Biomedical Engineering Reference
In-Depth Information
6
Carbon Nanotubes and
Pulmonary Toxicity
Malay K. Das and Charles Preuss
CONTENTS
6.1 Introduction .......................................................................................................................... 131
6.2 Potential Applications ........................................................................................................... 132
6.3 CNT-Mediated Toxicity ........................................................................................................ 132
6.4 Pulmonary Toxicity of SWCNTs .......................................................................................... 134
6.5 Pulmonary Toxicity of MWCNTs ........................................................................................ 135
6.6 Metallic Contamination of CNTs and Pulmonary Toxicity ................................................. 135
6.7 Pulmonary Toxicity of Functionalized CNTs....................................................................... 136
6.8 Conclusion ............................................................................................................................ 137
References ...................................................................................................................................... 137
6.1 INTRODUCTION
Carbon nanotubes (CNTs), a distinct molecular form of carbon atoms that was discovered in the late
1980s (Kelly and Kim, 2007), were exhaustively discovered by Sumio Iijima in 1991 (Iijima, 1991).
Later on in the year 2000, President Bill Clinton established the National Nanotechnology Initiative
to lead the United States into the next industrial revolution (White House, 2000). Nanomaterials
are the building blocks of this new industry. One of the major objectives of the initiative was to
develop materials that are 10 times stronger than steel but a fraction of the weight for making all
kinds of land, sea, air, and space vehicles lighter and more fuel efficient. This statement specifically
implicates CNTs, a novel and lightweight material with the strongest tensile strength of all synthetic
fibers (Ball, 1999). The presidential initiative directed NASA to search for applications of carbon
nanotubes and other nanomaterial in aerospace.
CNTs are allotropes of carbon with a thin cylindrical nanostructure (their diameter is about
10,000 times smaller than a human hair). Nanotubes have been constructed with a length-to-diameter
ratio of up to 132,000,000:1 (Wang et al., 2009), significantly larger than any other material. These
cylindrical carbon molecules have unusual properties, which are valuable for nanotechnology, elec-
tronics, optics, and other fields of material science and technology. In particular, owing to their
extraordinary thermal conductivity and mechanical and electrical properties, CNTs find applica-
tions as additives to various structural materials. For instance, nanotubes form a tiny portion of the
material(s) in some (primarily carbon fiber) baseball bats, golf clubs, or car parts (Gullapalli and
Wong, 2011).
CNTs can be produced by the deposition of carbon atoms vaporized from graphite by electric arcs
or by laser onto metal particles. More recently, they have been produced by chemical vapor deposi-
tion (CVD). High-pressure carbon monoxide conversion (HiPco™, Rice University, TX) is a CVD
process and is a more advanced method that uses CO as a carbon source; up to 97% of the carbon in
the HiPco product ends up in CNTs (Bronikowski et al., 2001). An individual CNT molecule is about
1 nm in diameter and several microns long (Ajayan and Ebbesen, 1997). Microscopically, individual
CNT fibers aggregate into bundles or ropes, which in turn agglomerate loosely into small clumps.
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