Biological response to purification and acid functionalization of carbon nanotubes

Abstract

The final publication is available at Springer via: http://link.springer.com/article/10.1007/s11051-014-2507-yInternational audienceAcid functionalization has been considered as an easy way to enhance the dispersion and biodegradation of carbon nanotubes (CNT). However, inconsistencies between toxicity studies of acid functionalized CNT remain unexplained. This could be due to a joint effect of the main physicochemical modifications resulting from an acid functionalization: addition of surface acid groups and purification from catalytic metallic impurities. In this study, the impact on CNT biotoxicity of these two physiochemical features was assessed separately. The in vitro biological response of RAW 264.7 macrophages was evaluated after exposure to 15-240 µg x mL⁻¹ of two types of multi-walled CNT. For each type of CNT (small: 20 nm diameter, and big: 90 nm diameter), three different surface chemical properties were studied (total of six CNT samples): pristine, acid functionalized and desorbed. Desorbed CNT were purified by the acid functionalization but presented a very low amount of surface acid groups due to a thermal treatment under vacuum. A Janus effect of acid functionalization with two opposite impacts is highlighted. The CNT purification decreased the overall toxicity, while the surface acid groups intensified it when present at a specific threshold. These acid groups especially amplified the pro-inflammatory response. The threshold mechanism which seemed to regulate the impact of acid groups should be further studied to determine its value and potential link to the other physicochemical state of the CNT. The results suggest that, for a safer-design approach, the benefit-risk balance of an acid functionalization has to be considered, depending on the CNT primary state of purification. Further research should be conducted in this direction

Thermal annealing of carbon nanotubes reveals a toxicological impact of the structural defects

“…Thus, the absence of oxidative stress could not be due to the scavenging activity, but may be due to the MWCNT characteristics. Likely, in our latest study (Figarol et al 2014), the oxidative stress of annealed (2600°C) large MWCNT with high crystallinity and no distinguishable impurities was assessed and no response was found either. We thus suggest that the oxidative stress can be enhanced either by metallic impurities or by the simple presence of CNT, depending on the CNT physicochemical characteristics; and that the oxidative stress can be reduced by the scavenging activity, due to the defects in crystalline lattice.…”

In vitro toxicity of carbon nanotubes, nano-graphite and carbon black, similar impacts of acid functionalization

“…One way to equalize the surface chemistry of carbon-based nanomaterials is to functionalize their surface by an acid treatment (Figarol et al, 2014). Acid functionalization of CNT is relatively easy to carry out and of great interest for industrials.…”

New cementitious composite building material with enhanced toughness

“…However, agglomeration and the relative high price seem to limit the application of this type of microfiber in cement based composite materials [9]. Finally, acid functionalization is often used to improve the adhesion between carbon nanotubes and the cementitious matrix, leading to an increase of the toxicity of CNTs, depending on their degree of catalytic impurities and of a threshold [10].…”