Pore Orientation Research Articles

Microstructure-Property Relationship of Polyurethane Foams Modified with Baltic Sea Biomass: Microcomputed Tomography vs. Scanning Electron Microscopy.

In this paper, novel rigid polyurethane foams modified with Baltic Sea biomass were compared with traditional petro-based polyurethane foam as reference sample. A special attention was focused on complex studies of microstructure, which was visualized and measured in 3D with high-resolution microcomputed tomography (microCT) and, as commonly applied for this purpose, scanning electron microscopy (SEM). The impact of pore volume, area, shape and orientation on appearance density and thermal insulation properties of polyurethane foams was determined. The results presented in the paper confirm that microcomputed tomography is a useful tool for relatively quick estimation of polyurethane foams’ microstructure, what is crucial especially in the case of thermal insulation materials.

Preferred Pore Orientation as a Complement to Anisotropy of Magnetic Susceptibility: A Case Study of Lava Flows From Batur Volcano, Bali, Indonesia

Anisotropy of magnetic susceptibility (AMS) analyses have been used widely in many applications that include studying lava flows. In this paper, we introduce an auxiliary parameter, i.e., preferred pore orientation, on the use of AMS for lava flow studies on the basaltic lava samples from Batur Volcano in Bali Indonesia. We also examine the effect of sample position in lava flow outcrop to the relationship between preferred pore orientation and AMS. The samples are subjected to petrographic analyses as well as to magnetic measurements and micro-computed tomography (μCT) imaging. Preferred pore orientations were obtained by quantified the long-axis of the vesicles from the images. The correlation was evaluated by measuring the angle between the maximum susceptibility axes and the preferred pore orientations. All samples show that the maximum susceptibility axes are parallel with the flow direction. Three out of six samples of two lava flows from the same eruption show a positive correlation between AMS and preferred pore orientation, where both parameters point to the northeast direction. A difference of sample position in the outcrop of lava flow was observed as a possible factor that influenced the results for the preferred pore orientations. Samples which were taken from the summit of the lava flow have pore orientation parallel to the lava flow direction. While samples which were taken from the foot slope of the lava flow have pore orientation perpendicular to the lava flow direction. This study provides further evidence that pore orientation might be positively correlated with the AMS.

Microstructure and water absorption of ancient concrete from Pompeii: An integrated synchrotron microtomography and neutron radiography characterization

There is renewed interest in using advanced techniques to characterize ancient Roman concrete due to its exceptional durability and low-carbon footprint. In the present work, samples were drilled from the “Hospitium” in Pompeii and were analyzed by synchrotron microtomography (μCT) and neutron radiography to study how the microstructure, including the presence of induced cracks, affects their water adsorption. The water distribution and absorptivity were quantified by neutron radiography. The 3D crack propagation, pore size distribution and orientation, tortuosity, and connectivity were analyzed from μCT results using advanced imaging methods. Porosity was also measured by mercury intrusion porosimetry (MIP) as a reference. Ductile fracture patterns were observed once cracks were introduced. Compared to Portland cement mortar/concrete, the Pompeii samples had relatively high porosity, low connectivity, and a similar coefficient of capillary penetration. In addition, permeability was predicted from models based on percolation theory and pore structure data to evaluate the fluid transport properties. Understanding the microstructure of ancient Pompeii concrete is important because it could inspire the development of modern concrete with high durability.

Segmentation and Pore Structure Estimation in SEM Images of Tissue Engineering Scaffolds Using Genetic Algorithm.

A python computer package is developed to segment and analyze scanning electron microscope (SEM) images of scaffolds for bone tissue engineering. The method requires only a portion of an SEM image to be labeled and used for training. The algorithm is then able to detect the pore characteristics for other SEM images acquired at different ambient conditions from different scaffolds with the same material as the labeled image. The quality of SEM images is first enhanced using histogram equalization. Then, a global thresholding method is used to perform the image analysis. The thresholding values for the SEM images are obtained using genetic algorithm (GA). The image analysis results include pore distributions of pore size, pore elongation and pore orientation. The results agree satisfactorily with the experimental data for the chitosan-alginate porous scaffolds considered. Applications of the method developed for image segmentation is not limited to scaffold pore structure analysis. The method can also be used for any SEM image containing multiple objects such as different types of cells and subcellular components.

