RESUMO
Carbon nanotubes (CNTs), a prototypical engineered nanomaterial, have been increasingly manufactured for a variety of novel applications over the past two decades. However, since CNTs possess fiber-like shape and cause pulmonary fibrosis in rodents, there is concern that mass production of CNTs will lead to occupational exposure and associated pulmonary diseases. The aim of this study was to use contemporary proteomics to investigate the mechanisms of cellular response in E10 mouse alveolar epithelial cells in vitro after exposure to multi-walled CNTs (MWCNTs) that were functionalized by atomic layer deposition (ALD). ALD is a method used to generate highly uniform and conformal nanoscale thin-film coatings of metals to enhance novel conductive properties of CNTs. We hypothesized that specific types of metal oxide coatings applied to the surface of MWCNTs by ALD would determine distinct proteomic profiles in mouse alveolar epithelial cells in vitro that could be used to predict oxidative stress and pulmonary inflammation. Uncoated (U)-MWCNTs were functionalized by ALD with zinc oxide (ZnO) to yield Z-MWCNTs or aluminum oxide (Al2O3) to yield A-MWCNTs. Significant differential protein expression was found in the following critical pathways: mTOR/eIF4/p70S6K signaling and Nrf-2 mediated oxidative stress response increased following exposure to Z-MWCNTs, interleukin-1 signaling increased following U-MWCNT exposure, and inhibition of angiogenesis by thrombospondin-1, oxidative phosphorylation, and mitochondrial dysfunction increased following A-MWCNT exposure. This study demonstrates that specific types of metal oxide thin film coatings applied by ALD produce distinct cellular and biochemical responses related to lung inflammation and fibrosis compared to uncoated MWCNT exposure in vitro.
Assuntos
Células Epiteliais Alveolares/efeitos dos fármacos , Nanotubos de Carbono/toxicidade , Proteômica/métodos , Óxido de Alumínio/toxicidade , Células Epiteliais Alveolares/química , Animais , Células Cultivadas , Camundongos , Fibrose Pulmonar/etiologia , Óxido de Zinco/toxicidadeRESUMO
BACKGROUND: Multi-walled carbon nanotubes (MWCNTs) pose a possible human health risk for lung disease as a result of inhalation exposure. Mice exposed to MWCNTs develop pulmonary fibrosis. Lung macrophages engulf MWCNTs and produce pro-fibrogenic cytokines including interleukin (IL)-1ß, IL-6, tumor necrosis factor (TNF)-α, and osteopontin (OPN). Atomic layer deposition (ALD) is a novel process used to enhance functional properties of MWCNTs, yet the consequence of ALD-modified MWCNTs on macrophage biology and fibrosis is unknown. METHODS: The purpose of this study was to determine whether ALD coating with aluminum oxide (Al2O3) would alter the fibrogenic response to MWCNTs and whether cytokine expression in human macrophage/monocytes exposed to MWCNTs in vitro would predict the severity of lung fibrosis in mice. Uncoated (U)-MWCNTs or ALD-coated (A)-MWCNTs were incubated with THP-1 macrophages or human peripheral blood mononuclear cells (PBMC) and cell supernatants assayed for cytokines by ELISA. C57BL6 mice were exposed to a single dose of A- or U-MWCNTs by oropharyngeal aspiration (4 mg/kg) followed by evaluation of histopathology, lung inflammatory cell counts, and cytokine levels at day 1 and 28 post-exposure. RESULTS: ALD coating of MWCNTs with Al2O3 enhanced IL-1ß secretion by THP-1 and PBMC in vitro, yet reduced protein levels of IL-6, TNF-α, and OPN production by THP-1 cells. Moreover, Al2O3 nanoparticles, but not carbon black NPs, increased IL-1ß but decreased OPN and IL-6 in THP-1 and PBMC. Mice exposed to U-MWCNT had increased levels of all four cytokines assayed and developed pulmonary fibrosis by 28 days, whereas ALD-coating significantly reduced fibrosis and cytokine levels at the mRNA or protein level. CONCLUSION: These findings indicate that ALD thin film coating of MWCNTs with Al2O3 reduces fibrosis in mice and that in vitro phagocyte expression of IL-6, TNF-α, and OPN, but not IL-1ß, predict MWCNT-induced fibrosis in the lungs of mice in vivo.
