Carbon nanotubes (CNTs) are under investigation for a variety of applications in biomedicine, some of which would involve the carbon nanotubes coming in contact with blood. The assessment of the effect of CNTs in blood is, therefore, a critical safety issue. Now a new study reveals the molecular mechanism of CNTs’ role in arterial thrombosis, and found that multiwalled CNTs activate blood platelets. Thrombosis occurs when clots in the blood obstruct the flow of blood through the circulatory system – a leading cause of death and disability in the developed world. Jan Simak, a senior staff fellow at the United States Food and Drug Administration’s Center for Biologics Evaluation and Research, says, “In view of the rapid development of nanotechnology, the impact of the newly engineered nanomaterials as an additional thrombosis risk factor is not yet known but should not be underestimated. In fact, it has been reported that carbon nanotubes induce platelet aggregation and potentiate arterial thrombosis in animal model. However, a mechanism of thrombogenic effects of carbon nanotubes was not known.” The team found that CNTs act as “nanoneedles” and perforate platelets and cause injury to the platelet dense tubular systems. The team will next study how surface modifications of CNTs modulate their blood and vascular biocompatibility.