Graphene-based nanoplatelets: a new risk to the respiratory system as a consequence of their unusual aerodynamic properties

Evaluation of pulmonary and systemic toxicity following lung exposure to graphite nanoplates: a member of the graphene-based nanomaterial family

Background

Graphene, a monolayer of carbon, is an engineered nanomaterial (ENM) with physical and chemical properties that may offer application advantages over other carbonaceous ENMs, such as carbon nanotubes (CNT). The goal of this study was to comparatively assess pulmonary and systemic toxicity of graphite nanoplates, a member of the graphene-based nanomaterial family, with respect to nanoplate size.

Methods

Three sizes of graphite nanoplates [20 μm lateral (Gr20), 5 μm lateral (Gr5), and <2 μm lateral (Gr1)] ranging from 8–25 nm in thickness were characterized for difference in surface area, structure,, zeta potential, and agglomeration in dispersion medium, the vehicle for in vivo studies. Mice were exposed by pharyngeal aspiration to these 3 sizes of graphite nanoplates at doses of 4 or 40 μg/mouse, or to carbon black (CB) as a carbonaceous control material. At 4 h, 1 day, 7 days, 1 month, and 2 months post-exposure, bronchoalveolar lavage was performed to collect fluid and cells for analysis of lung injury and inflammation. Particle clearance, histopathology and gene expression in lung tissue were evaluated. In addition, protein levels and gene expression were measured in blood, heart, aorta and liver to assess systemic responses.

Results

All Gr samples were found to be similarly composed of two graphite structures and agglomerated to varying degrees in DM in proportion to the lateral dimension. Surface area for Gr1 was approximately 7-fold greater than Gr5 and Gr20, but was less reactive reactive per m². At the low dose, none of the Gr materials induced toxicity. At the high dose, Gr20 and Gr5 exposure increased indices of lung inflammation and injury in lavage fluid and tissue gene expression to a greater degree and duration than Gr1 and CB. Gr5 and Gr20 showed no or minimal lung epithelial hypertrophy and hyperplasia, and no development of fibrosis by 2 months post-exposure. In addition, the aorta and liver inflammatory and acute phase genes were transiently elevated in Gr5 and Gr20, relative to Gr1.

Conclusions

Pulmonary and systemic toxicity of graphite nanoplates may be dependent on lateral size and/or surface reactivity, with the graphite nanoplates > 5 μm laterally inducing greater toxicity which peaked at the early time points post-exposure relative to the 1–2 μm graphite nanoplate.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-016-0145-5) contains supplementary material, which is available to authorized users.

Synthesis, toxicity, biocompatibility, and biomedical applications of graphene and graphene-related materials

Graphene is a two-dimensional atomic crystal, and since its development it has been applied in many novel ways in both research and industry. Graphene possesses unique properties, and it has been used in many applications including sensors, batteries, fuel cells, supercapacitors, transistors, components of high-strength machinery, and display screens in mobile devices. In the past decade, the biomedical applications of graphene have attracted much interest. Graphene has been reported to have antibacterial, antiplatelet, and anticancer activities. Several salient features of graphene make it a potential candidate for biological and biomedical applications. The synthesis, toxicity, biocompatibility, and biomedical applications of graphene are fundamental issues that require thorough investigation in any kind of applications related to human welfare. Therefore, this review addresses the various methods available for the synthesis of graphene, with special reference to biological synthesis, and highlights the biological applications of graphene with a focus on cancer therapy, drug delivery, bio-imaging, and tissue engineering, together with a brief discussion of the challenges and future perspectives of graphene. We hope to provide a comprehensive review of the latest progress in research on graphene, from synthesis to applications.

The role of surface functionalization on the pulmonary inflammogenicity and translocation into mediastinal lymph nodes of graphene nanoplatelets in rats

Graphene, a two-dimensional monocrystalline layer of carbon atoms, has potential in many applications not only in material sciences, but also in the biomedical fields, but there is little information about the role of surface modification on the toxicity of graphene-based nanomaterials. Here, we evaluated the role of surface functionalization of the graphene nanoplatelets (GNPs) on the pulmonary inflammogenicity and translocation into mediastinal lymph nodes using a rat intratracheal instillation model. Six types of GNPs were used: All types of GNPs were based on the pristine GNPs (GNP_dot), and different functional groups were conjugated onto them including a COOH (GNP_COOH), COH [Formula: see text], N-H [Formula: see text], F _x (GNP_F), and N=H [Formula: see text]. All types of GNPs showed very high potential for the generation of reactive oxygen species (ROS) in a dose-dependent manner when measured by a 2'7'-dichlorofluorescin diacetate assay. GNPs were instilled into the lungs of rats at 0.3 and 1 mg/rat for the evaluation of acute (24 h) inflammation and at 3 mg/rat for chronic (1 and 4 weeks) inflammation. At 24 h after instillation, all types of GNPs showed good dose-dependent increases in polymorphonuclear leukocytes with a clear dose-dependency although significant increases compared to vehicle control were found only in positively charged GNPs [Formula: see text]. While the acute inflammation in all treatment groups was returned to control levels at 1 and 4 weeks after instillation, GNPs showed similar patterns of translocation into the mediastinal lymph nodes with a higher degree over time. This study implies that the main factors of GNPs for producing lung inflammation are the potential for ROS generation and surface charge. In addition, functional groups on the GNPs might not play an important role in the extrapulmonary translocation into the mediastinal lymph nodes.