Assuntos
Óxido de Alumínio/farmacologia , Citocinas/metabolismo , Leucócitos Mononucleares/metabolismo , Nanotecnologia/métodos , Nanotubos de Carbono/química , Fagócitos/metabolismo , Animais , Morte Celular/efeitos dos fármacos , Linhagem Celular , Humanos , Inflamação/patologia , Interleucina-1beta/biossíntese , Interleucina-6/metabolismo , Leucócitos Mononucleares/efeitos dos fármacos , Pulmão/efeitos dos fármacos , Pulmão/metabolismo , Pulmão/patologia , Macrófagos/efeitos dos fármacos , Macrófagos/metabolismo , Macrófagos/ultraestrutura , Camundongos Endogâmicos C57BL , Nanotubos de Carbono/ultraestrutura , Osteopontina/metabolismo , Fagócitos/efeitos dos fármacos , Fibrose Pulmonar , Fuligem/farmacologia , Propriedades de Superfície , Fator de Necrose Tumoral alfa/metabolismoRESUMO
Two-dimensional (2D) nanosheets with distinctive properties are often fabricated by exfoliation, hydrothermal synthesis, or vapor-phase reaction. While these approaches are useful to generate nanosheets, we show that free-floating 2D metal oxide flakes with nanometer-scale thickness can also be formed by atomic layer deposition (ALD), where the ALD process allows the thickness and composition to be precisely tuned. In this work, we describe in detail the ALD nanosheet fabrication process and demonstrate how the choice of the sacrificial substrate affects the subsequent ALD processing and the resulting nanosheet thickness and surface structure. In addition, we introduce the fabrication of organic/inorganic bilayer nanosheets with unique potential applications.
Assuntos
Óxido de Alumínio/química , Nanoestruturas/química , Propriedades de SuperfícieRESUMO
Low-temperature vapor-phase tungsten atomic layer deposition (ALD) using WF6 and dilute silane (SiH4, 2% in Ar) can yield highly conductive coatings on nylon-6 microfiber mats, producing flexible and supple nonwovens with conductivity of â¼1000 S/cm. We find that an alumina nucleation layer, reactant exposure, and deposition temperature all influence the rate of W mass uptake on 3D fibers, and film growth rate is calibrated using high surface area anodic aluminum oxide. Transmission electron microscopy (TEM) reveals highly conformal tungsten coatings on nylon fibers with complex "winged" cross-section. Using reactant gas "hold" sequences during the ALD process, we conclude that reactant species can transport readily to reactive sites throughout the fiber mat, consistent with conformal uniform coverage observed by TEM. The conductivity of 1000 S/cm for the W-coated nylon is much larger than found in other conductive nonwovens. We also find that the nylon mats maintain 90% of their conductivity after being flexed around cylinders with radii as small as 0.3 cm. Metal ALD coatings on nonwovens make possible the solvent-free functionalization of textiles for electronic applications.
