Pore Wall Thickness Research Articles

Sunflower pith inspired dual-gradient cellular polyurethane architecture with amplified mechanical functions

Artificial cellular materials with various mechanical functions are attracting increasing attentions from aerospace, transportation, and industrialization. However, many artificial cellular materials, despite of the hierarchically ordered structures and even unique performance to some, still lag behind many natural ones in amplification of mechanical functions owing to the limitations in intrinsic mechanical performance and sophisticated structural design. Herein, inspired with lightweight and high strength of sunflower piths, we proposed a dual-gradient structure consisting of pore size gradient and wall thickness gradient to engineer cellular architectures with desirable mechanical performance by harnessing vat photopolymerization 3D printing of double crosslinking networks polyurethane elastomer. The double-gradient cellular polyurethane architecture displays more exceptional capability in load-bearing and energy absorption compared with non– and single gradient structures. Besides, the specific compressive strength and energy absorption of the dual-gradient cellular architectures are 4 times higher than those of traditional mechanical metamaterial structures such as octet-truss lattice, gyroid lattice, and porous structure prepared with the same material. Potential mechanisms such as dual-gradient cellular structures to obtain selective flexural deformation behaviour increasing their energy absorption and dissipation capacity are fully elucidated. As the potential paradigms, we demonstrated the mechanical functions of biomimetic mechanical cellular architectures for efficient impact protection and noise isolation, which offered a promising perspective toward developing soft metamaterials with excellent mechanical functions for potential soft machines and engineering applications.

Cell-Shearing Chemistry Directed Closed-Pore Regeneration in Biomass-Derived Hard Carbons for Ultrafast Sodium Storage.

The closed-pore structure of hard carbons holds the key to high plateau capacity and rapid diffusion kinetics when applied as sodium-ion battery (SIB) anodes. However, understanding and establishing the structure-electrochemistry relationship still remains a significant challenge. This work, for the first time, introduces an innovative deep eutectic solvent (DES) cell-shearing strategy to precisely tailor the cell structure of natural bamboo and consequently the closed-pore in its derived hard carbons. The DES shearing force effectively modifies the pore architecture by simultaneously shearing and dissolving amorphous components to form closed pore cores with adjustable sizes, as well as disintegrating crystalline cellulose through generation of competing hydrogen bonds to elaborately tune the pore wall thickness and ordering. The optimized closed-pore structure featuring appropriate pore size (∼2 nm) and ultra-thin (1-3 layers) disordered pore walls, exhibits abundant active sites and delivers rapid ion diffusion kinetics and high reaction reversibility. Consequently, a high reversible capacity of 422 mAh g-1 at 30 mA g-1 along with an exceptional rate capability (318.6 mAh g-1 at 6 A g-1) are achieved, outperforming almost all previous reported hard carbons. The new concept of cell-shearing chemistry for closed-pore regeneration significantly advances the applications of biomass materials for energy storage.

Cellulose nanofiber aerogels: effect of the composition and the drying method

Highly porous and lightweight aerogels of cellulose nanofibers (CNFs) have emerged as a promising class of material. This study delves into the impact of the composition (lignocellulose nanofibers–LCNFs and CNFs) and the drying methods (supercritical drying and freeze-drying) on the morphology and the properties of nanocellulose-based aerogels. The investigation evaluates the concentrations of nanofibers and the influence of lignin, a constituent of LCNFs recognized for enhancing the rigidity of plant cell walls, on the aerogel’s properties. The shrinkage rates, density, pore structure, and mechanical properties of the obtained aerogels are comprehensively compared. Supercritical drying proves advantageous for aerogel formation, resulting in materials with lower density and higher surface area than their freeze-dried counterparts at each concentration level. The use of acetone for supercritical drying contributes to reduce the shrinkage rates compared to ethanol. This decrease is attributed to the formation of a more rigid hydrogel during solvent exchange. Freeze-drying exhibits the lowest shrinkage rates and relatively higher porosity. The presence of lignin in the nanofibers influences the microstructure, yielding smoother and thicker pore walls. This study contributes to the comprehensive understanding of the intricate factors shaping nanocellulose aerogel properties, paving the way for the development of innovative and environmentally-friendly materials.

Emulsion-Templated Gelatin/Amino Acids/Chitosan Macroporous Hydrogels with Adjustable Internal Dimensions for Three-Dimensional Stem Cell Culture.

