The effect of grinding on cup-stacked carbon nanotubes is studied. The application of a bending force on the sidewall of such carbon nanotubes, that is higher than the Van der Waals force acting between the cups. results in the shortening of carbon nanotubes and the formation of nano-barrels exhibiting an increased number of accessible active sites (represented by the ends of graphitic planes) and anisotropic properties at both ends. (C) 2002 Elsevier Science B.V. All rights reserved.