Exposure monitoring of graphene nanoplatelets manufacturing workplaces

Graphenes have emerged as a highly promising, two-dimensional engineered nanomaterial that can possibly substitute carbon nanotubes. They are being explored in numerous R&D and industrial applications in laboratories across the globe, leading to possible human and environmental exposures to them. Yet, there are no published data on graphene exposures in occupational settings and no readily available methods for their detection and quantitation exist. This study investigates for the first time the potential exposure of workers and research personnel to graphenes in two research facilities and evaluates the status of the control measures. One facility manufactures graphene using graphite exfoliation and chemical vapor deposition (CVD), while the other facility grows graphene on a copper plate using CVD, which is then transferred to a polyethylene terephthalate (PET) sheet. Graphene exposures and process emissions were investigated for three tasks - CVD growth, exfoliation, and transfer - using a multi-metric approach, which utilizes several direct reading instruments, integrated sampling, and chemical and morphological analysis. Real-time instruments included a dust monitor, condensation particle counter (CPC), nanoparticle surface area monitor, scanning mobility particle sizer, and an aethalometer. Morphologically, graphenes and other nanostructures released from the work process were investigated using a transmission electron microscope (TEM). Graphenes were quantified in airborne respirable samples as elemental carbon via thermo-optical analysis. The mass concentrations of total suspended particulate at Workplaces A and B were very low, and elemental carbon concentrations were mostly below the detection limit, indicating very low exposure to graphene or any other particles. The real-time monitoring, especially the aethalometer, showed a good response to the released black carbon, providing a signature of the graphene released during the opening of the CVD reactor at Workplace A. The TEM observation of the samples obtained from Workplaces A and B showed graphene-like structures and aggregated/agglomerated carbon structures. Taken together, the current findings on common scenarios (exfoliation, CVD growth, and transfer), while not inclusive of all graphene manufacturing processes, indicate very minimal graphene or particle exposure at facilities manufacturing graphenes with good manufacturing practices.

Toxicity Evaluation of Graphene Oxide in Kidneys of Sprague-Dawley Rats

Recently, graphene and graphene-related materials have attracted a great deal of attention due their unique physical, chemical, and biocompatibility properties and to their applications in biotechnology and medicine. However, the reports on the potential toxicity of graphene oxide (GO) in biological systems are very few. The present study investigated the response of kidneys in male Sprague-Dawley rats following exposure to 0, 10, 20 and 40 mg/Kg GO for five days. The results showed that administration of GOs significantly increased the activities of superoxide dismutase, catalase and glutathione peroxidase in a dose-dependent manner in the kidneys compared with control group. Serum creatinine and blood urea nitrogen levels were also significantly increased in rats intoxicated with GO compared with the control group. There was a significant elevation in the levels of hydrogen peroxide and lipid hydro peroxide in GOs-treated rats compared to control animals. Histopathological evaluation showed significant morphological alterations of kidneys in GO-treated rats compared to controls. Taken together, the results of this study demonstrate that GO is nephrotoxic and its toxicity may be mediated through oxidative stress. In the present work, however, we only provided preliminary information on toxicity of GO in rats; further experimental verification and mechanistic elucidation are required before GO widely used for biomedical applications.

Biological and environmental interactions of emerging two-dimensional nanomaterials

Two-dimensional materials have become a major focus in materials chemistry research worldwide with substantial efforts centered on synthesis, property characterization, and technological application. These high-aspect ratio sheet-like solids come in a wide array of chemical compositions, crystal phases, and physical forms, and are anticipated to enable a host of future technologies in areas that include electronics, sensors, coatings, barriers, energy storage and conversion, and biomedicine. A parallel effort has begun to understand the biological and environmental interactions of synthetic nanosheets, both to enable the biomedical developments and to ensure human health and safety for all application fields. This review covers the most recent literature on the biological responses to 2D materials and also draws from older literature on natural lamellar minerals to provide additional insight into the essential chemical behaviors. The article proposes a framework for more systematic investigation of biological behavior in the future, rooted in fundamental materials chemistry and physics. That framework considers three fundamental interaction modes: (i) chemical interactions and phase transformations, (ii) electronic and surface redox interactions, and (iii) physical and mechanical interactions that are unique to near-atomically-thin, high-aspect-ratio solids. Two-dimensional materials are shown to exhibit a wide range of behaviors, which reflect the diversity in their chemical compositions, and many are expected to undergo reactive dissolution processes that will be key to understanding their behaviors and interpreting biological response data. The review concludes with a series of recommendations for high-priority research subtopics at the "bio-nanosheet" interface that we hope will enable safe and successful development of technologies related to two-dimensional nanomaterials.

A Novel Biomolecule-Mediated Reduction of Graphene Oxide: A Multifunctional Anti-Cancer Agent

Graphene oxide (GO) is a monolayer of carbon atoms that form a dense honeycomb structure, consisting of hydroxyl and epoxide functional groups on the two accessible sides and carboxylic groups at the edges. In contrast, graphene is a two-dimensional sheet of sp2-hybridized carbon atoms packed into a honeycomb lattice. Graphene has great potential for use in biomedical applications due to its excellent physical and chemical properties. In this study, we report a facile and environmentally friendly approach for the synthesis of reduced graphene oxide (rGO) using uric acid (UA). The synthesized uric acid-reduced graphene oxide (UA-rGO) was fully characterized by ultraviolet-visible (UV-Vis) absorption spectra, X-ray diffraction (XRD), dynamic light scattering (DLS), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and Raman spectroscopy. GO and UA-rGO induced a dose-dependent decrease in cell viability and induced cytotoxicity in human ovarian cancer cells. The results from this study suggest that UA-rGO could cause apoptosis in mammalian cells. The toxicity of UA-rGO is significantly higher than GO. Based on our findings, UA-rGO shows cytotoxic effects against human ovarian cancer cells, and its synthesis is environmentally friendly. UA-rGO significantly inhibits cell viability by increasing lactate dehydrogenase (LDH) release, reactive oxygen species (ROS) generation, activation of caspase-3, and DNA fragmentation. This is the first report to describe the comprehensive effects of UA-rGO in ovarian cancer cells. We believe that the functional aspects of newly synthesized UA-rGO will provide advances towards various biomedical applications in the near future.

