Their conclusions, to be published in June 2007 issue of Biomaterials, are that animals studies into the long-term effects of iron oxide nanoparticles is vital to prevent health hazards. Jin recommended studies that quantify both the dose and types of nanoparticles that cause the observed muting of signal transmissions.
"We should be doing toxicity testing simultaneously with the research and development of applications using nanoparticles," said Jin. "We should also develop methods to avoid toxicity in the first place. For instance, sometimes you can coat a toxic nanoparticle with a biocompatible layer," he said.
Nanotubes unsafe too?
Separately, NIST performed lab studies of human lung cells coming into contact with carbon nanotubes. The government researchers concluding that short nanotubes "may pose an increased risk to health."
"We were puzzled at why results of in vivo [animal] studies of the toxicity of nanotubes were so widely varied, so we studied whether their length was what might be making the difference," said NIST biomaterials scientist Matthew Becker.
What NIST found was that single-walled carbon nanotubes shorter than about 200 nanometers readily entered human lung cells in test tubes. After absorption, the lungs cells either died or showed other signs of toxicity, depending on the concentration level of nanotubes.
"The good news for EEs, is that for electronic applications nanotubes are almost always longer than 200 nanometers," said Becker. "But for scientists doing in vivo studies on the toxicity of nanotubes, we hope that our results will force them to characterize their nanotubes by length."
The NIST scientists do not plan further studies into why short nanotubes appear to pose a health hazard, but instead will concentrate on research into new nanotube engineering and manufacturing methods to reduce health risks.
"We believe that scientists doing in vivo studies should characterize their nanotube not only by length, but also by their concentration and dispersion," said Becker. "The big problem with most nanomaterials is exposurewhether its inhaled or ingested or goes through the skin. We need to define what constitutes chronic and acute exposure to nanotubes."
The NIST study will be published later this month in the journal Advanced Materials.