Carbon Nanotubes

Abstract: Carbon nanotubes (CNTs) are promising candidates for a wide range of applications that are expected to improve our lifestyles, such as alternative forms of energy production, energy storage, and drug delivery. At the same time, there are concerns about their possible adverse effects on human health, since there is evidence that exposure to CNTs induces toxic effects in experimental models. However, CNTs are not a single substance but a growing

family of different materials possibly eliciting different biological responses. As a consequence, the hazards associated with the exposure of humans to the different forms of CNTs may be different. Understanding the structure–toxicity relationships would help towards the assessment of the risk related to these materials. Here, we present a snapshot of the current state-of-the art of CNT production, applications, and safety.

Key words: carbon nanotubes, physico-chemical properties, nanomedicine, toxicity, biocompatibility, safety.

8.1 Introduction

Since their discovery in 1991 (Iijima, 1991), the interest of the scientific community and of industry in carbon nanotubes (CNTs) has increased dramatically. Carbon nanotubes exhibit properties that include high thermal and electrical conductivity, mechanical resistance, low density, and tuneable semiconductivity, which renders them useful in a variety of industrial applications, such as components in electronics, energy-storage devices, solar cells, sensors, and as filler in polymeric composites in mechanical applications (Endo et al., 2008). Today, the annual global market in CNTs is estimated to be of the order of hundreds of tons. Carbon nanotubes are mainly used as components of electrodes in lithium batteries or as filler for electrical discharge in composites (Endo et al.,

2008). Since the physical properties of CNTs largely depend upon their structure, researchers are endeavouring to produce different types of engineered CNTs with tailored physico-chemical features. Carbon nanotubes should therefore be considered not a single substance but a family of different materials.

Carbon nanotubes have attracted a great interest for their application in medicine (Lacerda et al., 2006, 2007; Boczkowski and Lanone, 2007; Liu et al.,

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2009; Ji et al., 2010; Zhang et al., 2010). Like fullerenes, CNTs have been shown to rapidly cross the cell membranes (Raffa et al., 2008) and therefore they have been proposed as nanovectors. For this application, CNTs need to be modified to increase their compatibility in water and to bind other entities such as drugs or biomolecules (Cheung et al., 2010). Furthermore, some authors have proposed using CNTs in the manufacture of alternative artificial hard tissues (Sato

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