Nanoporous Alumina

regeneration [2]. Current research has focused on the creation of highly porous, three dimensional, scaffolds that can be loaded with specific tissue inducing factors to promote tissue regeneration [3]-[5]. It is believed that the surface properties of the surrounding microenvironment, such as surface roughness, elastic modulus, chemical reactivity, wettability, nanoscale features (pores, pillars, pits, etc.), have a significant influence on the stem cell responses, including cell proliferation and differentiation [6]. Studies have suggested that scaffold pore size and geometry can affect stem cell differentiation. For example, some have observed that pores ranging from 70 - 100 nm facilitate osteoblast differentiation via increased stem cell elongation, and by inducing cytoskeletal stress [7]. In contrast, others reported that a smaller pore size, between 20 - 30 nm, enhanced osteogenic differentiation with increased focal adhesions [8]. The purpose of this study was to identify pore size ranges that affect stem cell proliferation and subsequent osteogenic differentiation. To determine the critical pore sizes for cell osteo- genic responses, we used nanoporous alumina as a model substrate. Nanoporous alumina is created by anodic oxidation of aluminium (anodization) in polyprotic acids, producing a well-ordered structure of nanopores. Moreover, nanoporous alumina has shown promising potential to be implemented as a bone implant coating [9], immunoisolation device [10], and for drug delivery applications [11]-[14]. It should be noted that human os- teoblasts cultured on nanoporous alumina maintain a physiological phenotype [9] [15].

Figure 1A–C shows scanning electron microscopic images of the surface topography of smooth alumina and nanoporous alumina with 20 nm and 100 nm pores, respectively. The nanoporous alumina surfaces were flat, and the circular pores were homogeneously distributed on the surface. The depth of the pores was 60 µ m, which is the same as the thickness of the membranes. Figure 1D shows a cross-sectional scan- ning electron microscopic image of nanoporous alumina with pores of 100 nm. The surface contact area of porous alumina was obtained by calculations from the scanning electron microscopic images in Figure 1B and C using ImageJ software (Figure 1E). Porous alumina with 20 nm pores showed a larger contact area than alumina with 100 nm pores. The surface topography and profile of the alumina substrates was characterized by atomic force microscopy. Three-dimensional surface topographies of the smooth alu- mina and nanoporous alumina are shown in Figure 2A–C, respectively, and their corresponding surface profiles are shown in Figure 2D–F. The valleys observed in Figure 2B and C indicate pores on the membranes. The profiles shown in Figure 2E and F suggest that the pores were uniformly distributed on the alumina surfaces and that the pore diameter corresponded to the values measured by scanning electron microscopy.

Hybrid structures based on nanowires and nanotubes grown on solid matrices are promising materials for various applications ranging from nanoelectronics [1,2] and biotechnology [3] to superhydrophobic surfaces [4], reinforced composite materials [5] and polymers [6]. Application of the hybrid nanotube-based structures for water desalination can have alluring prospects [7,8]. Among others, nanoporous aluminium oxide (alumina) membranes are often used as a base for such structures [9,10]. Carbon nanotubes embedded in the nanoporous alumina membrane demonstrate promising properties [11], but controllability of the nanotube growth in the membrane is still a challenge. Carbon nanotubes and gra- phene flakes have been successfully grown using high- temperature reactions in the gas phase [12,13]. However, this method has not been able to synthesize nanotube ar- rays and meshes with controlled structure and morph- ology. In particular, it is still a challenge to grow carbon nanotubes selectively in the channels only or on the

Figure 1 shows the FE-SEM of nanoporous alumina fabricated at room temperature in 1.5 M phosphoric acid electrolyte. The pores were observed to be randomely distributed on the surface of the template. The current generated during the anodization from a 50 V potential was between 70 – 100 mA to produce an average pore size of 75 nm. The size of the pores produced is comparable to what others have reported

