**Acknowledgements**

As a novel nanomaterial of great potentials in medicine, the toxicology of CNTs has received much attention in recent years. Pristine CNTs are very light powders and they can enter the body through inhalation via the respiratory tract, ingestion via the gastrointestinal tract or, dermal absorption via the skin. Following entering, CNTs distribute rapidly in the central and peripheral nervous system, lymphatic and blood circulation and potentially cause toxic effects in a variety of tissues and organs that they reach, such as heart, spleen, kidney, bone marrow and liver, etc. Toxicity of CNTs has been evaluated in a variety of cell or animal models for assessing pulmonary, dermal and immune effects. However, the published re‐ sults have not led to any consensus on the toxicity profile of pristine or functionalized SWNTs and MWNTs. Some investigators reported that pristine SWNTs that were purified by acid treatment demonstrated no acute toxicity, as opposed to non-purified CNTs, howev‐ er, they induced reactive oxygen species (ROS) in human lung carcinoma epithelial A549 cells and NR8383 cells [110]. Others demonstrated that pristine SWNTs, either acid-treated or non-treated, were capable of increasing chromosome and DNA damage, and oxidative

In contrast to raw or acid treated CNTs, the well-dispersed CNTs with high levels of surface functionalization can reduce the toxicity of MWNTs. One study demonstrated that taurine-MCWNTs in low and medium doses induced slight and recoverable pulmonary inflamma‐ tion in mice, and are less toxic than raw MCWNTs [113]. This is supported by other studies indicating that the damage caused by non-PEGylated MWNTs is slightly more severe than that of PEGylated MWNTs [114]. Furthermore, administrations of high doses of PL-PEG functionalized SWNTs following intravenous injection did not lead to acute or chronic toxic‐ ity in nude mice, albeit SWNTs persisted within liver and spleen macrophages for 4 months in mice without apparent toxicity [115] and the SWNTs-PL-PEG were excreted from mice via the biliary and renal pathways [116]. It is hypothesized that the van der Waals forces on the surfaces of pristine CNTs cause hydrophobic interactions between CNTs, resulting in ag‐ gregation and network formation, which further induce prolonged toxicity. Thus, function‐ alization of CNTs overcomes the aggregate-forming surface properties of CNTs, and

CNTs have exhibited diverse physical, chemical and mechanical properties suitable for a va‐ riety of applications. In last decade, biomedical applications of CNTs have undergone rapid progress. Their unique properties, such as, ultrahigh surface area, high aspect ratio, distinct optical properties have been applied to develop innovative, multi-functional CNT-based nanodevices for broad applications. This chapter have described the chemical and physical methods to prepare CNTs for used in medicine. With these methods, targeting molecules are attached on CNTs for targeted drug delivery, selective imaging, and other therapies. As a new type of nanomaterial, the toxicity of CNTs has been extensively investigated. To date, tremendous toxicity studies on CNTs have been published. However, the published data are inconsistent. The reason is that CNTs used in these studies vary in dispersion status, size

stress in macrophage cell lines [111, 112].

302 Syntheses and Applications of Carbon Nanotubes and Their Composites

therefore, reduces toxicity.

**7. Conclusions:**

This work is partially supported by research grant to Satya Prakash from Canadian Insti‐ tutes of Health Research (CIHR) (MOP 93641). W. Shao and L. Rodes acknowledges Doctor Training Award from Fonds de Research Sante (FRSQ). A. Paul acknowledges Post-Doctoral Award from FRSQ.
