Controllable Pore Diameters Research Articles

Development of biodegradable scaffolds based on magnetically guided assembly of magnetic sugar particles

Biodegradable scaffolds with controlled pore layout and porosity have great significance in tissue engineering for cell penetration, tissue ingrowth, vascularization, and nutrient delivery. Porogen leaching has been commonly used to control pore size, pore structure and porosity in the scaffold. In this paper we focus on the use/development of two magnetically guided porogen assembly methods using magnetic sugar particles (MSPs) for scaffold fabrication. First, a patterning device is utilized to align MSPs following designed templates. Then a magnetic sheet film is fabricated by mixing poly(vinyl alcohol, PVA) and NdFeB powder for steering the MSPs. After poly(l-lactide-co-ɛ-caprolactone) (PLCL) casting and removal of the sugar template, a scaffold with spherical pores is obtained. The surface and the inner structure of the scaffolds are evaluated using light and electron micrographs showing their interconnection of pores, pore wall morphology and porosity. Single layer scaffolds with the size of 8mm in width and 10mm in length were constructed with controllable pore diameters in the ranges of 105-150 μm, 250-300 μm and 425-500 μm.

Fabricating Anodic Aluminum Oxide by Anodic-Oxidation

Uniform parallel pores and controllable pore diameter make Anodic Aluminum Oxide (AAO) membrane one of the best materials in synthesis of one-dimensional nano-structured material. High orderly AAO template was prepared by anodic-oxidation. The prepared AAO membrane’s apertures ranged from 30 nm to 75 nm. Within a few microns, holes were orderly arranged. The fabricating methods of AAO template in different electrolyte were studied and the factors which affect the pore distribution, such as electrolyte types, voltage and concentration were discussed.

Dye‐Sensitised Solar Cells Based on Large‐Pore Mesoporous TiO2 with Controllable Pore Diameters

AbstractMesoporous TiO2 (meso‐TiO2) is a promising photoelectrical nanomaterial for high dye‐sensitised solar cell (DSSC) performance, because its nanochannels offer a large internal surface area to allow for more dye adsorption. The interconnected grains facilitate rapid electron transport both within the meso‐TiO2 film and at the film electrode dye/redox shuttle electrolyte interfaces. In this work, a series of DSSCs has been fabricated on the basis of meso‐TiO2 with large controllable pore sizes (6.5, 8.2 and 11.0 nm). It was found that the DSSC with the 8.2 nm meso‐TiO2 photoelectrode has the highest photoelectrical conversion efficiency, which is higher than that of the conventional P25 nanoparticulate DSSC under the same conditions. The measurements of the N2 sorption isotherms and the photovoltage transient demonstrates that such improved efficiency can be ascribed to the larger surface area and the fastest interfacial charge transfer. Meanwhile, the effect of different pore sizes on the photoelectrical conversion efficiency has been systematically investigated, and a possible model for the efficient electrolyte percolation in the dye‐sensitised mesoporous photoelectrode has been proposed.

A green process for the synthesis of controllable mesoporous silica materials

The synthesis, characterization, and application of mesoporous silicas have attracted a lot of attention for over two decades, which stems from their fascinating structures, formation mechanisms and prospects of their applications. Various methods have been developed for the synthesis of these silicas with a tunable pore diameter and a narrow pore size distribution. In this paper, mesoporous silica materials with controllable pore diameters (3–9 nm), narrow pore size distributions, high surface area (>700 m 2 g −1) and pore volume (>1 cm 3 g −1) were prepared by a green template, amphiphilic dendritic polyamidoamine. The resulting silica materials were characterized by 1H, 13C NMR spectroscopy; thermogravimetic analysis; nitrogen adsorption; transmission electron microscope. It was shown that the template could be completely removed and recycled from the silica in an environmentally friendly way by means of a simple water extraction. Furthermore, it was shown that the pore diameter of these materials could be controlled by dendritic polyamidoamine with different generations and functional groups. Meanwhile, the porous framework showed strong thermal stability. Thus, a new environmentally friendly pathway for the controllable synthesis of this fascinating silicas has been proposed.

