Tubular Pores Research Articles

SBA-15 Mesoporous Silica as Delivery Vehicle for rhBMP-2 Bone Morphogenic Protein for Dental Applications.

(1) Background: A proposed approach to promote periodontal tissue regeneration in cases of peri-implantitis is the local administration of growth factors at the implant site. Recombinant human bone morphogenetic protein-2 (rh-BMP-2) can effectively promote bone regeneration and osseointegration and the development of appropriate carriers for its delivery is of paramount importance. The aim of the present study was to develop SBA-15 mesoporous nanoparticles (MSNs) with varying porosity, evaluate their biocompatibility with human Periodontal Ligament Cells (hPDLCs) and to investigate their effectiveness as carriers of rh-BMP-2. (2) Methods: SBA-15 type mesoporous silicas were synthesized via sol–gel reaction. The calcined SBA-15 samples were characterized by N2 porosimetry, Fourier transform–infrared spectrometry (FTIR), Scanning (SEM) and Transmission Electron Microscopy (TEM). Rh-BMP-2 loading and release kinetics were evaluated by UV spectroscopy. (3) Results: MSNs presented hexagonally arranged, tubular pores of varying length and diameter. Slightly higher loading capacity was achieved for SBA-15 with large pores that presented good hemocompatibility. MTT assay revealed no cytotoxic effects for all the tested materials, while SBA-15 with large pores induced a significant upregulation of cell viability at day 5. (4) Conclusions: SBA-15 MSNs may prove a valuable delivery platform towards the effective release of bone-inducing proteins.

Poly (methyl methacrylate) grafted wheat straw for economical and eco-friendly treatment of oily wastewater

The sustainable development of oil–gas and petrochemical industries necessitates the development of cost-effective and eco-friendly technologies to treat mass-produced oily wastewater discharge from these industries. This study applied a simple radical polymerization to enhance the oil adsorption efficiency of agricultural waste biomass wheat straw (WS) by grafting biocompatible poly(methyl methacrylate) (PMMA). Diesel oil adsorption from oil-in-water emulsion using the PMMA grafted WS was thoroughly studied for the first time in the quest of developing an economical and eco-friendly adsorbent for the adsorptive treatment of oily wastewater. The success of pre-treatment of pristine WS and the subsequent PMMA grafting were evaluated by SEM morphology, BET analysis, EDX and XPS elemental analysis, FTIR, and contact angle measurements. SEM images indicated that the inner interconnected tubular pore channels of WS are exposed significantly upon alkaline hydrogen peroxide pre-treatment. PMMA grafting substantially improved oil adhesivity, as evident from the 0° oil contact angle for WS-g-PMMA film. Oil absorptivity was thoroughly evaluated by batch oil adsorption study using variable adsorbent dosages and oil emulsion concentrations. The WS-g-PMMA exhibited explicitly higher adsorption capacity (ca. 1129 mg/g) compared to that of the pristine (ca. 346 mg/g) and pretreated (ca. 741 mg/g) due to high accessibility to exposed inner interconnected tubular pore channels and strong hydrophobic interactions between the WS-g-PMMA surface and oil droplets. Langmuir and Freundlich adsorption isotherms were applied to evaluate the adsorption mechanism. The experimental data fit well with the Freundlich isotherm, clearly indicating the heterogeneity of adsorption sites, as well as multilayer adsorption of oil. The experimental adsorption data fit well with the pseudo-second-order rate equation with R2 as high as 0.999, which confirmed the multilayer adsorption of oil. The high oil adsorption capacity of the WS-g-PMMA makes it a very promising material for oily wastewater treatment. The oil removal efficiency declined by < 4% at the end of 3 adsorption-regeneration cycles, indicating the possibility for long-term usage, which is beneficial for cost-effectiveness and lower frequency for end-use waste management. This will simultaneously resolve issues with the treatment of oily wastewater and facilitate the recycling of abundant quantities of waste WS. This study serves as a reference for analyzing the suitability of wheat straw for treating extremely challenging waste streams, such as steam assisted gravity drainage (SAGD) produced water containing BTEX and PAHs that are also hydrophobic like diesel oil.