Enhancing the Gas Separation Selectivity of Mixed-Matrix Membranes Using a Dual-Interfacial Engineering Approach.

We report a dual-interfacial engineering approach that uses a sub-20 nm polycrystalline MOF-74 shell as a transition phase to engineer the MOF-polymer interface. The application of a shell MOF layer divides the original single interface problem into two interfaces: MOF-MOF and MOF-polymer, which can be individually addressed. The greater external surface area created by the uneven MOF-74 shell containing high-density open metal sites allows the MOF to interact with 300% polymer at the interface compared to traditional MOF, thereby ensuring good interfacial compatibility. When applied on UiO-66-NH2, its respective mixed-matrix membranes exhibit a simultaneous increase of CO2/CH4 separation selectivity and CO2 permeability with increasing MOF loading, implying a defect-free interface. When applied on MOF-801, the mixed-matrix membranes exhibit an ethylene/ethane separation selectivity up to 5.91, a drastic 76% increase compared to that of the neat polymer owing to a "gas focusing" mechanism promoted by the preferred pore orientation in the MOF-74 layer. This represents one of the most selective ethylene/ethane separation membranes reported to date.

Towards designing strong porous carbon fibers through gel spinning of polymer blends

Blends of polyacrylonitrile (PAN) with three different sacrificial polymers: poly (acrylic acid) (PAA), poly (methyl methacrylate) (PMMA), and poly (styrene-co-acrylonitrile) (SAN), were gel spun, oriented through the drawing process, stabilized and carbonized to obtain porous carbon fibers. Carbon fibers with an average pore diameter of 15 nm, 31 nm, 37 nm and 115 nm have been obtained from PAN-PAA (90/10), PAN-PMMA (90/10), PAN-SAN (90/10) and PAN-SAN (80/20) precursor fibers, respectively. The variation in pore size caused by the differences in compatibility between PAN and the sacrificial polymer was evaluated experimentally through blend rheology and theoretically using interaction parameter values. Despite their porosity, carbon fibers from PAN-PAA (90/10) and PAN-PMMA (90/10) exhibited tensile strength (∼1.6 GPa) comparable to that of the non-porous PAN based carbon fibers, processed under similar conditions. Specific tensile modulus of the porous carbon fibers was 15–40% higher than that for the PAN based carbon fibers, and the electrical conductivity was as high as 74 kS/m due to high graphitic ordering. Porous channels presented in this study were obtained by combining phase separation in the nano/micro scale range, with pore orientation and elongation achieved through gel spinning.

Effect of pore orientation on shear viscoelasticity of cellulose nanocrystal/collagen hydrogels

AbstractMotivated by a need to replicate structural and viscoelastic properties of soft tissue, such as cartilage, the structural hydrogels with viscoelastic feature have been of interest in biomedical application. However, the effect of pore alignment on their viscoelastic properties has been largely underestimated. This work prepared cellulose nanocrystal (CNC)/collagen hydrogels with different pore orientations, including horizontally aligned pores, random pores and vertically aligned pores, and integrated them into a multilayered hydrogel with multi‐structure which mimics cartilage construct. The stress relaxation rate (τ1/2), creep rate (γ1/2), storage modulus (G′) and loss modulus (G″) increased in the order of the vertical, random, multi‐structural, and horizontal. G′ value of the horizontal increased up to 300% relative to the vertical in the strain amplitude and frequency sweep. Maxwell–Weichert and Variable Network Density models were used to explain phenomena, and the experimental curves fitted well with the theoretical models. These results reveal that the viscoelastic properties of hydrogel can be influenced by pore orientation except conventional component concentration.