Differential genotoxic and epigenotoxic effects of graphene family nanomaterials (GFNs) in human bronchial epithelial cells

The widespread applications of graphene family nanomaterials (GFNs) raised the considerable concern over human health and environment. The cyto-genotoxic potentiality of GFNs has attracted much more attention, albeit the potential effects on the cellular epigenome remain largely unknown. The effects of GFNs on cellular genome were evaluated with single and double stranded DNA damage and DNA repair gene expressions while the effects on epigenome was accomplished by addressing the global DNA methylation and expression of DNA methylation machineries at non-cytotoxic to moderately cytotoxic doses in in vitro system. We used five different representatives of GFNs-pristine (GNP-Prist), carboxylated (GNP-COOH) and aminated (GNP-NH2) graphene nanoplatelets as well as single layer (SLGO) and few layer (FLGO) graphene oxide. The order of single stranded DNA damage was observed as GNP-Prist ≥ GNP-COOH>GNP-NH2≥FLGO>SLGO at 10mg/L and marked dose dependency was found in SLGO. The GFNs possibly caused genotoxicity by affecting nucleotide excision repair and non-homologus end joining repair systems. Besides, dose dependent increase in global DNA methylation (hypermethylation) were observed in SLGO/FLGO exposure and conversely, GNPs treatment caused hypomethylation following the order as GNP-COOH>GNP-NH2 ≥ GNP-Prist. The decrements of DNA methyltransferase (DNMT3B gene) and methyl-CpG binding domain protein (MBD1) genes were probably the cause of global hypomethylation induced by GNPs. Conversely, the de novo methylation through the up-regulation of DNMT3B and MBD1 genes gave rise to the global DNA hypermethylation in SLGO/FLGO treated cells. In general, the GFNs induced genotoxicity and alterations of global DNA methylation exhibited compounds type specificity with differential physico-chemical properties. Taken together, our study suggests that the GFNs could cause more subtle changes in gene expression programming by modulating DNA methylation status and this information would be helpful for their prospective use in biomedical field.

Comparative in vitro toxicity of a graphene oxide-silver nanocomposite and the pristine counterparts toward macrophages

BACKGROUND

Graphene oxide (GO) is a highly oxidized graphene form with oxygen functional groups on its surface. GO is an excellent platform to support and stabilize silver nanoparticles (AgNP), which gives rise to the graphene oxide-silver nanoparticle (GOAg) nanocomposite. Understanding how this nanocomposite interacts with cells is a toxicological challenge of great importance for future biomedical applications, and macrophage cells can provide information concerning the biocompatibility of these nanomaterials. The cytotoxicity of the GOAg nanocomposite, pristine GO, and pristine AgNP was compared toward two representative murine macrophages: a tumoral lineage (J774) and peritoneal macrophages collected from Balb/c mouse. The production of reactive oxygen species (ROS) by J774 macrophages was also monitored. We investigated the internalization of nanomaterials by transmission electron microscopy (TEM). The quantification of internalized silver was carried out by inductively coupled plasma mass spectrometry (ICP-MS). Nanomaterial stability in the cell media was investigated overtime by visual observation, inductively coupled plasma optical emission spectrometry (ICP OES), and dynamic light scattering (DLS).

RESULTS

The GOAg nanocomposite was more toxic than pristine GO and pristine AgNP for both macrophages, and it significantly induced more ROS production compared to pristine AgNP. TEM analysis showed that GOAg was internalized by tumoral J774 macrophages. However, macrophages internalized approximately 60 % less GOAg than did pristine AgNP. The images also showed the degradation of nanocomposite inside cells.

CONCLUSIONS

Although the GOAg nanocomposite was less internalized by the macrophage cells, it was more toxic than the pristine counterparts and induced remarkable oxidative stress. Our findings strongly reveal a synergistic toxicity effect of the GOAg nanocomposite. The toxicity and fate of nanocomposites in cells are some of the major concerns in the development of novel biocompatible materials and must be carefully evaluated.

Biodistribution and toxicity of radio-labeled few layer graphene in mice after intratracheal instillation

BACKGROUND

The potential human health risks from graphene inhalation exposure have attracted substantial scientific interest as a result of the numerous exciting potential commercial applications of graphene. However, the long-term distribution of graphene in organisms after inhalation is unknown, largely as a result of challenges associated with accurate graphene quantification.

METHODS

Carbon-14 labeled FLG was used to quantify the in vivo distribution of FLG in mice after oral gavage or intratracheal instillation for up to 3 or 28 days after exposure, respectively.

