Peterborough, N.H. Nanostructured materials are poised to revolutionize engineering, offering an unprecedented level of control over physical properties. But environmental and health implications may impede the potential gains. A recent panel discussion explored how society might extract the benefits of the new technology without creating intractable problems for the environment.
Nanotechnology is popularly viewed as a futuristic era of molecular-scale robots that will perform useful tasks such as cleaning cholesterol and bacteria out of the bloodstream, said nanotech advocate Kevin Ausman, executive director of the Center for Biological and Environmental Nanotechnology at Rice University(Houston). But nearer term, this new frontier promises tailored materials that can give engineers greater control over design parameters, Ausman said.
What can be done with nanostructured materials is illustrated by a new field called targeted photothermal therapy. "You take a gold nanoshell that absorbs infrared light and attach a biomolecule to those shells that targets cancer cells. You inject them, and they flow throughout the body, stick to the cancer cells and flush out everywhere else," Ausman said.
The gold nanoshells are calibrated to a diameter that makes them absorb a specific wavelength of infrared light. "The nanoshells absorb the light, which would otherwise just pass through the body, and convert it to heat. So if you have tagged the cancer cells with these nanoshells, you can use them to cook the cancer to death," Ausman said. "We are in negotiation with the FDA on bringing it to stage-one clinical trials.
"This example gives you a flavor of the way that tuning these special properties of materials by controlling their size can do some exciting things. [In this case] it's for bioengineering, but it also shares that promise for mechanical engineering, for new forms of water treatment and new types of [stain repellent] clothing."
But nanotech may also introduce unwanted side effects that, if not managed effectively, might prompt bans on useful nanomaterials.
Nanotech pioneers can look to asbestos and DDT as examples of materials that solved critical long-standing problems but that, in turn, caused health and environmental problems so severe as to nullify the materials' benefits. Nanotechnology is setting out on the same road, promising effective medical treatments and "miracle" consumer products but also posing threats that must be neutralized if the technology is to be accepted.
Environmental Defense is a nonprofit corporation that has been monitoring such issues since 1967. During the panel discussion, program director John Balbus cited recent discoveries that he said reveal the downside of nanotech. "My role is to explain why people in the field of environmental health are developing strong concerns about the widespread distribution of nanomaterials [before] an adequate evaluation of their potential risks" has been made, Balbus said.
An example of what can go wrong turned up in an experiment to use quantum dots to make tumors visible. As in the targeted-photothermal-therapy technique, the quantum dots were treated with a biomolecule that caused them to stick to tumor cells. Made from small clusters of gold atoms, the quantum dots resonated at a specific wavelength of light and emitted light themselves, thus providing a visual map of tumor cells in the body. In tests of the technique on rats, however, the researchers discovered that the quantum dots depressed the rats' immune systems and caused sometimes-fatal kidney damage.
Indeed, the same ability to travel throughout the body that makes nanoparticles potentially useful in medical research also makes them potentially harmful to hosts. Below a diameter of 20 nanometers, nanoparticles travel easily through the body so easily that nanoparticles inhaled into the nasal passages, for example, can enter nerve cells and then travel up into the brain, bypassing the blood/brain barrier.
In the case of the tumor experiment that caused kidney damage in the lab animals, Balbus said, "getting this information allowed the researchers to go back, modify the nanoparticles and develop safer diagnostic tools. [But] these nanoparticles had to be tested in a laboratory setting because they were being used in a biomedical research. We need some kind of analogous evaluation for nanomaterials not intended for biomedical applications."
Ultimately, however, Balbus' message was upbeat. "The encouraging aspect of the debate is that insurance companies, environmental groups and others are calling for the same thing: an evaluation of nanoproducts, a consideration of their risks before commercialization.
"By evaluating the materials and modifying them, we hope to realize all benefits of nanotechnology without falling into the trap of the downside risks," he said.