Cytocompatibility studies of vertically-aligned multi-walled carbon nanotubes: Raw material and functionalized by oxygen plasma

It was presented a strong difference on cell adhesion and proliferation of functionalized vertically-aligned multi-walled carbon nanotube (VACNT) scaffolds compared to raw-VACNT. Biocompatibility in vitro tests were performed on raw-VACNT after superficial modification by oxygen plasma, which changes its superhydrophobic character to superhydrophilic. Two cytocompatibility tests were applied: 1) total lactate dehydrogenase colorimetric assay for the study of proliferating cells; and 2) cellular adhesion by scanning electron microscopy. Results showed that superhydrophilic VACNT scaffolds stimulate cell growth with proliferation up to 70% higher than normal growth of cell culture.     

An evaluation of chondrocyte morphology and gene expression on superhydrophilic vertically-aligned multi-walled carbon nanotube films

Cartilage serves as a low-friction and wear-resistant articulating surface in diarthrodial joints and is also important during early stages of bone remodeling. Recently, regenerative cartilage research has focused on combinations of cells paired with scaffolds. Superhydrophilic vertically aligned carbon nanotubes (VACNTs) are of particular interest in regenerative medicine. The aim of this study is to evaluate cell expansion of human articular chondrocytes on superhydrophilic VACNTs, as well as their morphology and gene expression. VACNT films were produced using a microwave plasma chamber on Ti substrates and submitted to an O₂ plasma treatment to make them superhydrophilic. Human chondrocytes were cultivated on superhydrophilic VACNTs up to five days. Quantitative RT-PCR was performed to measure type I and type II Collagen, Sox9, and Aggrecan mRNA expression levels. The morphology was analyzed by scanning electron microscopy (SEM) and confocal microscopy. SEM images demonstrated that superhydrophilic VACNTs permit cell growth and adhesion of human chondrocytes. The chondrocytes had an elongated morphology with some prolongations. Chondrocytes cultivated on superhydrophilic VACNTs maintain the level expression of Aggrecan, Sox9, and Collagen II determined by qPCR. This study was the first to indicate that superhydrophilic VACNTs may be used as an efficient scaffold for cartilage or bone repair.     

Optimizing reaction condition for synthesizing spinnable carbon nanotube arrays by chemical vapor deposition

Compared with the ordinary vertically aligned carbon nanotube (VACNT) arrays, the carbon nanotubes in spinnable VACNT arrays have better alignment, higher density, and narrower diameter distribution. The synthesis of spinnable VACNT arrays is sensitive to the reaction condition and the repeatable prepared of spinnable VACNT arrays still need improvement. In this paper, spinnable VACNT arrays were grown by chemical vapor deposition from C₂H₂/Ar using Fe coated on Si wafers as a catalyst. With the aim of improving the yield and reproducibility of spinnable VACNT arrays, the reaction conditions were systematically investigated. The growth kinetics of VACNT arrays was also investigated. The rate of growth of VACNT arrays can reach 465 μm/min at the initial growth stage and the activation energy of VACNT array growth is determined to be 112.2 kJ/mol. Meanwhile, a collective growth model for the evolution of spinnable VACNT arrays is also proposed.     

Preparation of Co-Ni Oxide/Vertically Aligned Carbon Nanotube and Their Electrochemical Performance in Supercapacitors

A Co-Ni oxide/vertically aligned carbon nanotube (VACNT) composite was prepared by thermal decomposition of cobalt-nickel nitrate precursor on the surface of VACNT electrode. VACNTs were used as 3D nanoporous substrate and were grown by plasma-enhanced chemical vapor deposition from a mixture of H₂ and C₂H₂. The specific capacitance of Co-Ni oxide (5:5)/VACNT (with equal Co⁺²/Ni⁺² mole ratio) was measured to be 1050 Fg^?1, which is about 1.9- and 3-fold that of Ni oxide/VACNT (540 Fg^?1) and Co oxide/VACNT (341 Fg^?1), respectively. The results show Co-Ni oxide (5:5)/VACNT composite electrode has excellent specific capacitance because of porous network structure, good electrical conduction pathways, high access for the electrolyte solution, and consequently increased composite/solution interfacial contact area. The capacitance property of the Co-Ni oxide/VACNT composite electrode with different Co⁺²/Ni⁺² mole ratios was also investigated and the highest specific capacitance is achieved at equal Co⁺²/Ni⁺² mole ratio.     