Super high-quality SEM/FIB imaging of dentine structures without collagen fiber loss through a metal staining process

Scanning Electron Microscope/Focused Ion Beam (SEM/FIB) system has become valuable and popular tool for the analysis of biological materials such as dentine structures. According to physiological and anatomical studies, dentine structures are a complicated system containing collagen fibers, nanocrystalline hydroxyapatite, and numerous networks of tubular pores. During a routine FIB milling process, collagen fibers and other organic structures are vaporized, which increases the number of pores on the milled surface of the dentine. This causes the final cross-section to be more porous than the pristine sample. Unfortunately, little attention has been paid to the collagen fiber loss and how to preserve them during a FIB milling process. In this work, we present a novel and simple approach to preserve the organic portions of the dentine structure through metal staining. By using this method, the porosity of the dentine structure after the FIB milling process is significantly reduced similar to the pristine sample. This indicates that the organic portion of the dentine structure is well protected by the metal staining. This approach enables the SEM/FIB system to generate super-high quality SEM images with less ion beam damage; and the SEM images can better reflect the original condition of the dentine structure. Further, serial energy-dispersive X-ray spectroscopy (EDS) mapping of the stained dentine structure is achieved without an additional metal coating; and three-dimensional (3-D) elemental mapping of an occluded dentine is achieved with a significantly reduced data acquisition time.

Studies and Applications of Dual Pore Saturation Model Based on Pore Structure Classification in Tight Reservoirs

The complex pore structure of rock may influence resistivity logs and make it challenging to perform saturation estimations with better precision. For example, water saturation may go higher or lower when Archie’s formulae are used to obtain the saturation as the logging resistivity may become greater or smaller, due to the influences of complex pore structures in the reservoirs. In this paper, having considered the influences of pore structure on logging resistivity, we have developed a different algorithm to improve the equivalent rock element model (EREM, a rock conduction model) to have better water saturation. First of all, the nuclear magnetic resonance (NMR) echo data of cores are inverted by using the optimized inversion to calculate pore parameters, such as the average radius of spherical pore tubular pore, Cd path, and sorting coefficient. Secondly, according to the parameters derived from the optimization inversions, the pore structures of the core are divided into different groups. Based on the classifications of the pore structure, the conduction parameters of rock for different pore structures are determined by fitting the experimental conduction data of rock with a damping factor. Finally, the working flow of calculating fluid saturation according to the EREM model is determined for different conduction parameters. The key feature of the improved EREM saturation model is to eliminate the influence of pore structure on rock conduction, highlight the influence of pore fluid on rock conduction, and then improve the calculation accuracy of saturation in it. The applications of our research show that the saturation estimations derived from the improved EREM model appear to be more reasonable in terms of the saturation value and its numerical trend. Thus, the improved EREM model has potential in petroleum exploration and exploitation.

Nanoporous anodic alumina with ohmic contact between substrate and infill: Application to perovskite solar cells

AbstractThe use of a nanostructured aluminum substrate as the cathode for a perovskite photovoltaic device is described. This cathode consists of an aluminum substrate onto which a highly ordered array of aluminum oxide tubular pores was grown via anodization. The 1‐μm thick pores – arranged in a closed‐packed hexagonal pattern – were subsequently selectively etched at the bottom to remove the so‐called aluminum oxide barrier layer. The subsequent infiltration of the pores with the components of a methylammonium lead iodide perovskite solar cells, and the completion with a semi‐transparent anode, have shown to allow the establishment of an ohmic contact between the substrate itself and the components infiltrated into the Al2O3 pores. Indeed, a clear rectifying behavior was observed on the full devices, as well as modest photovoltaic conversion efficiencies. This paper demonstrates that an ohmic contact can be established between the aluminum substrate from which nanoporous anodic alumina was grown, and that the pores can be used to compartmentalize the infill material down to the nanoscopic level.