Effective thermal conductivity of porous biomaterials: Numerical investigation

The present research paper aims to predict the effective thermal properties; effective thermal conductivity (ETC) and effective thermal diffusivity (ETD) of porous biocomposites materials (PBCs) used as thermal insulator in construction building. The composite matrix consists on porous material namely gypsum reinforced with Date Palm Fibers (DPF). The experimental results of the Effective thermal conductivity (ETC) are obtained using the Ct-meter apparatus. The numerical study is conducted using the finite element Comsol MultiPhysics software resolving the heat transfer equation in stationary state. To evaluate the pores effect on ETC of PBCs, several parameters related on the pores such as its shape, position and weight fraction are considering in the numerical model. The numerical results are fitted with theoretical models and experimental values. The results of this study indicate that the porosity content has an important effect on the ETC of biocompoites whose decreases increasing the pores quantity. It is noted that the numerical models developed in this study are in agree with experimental values for fibers weight content up to 5%. Others parameters are not taken into account such as the pores orientation, contact resistance within the composites may be introduced in the model to minimize the error with the experimental results. The variation effect of pores shapes and positions conserving the same volume on biocomposites ETC are negligible.

Preliminary design of a novel AlN-Al composite coating used for micro-electronic packaging via finite element modeling

In this study, a novel AlN-Al composite coating (AACC) is proposed for micro-electronic packaging. By adjusting the proportion of AlN in the AACC, the effective thermal conductivity and coefficient of thermal expansion of the AACC can be controlled. The powder of AlN and Al sprayed onto the surface of the W-Cu alloy to form the AACC that acts as a buffer layer to reduce the thermal mismatch between the W-Cu alloy and microchip. Finite element simulation results show that the thermal conductivity decreases from 240.64 to 179.99 W m−1 K−1 with increasing AlN content. The coefficient of thermal expansion ranges from 8.39 to 205 MPa in the case of a selected W-Cu alloy (W70-Cu30). Some microscopic features that affect the thermal conductivity of the coating, such as porosity, pore shape, and pore orientation, have been investigated. Macroscopic properties from an SEM image of real microstructures were studied using the Object-oriented finite element (OOF) analysis.

Bioactive glass scaffold architectures regulate patterning of bone regeneration in vivo

The architecture of bone scaffolds, such as pore dimensions, connectivity and orientation can regulate osteogenic defect repair, as can their rate of degradation. Synthetic bone grafts have historically been developed with foam structures to mimic trabecular bone. Now, Additive Manufacturing techniques enable production of open and regular pore architectures with improved compressive strengths. Here, we compare two types of bioactive glass scaffolds, made of the highly biodegradable ICIE16 composition, with distinctively different architectures but matched interconnect sizes (~150 µm), produced via two different techniques: gel-cast foaming and direct ink writing. A rabbit lateral femoral defect model was used to compare the effect of their architecture on in vivo bone regeneration, relative to a defect only control group, after 4 and 10 weeks of implantation. 3D X-ray microcomputed tomography (micro-CT), correlated to histology and back-scatter electron microscopy (BS-SEM) permitted quantitative evaluation of new bone ingrowth and degradation of the scaffolds. Both foam and printed scaffolds showed equal or higher bone ingrowth compared to the control group. After 4 weeks, the foam group showed the highest osteogenesis, with 51% more bone ingrowth than the defect only controls, but after 10 weeks the defect treated with the printed scaffold had the most bone ingrowth (40% more than the empty defect). Energy dispersive X-ray (EDS) mapping revealed degradation of the glass and calcium-phosphate deposition. The foam group showed more rapid degradation than the printed group, due to higher total porosity (even though interconnected pore size was equivalent). The foam scaffold appeared to allow rapid bone ingrowth and cancellous bone formation, whereas the printed scaffold seemed to provoke cortical-like bone formation, while remaining in place for longer than the 10 week study. While the foam's concave architectures promote initial bone ingrowth, the higher strength open pore channels of the printed scaffolds are beneficial for scaffolds made of highly degradable bioactive glasses.