Coating alumina on catalytic iron oxide nanoparticles for synthesizing vertically aligned carbon nanotube arrays

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.     

Increasing mouse embryonic fibroblast cells adhesion on superhydrophilic vertically aligned carbon nanotube films

We have analyzed the adhesion of mouse embryonic fibroblasts (MEFs) genetically modified by green fluorescence protein (GFP) gene cultured on vertically-aligned carbon nanotubes (VACNTs) after 6 days. The VACNTs films grown on Ti were obtained by microwave plasma chemical vapor deposition process using Fe catalyst and submitted to an oxygen plasma treatment, for 2 min, at 400 V and 80 mTorr, to convert them to superhydrophilic. Cellular adhesion and morphology were analyzed by scanning electron, fluorescence microscopy, and thermodynamics analysis. Characterizations of superhydrophilic VACNTs films were evaluated by contact angle and X-Ray Photoelectron Spectroscopy. Differences of crowd adhered cells, as well as their spreading on superhydrophilic VACNTs scaffolds, were evaluated using focal adhesion analysis. This study was the first to demonstrate, in real time, that the wettability of VACNTs scaffolds might have enhanced and differential adherence patterns to the MEF-GFP on VACNTs substrates.     

Fabrication of carbon nanotube thermal interface material on aluminum alloy substrates with low pressure CVD

High quality vertically aligned carbon nanotube (VACNT) arrays have been synthesized on bulk Al alloy (Al6063) substrates with an electron-beam (E-beam) evaporated Fe catalyst using low pressure chemical vapor deposition (LPCVD). The pretreatment process of the catalyst was shown to play a critical role. This was studied comprehensively and optimized to repeatedly grow high quality VACNT arrays within a wide range of thicknesses of catalyst layer (2-11 nm) and acetylene (C(2)H(2)) flow rates (100-300 sccm). The thermal performance of the resulting VACNT arrays was evaluated. The minimum interfacial thermal resistance of the Si/VACNT/Al interfaces achieved so far is only 4 mm(2) K W(-1), and the average value is 14.6 mm(2) K W(-1).     

A metallization and bonding approach for high performance carbon nanotube thermal interface materials

A method has been developed to create vertically aligned carbon nanotube (VACNT) thermal interface materials that can be attached to a variety of metallized surfaces. VACNT films were grown on Si substrates using standard CVD processing followed by metallization using Ti/Au. The coated CNTs were then bonded to metallized substrates at 220?°C. By reducing the adhesion of the VACNTs to the growth substrate during synthesis, the CNTs can be completely transferred from the Si growth substrate and used as a die attachment material for electronic components. Thermal resistance measurements using a photoacoustic technique showed thermal resistances as low as 1.7 mm(2) K W(-1) for bonded VACNT films 25-30 μm in length and 10 mm(2) K W(-1) for CNTs up to 130 μm in length. Tensile testing demonstrated a die attachment strength of 40 N cm(-2) at room temperature. Overall, these metallized and bonded VACNT films demonstrate properties which are promising for next-generation thermal interface material applications.     

Aerosol assisted deposition of melamine-formaldehyde resin: Hydrophobic thin films from a hydrophilic material

An intrinsically hydrophilic melamine-formaldehyde thin film (water contact angle of 34° for a cast flat surface) was deposited on a glass substrate using aerosol assisted chemical vapour deposition. The resultant resin films showed a highly developed microstructure consisting of spherical structures that were agglomerated into towers. The surface wetted via a Cassie-Baxter mechanism with air trapped underneath the water droplets and resultant water contact angles as high as 135°. Film thickness and coverage were crucial in determining the wetting properties. Films with limited deposition gave hydrophilic results, whereas thicker films greater than 4 μm were superhydrophilic. This behaviour could be explained by the ease of trapping air under the coating. It is shown that the water wetting properties of a single material can be altered from superhydrophilic to near superhydrophobic by controlling the surface microstructure in a single-step aerosol route.     