Nanoporous alumina which was produced by a conventional direct current anodization [DCA] process at low temperatures has received much attention in various applications such as nanomaterial synthesis, sensors, and photonics. In this article, we employed a newly developed hybrid pulse anodization [HPA] method to fabricate the nanoporous alumina on a flat and curved surface of an aluminum [Al] foil at room temperature [RT]. We fabricate the nanopores to grow on a hemisphere curved surface and characterize their behavior along the normal vectors of the hemisphere curve. In a conventional DCA approach, the structures of branched nanopores were grown on a photolithography-and-etched low-curvature curved surface with large interpore distances. However, a high- curvature hemisphere curved surface can be obtained by the HPA technique. Such a curved surface by HPA is intrinsically induced by the high-resistivity impurities in the aluminum foil and leads to branching and bending of nanopore growth via the electric field mechanism rather than the interpore distance in conventional approaches. It is noted that by the HPA technique, the Joule heat during the RT process has been significantly suppressed globally on the material, and nanopores have been grown along the normal vectors of a hemisphere curve. The curvature is much larger than that in other literatures due to different fabrication methods. In theory, the number of nanopores on the hemisphere surface is two times of the conventional flat plane, which is potentially useful for photocatalyst or other applications.

Superhydrophobic nanoporous anodic aluminum oxide (alumina) surfaces were prepared using treatment with vapor-phase hexamethyldisilazane (HMDS). Nanoporous alumina substrates were first made using a two-step anodization process. Subsequently, a repeated modification procedure was employed for efficient incorporation of the terminal methyl groups of HMDS to the alumina surface. Morphology of the surfaces was characterized by scanning electron microscopy, showing hexagonally ordered circular nanopores with approximately 250 nm in diameter and 300 nm of interpore distances. Fourier transform infrared spectroscopy-attenuated total reflectance analysis showed the presence of chemically bound methyl groups on the HMDS-modified nanoporous alumina surfaces. Wetting properties of these surfaces were characterized by measurements of the water contact angle which was found to reach 153.2 ± 2°. The contact angle values on HMDS-modified nanoporous alumina surfaces were found to be significantly larger than the average water contact angle of 82.9 ± 3° on smooth thin film alumina surfaces that underwent the same HMDS modification steps. The difference between the two cases was explained by the Cassie-Baxter theory of rough surface wetting.

Notably, lower dimension is beneficial to illustrate the nature of material, and ordered arrays of isolated nano- structures are of considerable to elucidate the RS physical mechanism. Typically, various lithographic techniques have been used to fabricate regular arrays of nanostructures, such as electron-beam lithography and focused ion beam technology, [14-16] but high production cost and long pro- cessing time are needed. Relatively, nanoporous anodized aluminum oxide (AAO) have been widely used as the mask for the fabrication of uniform nanoscale patterns because nanoscale materials/devices can be easily synthesized through electro-deposition or physical vapor deposition [17,18].

Porous alumina was fabricated electrochemically through anodic oxidation of aluminum by means of such a self-or- ganized method. Anodic aluminium oxide (AAO) template with nanopores was grown by two-steps anodization proc- esses from a high purity aluminium foil. The anodization process was carried out in a phosphoric acid electrolyte at ambient temperature with a different duration of anodization. The analysis observation by Atomic Force Microscopy (AFM) showed that nanopore size increased with anodization time. The nanopore sizes of porous alumina were (16.04, 26.19 and 37.39 nm) for (1, 2 and 3 hour) respectively.

Template-assist method is one of the most important techniques for synthesize nanostructures , because of more parameters that can be change to fabricate different nanostructures with desired nano-scale features. self- ordered anodic alumina is one of the most important honeycomb structure that can be used as a template. by using self-ordered nanoporous as a template and hydrothemal process as a deposition technique,different structures like nanowire,nanotube and nanoparticle was fabricated. The effect of surfactant and temperature on the formation of various nano-structures were investigated by SEM (scanning electron microscopy) and EDX (Energy dispersive x- ray) analysis. Electrical properties and I(Current)- Voltage (V)- Gate - source behavior of the samples was measured by four-probe (4- probes) method. Tin oxide nanoparticle array on the surface of alumina membrane used as chemical sensor in case of detecting hydrazine. The obtained results indicate that Alumina doped with tin oxide nanoparticle is suitable for detection of toxic chemicals in water such as hydrazine.