Hardened wood as a renewable alternative to steel and plastic

Hardened wood as a renewable alternative to steel and plastic

Simulation of Permeation of Saturated Cement Paste Based on a New Meso-scale Pore Network Model

This paper presents the simulation of the permeation of saturated cement paste based on a novel pore network model. First, a 2D hydration model of cement particles was developed by extending the work of Zheng et al. 2005 to provide the background for the network construction. Secondly, the establishment of the pore network model and simulation of permeation of saturated cement paste were carried out. The irregular pores between any two hydrated cement particles were linearized with clear distances as the diameters of pores. The straight tubular pores were interconnected with one another to form the network model. During this process, the weighted Voronoi diagram was employed to operate on the graphical expression of the hydrated cement particles. Water permeation in saturated cement paste was simulated to verify the pore network model. Finally, the factors including water–cement ratio, reaction temperature, reaction time and cement particle size that would influence water permeation were numerically investigated.

Adsorption from binary liquid solutions into mesoporous silica: a capacitance isotherm on 5CB nematogen/cyclohexane mixtures

ABSTRACT We present a capacitance method to measure the adsorption of rod-like nematogens (4-cyano--pentylbiphenyl, 5CB) from a binary liquid 5CB/cyclohexane solution into a monolithic mesoporous silica membrane traversed by tubular pores with radii of 5.4 nm at room temperature. The resulting adsorption isotherm is reminiscent of classical type II isotherms of gas adsorption in mesoporous media. Its analysis by a model for adsorption from binary solutions, as inspired by the Brunauer–Emmett–Teller (BET) approach for gas adsorption on solid surfaces, indicates that the first adsorbed monolayer consists of flat-lying (homogeneously anchored) 5CB molecules at the pore walls. An underestimation of the adsorbed 5CB amount by the adsorption model compared to the measured isotherm for high 5CB concentrations hint towards a capillary filling transition in the mesopores similar to capillary condensation, i.e. film-growth at the pore walls is replaced by filling of the pore centres by the liquid crystal. The experimental method and thermodynamic analysis presented here can easily be adapted to other binary liquid solutions and thus allows a controlled filling of mesoporous materials with non-volatile molecular systems.

A positronium-based systematic study of the physico-chemical properties of zeolite pores

A systematic study of the influence of surface acidity of pores, water content, crystal size and structural type of zeolites on positronium behavior was carried out over a wide range of Si/Al ratios using the positron annihilation lifetime spectroscopy technique. A clear decrease in the ortho-positronium pick-off annihilation lifetime, as well as the total ortho-positronium formation fraction, was detected at lower Si/Al ratios due to the positronium oxidizing effect and positron trapping of the Brønsted acid sites. Upon water adsorption, the suppression of the positronium diffusion by the water molecules adsorbed in the tubular pores and their trapping action of positrons and electrons was found to significantly reduce both the ortho-positronium lifetime and intensity. These results clarified the relation between positronium behavior and the chemical reactivity of the zeolite pores.

Magnesium gasar as a potential monolithic hydrogen absorbent

The study focuses on the aspect of using the structure of gasars, i.e. materials with directed open porosity, as a potential hydrogen storage. The structure of the tested gasar is composed of a large number of thin, open tubular pores running through the entire longitudinal section of the sample. This allows hydrogen to easily penetrate into the entire sample volume. The analysis of pore distribution showed that the longest diffusion path needed for full penetration of the metal structure with hydrogen is about L = 50–70 μm, regardless of the external dimensions of the sample. Attempts to hydrogenate the magnesium gasar structure have shown its ability to accumulate hydrogen at a level of 1 wt%. The obtained results were compared with the best result was obtained for the ZK60 alloy after equal channel angular pressing (ECAP) and crushed to a powder form. The result obtained exceeded 4 wt% of hydrogen accumulated in the metal structure, at theoretical 6.9 wt% maximum capacity. A model analysis of the theoretic absorption capacity of pure magnesium was also carried out based on the concentration of vacancies in the metal structure. The theoretical results obtained correlate well with experimental data.

The effect of water cooling conditions on the mechanisms of porous ice formation

Experimental data on the freezing rate and formation of cylindrical and spherical gas inclusions occurring in ice during the cooling of distilled water being in equilibrium with air at different initial temperatures of water and air and during the nonuniform cooling of a vessel with water have been obtained. The shape, size, and location of emerging gas formations are explained in a qualitative manner. It is shown that, with sufficiently slow freezing of water, conditions are created for the formation of thin (0.05 to 0.4 mm) and long (5 to 40 mm) fairly uniform gas tubes. With the acceleration of water freezing, the length of the gas tubes decreases significantly, whereas spherical gas inclusions are formed. The main processes occurring in water are mathematically analyzed. The specified processes include the temperature reduction, variation of the water aggregate state, gas concentration, and creation of conditions for the formation of gas cavities. The quantitative estimates of typical sizes of the forming tubular pores and the distances between them are obtained.

