6 research outputs found
Colloidal Properties and Stability of Graphene Oxide Nanomaterials in the Aquatic Environment
While
graphene oxide (GO) has been found to be the most toxic graphene-based
nanomaterial, its environmental fate is still unexplored. In this
study, the aggregation kinetics and stability of GO were investigated
using time-resolved dynamic light scattering over a wide range of
aquatic chemistries (pH, salt types (NaCl, MgCl<sub>2</sub>, CaCl<sub>2</sub>), ionic strength) relevant to natural and engineered systems.
Although pH did not have a notable influence on GO stability from
pH 4 to 10, salt type and ionic strength had significant effects on
GO stability due to electrical double layer compression, similar to
other colloidal particles. The critical coagulation concentration
(CCC) values of GO were determined to be 44 mM NaCl, 0.9 mM CaCl<sub>2</sub>, and 1.3 mM MgCl<sub>2</sub>. Aggregation and stability of
GO in the aquatic environment followed colloidal theory (DLVO and
Schulze-Hardy rule), even though GOās shape is not spherical.
CCC values of GO were lower than reported fullerene CCC values and
higher than reported carbon nanotube CCC values. CaCl<sub>2</sub> destabilized
GO more aggressively than MgCl<sub>2</sub> and NaCl due to the binding
capacity of Ca<sup>2+</sup> ions with hydroxyl and carbonyl functional
groups of GO. Natural organic matter significantly improved the stability
of GO in water primarily due to steric repulsion. Long-term stability
studies demonstrated that GO was highly stable in both natural and
synthetic surface waters, although it settled quickly in synthetic
groundwater. While GO remained stable in synthetic influent wastewater,
effluent wastewater collected from a treatment plant rapidly destabilized
GO, indicating GO will settle out during the wastewater treatment
process and likely accumulate in biosolids and sludge. Overall, our
findings indicate that GO nanomaterials will be stable in the natural
aquatic environment and that significant aqueous transport of GO is
possible
Deposition and Release of Graphene Oxide Nanomaterials Using a Quartz Crystal Microbalance
Interactions of graphene oxide (GO)
with silica surfaces were investigated
using a quartz crystal microbalance with dissipation monitoring (QCM-D).
Both GO deposition and release were monitored on silica- and poly-l-lysine (PLL) coated surfaces as a function of GO concentration
and in NaCl, CaCl<sub>2</sub>, and MgCl<sub>2</sub> as a function
of ionic strength (IS). Under favorable conditions (PLL-coated positive
surface), GO deposition rates increased with GO concentration, as
expected from colloidal theory. Increased NaCl concentration resulted
in a greater deposition attachment efficiency of GO on the silica
surface, indicating that deposition of GO follows DerjaguināLandauāVerweyāOverbeek
(DLVO) theory; GO deposition rates decreased at high IS, however,
due to large aggregate formation. GO critical deposition concentration
(CDC) on the silica surface is determined to be 40 mM NaCl which is
higher than the reported CDC values of fullerenes and lower than carbon
nanotubes. A similar trend is observed for MgCl<sub>2</sub> which
has a CDC value of 1.2 mM MgCl<sub>2</sub>. Only a minimal amount
of GO (frequency shift <2 Hz) was deposited on the silica surface
in CaCl<sub>2</sub> due to the bridging ability of Ca<sup>2+</sup> ions with GO functional groups. Significant GO release from silica
surface was observed after adding deionized water, indicating that
GO deposition is reversible. The release rates of GO were at least
10-fold higher than the deposition rates under similar conditions
indicating potential high release and mobility of GO in the environment.
Under favorable conditions, a significant amount of GO was released
which indicates potential multilayer GO deposition. However, a negligible
amount of deposited GO was released in CaCl<sub>2</sub> under favorable
conditions due to the binding of GO layers with Ca<sup>2+</sup> ions.
Release of GO was significantly dependent on salt type with an overall
trend of NaCl > MgCl<sub>2</sub> > CaCl<sub>2</sub>
Three-Dimensional Printing of Cytocompatible, Thermally Conductive Hexagonal Boron Nitride Nanocomposites
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 polyĀ(lactic-<i>co</i>-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<sup>ā1</sup> m<sup>ā1</sup>) 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
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Surface Oxidation of Graphene Oxide Determines Membrane Damage, Lipid Peroxidation, and Cytotoxicity in Macrophages in a Pulmonary Toxicity Model
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 <i>in vitro</i> 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
Toxicological Profiling of Highly Purified Metallic and Semiconducting Single-Walled Carbon Nanotubes in the Rodent Lung and <i>E. coli</i>
The electronic properties of single-walled
carbon nanotubes (SWCNTs)
are potentially useful for electronics, optics, and sensing applications.
Depending on the chirality and diameter, individual SWCNTs can be
classified as semiconducting (S-SWCNT) or metallic (M-SWCNT). From
a biological perspective, the hazard profiling of purified metallic <i>versus</i> semiconducting SWCNTs has been pursued only in bacteria,
with the conclusion that aggregated M-SWCNTs are more damaging to
bacterial membranes than S-SWCNTs. However, no comparative studies
have been performed in a mammalian system, where most toxicity studies
have been undertaken using relatively crude SWCNTs that include a
M:S mix at 1:2 ratio. In order to compare the toxicological impact
of SWCNTs sorted to enrich them for each of the chirality on pulmonary
cells and the intact lung, we used density gradient ultracentrifugation
and extensive rinsing to prepare S- and M-SWCNTs that are >98%
purified. <i>In vitro</i> screening showed that both tube
variants trigger
similar amounts of interleukin 1Ī² (IL-1Ī²) and transforming
growth factor (TGF-Ī²1) production in THP-1 and BEAS-2B cells,
without cytotoxicity. Oropharyngeal aspiration confirmed that both
SWCNT variants induce comparable fibrotic effects in the lung and
abundance of IL-1Ī² and TGF-Ī²1 release in the bronchoalveolar
lavage fluid. There was also no change in the morphology, membrane
integrity, and viability of <i>E. coli</i>, in contradistinction
to the previously published effects of aggregated tubes on the bacterial
membrane. Collectively, these data indicate that the electronic properties
and chirality do not independently impact SWCNT toxicological impact
in the lung, which is of significance to the safety assessment and
incremental use of purified tubes by industry
Graphene Oxide Enhances Cellular Delivery of Hydrophilic Small Molecules by Co-incubation
The delivery of bioactive molecules into cells has broad applications in biology and medicine. Polymer-modified graphene oxide (GO) has recently emerged as a <i>de facto</i> noncovalent vehicle for hydrophobic drugs. Here, we investigate a different approach using native GO to deliver hydrophilic molecules by co-incubation in culture. GO adsorption and delivery were systematically studied with a library of 15 molecules synthesized with Gd(III) labels to enable quantitation. Amines were revealed to be a key chemical group for adsorption, while delivery was shown to be quantitatively predictable by molecular adsorption, GO sedimentation, and GO size. GO co-incubation was shown to enhance delivery by up to 13-fold and allowed for a 100-fold increase in molecular incubation concentration compared to the alternative of nanoconjugation. When tested in the application of Gd(III) cellular MRI, these advantages led to a nearly 10-fold improvement in sensitivity over the state-of-the-art. GO co-incubation is an effective method of cellular delivery that is easily adoptable by researchers across all fields