RESULTS

Intratracheally instilled FLG was mainly retained in the lung with 47% remaining after 4 weeks. Exposure to non-labeled FLG resulted in dose-dependent acute lung injury and pulmonary edema, but these effects were alleviated with time despite the continued presence of FLG in the lungs. One percent and 0.18% of the intratracheally instilled FLG was present in the liver and spleen, respectively, after 14 days by passing through the air-blood barrier, a finding supported by the results of oral gavage experiments which did not show detectable absorption through the gastrointestinal tract. In addition, 46.2% of the intratracheally instilled FLG was excreted through the feces 28 d after exposure.

CONCLUSIONS

Quantitative measurements revealed the elimination mechanism for FLG and its biodistribution for two exposure pathways. Graphene persistence in the lung only caused transient pulmonary effects. The in vivo distribution, elimination, and toxicity results provided here measured using a robust quantitative method support the human health risk assessment of graphene.

28-Day inhalation toxicity of graphene nanoplatelets in Sprague-Dawley rats

Graphene, a two-dimensional engineered nanomaterial, is now being used in many applications, such as electronics, biological engineering, filtration, lightweight and strong nanocomposite materials, and energy storage. However, there is a lack of information on the potential health effects of graphene in humans based on inhalation, the primary engineered nanomaterial exposure pathway in workplaces. Thus, an inhalation toxicology study of graphene was conducted using a nose-only inhalation system for 28 days (6 h/day and 5 days/week) with male Sprague-Dawley rats that were then allowed to recover for 1-, 28-, and 90-day post-exposure period. Animals were separated into 4 groups (control, low, moderate, and high) with 15 male rats (5 rats per time point) in each group. The measured mass concentrations for the low, moderate, and high exposure groups were 0.12, 0.47, and 1.88 mg/m(3), respectively, very close to target concentrations of 0.125, 0.5, and 2 mg/m(3). Airborne graphene exposure was monitored using several real-time instrumentation over 10 nm to 20 μm for size distribution and number concentration. The total and respirable elemental carbon concentrations were also measured using filter sampling. Graphene in the air and biological media was traced using transmission electron microscopy. In addition to mortality and clinical observations, the body weights and food consumption were recorded weekly. At the end of the study, the rats were subjected to a full necropsy, blood samples were collected for blood biochemical tests, and the organ weights were measured. No dose-dependent effects were recorded for the body weights, organ weights, bronchoalveolar lavage fluid inflammatory markers, and blood biochemical parameters at 1-day post-exposure and 28-day post-exposure. The inhaled graphenes were mostly ingested by macrophages. No distinct lung pathology was observed at the 1-, 28- and 90-day post-exposure. The inhaled graphene was translocated to lung lymph nodes. The results of this 28-day graphene inhalation study suggest low toxicity and a NOAEL of no less than 1.88 mg/m(3).

Dispersal of pristine graphene for biological studies

Herein, we address the conflicting behaviour of different pristine graphene dispersions through their careful preparation and characterization in aqueous media.

Deposition of graphene nanomaterial aerosols in human upper airways

Graphene nanomaterials have attracted wide attention in recent years on their application to state-of-the-art technology due to their outstanding physical properties. On the other hand, the nanotoxicity of graphene materials also has rapidly become a serious concern especially in occupational health. Graphene naomaterials inevitably could become airborne in the workplace during manufacturing processes. The inhalation and subsequent deposition of graphene nanomaterial aerosols in the human respiratory tract could potentially result in adverse health effects to exposed workers. Therefore, investigating the deposition of graphene nanomaterial aerosols in the human airways is an indispensable component of an integral approach to graphene occupational health. For this reason, this study carried out a series of airway replica deposition experiments to obtain original experimental data for graphene aerosol airway deposition. In this study, graphene aerosols were generated, size classified, and delivered into human airway replicas (nasal and oral-to-lung airways). The deposition fraction and deposition efficiency of graphene aerosol in the airway replicas were obtained by a novel experimental approach. The experimental results acquired showed that the fractional deposition of graphene aerosols in airway sections studied were all less than 4%, and the deposition efficiency in each airway section was generally lower than 0.03. These results indicate that the majority of the graphene nanomaterial aerosols inhaled into the human respiratory tract could easily penetrate through the head airways as well as the upper part of the tracheobronchial airways and then transit down to the lower lung airways, where undesired biological responses might be induced.

Applications of graphene and its derivatives in intracellular biosensing and bioimaging

Graphene has a unique planar structure, as well as excellent electronic properties, and has attracted a great deal of interest from scientists.

Nano-biointeractions of PEGylated and bare reduced graphene oxide on lung alveolar epithelial cells: A comparative in vitro study

Graphene and its derivatives have garnered significant scientific interest and have potential use in nano-electronics as well as biomedicine. However the undesirable biological consequence, especially upon inhalation of the particle, requires further investigations. This study aimed to elucidate the nano-biointeractions of PEGylated reduced graphene oxide (PrGO) and reduced graphene oxide (rGO) with that of lung alveolar epithelial cells (A549). Both nanomaterials showed dose dependent decrease in cell viability and alteration of cell morphology after 24h. Upon intracellular uptake of PrGO, it elicited oxidative stress mediated apoptosis in the cells by inducing ROS, loss of mitochondrial membrane potential (MMP) and inflammatory response by NF-κB activation. Conversely, rGO was found to scavenge ROS efficiently except at high dose after 24h. It was found that ROS at high dose of rGO prompted loss of MMP. rGO was found to adhere to the cell membrane, where it is assumed to bind to cell surface Toll like receptors (TLRs) thereby activating NF-κB mediated inflammatory response. All these events culminated in an increase in apoptosis of A549 cells after 24h of rGO exposure. It was also noticed that both the nanomaterials did not initiate lysosomal pathway but instead activated mitochondria mediated apoptosis. This study highlights the possible adverse toxic effect of PrGO and rGO upon inhalation and persistence of these particles in the lungs. Further research is required to comprehend the biological response of PrGO and rGO so as to advance its biomedical application and safety.

