polish partner in the team, the Military University of Technology of Warsaw, has been in charge of the development of the new laser-based technology called EUV (Extreme Ultra-Violet) that was used for the creation of the nano-structured polymer surfaces. A beam of EUV light formed with a unique mirror developed by the Czech partner REFLEX S.R.O is directed on the surface allowing the creation of new kinds of polymeric materials. This innovative technique allows for a very high degree of precision, from 10 to 20 nanometres, whereas conventional techniques allowed only for a maximal precision level of 100 nanometres. 'One of the newest theories in the field of cell growing is that the smaller the structure, the wider the possibilities to manipulate cells,' says Professor Heitz.

A wide range of human cells

The EUV technique, thanks to its particular level of precision, also allows for the conservation of the material's structure, which was not the case with other methods used to modify the polymer. 'A regular structure is essential if the material is to be used for the purpose of growing human cells,' says Dr Henry k Fiederowicz, Professor at the Military University of Technology.

The story does not end there. Nano-structures built through the EUV technique have the ability to influence the behaviour of organic cells and different kind of cells can be grown better and faster depending on the type of polymer surface used.

The variety of material used to grow human stem cells will determinate the way cells will differentiate, meaning that they will transform into another human cell type. In other words: 'Using one type of polymer material or another will help you grow different types of muscle, nerves, cells adapted to a human heart, bone or any other part of the human body,' says Professor Heitz.

Thanks to their affinity to human tissue and cells, polymeric materials could also be used for designing entire artificial implants. Indeed, many types of implants are already being made out of polymer materials, such as heart valves and bloods vessels. Using the EUV technique would reduce the odds of implant rejection, as the range of new materials created could be adapted to interact perfectly with specific parts of a patient's body.

Broad applications

All partners agree on the fact that EUREKA has helped them to find elsewhere in Europe the expertise and skills unavailable in their own countries. The next step is to bring their innovation to the market.

The Military Institute of Technology has already handled several EUV installations to laboratories in the USA, Germany, the Czech Republic, France, Japan, China and South Korea. It is now preparing for a full commercial phase, in partnership with the Polish company PREVAC, a leader in the market of high-precision instruments.

Applications of this novel technique could go far beyond nano-medicine and bio-technologies. An important potential market could be the one of micro-electronics, with its ever-expanding need for high-precision lithography; applications could be proposed to every type of industry where nano-structures are used. For instance, in micro-mechanics, integrated optics, wear reduction or the production of nano-composite materials.

For researchers at Linz University, the cell-growing technology is still in a testing phase and Professor Heitz prefers not to be overwhelmed by enthusiasm, even though he concedes that results have been 'very encouraging so far'. 'The interaction of cells with which structure dimensions are below 100 nanometres is currently the topic of a huge international effort,' he says. Despite the importance of the innovation 'our contribution is very small when compared to the many other laboratories working in this field at the moment'.

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