Study on micro-patterning process of vertically aligned carbon nanotubes (VACNTs)

Vertically aligned carbon nanotubes (VACNTs) have drawn significant attention by the researchers because of their nanometric size and favorable material properties. Patterning of CNT forests in the micrometric domain is very important for their application in the area of microelectromechanical system (MEMS). For the first time this paper reports, detailed experimental investigation on a post growth μ-patterning process of VACNT forests. The micromechanical bending (M2B) process was locally applied at the targeted area in order to change the alignment of VACNT forests. Interestingly, the VACNT forest was transformed from typical black body absorber to reflective mirror as the M2B process was applied. Several parameters were identified that govern the resultant patterns such as rotational spindle speed, lateral bending speed, step size, tool morphology, and total depth of bend. Optimization of the parameters was carried out experimentally to obtain the best surface roughness and integrity of the microstructure. A minimum average surface roughness of Ra = 15 nm was achieved with 2000 rpm spindle speed, 1 mm/min bending speed and 1 µm step size.     

Growth of ultra long multiwall carbon nanotube arrays by aerosol-assisted chemical vapor deposition

Using a home-made aerosol nebulizer, we developed a new aerosol-assisted chemical vapor deposition (AACVD) process that made it possible to synthesize vertically-aligned carbon nanotube (VACNT) arrays with heights over a few millimeters routinely. An essential part of this technique was in-situ formation of metal catalyst nanoparticles via pyrolysis of ferrocene-ethanol aerosol right before CNT synthesis. Through the optimization of aerosol supply and CVD process parameters, we were able to synthesize clean VACNT arrays as long as 4.38 mm with very low metal contents in 20 min. Furthermore, it is worthy noting that such an outstanding height is achieved very quickly without supporting materials and water-assistance. By taking advantage of almost complete inhibition of CNT growth on low melting-temperature metals, we were able to fabricate patterned VACNT arrays by combining AACVD process with a conventional photolithograpic patterning of gold lines. Characterizations of as-grown nanotubes such as morphology, purity, and metal contents are presented.     

Preparation of superhydrophilic microrough titanium implant surfaces by alkali treatment

A new strategy to render intrinsically hydrophobic microrough titanium implant surfaces superhydrophilic is reported, which is based on a rapid treatment with diluted aqueous sodium hydroxide solutions. The physicochemical characterization and protein interaction of the resulting superhydrophilic implant surfaces are presented. The superhydrophilicity of alkali treated microrough titanium substrates was mainly attributed to deprotonation and ion exchange processes in combination with a strong enhancement of wettability due to the roughness of the used substrates. Albeit these minor and mostly reversible chemical changes qualitative and quantitative differences between the protein adsorption on untreated and alkali treated microrough titanium substrates were detected. These differences in protein adsorption might account for the enhanced osseointegrative potential of superhydrophilic alkali treated microrough implant surfaces. The presented alkali treatment protocol represents a new clinically applicable route to superhydrophilic microrough titanium substrates by rendering the implant surface superhydrophilic “in situ of implantation”.     

Illumination-induced properties of highly ordered mesoporous TiO2 layers with controlled crystallinity

The evaporation-induced self-assembly method using a novel diblock (poly(ethylene-co-butylene)-b-poly(ethylene oxide)) copolymer (KLE) provides fully crystalline mesoporous layers of TiO₂ exhibiting high thermal stability up to 700 °C, high photocatalytic activity in the decomposition of methyl stearate and facile transformation into a substantially stable superhydrophilic state by 1 mW/cm² UV-illumination.     

Effect of film thickness and agglomerate size on the superwetting and fog-free characteristics of TiO2 films

The effect of TiO₂ film thickness and agglomerate size on the non-UV activated superhydrophilic wetting and antifogging characteristics of TiO₂ films was investigated. Evidence from Atomic Force Microscopy analysis showed that surface roughness is the key parameter requiring control so as to retain the superhydrophilic wetting and antifogging behaviour of the synthesised films. Surface roughness can be tuned by simple manipulation of the multilayer assembly of TiO₂ nanoparticles through varying the film thickness and agglomerate size. A film thickness of ~ 140 nm yielded the optimum roughness (root mean square = 23 nm) to give the best superhydrophilic wetting behaviour. Thicker films reduced the film roughness and were detrimental to their superhydrophilic wetting properties. Smaller agglomerate size was also found to be important in retaining film roughness.     

基于超亲水原理的自清洁表面研究进展及产业化状况

简要介绍了超亲水表面的自清洁原理、各种制备方法及目前超亲水自清洁表面的产业化状况.从初始接触角、光谱响应范围和超亲水持久性角度出发,指出了当前超亲水自清洁表面研究中存在的问题.最后对其未来发展进行了展望.     