Effects of graphene oxide nanosheets on the ultrastructure and biophysical properties of the pulmonary surfactant film

Graphene oxide (GO) is the most common derivative of graphene and has been used in a large range of biomedical applications. Despite considerable progress in understanding its cytotoxicity, its potential inhalation toxicity is still largely unknown. As the pulmonary surfactant (PS) film is the first line of host defense, interaction with the PS film determines the fate of the inhaled nanomaterials and their potential toxicity. Using a coarse-grained molecular dynamics model, we reported, for the first time, a novel mechanism of toxicity caused by the inhaled GO nanosheets. Upon deposition, the GO nanosheets induce pores in the PS film and thus have adverse effects on the ultrastructure and biophysical properties of the PS film. Notably, the pores induced by GO nanosheets result in increasing the compressibility of the PS film, which is an important indication of surfactant inhibition. In vitro experiments have also been conducted to study the interactions between GO and animal-derived natural PS films, qualitatively confirming the simulation results.

The Molecular Influence of Graphene and Graphene Oxide on the Immune System Under In Vitro and In Vivo Conditions

Graphene and graphene oxide (GO), due to their physicochemical properties and biocompatibility, can be used as an innovative biomedical material in biodetection, drug distribution in the body, treating neoplasms, regenerative medicine, and in implant surgery. Research on the biomedical use of graphene and GO that has been carried out until now is very promising and shows that carbon nanomaterials present high biocompatibility. However, the intolerance of the immune system to graphene nanomaterials, however low, may in consequence make it impossible to use them in medicine. This paper shows the specific mechanism of the molecular influence of graphene and GO on macrophages and lymphocytes under in vitro and in vivo conditions and their practical application in medicine. Under in vitro conditions graphene and GO cause an increased production of pro-inflammatory cytokines, mainly IL-1, IL-6, IL-10 and TNF-α, as a result of the activation of Toll-like receptors in macrophages. Graphene activates apoptosis in macrophages through the TGFbr/Smad/Bcl-2 pathway and also through JNK kinases that are stimulated by an increase of ROS in the cell or through a signal received by Smad proteins. Under in vivo conditions, graphene nanomaterials induce the development of the local inflammatory reaction and the development of granulomas in parenchymal organs. However, there is a huge discrepancy between the results obtained by different research groups, which requires a detailed analysis. In this work we decided to collect and analyze existing research and tried to explain the discrepancies. Understanding the precise mechanism of how this nanomaterial influences immune system cells allows estimating the potential influence of grapheme and GO on the human body.

5-Day repeated inhalation and 28-day post-exposure study of graphene

Graphene has recently been attracting increasing attention due to its unique electronic and chemical properties and many potential applications in such fields as semiconductors, energy storage, flexible electronics, biosensors and medical imaging. However, the toxicity of graphene in the case of human exposure has not yet been clarified. Thus, a 5-day repeated inhalation toxicity study of graphene was conducted using a nose-only inhalation system for male Sprague-Dawley rats. A total of three groups (20 rats per group) were compared: (1) control (ambient air), (2) low concentration (0.68 ± 0.14 mg/m(3) graphene) and (3) high concentration (3.86 ± 0.94 mg/m(3) graphene). The rats were exposed to graphene for 6 h/day for 5 days, followed by recovery for 1, 3, 7 or 28 days. The bioaccumulation and macrophage ingestion of the graphene were evaluated in the rat lungs. The exposure to graphene did not change the body weights or organ weights of the rats after the 5-day exposure and during the recovery period. No statistically significant difference was observed in the levels of lactate dehydrogenase, protein and albumin between the exposed and control groups. However, graphene ingestion by alveolar macrophages was observed in the exposed groups. Therefore, these results suggest that the 5-day repeated exposure to graphene only had a minimal toxic effect at the concentrations and time points used in this study.

Dispersibility-Dependent Biodegradation of Graphene Oxide by Myeloperoxidase

Understanding human health risk associated with the rapidly emerging graphene-based nanomaterials represents a great challenge because of the diversity of applications and the wide range of possible ways of exposure to this type of materials. Herein, the biodegradation of graphene oxide (GO) sheets is reported by using myeloperoxidase (hMPO) derived from human neutrophils in the presence of a low concentration of hydrogen peroxide. The degradation capability of the enzyme on three different GO samples containing different degree of oxidation on their graphenic lattice, leading to a variable dispersibility in aqueous media is compared. hMPO fails in degrading the most aggregated GO, but succeeds to completely metabolize highly dispersed GO samples. The spectroscopy and microscopy analyses provide unambiguous evidence for the key roles played by hydrophilicity, negative surface charge, and colloidal stability of the aqueous GO in their biodegradation by hMPO catalysis.

Graphene-based nanomaterials: biological and medical applications and toxicity

Graphene and its derivatives, due to a wide range of unique properties that they possess, can be used as starting material for the synthesis of useful nanocomplexes for innovative therapeutic strategies and biodiagnostics. Here, we summarize the latest progress in graphene and its derivatives and their potential applications for drug delivery, gene delivery, biosensor and tissue engineering. A simple comparison with carbon nanotubes uses in biomedicine is also presented. We also discuss their in vitro and in vivo toxicity and biocompatibility in three different life kingdoms (bacterial, mammalian and plant cells). All aspects of how graphene is internalized after in vivo administration or in vitro cell exposure were brought about, and explain how blood-brain barrier can be overlapped by graphene nanomaterials.