Nanocrystalline SrMnO3 perovskite prepared by sol–gel self-combustion method for sensor applications

Oxide compound with perovskite-type structure, SrMnO3, was investigated in view of its application as capacitive and/or resistive humidity sensor. The compound presents a porous structure with prevailing open tubular pores systems and it was obtained by sol–gel self-combustion method using polyvinyl alcohol as colloidal medium, followed by heat treatment. Air relative humidity (RH) has a big influence on sensor electric capacity. The best sensitivity as capacitive humidity sensor was found at working frequency of 40 Hz over a wide range of relative humidity (0–98% RH). At this frequency, within the interval 0–98% RH the capacity increases by 1200%, and the resistance decreases by only 18%. The sensor has a good linearity of the logC vs. RH characteristics. The sensor exhibits very small hysteresis, and a short response time. The investigated material holds promise for humidity monitoring applications, taking into account the low cost, a wide range of relative humidity and a low-contamination impact, as well as for the realization of some electronic components, which requires good stability of resistivity in the presence of environmental humidity factors.

Formation of oriented fishbone-like pores in biodegradable polymer scaffolds using directional phase-separation processing

The scaffold is a dreamed biomaterial of tissue engineers which can culture cells three-dimensionally outgrowing the two-dimensional cell culture in a petri dish to repair or regenerate tissues and organs. To maximize the performance of this dreamed material, complex three-dimensional (3D) structures should be generated with a simple technique and nontoxic ingredients. Many tissues have tubular or fibrous bundle architectures such as nerve, muscle, tendon, ligament, blood vessel, bone and teeth. The concept of mimicking the extracellualr matrix in real tissue has recently been applied to scaffold development. In this study, a novel method for preparing the poly(l-lactic acid) (PLLA) scaffold with a tubular architecture is presented. Solid–liquid phase-separation was applied to form tubular pores in the scaffold using the directional freezing apparatus. Pores formed in this manner exhibited a fishbone like morphology due to the two crystalline phases of 1,4-dioxane. A tubular diameter of ca. 60–250 μm was achieved by regulating the PLLA concentration and the cooling rate. The compressive modulus of the fishbone-like porous scaffold showed higher values than that of non-directional porous scaffold.

Designer Hydrogel with Intelligently Switchable Stem-Cell Contact for Incubating Cartilaginous Microtissues.

Stem-cell-derived organoid can resemble in vivo tissue counterpart and mimic at least one function of tissue or organ, possessing great potential for biomedical application. The present study develops a hydrogel with cell-responsive switch to guide spontaneous and sequential proliferation and aggregation of adipose-derived stem cells (ASCs) without inputting artificial stimulus for in vitro constructing cartilaginous microtissues with enhanced retention of cell-matrix and cell-cell interactions. Polylactic acid (PLA) rods are surface-aminolyzed by cystamine, followed by being involved in the amidation of poly(( l-glutamic acid) and adipic acid dihydrazide (ADH) to form a hydrogel. Along with tubular pore formation in hydrogel after dissolution of PLA rods, aminolyzed PLA molecules with disulfide bonds on rod surfaces are covalently transferred to the tubular pore surfaces of poly(l-glutamic acid)/ADH hydrogel. Because PLA attaches cells, while poly(l-glutamic acid)/ADH hydrogel repels cells, ASCs are found to adhere and proliferate on the tubular pore surfaces of hydrogel first and then cleave disulfide bonds by secreting molecules containing thiol, thus inducing desorption of PLA molecules and leading to their spontaneous detachment and aggregation. Associated with chondrogenic induction by TGF-β1 and IGF-1 in vitro for 28 days, the hydrogel as an all-in-one incubator produces well-engineered columnar cartilage microtissues from ASCs, with the glycosaminoglycans (GAGs) and collagen type II (COL II) deposition achieving 64 and 69% of those in chondrocytes pellet, respectively. The cartilage microtissues further matured in vivo for 8 weeks to exhibit extremely similar histological features and biomechanical performance to native hyaline cartilage. The GAGs and COL II content, as well as compressive modulus of the matured tissue show no significant difference with native cartilage. The designer hydrogel may hold a promise for long-term culture of other types of stem cells and organoids.