Molecular scale insight of pore morphology relation with mechanical properties of amorphous silica using ReaxFF

Porous materials are typically heterogeneous and they contain large variations of micro-/nano-pore structures, causing complicated behaviors. In continuum models, most mechanical properties of porous materials are estimated based on porosity, while the variations of micro/nano structures are ignored. That could be problematic as the microscopic heterogeneity may affect the mechanical response of porous materials. Thus, understanding micro/nano heterogeneity impact has been the focus in many scientific and engineering subjects. In the present study, we investigated the effect of nanopore structure (including pore shape and orientation) as well as porosity on mechanical properties of amorphous silica (a-SiO2). The pore sizes in our simulations are comparable to the corresponding ones observed in a-SiO2 based materials. We found that the existing of nanopores strongly influences Young’s modulus (E) and critical energy release rate (GIC). These properties decrease with increasing porosity. Importantly, the impact of nanopores was characterized by structural parameters of porous materials. In addition to dependency on porosity, Young’s modulus also was found to vary as a function of potential energy per atom, which highly depends on nanopore shape. Furthermore, critical energy release rate was found to increase with increasing ligament length (also known as pore wall thickness). The results highlighted the importance of nanopore structures, which must be taken into account when studying fracture mechanisms in porous materials. Based on our findings, it was proposed that mechanical properties of porous materials can be controlled by nano-engineering pore structures.

In vivo Regeneration of Mineralized Bone Tissue in Anisotropic Biomimetic Sponges

In the last two decades, alginate scaffolds have been variously studied as extracellular matrix analogs for tissue engineering. However, relevant evidence is still lacking concerning their ability to mimic the microenvironment of hierarchical tissues such as bone. Hence, an increasing amount of attention has recently been devoted to the fabrication of macro/microporous sponges with pore anisotropy able to more accurately replicate the cell niche structure as a trigger for bioactive functionalities. This paper presents an in vivo study of alginate sponges with anisotropic microporous domains (MAS) formed by ionic crosslinking in the presence of different fractions (30 or 50% v) of hydroxyapatite (HA). In comparison with unloaded sponges (MAS0), we demonstrated that HA confers peculiar physical and biological properties to the sponge, depending upon the inorganic fraction used, enabling the sponge to bio-mimetically support the regeneration of newly formed bone. Scanning electron microscopy analysis showed a preferential orientation of pores, ascribable to the physical constraints exerted by HA particles during the pore network formation. Energy dispersive spectroscopy (EDS) and X-Ray diffraction (XRD) confirmed a chemical affinity of HA with the native mineral phase of the bone. In vitro studies via WST-1 assay showed good adhesion and proliferation of human Dental Pulp-Mesenchymal Stem Cells (hDP-MSC) that increased in the presence of the bioactive HA signals. Moreover, in vivo studies via micro-CT and histological analyses of a bone model (e.g., a rat calvaria defect) confirmed that the maximum osteogenic response after 90 days was achieved with MAS30, which supported good regeneration of the calvaria defect without any evidence of inflammatory reaction. Hence, all of the results suggested that MAS is a promising scaffold for supporting the regeneration of hard tissues in different body compartments.

Advances in the Interfacial Assembly of Mesoporous Silica on Magnetite Particles

AbstractInterfacing magnetic particles with ordered mesoporous materials is an effective direction for the development of functional porous composite materials with rationally designed core–shell structures. Owing to the combined properties of magnetic nanoparticles and mesoporous silica (high surface area, large pore volume, porosity, and biocompatibility), core–shell magnetic mesoporous silica materials have generated tremendous interest in various disciplines, including chemistry, materials, bioengineering, and biomedicine. Interfacial assembly strategies enable the rational construction of magnetic mesoporous silica materials with well‐defined core–shell structure, morphology, pore parameters, and surface wettability, which can decisively influence their physical and chemical properties and thus improve their application performance. This Minireview summarizes recent progress in the synthesis of core–shell magnetic mesoporous silica and the adjustment of key parameters, including pore size, morphology, and pore orientation.

Advances in the Interfacial Assembly of Mesoporous Silica on Magnetite Particles.

