While two-dimensional graphene oxide (GO) is used increasingly in biomedical applications, there is uncertainty on how specific physicochemical properties relate to biocompatibility in mammalian systems. Although properties such as lateral size and the colloidal properties of the nanosheets are important, the specific material properties that we address here is the oxidation state and reactive surface groups on the planar surface. In this study, we used a GO library, comprising pristine, reduced (rGO), and hydrated GO (hGO), in which quantitative assessment of the hydroxyl, carboxyl, epoxy, and carbon radical contents was used to study the impact on epithelial cells and macrophages, as well as in the murine lung. Strikingly, we observed that hGO, which exhibits the highest carbon radical density, was responsible for the generation of cell death in THP-1 and BEAS-2B cells as a consequence of lipid peroxidation of the surface membrane, membrane lysis, and cell death. In contrast, pristine GO had lesser effects, while rGO showed extensive cellular uptake with minimal effects on viability. In order to see how these in vitro effects relate to adverse outcomes in the lung, mice were exposed to GOs by oropharyngeal aspiration. Animal sacrifice after 40 h demonstrated that hGO was more prone than other materials to generate acute lung inflammation, accompanied by the highest lipid peroxidation in alveolar macrophages, cytokine production (LIX, MCP-1), and LDH release in bronchoalveolar lavage fluid. Pristine GO showed less toxicity, whereas rGO had minimal effects. We demonstrate that the surface oxidation state and carbon radical content play major roles in the induction of toxicity by GO in mammalian cells and the lung.

While the antibacterial properties of graphene oxide (GO) have been demonstrated across a spectrum of bacteria, the critical role of functional groups is unclear. To address this important issue, we utilized reduction and hydration methods to establish a GO library with different oxidation, hydroxyl, and carbon radical (•C) levels that can be used to study the impact on antibacterial activity. Using antibiotic-resistant (AR) bacteria as a test platform, we found that the •C density is most proximately associated with bacterial killing. Accordingly, hydrated GO (hGO), with the highest •C density, had the strongest antibacterial effects through membrane binding and induction of lipid peroxidation. To explore its potential applications, we demonstrated that coating of catheter and glass surfaces with hGO is capable of killing drug-resistant bacteria. In summary, •C is the principle surface moiety that can be utilized for clinical applications of GO-based antibacterial coatings.

The aggregation and stability of graphene oxide (GO) and three successively reduced GO (rGO) nanomaterials were investigated. Reduced GO species were partially reduced GO (rGO-1h), intermediately reduced GO (rGO-2h), and fully reduced GO (rGO-5h). Specifically, influence of pH, ionic strength, ion valence, and presence of natural organic matter (NOM) were studied. Results show that stability of GO in water decreases with successive reduction of functional groups, with pH having the greatest influence on rGO stability. Stability is also dependent on ion valence and the concentration of surface functional groups. While pH did not noticeably affect stability of GO in the presence of 10 mM NaCl, adding 0.1 mM CaCl2 reduced stability of GO with increased pH. This is due to adsorption of Ca(2+) ions on the surface functional groups of GO which reduces the surface charge of GO. As the concentration of rGO functional groups decreased, so did the influence of Ca(2+) ions on rGO stability. Critical coagulation concentrations (CCC) of GO, rGO-1h, and rGO-2h were determined to be ∼ 200 mM, 35 mM, and 30 mM NaCl, respectively. In the presence of CaCl2, CCC values of GO and rGO are quite similar, however. Long-term studies show that a significant amount of rGO-1h and rGO-2h remain stable in Call's Creek surface water, while effluent wastewater readily destabilizes rGO. In the presence NOM and divalent cations (Ca(2+), Mg(2+)), GO aggregates settle from suspension due to GO functional group bridging with NOM and divalent ions. However, rGO-1h and rGO-2h remain suspended due to their lower functional group concentration and resultant reduced NOM-divalent cation bridging. Overall, pH, divalent cations, and NOM can play complex roles in the fate of rGO and GO.

Two-dimensional molybdenum disulfide (MoS2) has distinct optical and electronic properties compared to aggregated MoS2, enabling wide use of these materials for electronic and biomedical applications. However, the hazard potential of MoS2 has not been studied extensively. Here, we present a comprehensive analysis of the pulmonary hazard potential of three aqueous suspended forms of MoS2: aggregated MoS2 (Agg-MoS2), MoS2 exfoliated by lithiation (Lit-MoS2) and MoS2 dispersed by Pluronic F87 (PF87-MoS2). No cytotoxicity was detected in THP-1 and BEAS-2B cell lines. However, Agg-MoS2 induced strong pro-inflammatory and pro-fibrogenic responses in vitro. In contrast, Lit- and PF87-MoS2 had little or no effect. In an acute toxicity study in mice, Agg-MoS2 induced acute lung inflammation, while Lit-MoS2 and PF87-MoS2 had little or no effect. In a sub-chronic study, there was no evidence of pulmonary fibrosis in response to all forms of MoS2. These data suggest that exfoliation attenuates the toxicity of Agg-MoS2, which is an important consideration towards the safety evaluation and use of nanoscale MoS2 materials for industrial and biological applications.

Hexagonal boron nitride (hBN) is a thermally conductive yet electrically insulating two-dimensional layered nanomaterial that has attracted significant attention as a dielectric for high-performance electronics in addition to playing a central role in thermal management applications. Here, we report a high-content hBN-polymer nanocomposite ink, which can be 3D printed to form mechanically robust, self-supporting constructs. In particular, hBN is dispersed in poly(lactic- co-glycolic acid) and 3D printed at room temperature through an extrusion process to form complex architectures. These constructs can be 3D printed with a composition of up to 60% vol hBN (solids content) while maintaining high mechanical flexibility and stretchability. The presence of hBN within the matrix results in enhanced thermal conductivity (up to 2.1 W K m) directly after 3D printing with minimal postprocessing steps, suggesting utility in thermal management applications. Furthermore, the constructs show high levels of cytocompatibility, making them suitable for use in the field of printed bioelectronics.