Patterned arrays of vertically aligned carbon nanotube microelectrodes on carbon films prepared by thermal chemical vapor deposition

A straightforward procedure is described for preparation of arrays of microdisk electrodes comprising bundles of vertically aligned carbon nanotubes (VACNTs). The arrays are fabricated by thermal chemical vapor deposition synthesis directly on a planar carbon film support. Use of standard micro- and nanolithography procedures for patterning the bilayer catalyst spots enables arrays to be grown with controlled electrode diameters and spacings. The minimum accessible VACNT bundle diameter, and hence microelectrode diameter, is 2 microm. After insulating the arrays with SU-8 epoxy and exposing the VACNT ends by polishing or treating with O2 plasma, the microdisk electrodes exhibit attractive electrochemical properties.     

Superhydrophilicity of anodic aluminum oxide films: From “honeycomb” to “bird's nest”

An electrochemical method has been used to prepare different kinds of surfaces including “honeycomb”-like and “bird's nest”-like surfaces on anodic aluminum oxide (AAO) films. The relationship between the morphology and wettability of the AAO films was investigated by scanning electron microscopy and the measurement of water contact angles. The results show that the “bird's nest”-like structure is necessary for superhydrophilic property, which provide direct experimental evidences for the 3D capillary theory concerning superhydrophilicity. It is expected that this investigation will be devoted to guiding the fabrication of superhydrophilic and superhydrophobic surfaces.     

Superhydrophilic surface treatment for thin film NiTi vascular applications

A variety of surface treatment methods were evaluated to modify the hydrophilic nature of thin film nitinol (NiTi). It has been suggested that increasing hydrophilicity reduces the prevalence of platelet adhesion and thrombosis in the vascular system. In this study, thin film NiTi was treated with three pretreatments cleaning, buffered oxide etchant (BOE), and BOE/nitric acid (HNO₃), followed by one surface treatment. The three surface treatment studied were UV irradiation, thermal treatment, or hydrogen peroxide. Two surface treatments, i.e., thermal at 600 °C for 30 min and 30% hydrogen peroxide treatment for 15 h, produced superhydrophilic surfaces, i.e., wetting angle = 0°. However, the superhydrophilic surface produced by the thermal treatment also embrittled the thin film due to the relative thickness of the oxide grown. Long term studies in air showed that all surface treatments trend toward hydrophobic natures. However, storage of the surface treated thin film NiTi in Deionized (DI) water preserved even the superhydrophilic surfaces indefinitely.     

Low temperature thermocompression bonding between aligned carbon nanotubes and metallized substrate

Vertically aligned carbon nanotube (VACNT) turf is proposed for use as an electrical and thermal contact material. For these applications, one route for circumventing the high temperatures required for VACNT growth using chemical vapor deposition (CVD) is used to grow firstly VACNTs on one substrate and then transfer them to other substrates. In this work, a nano thermocompression bonding technique between VACNTs and a metallized substrate is developed to allow dry mechanical transfer of the VACNTs. Unlike the diffusion bonding between two bulk materials, nano metal clusters have a high surface energy and the atoms are very active to form alloy with the contacted bulk metal material even at much lower temperatures, so nano thermocompression bonding can decrease the bonding temperature (150?°C) and pressure (1?MPa) and greatly shorten the bonding time from hours to 20?min. A debonding experiment shows that the bonding strength between VACNTs and the metallized layer is so high that a break is less likely to occur at the bonding interface.     

Bio-inspired design of a transparent TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> composite gel coating with adjustable wettability

Although the superhydrophobicity and transparence are generally two contradictory characters as the roughness factor, it is literature abundant for achieving both of these two purposes. To our knowledge, the integration multipurpose (transparent, superhydrophobic, superhydrophilic, underwater superoleophobicity, anti-fogging, and photo-controllable ability) in one has not been reported so far and these are vital for their promising applications in various aspects which can attract broad attention from scholars to engineers. In this work, we are successful to bio-inspired design of a kind versatile transparent nanocoating with superhydrophobic or superhydrophilic/underwater superoleophobic properties. The TiO₂/SiO₂ nanocoatings can be transformed from superhydrophobicity into superhydrophilicity and underwater superoleophobicity after heat treatment (450 °C and 2 h). If it was coated on conductive glass, the electrical conductivity was impervious, while the wettability can be manipulated. Importantly, both these superhydrophobic and superhydrophilic TiO₂/SiO₂ composite nanocoatings were endowed with photo-induced self-cleaning nature and these antifouling coatings could prolong their service life.