Carbon Nanotubes: Toxicological Properties, Use as Drug Delivery Material and Computational Contribution to Predict their Properties Including Structures with Topological Defects

Carbon nanotubes (CNTs) are a material that surprises with their properties. They can transport drugs to specific targets which makes them very useful in biomedicine. The CNTs consist of hexagonal rings that can be of a single-wall (SWCNT) or concentric multi-walls (MWCNT). They are stable structures that however could be toxic. Fortunately, they can be functionalized with different molecular fragments that make them soluble and nontoxic molecules. Several toxicity studies of CNTs are known with results that still need further research. Several experimental and theoretical examples of drugs that have been adsorbed on the surface of the nanotubes or encapsulated within them are also known. There are also CNTs that have non-hexagonal rings (called defects) embedded in the network of hexagonal rings. Several types of defects (with different combinations of four, five, seven, or eight membered rings) are known and their presence modifies the properties of the perfect nanotubes. So far, some theoretical studies of CNTs with defects are reported aimed at assessing their behavior as drug carriers; but no experimental work is known to assess its toxicity, efficacy and real mechanism of action. Herein, an updated but not exhaustive review of different studies of nanotube toxicity, their influencing factors and some proposed mechanisms is made. Cases of toxicity and non-toxicity are shown, SWCNT and MWCNT are compared and the important effect of functionalization, purity and dose among other factors are discussed. Further, a brief review of some cases of drug delivery by regular CNTs and some theoretical drug delivery studies of Density Functional Theory (DFT) and molecular dynamics simulation (DM) for defective nanotubes is presented with the aim of predicting CNTs molecular parameters that favor drug-nanotube molecular interactions. Finally, a recommendation is done to be followed before any clinical trial is undertaken.