Assuntos
Técnicas Biossensoriais/métodos , Caprolactama/análogos & derivados , Eletrônica Médica/métodos , Nanofibras/química , Polímeros/química , Tungstênio/química , Óxido de Alumínio/química , Caprolactama/química , Condutividade Elétrica , Microscopia Eletrônica de Transmissão , TêxteisRESUMO
The presence of nanostructured materials in the workplace is bringing attention to the importance of safe practices for nanomaterial handling. We explored novel fiber containment methods to improve the handling of carbon nanotube (CNT) powders in the laboratory while simultaneously allowing highly uniform and controlled atomic layer deposition (ALD) coatings on the nanotubes, down to less than 4 nm on some CNT materials. Moreover, the procedure yields uniform coatings on milligram quantities of nanotubes using a conventional viscous flow reactor system, circumventing the need for specialized fluidized bed or rotary ALD reactors for laboratory-scale studies. We explored both fiber bundles and fiber baskets as possible containment methods and conclude that the baskets are more suitable for coating studies. An extended precursor and reactant dose and soak periods allowed the gases to diffuse through the fiber containment, and the ALD coating thickness scaled linearly with the number of ALD cycles. The extended dose period produced thicker coatings compared to typical doses on CNT controls not encased in the fibers, suggesting some effects due to the extended reactant dose. Film growth was compared on a range of single-walled NTs, double-walled NTs, and acid-functionalized multiwalled NTs, and we found that ultrathin coatings were most readily controlled on the multiwalled NTs.
Assuntos
Óxido de Alumínio/química , Laboratórios , Nanoestruturas/química , Nanotecnologia/métodos , Nanotubos de Carbono/química , Manejo de Espécimes , Tamanho da Partícula , Porosidade , Propriedades de SuperfícieRESUMO
To synthesize long and uniform vertically aligned carbon nanotube (VACNT) arrays, it is essential to use catalytic nanoparticles (NPs) with monodisperse sizes and to avoid NP agglomeration at the growth temperature. In this work, VACNT arrays were grown on chemically synthesized Fe(3)O(4) NPs of diameter 6 nm by chemical vapor deposition. Coating the NPs with a thin layer of Al(2)O(3) prior to CNT growth preserves the monodisperse sizes, resulting in uniform, thick and dense VACNT arrays. Comparison with uncoated NPs shows that the Al(2)O(3) coating effectively prevents the catalyst NPs from sintering and coalescing, resulting in improved control over VACNT growth.
Assuntos
Óxido de Alumínio/química , Compostos Férricos/química , Nanotecnologia/instrumentação , Nanotubos de Carbono/química , CatáliseRESUMO
Thermally robust monolayers of 4-6 nm diameter FePt nanoparticles (NPs) were fabricated by combining chemical synthesis and atomic layer deposition. Spin-cast monolayers of FePt NPs were coated with thin, 11 nm-thick layers of amorphous Al(2)O(3), followed by annealing to convert the FePt NPs from an alloy (A1) into intermetallic FePt (L1(0)) and FePt(3) (L1(2)) phases. The Al(2)O(3) layer serves as a barrier that prevents sintering between NPs during annealing at temperatures up to 730 °C. Electron and X-ray diffraction in conjunction with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) show that as-synthesized A1 FePt NPs convert into L1(0) and L1(2) phase NPs through annealing. HAADF-STEM measurements of individual NPs reveal imperfect ordering and show that the NP composition determines which intermetallic phase is obtained. Mixed-phase NPs with L1(0) cores and FePt(3) L1(2) shells were also observed, as well as a smaller number of unconverted A1 NPs. These results highlight the need for improved control over the compositional uniformity of FePt NPs for their use in bit-patterned magnetic recording.
Assuntos
Ferro/química , Nanopartículas Metálicas/química , Platina/química , Óxido de Alumínio/química , Magnetismo , Nanopartículas Metálicas/ultraestrutura , Microscopia Eletrônica de Transmissão e Varredura , Tamanho da Partícula , TemperaturaRESUMO
Uniformly grafting organic reactive molecular species, e.g. -NH2, onto substrates that have three-dimensional complex structures and are chemically inert is challenging. The vapor phase chemical grafting of organic molecules enabled by low temperature metal oxide atomic layer deposition (ALD) is presented as a general and promising solution to functionalize inert matrices with complex morphology, such as nonwoven polypropylene mats, through the controllable self-limited molecular assembly mechanism in a combined ALD and vapor phase chemical grafting process.
