Biological interactions and safety of graphene materials
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ction Environment, health, and safety have become critical issues for the successful commercialization of nanomaterial products. One might think that graphene would be an exception because extended monolayers on electronic substrates seem to pose little risk of large-scale exposures. As graphene research has expanded beyond nanoelectronics, however, interest has grown in related materials, including few-layer graphene (FLG), graphene oxide (GO), and other graphene-derived materials, that exist, at some stage in processing or use, as dry powders1 or aerosols.2 These materials are being developed for applications that include conducting polymers,3 battery electrodes,4,5 supercapacitors,6 printable inks,7 transport barriers,8,9 structural composites,3 antibacterial papers,6 and biomedical technologies,3,10,11 and in many cases, occupational exposures are probable. The interest in biological applications and implications (potential health risks) is centered not on pristine epitaxial monolayer graphene, but on these related forms. In general, graphene materials vary greatly in number of layers, lateral dimensions, and surface chemistry and are best regarded as a family of related materials, whose biological responses will vary much as they do across the carbon nanotube family.12–14 The structure–property variations in these graphene-family nanomaterials (GFNs) present significant
challenges for the field of nanotoxicology, but also open up the potential for influencing safety through material design.12 At the same time, this material family offers potential opportunities for biological applications such as drug delivery.
Material properties relevant to biological effects The literature on biological interactions of GFNs is sparse but growing rapidly, and aspects of it have been reviewed recently.1,15–17 The graphene properties most likely to determine biological response are surface area, number of layers, lateral dimensions, surface chemistry, and purity.
Surface area Surface area plays a central role in the biological interactions of nanomaterials.18 Small nanoparticles ( 20 μm still lie in the respirable region (Dae < 5 μm) because they are ultrathin, but might not be cleared effectively following lung deposition. One commercial sample falls into this category.
increases according to the scaling law A/m ∼ 1/N, where A/m is the specific surface area, or total area per unit mass. Because of their high surface areas, surface phenomena such as physical adsorption and catalytic chemical reactions can affect the biological response to GFNs. The closest analogue to graphene is a pristine single-walled carbon nanotube (SWCNT), which is similarly hydrophobic and has a theoretical outer surface area of 1300 m2/g (although this surface area is significantly reduced in many cases to values below 500 m2/g by bundling). The high hydrophobic area of SWCNTs has been associated with the adsorption of molecular probe dyes and in vitro artifacts in toxicology assays,23,24 as well as the depletion of folic acid and other micronutrients fro
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