Emerging advances in cancer nanotheranostics with graphene nanocomposites: opportunities and challenges

As an inorganic nanomaterial, graphene nanocomposites have gained much attention in cancer nanotechnology compared with the other inorganic nanomaterial in recent times. Although a relatively new drug carrier, it has been extensively explored as a potential chemotherapeutic carrier and theranostic because of its numerous physicochemical properties, including, capability of multiple pay load, functionalization for drug targeting and photothermal effect. Despite potential benefit, its translation from bench to bed-side in cancer therapy is challenged due to its toxicity concern. Here, we discussed the present progress and future possibilities of graphene nanocomposites as a cancer theranostic. Moreover, the paper also exemplifies the effects of graphene/graphene oxide on tissues and organ functions in order to understand the extent and mechanism of toxicity.

Pulmonary Responses of Sprague-Dawley Rats in Single Inhalation Exposure to Graphene Oxide Nanomaterials

Graphene is receiving increased attention due to its potential widespread applications in future. However, the health effects of graphene have not yet been well studied. Therefore, this study examined the pulmonary effects of graphene oxide using male Sprague-Dawley rats and a single 6-hour nose-only inhalation technique. Following the exposure, the rats were allowed to recover for 1 day, 7 days, or 14 days. A total of three groups were compared: control (fresh air), low concentration (0.46 ± 0.06 mg/m(3)), and high concentration (3.76 ± 0.24 mg/m(3)). The exposure to graphene oxide did not induce significant changes in the body weights, organ weights, and food consumption during the 14 days of recovery time. The microalbumin and lactate dehydrogenase levels in the bronchoalveolar lavage (BAL) fluid were not significantly changed due to the exposure. Similarly, total cell count, macrophages, polymorphonuclear leukocytes, and lymphocytes were not significantly altered in the BAL fluid. Plus, the histopathological examination of the rat lungs only showed an uptake of graphene oxide in the alveolar macrophages of the high-concentration group. Therefore, these results demonstrate that the single inhalation exposure to graphene oxide induce minimal toxic responses in rat lungs at the concentrations and time points used in the present study.

Tissue distribution and urinary excretion of intravenously administered chemically functionalized graphene oxide sheets

The design of graphene-based materials for biomedical purposes is of great interest. Graphene oxide (GO) sheets represent the most widespread type of graphene materials in biological investigations. In this work, thin GO sheets were synthesized and further chemically functionalized with DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid), a stable radiometal chelating agent, by an epoxide opening reaction. We report the tissue distribution of the functionalized GO sheets labeled with radioactive indium (111In) after intravenous administration in mice. Whole body single photon emission computed tomography (SPECT/CT) imaging, gamma counting studies, Raman microscopy and histological investigations indicated extensive urinary excretion and predominantly spleen accumulation. Intact GO sheets were detected in the urine of injected mice by Raman spectroscopy, high resolution transmission electron microscopy (HR-TEM) and electron diffraction. These results offer a previously unavailable pharmacological understanding on how chemically functionalized GO sheets transport in the blood stream and interact with physiological barriers that will determine their body excretion and tissue accumulation.

Screening of toxic potential of graphene family nanomaterials using in vitro and alternative in vivo toxicity testing systems

OBJECTIVES

The widely promising applications of graphene nanomaterials raise considerable concerns regarding their environmental and human health risk assessment. The aim of the current study was to evaluate the toxicity profiling of graphene family nananomaterials (GFNs) in alternative in vitro and in vivo toxicity testing models.

METHODS

The GFNs used in this study are graphene nanoplatelets ([GNPs]-pristine, carboxylate [COOH] and amide [NH2]) and graphene oxides (single layer [SLGO] and few layers [FLGO]). The human bronchial epithelial cells (Beas2B cells) as in vitro system and the nematode Caenorhabditis elegans as in vivo system were used to profile the toxicity response of GFNs. Cytotoxicity assays, colony formation assay for cellular toxicity and reproduction potentiality in C. elegans were used as end points to evaluate the GFNs' toxicity.

RESULTS

In general, GNPs exhibited higher toxicity than GOs in Beas2B cells, and among the GNPs the order of toxicity was pristine>NH2>COOH. Although the order of toxicity of the GNPs was maintained in C. elegans reproductive toxicity, but GOs were found to be more toxic in the worms than GNPs. In both systems, SLGO exhibited profoundly greater dose dependency than FLGO. The possible reason of their differential toxicity lay in their distinctive physicochemical characteristics and agglomeration behavior in the exposure media.

CONCLUSIONS

The present study revealed that the toxicity of GFNs is dependent on the graphene nanomaterial's physical forms, surface functionalizations, number of layers, dose, time of exposure and obviously, on the alternative model systems used for toxicity assessment.

The global variability of diatomaceous earth toxicity: a physicochemical and in vitro investigation

Background

Diatomaceous earth (DE) is mined globally and is potentially of occupational respiratory health concern due to the high crystalline silica content in processed material. DE toxicity, in terms of variability related to global source and processing technique, is poorly understood. This study addresses this variability using physicochemical characterisation and in vitro toxicology assays.

Methods

Nineteen DE samples sourced from around the world, comprising unprocessed, calcined and flux-calcined DE, were analysed for chemical and mineral composition, particle size and morphology, and surface area. The potential toxicity of DE was assessed by its haemolytic capacity, and its ability to induce cytotoxicity or cytokine release by J774 macrophages.