Maximum efficiency of the electro-osmotic pump

Electro-osmotic effect in a porous medium arises from the electrically charged double layer at the fluid-solid interface, whereby an externally applied electric field can give rise to fluid flow. The electro-osmotic pump (EOP) is potentially useful for a variety of engineering and biorelated applications, but its generally low efficiency is a negative factor in this regard. A study to determine the optimal efficiency of the EOP and the condition(s) under which it can be realized is therefore of scientific interest and practical importance. We present the results of a theoretical and experimental study on the maximum efficiency optimization of the electrokinetic effect in artificially fabricated porous media with controlled pore diameters. It is shown that whereas the EOP efficiency increases with decreasing channel diameter, from 4.5 to 2.5 μm for samples fabricated on oxidized silicon wafers as expected for the interfacial nature of the electro-osmotic effect, the opposite trend was observed for samples with much smaller channel diameters fabricated on anodized aluminum oxide films, with the pore surface coated with silica. These results are in agreement with the theoretical prediction, based on the competition between interfacial area and the no-slip flow boundary condition, that an optimal efficiency of ~1% is attained at a microchannel diameter that is five times the Debye length, with a zeta potential of ~100 mV.

Sodium Fluoride-Assisted Modulation of Anodized TiO2 Nanotube for Dye-Sensitized Solar Cells Application

This work reports the use of sodium fluoride (in ethylene glycol electrolyte) as the replacement of hydrofluoric acid and ammonium fluoride to fabricate long and perpendicularly well-aligned TiO₂ nanotube (TNT) (up to 21 μm) using anodization. Anodizing duration, applied voltage and electrolyte composition influenced the geometry and surface morphologies of TNT. The growth mechanism of TNT is interpreted by analyzing the current transient profile and the total charge density generated during anodization. The system with low water content (2 wt %) yielded a membrane-like mesoporous TiO₂ film, whereas high anodizing voltage (70 V) resulted in the unstable film of TNT arrays. An optimized condition using 5 wt % water content and 60 V of anodizing voltage gave a stable array of nanotube with controllable length and pore diameter. Upon photoexcitation, TNTs synthesized under this condition exhibited a slower charge recombination rate as nanotube length increased. When made into cis-diisothiocyanato-bis(2,2̀-bipyridyl-4,4̀-dicarboxylato) ruthenium(II) bis (tetrabutyl-ammonium)(N719) dye-sensitized solar cells, good device efficiency at 3.33 % based on the optimized TNT arrays was achieved with longer electron time compared with most mesoporous TiO₂ films.

Progress in Nano-Engineered Anodic Aluminum Oxide Membrane Development.

The anodization of aluminum is an electro-chemical process that changes the surface chemistry of the metal, via oxidation, to produce an anodic oxide layer. During this process a self organized, highly ordered array of cylindrical shaped pores can be produced with controllable pore diameters, periodicity and density distribution. This enables anodic aluminum oxide (AAO) membranes to be used as templates in a variety of nanotechnology applications without the need for expensive lithographical techniques. This review article is an overview of the current state of research on AAO membranes and the various applications of nanotechnology that use them in the manufacture of nano-materials and devices or incorporate them into specific applications such as biological/chemical sensors, nano-electronic devices, filter membranes and medical scaffolds for tissue engineering.

Molecular selective photocatalysis by TiO 2/nanoporous silica core/shell particulates

The coating of TiO 2 particles (P25) by a nanoporous silica layer was conducted to impart molecular recognitive photocatalytic ability. TiO 2/nanoporous silica core/shell particles with varied pore diameters of the shell were synthesized by the reaction of P25 with an aqueous mixture of tetraethoxysilane and alkyltrimethylammonium chloride with varied alkyl chain lengths, followed by calcination. The TEM and nitrogen adsorption/desorption isotherms of the products showed that a nanoporous silica shell with a thickness of ca. 2 nm and controlled pore diameter (1.2, 1.6, and 2.7 nm) was deposited on the titania particle when surfactants with different alkyl chain lengths (C12, C16 and C22) were used. The water vapor adsorption/desorption isotherms of the core/shell particles revealed that a larger amount of water adsorbed on the core/shell particles when the pore diameter is larger. The 29Si MAS NMR spectra of the core/shell particles showed that the amount of surface silanol groups was independent of the water vapor adsorption capacity of the products. The possible molecular recognitive photocatalysis on the products was investigated under UV irradiation using two kinds of aqueous mixtures containing different organic compounds with varied sizes and functional groups: a 4-butylphenol, 4-hexylphenol, and 4-nonylphenol mixture and a 2-nitrophenol, 2-nitro-4-phenylphenol, and 4-nitro-2,6-diphenylphenol mixture. It was found that the core/shell particles exhibited selective adsorption-driven molecular recognitive photocatalytic decomposition of 4-nonylphenol and 2-nitrophenol in the two mixtures.

