Evaluation of CNT toxicity by comparison to tattoo ink

The absence of an optimal nano-sized reference material has been the biggest obstacle in evaluating the safety of carbon nanotubes as biomaterials. In this study, black tattoo inks, which have a long history of use by humans, are shown to be suitable reference materials composed of nano-sized carbon black particles. We have also demonstrated that multi-walled carbon nanotubes have comparable basic safety properties to those of tattoo inks when used as biomaterials.