Comparing in vitro cytotoxicity of graphite, short multi-walled carbon nanotubes, and long multi-walled carbon nanotubes

Unravelling the toxicity of carbon nanomaterials - From cellular interactions to mechanistic understanding

The application of carbon nanomaterials in diverse fields has substantially increased their demand for commercial usage. Within the earliest decade, the development of functional materials has further increased the significance of this element. Despite the advancements recorded, the potential harmful impacts of embracing carbon nanomaterials for biological applications must be balanced against their advantages. Interestingly, many studies have neglected the intriguing and dynamic cellular interaction of carbon nanomaterials and the mechanistic understanding of their property-driven behaviour, even though common toxicity profiles have been reported. Reiterating the toxicity issue, several researchers conclude that these materials have minimal toxicity and may be safe for contact with biological systems at certain dosages. Here, we aim to provide a report on the significance of some of the properties that influence their toxicity. After that, a description of the implication of nanotoxicology in humans and living systems, revealing piece by piece their exposure routes and possible risks, will be provided. Then, an extensive discussion of the mechanistic puzzle modulating the interface between various human cellular systems and carbon nanomaterials such as carbon nanotubes, carbon dots, graphene, fullerenes, and nanodiamonds will follow. Finally, this review also sheds light on the organization that handles the risk associated with nanomaterials.

Human epithelial lung cell toxicity assessment of collected graphite particles from an iron casting industry (in vitro study)

Workers in the iron casting industries are exposed to various chemicals, especially graphite in furnace process. This study aims to investigate the toxic effects of graphite particles on human lung cells. Particle characteristics were confirmed by electron microscope and light scattering. Cell viability and oxidative stress markers were measured. The expression of oxidative repair genes, namely OGG1, MTH1, and ITPA, was evaluated. The average particle size was determined to be 172.1 ± 11.96 nm. The median inhibition concentration (IC50) of graphite particles was 46.75 µg/mL. Notably, 25 and 50 µg/mL concentrations resulted in significant GSH depletion and MDA production. The high concentration of graphite particles (200 µg/mL) led to OGG1 suppression and increased MTH1 expression. Based on these findings, graphite exposure may induce toxicity in human lung cells by increasing oxidative stress. Further research is necessary to fully understand the mechanisms underlying graphite toxicity.

In vitro cytotoxicity assessment of carbonaceous gels for bone marrow mesenchymal stem cells

The current work aimed to elucidate the potential applications of the carbonaceous gels and assess the in vitro cytotoxicity of these gels when suspended in a culture medium and exposed to bone marrow mesenchymal stem cells. Cellular viability, cell cycle distribution, apoptotic cell death, and mitochondrial membrane potential in bone marrow mesenchymal stem cells co-incubated with different concentrations of carbonaceous gels (0.1, 1, 10, 50, and 100 μg/mL) were evaluated. Flow cytometry and immunofluorescence were used to investigate apoptosis and cell cycle distribution. The expression of associated apoptotic proteins was analysed using Western Blot. Although the co-incubation of carbonaceous gels did not significantly affect cell viability, high dosages (100 μg/mL) of these gels led to cellular dysfunction. Specifically, cells exposed to high concentrations of these gels exhibited G2-phase arrest and increased levels of reactive oxygen species. However, the reported impacts did not cause considerable cell death. At the same time, carbonaceous gels did not significantly induce apoptosis. Compared to other carbon nanomaterials, carbonaceous gels' biotoxicity was relatively low, suggesting their potential for various biological applications. Nonetheless, caution should be exercised when considering the concentration of carbonaceous gels for future medical applications.

A cohesive effort to assess the suitability and disparity of carbon nanotubes for water treatment

Population growth, industrialization, and the extensive use of chemicals in daily life have all contributed to an increase in waste generation and an intensified release of organic pollutants into the aquatic environment. To ensure the quality of water (including natural resources), the removal of these pollutants from wastewater has become a challenging task for scientific community. Conventional physical, chemical, and biological treatment methods are commonly used in combinations and are not very effective. Recently, carbon nanotubes (CNTs) emerged as the most reliable and adaptable choice for efficient water treatment due to their extraordinary material properties appearing as a single-step solution for water treatment. High surface area, exceptional porosities, hollow and layered structures, and ease of chemical activation and functionalization are some properties which makes it excellent adsorption material. Hence, this review paper discusses the recent advances in the synthesis, purification, and functionalization of CNTs for water and wastewater treatment. In addition, this study also also provides a quick overview of CNTs-based advance technologies employed in water treatment and carefully assesses the benefits versus risks during large-scale water treatment. Furthermore, it concludes that identified risks to the environment and human health cannot be easily ignored and strict regulatory requirements are a must for producing low-cost innoxious CNTs.