Results

The potential toxicity of DE varied with source and processing technique, ranging from non-reactive to as cytotoxic and haemolytic as DQ12. Crystalline silica-rich, flux-calcined samples were all unreactive, regardless of source. The potential toxicity of unprocessed and calcined samples was variable, and did not correlate with crystalline silica content. Calcium-rich phases, iron content, amorphous material, particle size and morphology all appeared to play a role in sample reactivity. An increased surface area was linked to an increased reactivity in vitro for some sample types.

Conclusions

Overall, no single property of DE could be linked to its potential toxicity, but crystalline silica content was not a dominant factor. Occlusion of the potentially toxic crystalline silica surface by an amorphous matrix or other minerals and impurities in the crystal structure are suggested to pacify toxicity in these samples. In vivo verification is required, but these data suggest that crystalline silica content alone is not a sufficient indicator of the potential DE hazard.

Electronic supplementary material

The online version of this article (doi:10.1186/s12995-015-0064-7) contains supplementary material, which is available to authorized users.

Toxicity of Graphene Shells, Graphene Oxide, and Graphene Oxide Paper Evaluated with Escherichia coli Biotests

The plate-like graphene shells (GS) produced by an original methane pyrolysis method and their derivatives graphene oxide (GO) and graphene oxide paper (GO-P) were evaluated with luminescent Escherichia coli biotests and additional bacterial-based assays which together revealed the graphene-family nanomaterials' toxicity and bioactivity mechanisms. Bioluminescence inhibition assay, fluorescent two-component staining to evaluate cell membrane permeability, and atomic force microscopy data showed GO expressed bioactivity in aqueous suspension, whereas GS suspensions and the GO-P surface were assessed as nontoxic materials. The mechanism of toxicity of GO was shown not to be associated with oxidative stress in the targeted soxS::lux and katG::lux reporter cells; also, GO did not lead to significant mechanical disruption of treated bacteria with the release of intracellular DNA contents into the environment. The well-coordinated time- and dose-dependent surface charge neutralization and transport and energetic disorders in the Escherichia coli cells suggest direct membrane interaction, internalization, and perturbation (i.e., "membrane stress") as a clue to graphene oxide's mechanism of toxicity.

Biophysical influence of airborne carbon nanomaterials on natural pulmonary surfactant

Inhalation of nanoparticles (NP), including lightweight airborne carbonaceous nanomaterials (CNM), poses a direct and systemic health threat to those who handle them. Inhaled NP penetrate deep pulmonary structures in which they first interact with the pulmonary surfactant (PS) lining at the alveolar air-water interface. In spite of many research efforts, there is a gap of knowledge between in vitro biophysical study and in vivo inhalation toxicology since all existing biophysical models handle NP-PS interactions in the liquid phase. This technical limitation, inherent in current in vitro methodologies, makes it impossible to simulate how airborne NP deposit at the PS film and interact with it. Existing in vitro NP-PS studies using liquid-suspended particles have been shown to artificially inflate the no-observed adverse effect level of NP exposure when compared to in vivo inhalation studies and international occupational exposure limits (OELs). Here, we developed an in vitro methodology called the constrained drop surfactometer (CDS) to quantitatively study PS inhibition by airborne CNM. We show that airborne multiwalled carbon nanotubes and graphene nanoplatelets induce a concentration-dependent PS inhibition under physiologically relevant conditions. The CNM aerosol concentrations controlled in the CDS are comparable to those defined in international OELs. Development of the CDS has the potential to advance our understanding of how submicron airborne nanomaterials affect the PS lining of the lung.

Long-term toxicity of reduced graphene oxide nanosheets: Effects on female mouse reproductive ability and offspring development

Reduced graphene oxide (rGO) nanosheets have emerged as novel materials for cancer therapeutics. Their toxicity has attracted much attention since these nanomaterials may have great potential for clinical cancer treatment. Here we report the influence of rGO exposure on female mouse reproductive ability and offspring development. Mouse dams were injected with small or large rGO nanosheets at different doses and time points, pre- or post-fertilization. The sex hormone levels of adult female mice did not significantly change compared with the control group after intravenous injection with either small or large rGO, even at a high dose (25 mg/kg). Mouse dams could produce healthy offspring after treatment with rGO nanosheets before pregnancy and at an early gestational stage (∼6 days). Despite the successful delivery of offspring, malformed fetuses were found among rGO-injected dam litters. All mice had abortions when injected with low (6.25 mg/kg) or intermediate (12.5 mg/kg) doses at a late gestational stage (∼20 days); the majority of pregnant mice died when injected with the high dose of rGO at this stage of pregnancy. Interestingly, all surviving rGO-injected mouse mothers gave birth to another litter of healthy pups. The results presented in this work are important for a deeper understanding of the toxicity of rGO nanosheets on female reproductivity and their offspring development.

Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

Advances in studies of nanoparticle–biomembrane interactions

Nanoparticles (NPs) are widely applied in nanomedicine and diagnostics based on the interactions between NPs and the basic barrier (biomembrane). Understanding the underlying mechanism of these interactions is important for enhancing their beneficial effects and avoiding potential nanotoxicity. Experimental, mathematical and numerical modeling techniques are involved in this field. This article reviews the state-of-the-art techniques in studies of NP–biomembrane interactions with a focus on each technology's advantages and disadvantages. The aim is to better understand the mechanism of NP–biomembrane interactions and provide significant guidance for various fields, such as nanomedicine and diagnosis.