Characterizing the shape, size, and distribution heterogeneity of pore-fractures in high rank coal based on X-ray CT image analysis and mercury intrusion porosimetry

The shape, size, and surface characters of pore-fractures in coal are the basis for understanding the occurrence and migration of coalbed methane (CBM), which requires quantitative characterization. In this study, X-ray CT image analysis was used to quantitatively characterize the size distribution and volume contribution of pore-fractures in coal at three cohesive-scales (nanometer-scale, micrometer-scale, and macro-scale). A shape factor was introduced to divide the pore-fracture shapes into five types: spherical, tubular, slot, and slit pores and flat fractures, which mainly develop in diameters of 0.2–0.8 μm, 0.8–10 μm, 10–30 μm, 30–40 μm, and 50–240 μm, respectively. Compared to mercury intrusion porosimetry (MIP), it was found that the pore diameters measured by X-ray CT image analysis were relatively larger, the pore volume contribution increased then decreased with increasing pore diameter, and pores with diameters of 10–30 μm were the largest. When the pore diameter is 0.2–1 μm and 30–40 μm, the specific surface area by X-ray CT image analysis was 20.38% and 51.53% higher than that from MIP. When the pore diameter is 1–10 μm, the specific surface area measured by the two methods were similar. When the pore diameter is 10–30 μm, the specific surface area by MIP was 43.02% higher than that from X-ray CT image analysis. X-ray CT image analysis is more suitable for testing the morphologies than MIP. Additionally, these shape models of pore-fractures in this work can provide some understanding for the permeability calculations.

Methane dry reforming over Ni/fibrous SBA-15 catalysts: Effects of support morphology (rod-liked F-SBA-15 and dendritic DFSBA-15)

Santa Barbara Amorphous-15 (SBA-15) is a promising molecular sieve material with its highly uniform porosity; nonetheless, its tubular pore channels discouraged mass transfer of reactants during catalysis. Herein, SBA-15 was altered by microemulsion technique to prepare two fibrous SBA-15 with distinct morphologies, viz. rod-liked F-SBA-15 and dendritic DFSBA-15. After Ni impregnation, the Ni/fibrous SBA-15 catalysts (Ni/F-SBA-15 and Ni/DFSBA-15) were catalytically evaluated with methane dry reforming (MDR). From characterization, rod-shaped F-SBA-15 had outer fibrous layer whereas dendritic DFSBA-15 consisted of a solid core with radially projected fibres. Besides, Ni/F-SBA-15 possessed uneven sized NiO but Ni/DFSBA-15 had uniform NiO dispersion. Characterization also proved that fibrillation and Ni impregnation did not alter the pristine properties of SBA-15. However, the surface attributes of SBA-15 remarkably reduced after fibrillation and Ni impregnation. The strength of metal-support (Ni-SiO2) interaction could be ranked as: Ni/DFSBA-15 > Ni/F-SBA-15 > Ni/SBA-15 (previously reported). Both Ni/fibrous SBA-15 catalysts exhibited high proportion of moderate basicity, which favoured the carbon removal via reverse Boudouard reaction. In accordance with endothermicity, the optimal temperature of MDR over both catalysts was 800 °C as greater temperature provoked conspicuous CH4 thermal decomposition. For 50 h MDR at 800 °C, both catalysts presented superior catalytic activity and stability. With a fully accessible siliceous framework, Ni/DFSBA-15 attained greater reactant conversions (84.05–87.40% XCH4 and 81.80–85.60% XCO2) than Ni/F-SBA-15 (80.30–85.80% XCH4 and 76.73–84.10% XCO2). In overall, Ni/DFSBA-15 was more coke-resistant than Ni/F-SBA-15 by virtue of its fully accessible structure, uniformly dispersed Ni phase, and stronger metal-support interaction.