Ordered mesoporous carbon with tunable, unusually large pore size and well-controlled particle morphology

A method is proposed to synthesize well-ordered mesoporous carbon with a remarkably wide pore diameter using microwave-synthesized mesoporous silica, MWSBA-15, as the template. The pore size of the carbon is controlled by tuning the pore size of MWSBA-15, which is accomplished by varying the temperature of the hydrothermal treatment, while using the same amount of carbon precursor. Hereby the pore size can be systematically varied between 5 nm and 9 nm, and the pore volume between 1.4 cm3 g−1 and 1.9 cm3 g−1. A specific surface area between 1400 and 1500 m2 g−1 is obtained for all mesoporous carbon samples. The data suggest that the material, denoted by MWCMK-3, bears strong structural similarity to CMK-3. In addition, it was noted that the pore size of MWCMK-3 increases when the carbon rod size decreases, which correlates with an increasing distance between the rods. Both the MWSBA-15 and the MWCMK-3 particles have a rod-like morphology, and the particle size distribution exhibits low polydispersity. The merit of microwave synthesis lies in its rapid and homogeneous heating of the reacting mixture to the desired temperature. Hydrothermal treatment to as high as 220 °C was performed on MWSBA-15 to achieve an unusually large pore size and still retain a narrow pore size distribution, which is translated to similar properties in MWCMK-3. A partial breakdown of the ordered structure was observed when using MWSBA-15, hydrothermally treated at 240 °C. Results are backed by N2 adsorption isotherms, small-angle X-ray scattering, FESEM, and HRTEM images. Ordered mesoporous carbons with large controllable pore diameters are of interest to fuel cells, batteries, supercapacitors, and protein storage, sensing and release.

Size-Dependent Infiltration and Optical Detection of Nucleic Acids in Nanoscale Pores

Experiments and complimentary simulations are presented to demonstrate the size-dependent infiltration and detection of variable length nucleic acids in porous silicon with controllable pore diameters in the range of 15-60 nm. The pore diameter must be tuned according to target molecule size in order to most effectively balance sensitivity and size-exclusion. A quantitative relationship between pore size (15-60 nm), nucleic acid length (up to ~ 5.3 nm), and sensor response is presented with smaller molecules detected more sensitively in smaller pores as long as the pore diameter is sufficient to enable molecular infiltration and binding in the pores. The density of probe molecules on the pore walls and subsequent hybridization efficiency for target molecule binding are also reported and are shown to depend strongly on the method of infiltration as well as the target molecule size.

Oriented bioactive glass (13-93) scaffolds with controllable pore size by unidirectional freezing of camphene-based suspensions: Microstructure and mechanical response

Scaffolds of 13-93 bioactive glass (composition 6.0 Na 2O, 7.9 K 2O, 7.7 MgO, 22.1 CaO, 1.7 P 2O 5, 54.6 SiO 2 (mol.%)) containing oriented pores of controllable diameter were prepared by unidirectional freezing of camphene-based suspensions (10 vol.% particles) on a cold substrate (−196 °C or 3 °C). By varying the annealing time (0–72 h) to coarsen the camphene phase, constructs with the same porosity (86 ± 1%) but with controllable pore diameters (15–160 μm) were obtained after sublimation of the camphene. The pore diameters had a self-similar distribution that could be fitted by a diffusion-controlled coalescence model. Sintering (1 h at 690 °C) was accompanied by a decrease in porosity and pore diameter, the magnitude of which depended on the pore size of the green constructs, giving scaffolds with a porosity of 20–60% and average pore diameter of 6–120 μm. The compressive stress vs. deformation response of the sintered scaffolds in the orientation direction was linear, followed by failure. The compressive strength and elastic modulus in the orientation direction varied from 180 MPa and 25 GPa (porosity = 20%) to 16 MPa and 4 GPa (porosity = 60%), respectively, which were 2–3 times larger than the values in the direction perpendicular to the orientation. The potential use of these 13-93 bioactive glass scaffolds for the repair of large defects in load-bearing bones, such as segmental defects in long bones, is discussed.