Graphene-based nanomaterials for versatile imaging studies

This review highlights recent applications of graphene-based nanomaterials for various types of imaging studies.

Biocompatibility of graphene oxide intravenously administrated in mice—effects of dose, size and exposure protocols

The toxicity of graphene oxide intravenously injected into mice was dramatically tuned by dose, size and exposure protocols of graphene oxide.

Applications of graphene and its derivatives as an adsorbent for heavy metal and dye removal: a systematic and comprehensive overview

Because of their persistency and toxicity, dyes and heavy metal ions discharged to water bodies have become a worrisome issue.

Aqueous graphene dispersions-optical properties and stimuli-responsive phase transfer

We demonstrate essentially complete exfoliation of graphene aggregates in water at concentrations up to 5% by weight (166-fold greater than previous high concentration report) using recently developed triblock copolymers and copolymeric nanolatexes based on a reactive ionic liquid acrylate surfactant. We demonstrate that the visible absorption coefficient in aqueous dispersion, 48.9 ± 1.3 cm(2)/mg at 500 nm, is about twice that currently accepted, and we show that this value is a greatest lower bound to extant macroscopic single sheet optical studies of graphene when one considers both fine structure constant and excitonic mechanisms of visible absorption. We also show that dilute and concentrated graphene dispersions are rheo-optical fluids that exhibit an isotropic to nematic transition upon application of a shear field, and we demonstrate stimuli-responsive phase transfer.

Toxicology of chemically modified graphene-based materials for medical application

This review article aims to provide an overview of chemically modified graphene, and graphene oxide (GO), and their impact on toxicology when present in biological systems. Graphene is one of the most promising nanomaterials due to unique physicochemical properties including enhanced optical, thermal, and electrically conductive behavior in addition to mechanical strength and high surface-to-volume ratio. Graphene-based nanomaterials have received much attention over the last 5 years in the biomedical field ranging from their use as polymeric conduits for nerve regeneration, carriers for targeted drug delivery and in the treatment of cancer via photo-thermal therapy. Both in vitro and in vivo biological studies of graphene-based nanomaterials help understand their relative toxicity and biocompatibility when used for biomedical applications. Several studies investigating important material properties such as surface charge, concentration, shape, size, structural defects, and chemical functional groups relate to their safety profile and influence cyto- and geno-toxicology. In this review, we highlight the most recent studies of graphene-based nanomaterials and outline their unique properties, which determine their interactions under a range of environmental conditions. The advent of graphene technology has led to many promising new opportunities for future applications in the field of electronics, biotechnology, and nanomedicine to aid in the diagnosis and treatment of a variety of debilitating diseases.

Polyethylene glycol-coated graphene oxide attenuates antigen-specific IgE production and enhanced antigen-induced T-cell reactivity in ovalbumin-sensitized BALB/c mice

Background

Graphene oxide (GO) is a promising nanomaterial for potential application in the versatile field of biomedicine. Graphene-based nanomaterials have been reported to modulate the functionality of immune cells in culture and to induce pulmonary inflammation in mice. Evidence pertaining to the interaction between graphene-based nanomaterials and the immune system in vivo remains scarce. The present study investigated the effect of polyethylene glycol-coated GO (PEG-GO) on antigen-specific immunity in vivo.

Methods

BALB/c mice were intravenously administered with a single dose of PEG-GO (0.5 or 1 mg/kg) 1 hour before ovalbumin (OVA) sensitization, and antigen-specific antibody production and splenocyte reactivity were measured 7 days later.

Results

Exposure to PEG-GO significantly attenuated the serum level of OVA-specific immunoglobulin E. The production of interferon-γ and interleukin-4 by splenocytes restimulated with OVA in culture was enhanced by treatment with PEG-GO. In addition, PEG-GO augmented the metabolic activity of splenocytes restimulated with OVA but not with the T-cell mitogen concanavalin A.

Conclusion

Collectively, these results demonstrate that systemic exposure to PEG-GO modulates several aspects of antigen-specific immune responses, including the serum production of immunoglobulin E and T-cell functionality.

In vitro evaluation of graphene oxide nanosheets on immune function

HYPOTHESIS

Graphene oxide (GO) has attracted the scientific community attention due to its novel properties and wide range of potential applications including hyperthermia cancer therapy. However, little is known about the GO effects on the immune function which involves both innate and adaptive defence mechanisms through the activation of different cell populations and secretion of several cytokines. The effect of different GO nanosheets designed for hyperthermia cancer therapy on macrophage and lymphocyte function should be determined before using GO for this application.

EXPERIMENTS

The effects of GO nanosheets with 1 (1-GOs) and 6 arms (6-GOs) of polyethylene glycol on RAW-264.7 macrophages and primary splenocytes (as approximation to the in vivo situation) were evaluated through the proinflammatory cytokine secretion and the modulation of cell proliferation in the presence of specific stimuli for either T-lymphocytes (concanavalin A, anti-CD3 antibody) or B-lymphocytes/macrophages (lipopolysaccharide).

FINDINGS

6-GOs significantly increased the secretion of TNF-α by RAW-264.7 macrophages without alteration of IL-6 and IL-1β levels. The treatment of primary splenocytes with 1-GOs and 6-GOs in the presence of concanavalin A, anti-CD3 antibody and lipopolysaccharide, produced significant dose-dependent decreases of cell proliferation and IL-6 levels, revealing weak inflammatory properties of GOs which are favourable for hyperthermia cancer therapy.