Of course, cell attachment is a complicated process that involves numerous proteins. The conformation and bioactiv- ity of the protein is also crucial. All of the changes in protein interactions need to be determined to fully understand the greater cell growth on such PAA surfaces. This is especially intriguing as our results suggest that the aluminum nano- structure did not enhance cell adhesion during the initial stage of MC3T3-E1 cell culture. Similar results have been obtained by others. For example, Chung et al recently stud- ied the adhesion of epithelial cells on various nanoporous alumina surfaces and found that the adhesion rate of cells on nanoporous surfaces (0 [flat aluminum], 30, 40, and 45 nm) did not vary, and even the number of cells that adhered to the 50 nm and 80 nm sized nanoporous surfaces was slightly lower than controls. They explained that this phenomenon was most likely due to a lack of surface area to which the cells could adhere when the pore size increased. In other words, more open porosity leads to less surface area for cell attachment. 24 Therefore, the flat aluminum in the present

Commercially pure Al specimens were anodized in 0.3 M oxalic acid at 0 º C for 15 min using five different anodization voltages in the range 10 – 50 V. Current versus time transient plots for each anodization voltage were recorded via computer interfaced multimeter. Current density, amount of charge transferred, and thickness of anodized film were found to increase linearly with the increase in anodization voltage. Scanning electron microscope studies of the first – step anodized nanoporous alumina films show that the pore diameter, interpore distance and porosity increase linearly with the increase in anodization voltage. On the contrary, the pore circularity and pore density decrease linearly with the increase in anodization voltage. XRD studies of the un-anodized and anodized Al specimens show that the peak intensity of (111), (200), and (311) planes decreases with the increase in anodization voltage whereas reverse is true for the preferentially oriented (220) plane. The nature of lattice strain is compressive (–) for the anodization voltages 20 and 50 V, as is also the case with un-anodized Al specimen, and tensile (+) for 10, 30, and 40 V.

Abstract: Nanoporous alumina membranes produced by mild or hard anodisation in oxalic acid at potentials ranging from 5 – 140 V have a controllable pore surface area of up to 200 times the membrane area. They exhibit a saturating magnetic response that is temperature-independent and almost anhysteretic below room temperature. The magnetism cannot be explained by the ~1 ppm of transition-metal impurities present in the membranes. The magnetic moment increases with the area of the open nanopores, reaching values of 0.6 Bohr magnetons per square nanometer for mild anodisation and 8 µ B nm -2 for hard anodisation where the growth rate is faster. Crystallization of the

An efficient method based in template wetting is applied for fabrication of ordered Poly(9,9-dioctylfluorene) (PFO) nanopillars with b-phase morphology. In this process, nanoporous alumina obtained by anodization process is used as template. PFO nanostructures are prepared under ambient conditions via infiltration of the polymeric solution into the pores of the alumina with an average pore diameter of 225 nm and a pore depth of 500 nm. The geometric features of the resulting structures are characterized with environmental scanning electron microscopy (ESEM), luminescence fluorimeter (PL) and micro μ -X-ray diffractometer ( μ -XRD). The characterization demonstrates the b -phase of the PFO in the nanopillars fabricated. Furthermore, the PFO nanopillars are characterized by Raman spectroscopy to study the polymer conformation. These ordered nanostructures can be used in optoelectronic applications such as polymer light-emitting diodes, sensors and organic solar cells.

Nearly 90 % of the existing drugs are hydrophobic which means they cannot be dissolved in the blood. This re- duces their pharmacological efficiency. On the other hand, some bioactive agents such as proteins, nucleic acids, or enzymes administered though oral or intraven- ous routes can be easily degraded by metabolism or by enzymatic conditions and are unable to reach the de- sired sites [1–3]. Increasing the knowledge of materials at the nanoscale may accelerate the improvement of drug delivery systems, especially in treating life- threatening conditions such as cancer and heart disease. Nanoporous and nanotube carriers with their unique features such as low-cost fabrication, controllable pore/ nanotube structure, tailored surface chemistry, high sur- face area, high loading capability, chemical resistivity, and mechanical rigidity have affianced a special role in drug delivery technology. Drug release is a process in which a composite or a device releases a drug in a