Fabrication and photophysical properties of singlet oxygen generating nanoporous membrane

The nanoporous alumina membranes (NAMs) were fabricated by a two-step aluminium anodic oxidation process. The fabricated NAMs have controllable pore diameters (40–80 nm) and unidirectionally ordered pore direction. The surface of the NAM was modified with the organo-silane agent (APTES: (aminopropyl)triethoxysilane) to induce ionic bonding between the NAM and the photosensitizer (TSPP: tetrakis(p-sulfonatophenyl)porphyrin). The morphology and chemical nature of the surface modified NAM were studied by field emission scanning electron microscope (FE-SEM), FT-IR spectra, and thermo gravimetric analysis (TGA). Furthermore, this singlet oxygen generating nanoporous membranes (SGNMs) were investigated, in detail, to understand their photophysical properties and the singlet oxygen generation efficiency which were the essential factors for their applications. Steady-state spectroscopies and nanosecond laser induced time-resolved spectroscopy were applied to get information on all photophysical properties including the lifetime of singlet oxygen which depended on the pore diameter of the SGNM.

Fabrication and Characterization of Waterborne Biodegradable Polyurethanes 3-Dimensional Porous Scaffolds for Vascular Tissue Engineering

In this study, a series of 3-D interconnected porous scaffolds with various pore diameters and porosities was fabricated by freeze-drying with non-toxic biodegradable waterborne polyurethane (WBPU) emulsions of different concentration. The structures of these porous scaffolds were characterized by scanning electron microscopy (SEM), and the pore diameters were calculated using CIAS 3.0 software. The pores obtained were 3-D interconnected in the scaffolds. The scaffolds obtained at different pre-freeze temperatures showed a pore diameter ranging from 2.8 to 99.9 μm with a pre-freezing temperature of −60°C and from 13.1 to 229.1 μm with a pre-freezing temperature of −25°C. The scaffolds fabricated with WBPU emulsions of different concentration at the same pre-freezing temperature (−25°C) had pores with mean pore diameter between 90.8 and 39.6 μm and porosity between 92.0 and 80.0%, depending on the emulsion concentration. The effect of porous structure of the scaffolds on adhesion and proliferation of human umbilical vein endothelial cells (HUVECs) cultured in vitro was evaluated using the MTT assay and environmental scanning electron microscopy (ESEM). It was found that the better adhesion and proliferation of HUVECs on 3-D scaffolds of WBPU with relative smaller pore diameter and lower porosity than those on scaffolds with larger pore and higher porosity and film. Our work suggests that fabricating a scaffold with controllable pore diameter and porosity could be a good method to be used in tissue-engineering applications to obtain carriers for cell culture in vitro.

Nanoporous Anodic Alumina as Template and Mask for Functional Nanostructures Fabrication

AbstractNanoporous Anodic Alumina Films (NAAF) have been used for growing a lot of nanostructure functional materials. Of particular interest is the NAAF conversion into membranes (NAAM) with different highly controlled pore diameter and distribution to be used as templates and masks to grow a wide variety of nanomaterials. This work constitutes an approach to a review of our latest results regarding the use of NAAF and NAAM as templates in which II-VI semiconductor, functional oxides, hard materials and magnetic nanowires have been grown. The growth techniques and methods used include Isothermal Close Space Sublimation (ICSS), Magnetron Sputtering, electroplating and sol-gel. Ion Beam Irradiation (IBI) combined with different NAAM as masks has been also used for Titania substrates functionalization.

Preparation of highly mesoporous carbon membranes via a sol–gel process using resorcinol and formaldehyde

This paper reports the preparation of highly mesoporous carbon membranes, which are obtained by the pyrolysis of sol–gel derived mesoporous polymer membranes using resorcinol and formaldehyde (RF). Two series of RF carbon membranes were prepared by changing the resorcinol to catalyst molar ratio. The nitrogen adsorption–desorption measurement shows that the RF carbon membranes possess a well-developed mesoporous structure with controlled pore diameters of 5.48 nm and 13.9 nm. The helium and nitrogen permeances of both RF carbon membranes were independent of the feed pressure, indicating that there was no contribution of viscous flow and the membranes are initially crack-free. The gas permeation result showed that the dominant mechanism of gas transport through both the RF carbon membranes is Knudsen diffusion. With regard to the permeation of condensable gases such as CH 4 and CO 2, it was observed that the surface flow also contributes to the total permeation.

Fabrication of anodic aluminium oxide templates on curved surfaces

Aluminium anodization provides a simple and inexpensive way to obtain nanoporoustemplates with uniform and controllable pore diameters and periods over a wide range.Moreover, one of the interesting possibilities afforded by the anodization process is that theanodization can take place on arbitrary surfaces, such as curved surfaces, which has not yetbeen well studied or applied in nanofabrication. In this paper, we characterizethe anodization of Al films on silicon substrates with a curved top surface. Thestructures of the resultant anodic aluminium oxide (AAO) films are examinedby scanning electron microscopy. Unique features including cessation, bending,and branching of pore channels are observed in the curved area. Possible growthmechanisms are proposed, which can also contribute to the understanding of theself-organization mechanism in the formation of porous AAO membranes. The newstructures may open new opportunities in optical, electronic and electrochemicalapplications.

