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Biological Safety of Nanoscale Materials

As nanotechnology becomes more widely utilized in our society, concerns regarding the health and environmental effects of nanoparticles have been expressed. Thrust 3 has a small but growing effort in this area. Work on the impact of single-wall carbon nanotubes (SWNT) on smooth muscle cells continued from last year. The Seed Project with two junior faculty, entitled Health Effects of Nanoparticles Based on their Physico-Chemical Properties, has made significant progress this year.

Work by an undergraduate student on the cytotoxicity of single walled carbon nanotubes (SWNT) on Schwann cells (SC) was undertaken because it has been shown that by creating a scaffold consisting of collagen-matrigel with embedded SWNT to make it conductive, Schwann cells proliferation is enhanced and the conductive scaffold can help direct neurite orientation.  It was found that as the weight percent of SWNT increased, the ability for SC to proliferate decreased, resulting in smaller colonies. The construct digestion assay showed that high weight percentages of SWNT resulted in a smaller number of cells being released from the construct. This suggests that high weight percents have a toxic effect and kill cells.  The morphological assay showed that the presence of SWNT did not affect the morphology of the Schwann cells that were located within a construct.  However, the abundance of cells decreased as percent weight increased as shown in the following figure.

The strength of the seed project, initially funded in January 2007, is that the particles used in the cell studies will be well characterized.  We can now generate aerosol samples of specific particle sizes (monodisperse) starting from a polydisperse (multiples particle sizes) sample. We are also able to collect the aerosol samples into a liquid with the help of an impinger.  For example, alumina with a distribution of particle size ranging from 5 nm to 50 nm, was reduced to a set of particles ranging from 5-10 nm in size. This provides a means for focusing cytotoxic studies on specific size ranges to isolate size range effects. The preliminary cytotoxicity studies have looked at cell count, viability and proliferation of epithelial cells in the presence of nanoparticles using a six-day clonogenic assay and Dapi staining. The first results (see figure below) show that for Al2O3, the two particle sizes tested (10 nm and 30 nm) there is a decrease in cell count as the concentration of nanoparticles increases. There also appears to be a small effect of particle size at longer times with the 30 nm particles causing more of a decrease in cell count. The results from TiO2 are not as statistically significant, but indicate that the cell colony number decreases with increasing nanoparticle dose, and that the cells/colony increase with increasing nanoparticle dose.  These studies will be important in determining which nanoparticle size ranges and concentrations are toxic and allow us to ascertain appropriate levels of exposure.