Interfacing magnetic particles with ordered mesoporous materials is an effective direction for the development of functional porous composite materials with rationally designed core-shell structures. Owing to the combined properties of magnetic nanoparticles and mesoporous silica (high surface area, large pore volume, porosity, and biocompatibility), core-shell magnetic mesoporous silica materials have generated tremendous interest in various disciplines, including chemistry, materials, bioengineering, and biomedicine. Interfacial assembly strategies enable the rational construction of magnetic mesoporous silica materials with well-defined core-shell structure, morphology, pore parameters, and surface wettability, which can decisively influence their physical and chemical properties and thus improve their application performance. This Minireview summarizes recent progress in the synthesis of core-shell magnetic mesoporous silica and the adjustment of key parameters, including pore size, morphology, and pore orientation.

Self-assemblying behaviour of activated microporous carbon microspheres functionalized via water filtration process

Activated carbon spheres are truly innovative materials with their porous micro/nanostructure that gives them tunable and controllable surface properties (i.e. high surface area, size and orientation of pores etc.). They have great potential for applications as adsorbents for cleaning/purification of water, air and chemical substances, catalyst supports, energy storage and conversion, adsorption of chemical warfare agents, filtration and others. Magnetic functionalization of highly porous and high surface areas of activated carbons have received considerable attention for their more sophisticated and advanced utilization as “smart” and “self-assemblying” purposes. In this study, a novel fabrication technique was used to synthesize activated high compressive strength nanoporous carbon spheres. The functionalization via adsorption/impregnation of magnetic substances was occured during a well-known water treatment-filtering route to fill the pores with nano-sized magnetic particles. Unusually active and dynamic interactions of the magnetic phases were observed upon contacting into each other revealing self-assemblying behaviour of activated carbon microspheres. Dynamic magnetical interaction of self assemblying behaviour of these spheres may have further and advanced applications for variety of purposes.

Facilitated Structure Formation in Isoporous Block Copolymer Membranes upon Controlled Evaporation by Gas Flow.

The conventional fabrication of isoporous membranes via the evaporation-induced self-assembly of block copolymers in combination with non-solvent induced phase separation (SNIPS) is achieved under certain environmental conditions. In this study, we report a modification in the conventional fabrication process of (isoporous) flat sheet membranes in which the self-assembly of block copolymers is achieved by providing controlled evaporation conditions using gas flow and the process is introduced as gSNIPS. This fabrication approach can not only trigger and control the microphase separation but also provides isoporous structure formation in a much broader range of solution concentrations and casting parameters, as compared to fabrication under ambient, uncontrolled conditions. We systematically investigated the structure formation of the fabrication of integral asymmetric isoporous membranes by gSNIPS. A quantitative correlation between the evaporation conditions (causing solvent evaporation and temperature drop) and the self-assembly of block copolymers beginning from the top layer up to a certain depth, orientation of pores in the top layer and the substructure morphology has been discussed empirically.

New biomorphic filters to face upcoming particulate emissions policies: A review of the FIL-BIO-DIESEL project

With a high number of diesel vehicles worldwide, particulate emission control is an urgent issue with a global impact, from the health of citizens to commercial future of this technology in some transport segments. Particulate filters are widely used in automotive engines to comply emissions regulations, but current technologies have room for improvement as they add additional backpressure in the exhaust system, and efficient on-board regeneration process is challenging.The Fil-Bio-Diesel Project is a R&D initiative to improve current particle filtration systems, based on the development of novel biomorphic substrates. By replicating the biologic tissue of a wood precursor, a biomorphic silicon carbide with hierarchic orthotropic microstructure can be produced. The porosity, the pore size, and pore orientation of this bioceramic material can be tailored through the selection of a suitable precursor, widening the initially narrow relationship between filtration efficiency and pressure drop that characterizes granular ceramic materials. In this paper the methodology and main results of the Fil-Bio-Diesel Project are presented. This work shows the peculiar advantages of biomorphic silicon carbide through several experimental studies. The results show the potential of this novel filter substrate to be used in future particulate abatement systems.

