Carbon nanotubes in drug delivery: just a carrier?

Abstract

Iijima’s 1991 discovery brought to the attention of the research community a new allotrope of carbon: carbon nanotubes (CNTs). Since then CNTs have been extensively studied and have demonstrated to be of great potential in various industrial and biomedical fields of application [1]. CNTs can be described as rolled-up sheets of graphene forming single or multiwalled seamless cylinders; their diameters range from few to hundreds of nanometers, respectively. They generally present a length/diameter ratio higher than 10 and have exceptional electrical, thermal, mechanical and optical properties [2,3]. Notwithstanding their great potential, the observed toxicity of these novel materials caused major concerns. CNTs are highly hydrophobic in nature and tend to form bundles in aqueous environments, leading to unstable dispersions. Bundles are phagocyted and cause cellular necrosis and oxidative stress damage. Furthermore, their characteristic shape, similar to asbestos fibers, is responsible for pulmonary toxicity that results in granulomas and fibrosis [4]. However, great advances have been achieved in the last decades in improving the water compatibility and reducing the toxicity of CNTs via both covalent and noncovalent modification [5]. The strategies developed have allowed researchers to investigate numerous possible biomedical applications, including their use as drug carriers for anticancer drugs, gene therapy and as scaffold components in tissue engineering [4].