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D9.2.1

Sterilizing Properties of Carbon Nanotube Composites Roger J. Narayan School of Materials Science and Engineering Georgia Insitute of Technology Atlanta, GA 30332-0245 USA ABSTRACT Hydrogen-free carbon nanotube composites have been created that possess unusual free radical generation properties. These films have the ability to nonspecifically kill bacterial cells and can be used to sterilize a surface. These composites have been formed by simultaneous pulsed laser ablation of carbon and bombardment of nitrogen ions generated by a Kaufman ion source at high temperatures (600- 700°C). The results suggest the creation of a new form of carbon that is predominantly trigonally-coordinated, with small fractions of carbon-nitrogen bonds. TEM studies allow us to conclude that the material consists of sp2-bonded ribbons wrapped approximately +/-15° normal to the surface. Plan-view high resolution TEM specimens demonstrate layers with curvature similar to that seen in multiwalled nanotube structures. In addition, the interlayer order extends to approximately 15-30 nm. These novel structures result from the use of energetic ions, which create nonequilibrium conditions that alter the growth mode of graphitic planes. In vitro testing revealed significant antimicrobial activity against Staphylococcus aureus bacteria. Possible applications include use on the functional surfaces of dialysis equipment, scalpels, and other sterile equipment. INTRODUCTION Structures with grapheme bonding (e.g., fullerenes and nanotubes) are able to induce cell death on photosensitization by ultraviolet or tungsten lamp. The photo-induced biological activity of these materials is attributed to the generation of reduced oxygen species (O2
-,
OH) by the electron transfer reaction of a radical anion with molecular oxygen.1-2 Free radicals are chemical species that have a single unpaired electron in the outer orbit. Energy possessed by this unstable configuration is released through reactions with adjacent molecules. Molecules present in proteins, lipids, carbohydrates are often damaged in this manner by free radicals. Cell membranes and nucleic acids are particularly affected. Moreover, free radicals initiate autocatalytic reactions, whereby molecules with which free radicals react are themselves converted into free radicals. It has also been suggested that graphene bonded materials produce free radicals via both light- dependent and light- independent methods. Before going too far into the biocompatibility of nanotubes, it is worthwhile to note that individual nanotubes cannot be used in the body. In fact, individual nanotubes amay be quite toxic, as they may act like asbestos in the body. Questions have recently been raised over the possibility that foreign body neoplasia can be induced by the release of needlelike particles from composites in a mechanism that is analogous to that of asbestos- related mesothelioma. Animal experiments suggest that particles with high length-to-diameter ratios (>100) exhibit this effect.3 Thus, nanotubes need to b