Controlling Porosity of Anode Support in Tubular Solid Oxide Fuel Cells by Freeze Casting

Abstract Precise porosity control is highly desirable for improving the electrochemical performance of solid oxide fuel cells (SOFCs). Freeze casting is an established method for enabling high bulk porosity in structures and controlling pore orientation. In this study, freeze casting was used to fabricate tubular, anode-supported SOFCs with aligned and varying amounts of porosity by controlling the solids/water ratio in different casting slurries. SOFCs were prepared with a Ni/yttria and scandia stabilized zirconia (ScYSZ) anode support (AS), an anode functional layer (AFL), a ScYSZ electrolyte, a lanthanum strontium manganite (LSM)/ScYSZ cathode interlayer (CIL), and an LSM cathode. The permeability of the anode support was found to increase from 1.4 × 10−2 to 1.8 × 10−2 m2 as porosity was increased from 57 to 64 vol%, while the total cell resistance decreased by 35% from 0.93 to 0.60 Ohm cm2. When evaluated with 30 vol% H2 as the fuel at 800 °C, the decrease of concentration polarization enabled an increase in electrochemical performance by 42% from 0.35 to 0.50 W/cm2 as the porosity in the anode support was increased. Mechanical strength characterization using a three-point method showed there is a practical upper limit of the amount of porosity that can be designed into the anode support. This work paves a way for controlling porosity by freeze casting and understanding the correlation between porosity and concentration polarization losses in SOFCs.

Tissue Engineered Esophageal Patch by Mesenchymal Stromal Cells: Optimization of Electrospun Patch Engineering.

Aim of work was to locate a simple, reproducible protocol for uniform seeding and optimal cellularization of biodegradable patch minimizing the risk of structural damages of patch and its contamination in long-term culture. Two seeding procedures are exploited, namely static seeding procedures on biodegradable and biocompatible patches incubated as free floating (floating conditions) or supported by CellCrownTM insert (fixed conditions) and engineered by porcine bone marrow MSCs (p-MSCs). Scaffold prototypes having specific structural features with regard to pore size, pore orientation, porosity, and pore distribution were produced using two different techniques, such as temperature-induced precipitation method and electrospinning technology. The investigation on different prototypes allowed achieving several implementations in terms of cell distribution uniformity, seeding efficiency, and cellularization timing. The cell seeding protocol in stating conditions demonstrated to be the most suitable method, as these conditions successfully improved the cellularization of polymeric patches. Furthermore, the investigation provided interesting information on patches’ stability in physiological simulating experimental conditions. Considering the in vitro results, it can be stated that the in vitro protocol proposed for patches cellularization is suitable to achieve homogeneous and complete cellularizations of patch. Moreover, the protocol turned out to be simple, repeatable, and reproducible.

Effects of Room Temperature Stretching and Annealing on the Crystallization Behavior and Performance of Polyvinylidene Fluoride Hollow Fiber Membranes

A treatment consisting of room temperature stretching and subsequent annealing was utilized to regulate the morphology and performance of polyvinylidene fluoride (PVDF) hollow fiber membranes. The effects of stretching ratios and stretching rates on the crystallization behavior, morphology, and performance of the PVDF membranes were investigated. The results showed that the treatment resulted in generation of the β crystalline phase PVDF and increased the crystallinity of the membrane materials. The treatment also brought about the orientation of the membrane pores along the stretching direction and led to an increase in the mean pore size of the membranes. In addition, as the stretching ratio increased, the tensile strength and permeation flux were improved while the elongation at break was depressed. However, compared to the stretching ratio, the stretching rate had less influence on the membrane structure and performance. In general, as the stretching ratio was 50% and the stretching rate was 20 mm/min, the tensile strength was increased by 36% to 7.47 MPa, and the pure water flux was as high as 776.28 L/(m2·h·0.1bar), while the mean pore size was not changed significantly. This research proved that the room temperature stretching and subsequent annealing was a simple but effective method for regulating the structure and the performance of the PVDF porous membranes.