Electromagnetic Interference Shielding Performance of Anisotropic Polyimide/Graphene Composite Aerogels.

Anisotropic polyimide (PI)/graphene composite aerogels were fabricated by unidirectional freezing. A poly(amic acid) (PAA) ammonium salt/graphene dispersion was first synthesized by mixing together PAA, H2O, triethylamine (TEA), and graphene and then was successively subjected to one-way freezing, freeze-drying, and thermal imidization. The one-way growth of ice crystals endowed the composite aerogels with highly arranged tubular pores. The PI/graphene composite aerogels possessed anisotropic conductivity, electromagnetic interference (EMI) shielding, heat transfer, and compression performance. Moreover, the composite aerogels with low density (0.076 g·cm-3) exhibited high EMI shielding effectiveness (SE) of 26.1-28.8 dB, and its specific EMI SE value achieved 1373-1518 dB·cm2·g-1 when the graphene content was 13 wt %. The main electromagnetic interference shielding mechanism of these composite aerogels was microwave absorption. The composite aerogels had excellent thermal stability, and their 5% weight loss temperature was higher than 546 °C in nitrogen. This research provided an easy and environmentally friendly approach to prepare lightweight and anisotropic PI-based composite aerogels.

Cellulose nanocrystal/collagen hydrogels reinforced by anisotropic structure: Shear viscoelasticity and related strengthening mechanism

To meet the requirements of applications, the viscoelasticity of hydrogels is usually improved by some ways, such as incorporating nanoparticles, designing network nanostructure and regulating cross-linking density. However, it is rare to improve the viscoelasticity by designing pore microstructure for hydrogels. In this work, cellulose nanocrystal (CNC)/collagen hydrogels with different pore structures (ordered tubular pores and disordered interconnected pores) and CNC concentrations (2.5–15 wt%) were prepared. The hydrogen bonding interaction between CNCs and collagen was confirmed by FTIR. The effects of pore structure and CNC concentration on the shear viscoelasticity of hydrogels were investigated, including creep, stress relaxation, frequency and strain response. The anisotropic structure and CNCs affected the creep and stress relaxation of the hydrogels, and enhanced the stiffness and dissipated energy, which demonstrated their reinforcing effect. The anisotropic structure with horizontally tubular array not only constrained collagen network rearrangement, but enhanced the elastic properties and torsion resistance of the hydrogels under torsional oscillation compared to the disordered porous structure. The mechanism for the multi-complexation between CNCs, collagen network and pore structure was proposed to understand the relationship between component, structure and hydrogel properties.

Polypyridine-Based Helical Amide Foldamer Channels: Rapid Transport of Water and Protons with High Ion Rejection.

Synthetic strategies that enable rapid construction of covalent organic nanotubes with an angstrom-scale tubular pore remain scarcely reported. Reported here is a remarkably simple and mild one-pot polymerization protocol, employing POCl3 as the polymerization agent. This protocol efficiently generates polypyridine amide foldamer-based covalent organic nanotubes with a 2.8 nm length at a yield of 50 %. Trapping single-file water chains in the 2.8 Å tubular cavity, rich in hydrogen-bond donors and acceptors, these tubular polypyridine ensembles rapidly and selectively transport water at a rate of 1.6×109 H2 O⋅S-1 ⋅channel-1 and protons at a speed as fast as gramicidin A, with a high rejection of ions.

Polypyridine‐Based Helical Amide Foldamer Channels: Rapid Transport of Water and Protons with High Ion Rejection

AbstractSynthetic strategies that enable rapid construction of covalent organic nanotubes with an angstrom‐scale tubular pore remain scarcely reported. Reported here is a remarkably simple and mild one‐pot polymerization protocol, employing POCl3 as the polymerization agent. This protocol efficiently generates polypyridine amide foldamer‐based covalent organic nanotubes with a 2.8 nm length at a yield of 50 %. Trapping single‐file water chains in the 2.8 Å tubular cavity, rich in hydrogen‐bond donors and acceptors, these tubular polypyridine ensembles rapidly and selectively transport water at a rate of 1.6×109 H2O⋅S−1⋅channel−1 and protons at a speed as fast as gramicidin A, with a high rejection of ions.