solution pollution of the chromium-containing alumina sludge is mainly detoxicated and utilized. The former one transforms Cr(VI) to low toxicity Cr(III), and stocks it as a waste residue. Zhang Dalei [27] noted a pyrolysis method to transform Cr(VI) to Cr(III) using straw. Duan Suhua [28] pointed out that the chromium-containing slag could be treated with industrial alcohol. However, the methods mentioned above not only take up land, but also cause great resource waste. What is more, the secondary pollu- tion may occur unexpectedly. The latter method is to separate and utilize the useful components of the chromium-containing alumina sludge. Xue Wendong [29] reported that the chromium-containing alumina sludge could be used to prepare refractory. However, the above method may be limited due to its low added value. Conse- quently, some new methods should be put forward to eliminate pollution and promote comprehensive utilization of the chromium-containing alumina sludge, which can not only solve environmental problems but also bring great economic benefit.

In this study, macro- and nanoporous surfaces bio-activated with Col and Fn were prepared in order to analyse the effect of the surface topography on the cell behaviour. The cell ad- hesion of the HAECs is affected by surface functionalization and culture time. Cells have better adhesion to Fn than Col on both flat and porous surfaces. However, substrate’ s func- tionalization has no effect on the cell morphology. It is influ- enced by the pore size of the material employed. On MacroPSi lamellipodia is observed while filopodia are ob- served when the cells are cultured on NAA.

In this work, we have shown the effect on the reflectance spectra of nanoporous anodic alumina films of the sputtering of a gold overlayer, as a function of the NAA porosity and of the gold thickness. The results show that the gold overlayer improves dramatically the contrast of the oscillations in the reflectance spectrum, what would result in an improvement of NAA-based optical sensors. By adequately tuning the gold thickness, sharp valleys in the reflectance can be obtained in the near-IR range that can further contribute to a more accurate deter- mination of spectral shifts and a consequent sensitivity improvement. A model based on the effective medium approximation for the NAA layer and for the deposited

Selective melamine sensors based on nanoporous carbon paste /molecularly imprinted polymer have been studied. The study begins with the synthesis of MIP monomer mixture of methacrylic acid (MAA), and ethylene glycol dimethacrylate (EGDMA) cross linker, benzoyl peroxide initiator, and melamine template. Membrane electrodes are fabricated by mixing nanoporous carbon and MIP with a certain ratio of inserted into the electrode surface. The optimization of sample measurements which includes melamine test of pH value of a solution pH and membrane composition. Further characterization of the electrodes was done by determining the Nernst factor, measurement range, selectivity, and lifetime. Validation method was done by determining the accuracy, precision, and the detection limit. Based on the data from FTIR, has been successfully synthesized MIP with BET analysis showing that MIP has a larger surface area , a larger pore volume, and a larger pore diameter than the MIP before extraction. The optimum conditions for the analysis of melamine using potentiometric sensor of nanoporous carbon paste/MIP electrode are the ratio of nanoporous carbon, MIP, and paraffin by 45:20:35 and the optimum pH value of 3-4. Results of melamine analysis using this sensor are the measurement range of 10 -6 - 10 -2 M, the detection limit is 9.51 x 10 -7 M, the Nernst factor is 54.4 mV / decade, the accuracies of the concentration of 10 -4 M and 10 -3 M are respectively 106.1% and 104.3%, and this electrode is selective against melamine and is relatively undisturbed by Ca 2 + , K + , Mg 2 + , and Na + that are usually present in milk.

However, studies of Ag delivery in the form of nanoporous bioglass containing silver (n-BGS), particularly in terms of its antibacterial application to achieve hemostasis, has not been reported. In this study, a novel biomedical material made of n-BGS that contains Ag ions was developed for potential use in wound-healing applications. Its effects on intrinsic and extrinsic blood clotting systems were examined by testing the activated partial thromboplastin time (APTT) and prothrombin time (PT) in vitro. The high surface area of n-BGS could perform well hemostatically, making it good for incorporation into dressings that require antibacterial properties for achieving hemostasis.

The third step was to in situ grow CIS nanocrystals on nanoporous TiO2 film by the classic solvothermal process Figure 1C, where FTO/compact-TiO2/nanoporous-TiO2 film as the substrate wa[r]