Mesoporous Carbon Membranes with Controlled Pore Diameters

Mesoporous Carbon Membranes with Controlled Pore Diameters

Effect of Scaffold Design on Bone MorphologyIn Vitro

Silk fibroin is an important polymer for scaffold designs, forming biocompatible and mechanically robust biomaterials for bone, cartilage, and ligament tissue engineering. In the present work, 3D biomaterial matrices were fabricated from silk fibroin with controlled pore diameter and pore interconnectivity, and utilized to engineer bone starting from human mesenchymal stem cells (hMSC). Osteogenic differentiation of hMSC seeded on these scaffolds resulted in extensive mineralization, alkaline phosphatase activity, and the formation of interconnected trabecular- or cortical-like mineralized networks as a function of the scaffold design utilized; allowing mineralized features of the tissue engineered bone to be dictated by the scaffold features used initially in the cell culture process. This approach to scaffold predictors of tissue structure expands the window of applications for silk fibroin-based biomaterials into the realm of directing the formation of complex tissue architecture. As a result of slow degradation inherent to silk fibroin, scaffolds preserved their initial morphology and provided a stable template during the mineralization phase of stem cells progressing through osteogenic differentiation and new extracellular matrix formation. The slow degradation feature also facilitated transport throughout the 3D scaffolds to foster improved homogeneity of new tissue, avoiding regions with decreased cellular density. The ability to direct bone morphology via scaffold design suggests new options in the use of biodegradable scaffolds to control in vitro engineered bone tissue outcomes.

Ultraporous Nanosheath Materials by Layer‐by‐Layer Deposition onto Co‐continuous Polymer‐Blend Templates

Porous polymer materials with interconnected porosity have recently received great attention due to their wide range of possible applications and the challenges they pose in preparation. Their potential applications range from use in the biomedical and pharmaceutical fields (tissue engineering and drug delivery) [1–3] to chromatographic materials, [4] to catalysis of chemical and biochemical reactions, [5] and to electronic devices. [6] For tissue-engineering applications, for instance, at least four different techniques for fabricating interconnected porous polymer substrates have been developed: fiber bonding of unwoven meshes, [7] solvent casting/particulate leaching, [8] gas foaming, [9] and phase separation. [10] However, every one of these approaches suffers from severe limitations including low levels of interconnectivity, low void volume, poor control of pore size and distribution, and difficulties in obtaining materials of reproducible porosities. Previously, we advanced an approach to preparing microporous materials based on the melt-blending of two immiscible polymers [11] and demonstrated that selective extraction of one of two components in a co-continuous mixture can result in a single-component structure of fully interconnected porosity with highly controlled porosity, morphology, and pore diameters ranging from 100 nm to hundreds of micrometers. [12,13] However, this method was found to be limited in the void volume that can be attained, and able to be used to prepare only relatively low-void-volume substrates (75%). Layer-by-layer (LbL) deposition is a simple and effective approach to deposit ultrathin and uniform molecular layers onto surfaces in which polyelectrolytes are adsorbed on an oppositely charged surface, reversing the surface charge and leaving it primed for the next deposition cycle. [14–16] Originally

Concentración del virus de la necrosis pancreática infecciosa mediante ultrafiltración de flujo tangencial combinado con filtración de exclusión

SUMMARY The infectious pancreatic necrosis virus, IPNV, is the etiological agent of a highly contagious disease that affects young salmon. The virus is mostly horizontally transmitted; therefore virus quantitation in water is mandatory for a proper sanitary management in the salmon industry as well as in the environment close to the hatcheries. To evaluate the water as a risk factor for IPNV infection in cultured or wild animals, it is necessary to titrate the virus with a suitable sensitivity. Therefore, a methodology that allows IPNV concentration to be determined in water using two kinds of ultrafiltration was developed. One, based on the tangential flow of the sample along the surface of a membrane, the other based on the retention of the viral particles at the surface of membranes with controlled pore diameter. Reagents and conditions were selected to reduce virus inactivation and/or virus binding to the filters. Finally, a protocol was developed that allows the concentration of IPNV in three orders of magnitude and with a total recovery of infectivity to be determined. This method can be performed in less than one day including virus titration using the fluorescent foci method