Processing of carbon-reinforced construction materials releases PM2.5 inducing inflammation and (secondary) genotoxicity in human lung epithelial cells and fibroblasts

Building demolition following domestic fires or abrasive processing after thermal recycling can release particles harmful for the environment and human health. To mimic such situations, particles release during dry-cutting of construction materials was investigated. A reinforcement material consisting of carbon rods (CR), carbon concrete composite (C³) and thermally treated C³ (ttC³) were physicochemically and toxicologically analyzed in monocultured lung epithelial cells, and co-cultured lung epithelial cells and fibroblasts at the air-liquid interface. C³ particles reduced their diameter to WHO fibre dimensions during thermal treatment. Caused by physical properties or by polycyclic aromatic hydrocarbons and bisphenol A found in the materials, especially the released particles of CR and ttC³ induced an acute inflammatory response and (secondary) DNA damage. Transcriptome analysis indicated that CR and ttC³ particles carried out their toxicity via different mechanisms. While ttC³ affected pro-fibrotic pathways, CR was mostly involved in DNA damage response and in pro-oncogenic signaling.

In vitro toxicity of carbon nanotubes: a systematic review

Carbon nanotube (CNT) toxicity-related issues provoke many debates in the scientific community. The controversial and disputable data about toxicity doses, proposed hazard effects, and human health concerns significantly restrict CNT applications in biomedical studies, laboratory practices, and industry, creating a barrier for mankind in the way of understanding how exactly the material behaves in contact with living systems. Raising the toxicity question again, many research groups conclude low toxicity of the material and its potential safeness at some doses for contact with biological systems. To get new momentum for researchers working on the intersection of the biological field and nanomaterials, i.e., CNT materials, we systematically reviewed existing studies with in vitro toxicological data to propose exact doses that yield toxic effects, summarize studied cell types for a more thorough comparison, the impact of incubation time, and applied toxicity tests. Using several criteria and different scientific databases, we identified and analyzed nearly 200 original publications forming a "golden core" of the field to propose safe doses of the material based on a statistical analysis of retrieved data. We also differentiated the impact of various forms of CNTs: on a substrate and in the form of dispersion because in both cases, some studies demonstrated good biocompatibility of CNTs. We revealed that CNTs located on a substrate had negligible impact, i.e., 90% of studies report good viability and cell behavior similar to control, therefore CNTs could be considered as a prospective conductive substrate for cell cultivation. In the case of dispersions, our analysis revealed mean values of dose/incubation time to be 4-5 μg mL-1 h-1, which suggested the material to be a suitable candidate for further studies to get a more in-depth understanding of its properties in biointerfaces and offer CNTs as a promising platform for fundamental studies in targeted drug delivery, chemotherapy, tissue engineering, biosensing fields, etc. We hope that the present systematic review will shed light on the current knowledge about CNT toxicity, indicate "dark" spots and offer possible directions for the subsequent studies based on the demonstrated here tabulated and statistical data of doses, cell models, toxicity tests, viability, etc.

Polyurethane Sponge with a Modified Specific Surface for Repeatable Oil-Water Separation

Oil spill accidents contaminate the oceanic environment and cause economic distress, and they continue to occur. Many methods have been developed to restore waters contaminated with spilled oil. However, still most commercially available methods are not environmentally or economically sustainable solutions. Therefore, there is a need for the development of sustainable materials with running water treatment capabilities. In recent years, a polyurethane (PU) sponge-based adsorbent has been reported as an oil-water separation and reusable adsorbent. This is because the porous 3D structure of the PU sponge provides a large surface area. However, as the PU sponge has a carboxyl group and an amino group, it exhibits hydrophilicity, so surface modification is essential for oil-water separation. Therefore, to modify the surface of PU to have hydrophobic/oleophilic properties, a hydrophobic/oleophilic adsorbent (HOA) was prepared using graphite and polydimethylsiloxane. On the basis of this, a PU sponge, a porous material, was used to manufacture an adsorbent that can be used in a sustainable and environmentally friendly way. The prepared HOA can selectively adsorb water or oil and can be reused. Furthermore, continuous oil-water separation is possible through a simple flow of fluid. Therefore, it is confirmed that the studied HOA can have great potential for ocean restoration in the future as an adsorbent that mitigates the disadvantages of the currently commercialized method.

