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PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES

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PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES ( production-and-applications-graphene-and-its-composites )

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Chapter 6 – Production of Few Layer Graphene in Aqueous Media for Biological Studies The toxicity of pristine graphene (sp2 carbon lattice) remains largely unexplored, but increasingly indicates minimal toxicity. A recent study by Conroy et al. has shown no detectable cellular morphology changes in cultured human lung epithelial cell lines A549 grown on pristine graphene films (CVD and LPE-based) or when exposed to LPE graphene flakes (0.1 to 5 μg/ml).218 The lung has been most considered the most important organ with regard to entry by graphene into the external epithelial surfaces of the body. Aqueous surfactant-dispersed pristine FLG produced minimal inflammation in lung cells compared to GO.215 Pristine graphene nanoplatelets possessing a sufficiently large aerodynamic diameter to be deposited in lung alveolae were indicated as a possible inflammation risk with the alveolar macrophages up taking the flakes and producing reactive oxygen species.375 However, on extended medium term studies, minimal oxidation and lung inflammation damage was found by the same group.376 Surfactant polymer (Pluoronic F108) exfoliated FLG (~170 nm hydrodynamic diameter, 2-3 nm thickness & 𝜁 of -20 mV) decreased the viability of mitochondrial cells in a dose-dependent manner (50 % viability loss for 100 g/ml FLG).214 This cytotoxicity is believed to have resulted from both the loss of the mitochondrial membrane potential and intracellular reactive oxygen species (ROS), resulting in triggering of apoptosis.214 Sub-lethal concentrations (20 % viability loss for 20 g/ml) resulted in the secretion of pro-inflammatory cytokines of both Th1 and Th2, but reduced led to phagocytosis and binding to extracellular matrix, preventing over-activation.377 Pristine GBMs are often presumed to aggregate in aqueous biological media in the absence of added surfactants and to be unsuitable for biological studies. However, the more likely exposure risk will be from pristine GBMs. Pristine GBMs will associate with organic materials and adsorb biomolecules, which are likely to affect their dispersion- aggregation and biological behaviour.378 For example, suggest a ‘slice and dice’ action of pristine FLG on biomembranes,230 however, their experimental studies included mixing with phospholipids to disperse the FLG, which combination was found to be lytic and cytotoxic in this study. In this chapter, several routes for producing pristine graphene via LPE were explored in order to provide well-characterised aqueous preparations of pristine FLG for 162

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