A team of chemists and toxicologists was surprised to discover that repetitive movement can cause nanoparticles to penetrate the skin more deeply. The researchers said the results merit further study as scientists explore the medical potential of nanoparticles, such as drug delivery in the body."Our results confirm that repetitive motion can speed the passage of nanoparticles through the skin," said Nancy Monteiro-Riviere, professor of investigative dermatology and toxicology at North Carolina State University. "As more nanoparticles find their way into the workplace and consumer goods, and as scientists look for innovative ways to use nanoparticles to deliver drugs into the body, it is critical that the nanoscience community identify these types of external exposure factors."A three-dimensional model of a C60 molecule, which contains 60 carbon atoms and is also called a Buckyball. (Image: Michael Ströck) In the study, conducted by researchers at NC State and Rice University, a solution of Buckyball-containing amino acids was placed on small sections of pig skin. In some experiments the skin was held still, and in others it was flexed for either 60 or 90 minutes. Measurements were taken eight hours after exposure and 24 hours after exposure. The team found that the more the skin was flexed, the more Buckyballs it took up and the deeper they penetrated. Penetration was also found to be deeper after 24 hours than after just eight. Buckyballs are spherical, soccer-ball-shaped molecules containing 60 carbon atoms. The ones used in the study were part of an innovative molecule called Bucky amino acid, or Baa, that was created in the lab of Rice chemist Andrew Barron. Baa is a marriage of Buckyballs and phenylalanine, one of the 20 essential amino acids that are the building blocks of all proteins. "The findings were a bit surprising because the Bucky amino acids tend to form spherical clusters that are up to 12 times larger in diameter than the known width of intercellular gaps in the skin," said Barron, the Charles W. Duncan Jr.-Welch Professor of Chemistry, professor of materials science and associate dean for industry interactions and technology transfer. "It's not clear why flexing increases the uptake of fullerene peptides, but it will be important to further investigate these mechanisms as we study the medical potential of Bucky amino acids." The research appears in the Jan. 10 issue of the American Chemical Society's journal Nano Letters. Co-authors include NC State graduate student Jillian Rouse and Rice graduate student Jianzhong Yang. The research was funded by the Environmental Protection Agency, the National Academies Keck Futures Initiative and the Welch Foundation. For more information, visit: www.rice.edu