Assuntos
Óxido de Alumínio/química , Gases/química , Polipropilenos/química , Silanos/química , Adsorção , Aminas/química , Fluoresceínas/química , Ouro/química , Hidróxidos/química , Nanopartículas Metálicas/química , Microscopia Eletrônica de Varredura , Microscopia Eletrônica de Transmissão , Microscopia de Fluorescência , Espectroscopia Fotoeletrônica , Propilaminas , Espectroscopia de Infravermelho com Transformada de Fourier , Succinimidas/química , Propriedades de SuperfícieRESUMO
Atomic layer deposition (ALD) of aluminum oxide on nonwoven polypropylene and woven cotton fabric materials can be used to transform and control fiber surface wetting properties. Infrared analysis shows that ALD can produce a uniform coating throughout the nonwoven polypropylene fiber matrix, and the amount of coating can be controlled by the number of ALD cycles. Upon coating by ALD aluminum oxide, nonwetting hydrophobic polypropylene fibers transition to either a metastable hydrophobic or a fully wetting hydrophilic state, consistent with well-known Cassie-Baxter and Wenzel models of surface wetting of roughened surfaces. The observed nonwetting/wetting transition depends on ALD process variables such as the number of ALD coating cycles and deposition temperature. Cotton fabrics coated with ALD aluminum oxide at moderate temperatures were also observed to transition from a natural wetting state to a metastable hydrophobic state and back to wetting depending on the number of ALD cycles. The transitions on cotton appear to be less sensitive to deposition temperature. The results provide insight into the effect of ALD film growth mechanisms on hydrophobic and hydrophilic polymers and fibrous structures. The ability to adjust and control surface energy, surface reactivity, and wettability of polymer and natural fiber systems using atomic layer deposition may enable a wide range of new applications for functional fiber-based systems.
Assuntos
Fibra de Algodão , Polipropilenos/química , Óxido de Alumínio/química , Teste de Materiais , Tamanho da Partícula , Propriedades de Superfície , MolhabilidadeRESUMO
Three-dimensional nanoscale constructs are finding applications in many emerging fields, including energy generation and storage, advanced water and air purification, and filtration strategies, as well as photocatalytic and biochemical separation systems. Progress in these important technologies will benefit from improved understanding of fundamental principles underlying nanostructure integration and bottom-up growth processes. While previous work has identified hydrothermal synthesis conditions to produce nanoscale ZnO rods, sheets, and plates, strategies to systematically integrate these elements into more complex nano-architectures are not previously described. This article illustrates that amorphous nanoscale coatings formed by atomic layer deposition (ALD) are a viable means to modulate and screen the surface polarity of ZnO crystal faces and thereby regulate the growth morphology during successive hydrothermal nanocrystal synthesis. Using this new strategy, this work demonstrates direct integration and sequential assembly of nanocrystalline rods and sheets to produce complex three-dimensional geometric forms, where structure evolution is achieved by modifying the surface growth condition, keeping the hydrothermal growth chemistry unchanged. Therefore, rational planning of seed layer and feature spacing geometries may allow researchers to engineer, at the nanoscale, complex three-dimensional crystalline and semicrystalline constructs for a wide range of future applications.
Assuntos
Nanopartículas/química , Nanotecnologia/métodos , Óxido de Zinco/química , Óxido de Alumínio/química , Nanotubos/química , Silício/química , Propriedades de SuperfícieRESUMO
Atomic-scale material deposition is utilized to achieve uniform coverage and modification of the surface properties of natural fiber and woven fabric materials, where irregular nanoscale features are embedded in a macroscale interpenetrating fiber network. The complex surface topology of the woven fabric results in significantly different film-growth thickness per ALD cycle as compared to planar surfaces coated using the same process conditions, likely due to reactant adsorption within the fiber starting material, as well as impeded reactant transport out of the fabric system during the purge cycle. Cotton textiles modified with conformal nanoscale Al2O3 are found to show extreme hydrophobic effects, distinctly different from planar surfaces that receive the same coatings. The results highlight key concerns for achieving controlled conformal coatings on complex surfaces and open the possibility for new textile finishing approaches to create novel fabric-based materials with specialized function and performance.