New Multi-Walled carbon nanotube of industrial interest induce cell death in murine fibroblast cells

The search for new nanomaterials has brought to the multifactorial industry several opportunities for use and applications for existing materials. Carbon nanotubes (CNT), for example, present excellent properties which allow us to assume a series of applications, however there is concern in the industrial scope about possible adverse health effects related to constant exposure for inhalation or direct skin contact. Thus, using cell models is the fastest and safest way to assess the effects of a new material. The aim of this study was to investigate the cytotoxic profile in LA9 murine fibroblast lineage, of a new multi-walled carbon nanotube (MWCNT) that was functionalized with tetraethylenepentamine (TEPA) to obtain better physical-chemical characteristics for industrial use. The modifications presented in the CNT cause concern, as they can change its initial characteristics, making this nanomaterial harmful. HR-TEM, FE-SEM and zeta potential were used for the characterization. Cytotoxicity and cell proliferation tests, oxidative and nitrosative stress analyzes and inflammatory cytokine assay (TNF-α) were performed. The main findings demonstrated a reduction in cell viability, increased release of intracellular ROS, accompanied by an increase in TNF-α, indicating an important inflammatory profile. Confirmation of the data was performed by flow cytometry and ImageXpress with apoptosis/necrosis markers. These data provide initial evidence that OCNT-TEPA has a cytotoxic profile dependent on the concentration of LA9 fibroblasts, since there was an increase in free radicals, inflammation induction and cell death, suggesting that continuous exposure to this nanoparticle can cause damage to different tissues in the organism.

Enhanced phenols removal and methane production with the assistance of graphene under anaerobic co-digestion conditions

Coal gasification wastewater (CGW) contains high concentration phenols which lead to poor anaerobic biodegradability and resource utilization. In this paper, new insights to improve synthetic CGW anaerobic degradation with the help of graphene under co-digestion conditions were investigated. Batch tests showed that with the addition of graphene dosage of 10 g/L and glucose as a co-substrate with chemical oxygen demand (COD) concentration of 2000 mg/L, the average COD concentration decreased from 3995 mg/L on day 1 to 983 mg/L on day 12. The average total phenol (TP) concentration decreased from 431 mg/L on day 1 to 23 mg/L on day 12. The cumulative methane production for 12 days was about 200 mL. Long-term experiments showed the average effluent COD and total phenol reached 1137 mg/L and 200 mg/L, respectively. While methane production stabilized at 500 mL/d. In addition, the coenzyme F₄₂₀ concentration increased from 1.075 μmol/g/VSS to 2.3 μmol/g/VSS. The analysis of microbial community structure indicated that the performance of phenols removal and methane production was related to the main microbial flora. The enriched Clostridium, Pseudomonas and species from Firmicutes and Chloroflexi participated in the stages of hydrolysis and acidogenesis. The electrogens Pseudomonas and archaea Methanosaeta were likely the major groups taking part in the direct interspecies electron transfer (DIET). The results obtained in this paper provide a theoretical basis for high-efficiency anaerobic degradation of CGW in practical engineering applications.

Intracerebral Injection of Graphene Oxide Nanosheets Mitigates Microglial Activation Without Inducing Acute Neurotoxicity: A Pilot Comparison to Other Nanomaterials

Carbon-based nanomaterials (CNMs) are being explored for neurological applications. However, systematic in vivo studies investigating the effects of CNM nanocarriers in the brain and how brain cells respond to such nanomaterials are scarce. To address this, functionalized multiwalled carbon nanotubes and graphene oxide (GO) sheets are injected in mice brain and compared with charged liposomes. The induction of acute neuroinflammatory and neurotoxic effects locally and in brain structures distant from the injection site are assessed up to 1 week postadministration. While significant neuronal cell loss and sustained microglial cell activation are observed after injection of cationic liposomes, none of the tested CNMs induces either neurodegeneration or microglial activation. Among the candidate nanocarriers tested, GO sheets appear to elicit the least deleterious neuroinflammatory profile. At molecular level, GO induces moderate activation of proinflammatory markers compared to vehicle control. At histological level, brain response to GO is lower than after vehicle control injection, suggesting some capacity for GO to reduce the impact of stereotactic injection on brain. While these findings are encouraging and valuable in the selection and design of nanomaterial-based brain delivery systems, they warrant further investigations to better understand the mechanisms underlying GO immunomodulatory properties in brain.