The demand for macroporous hydrogel scaffolds with interconnected porous and open-pore structures is crucial for advancing research and development in cell culture and tissue regeneration. Existing techniques for creating 3D porous materials and controlling their porosity are currently constrained. This study introduces a novel approach for producing highly interconnected aspartic acid-gelatin macroporous hydrogels (MHs) with precisely defined open pore structures using a one-step emulsification polymerization method with surface-modified silica nanoparticles as Pickering stabilizers. Macroporous hydrogels offer adjustable pore size and pore throat size within the ranges of 50 to 130 μm and 15 to 27 μm, respectively, achieved through variations in oil-in-water ratio and solid content. The pore wall thickness of the macroporous hydrogel can be as thin as 3.37 μm and as thick as 6.7 μm. In addition, the storage modulus of the macroporous hydrogels can be as high as 7250 Pa, and it maintains an intact rate of more than 92% after being soaked in PBS for 60 days, which is also good performance for use as a biomedical scaffold material. These hydrogels supported the proliferation of human dental pulp stem cells (hDPSCs) over a 30 day incubation period, stretching the cell morphology and demonstrating excellent biocompatibility and cell adhesion. The combination of these desirable attributes makes them highly promising for applications in stem cell culture and tissue regeneration, underscoring their potential significance in advancing these fields.

Performance improvement of glass-based lightweight aggregates through thermodynamic modelling design and lightweight mortar validation

To reduce environmental impact of sintered lightweight aggregates (LWAs), in this study, novel glass-based LWAs were produced from municipal solid wastes at 900 °C. The mix was designed by thermodynamic modelling to optimize the phase composition, liquid phase properties, and microstructure of the LWAs. Results demonstrated that the inclusion of incinerated sewage sludge ash (ISSA) increased the viscosity of the liquid phase, resulting in a refined pore structure characterized by smaller, more isolated pores, and thicker pore walls. Additionally, ISSA facilitated the formation of various crystalline phases (e.g. wollastonite) to stabilize the pore structure, thereby enhancing densification and matrix strength. Leaching behaviour tests confirmed the suitability of glass-based LWAs for environmentally safe lightweight products. Lightweight mortars incorporating developed LWAs exhibited a high 28-day compressive strength (up to 57.9 MPa) with a low density of 1688 kg/m3 and a low thermal conductivity of 1.0 W/(m·K). The energy simulation revealed substantial reductions in energy consumption when the lightweight mortars were utilized in the building compared with the reference building using normal-weight C30 concrete, underscoring its promising role in conserving energy and reducing carbon emissions.

Co-pyrolysis of coal with biomass residues and coke breeze for superior quality coke via hot pressing technology

Superior quality coke is essential in the metallurgical industry. However, the coking coal source is limited. The biomass or breeze could be blended into the coking coal to produce high-standard cokes by hot pressing technology. High-standard cokes should have low reactivity (chemical reaction intensity of coke and CO2 at high temperature) and high strength. The influences of biomass category and blending ratio on pore structure, reactivity and crushing strength of cokes were explored. Pore evolution during the coking process was studied by experiments and simulations to reveal the mechanism of producing high-quality cokes with biomass and breeze blended into coking coal via hot pressing technology. Results show that hot pressing technology can make high-quality cokes when the blending ratio of biomass or breeze is appropriate. When 5% bamboo, wood or straw is blended to produce hot-pressed coke, the coke reactivity decreases by 6.58%, 7.66% and 6.41% and the crushing strength increases to 1.15, 1.19 and 1.12 times when compared with coke in case of no blending and no pressing, respectively. The proper blending ratio of the three biomasses should be less than 15% because the coke quality deteriorates greatly when the blending ratio increases to 15%. If the breeze is mixed with coal to produce high-standard cokes under hot pressing conditions, the blending ratio should not exceed 30%. Hot pressing technology can reduce the coke pores when the biomass or breeze is blended into the coal with a low ratio. When 5% bamboo or 10% breeze is blended, the porosity of hot-pressed coke in the center region decreases by 5.69% and 4.02% than coke with no blending and no pressing, respectively. The low porosity contributes to the reduction of coke reactivity. The fewer pores, thicker pore walls and higher carbon matrix strength impede the growth of cracks, resulting in a higher coke crushing strength. Therefore, hot pressing technology can effectively enhance coke quality if the biomass or breeze is mixed with the coking coal with an appropriate blending ratio.

Computed tomography technologies to measure key structural features of polymeric biomedical implants from bench to bedside.

Implanted polymeric devices, designed to encourage tissue regeneration, require porosity. However, characterizing porosity, which affects many functional device properties, is non-trivial. Computed tomography (CT) is a quick, versatile, and non-destructive way to gain 3D structural information, yet various CT technologies, such as benchtop, preclinical and clinical systems, all have different capabilities. As system capabilities determine the structural information that can be obtained, seamless monitoring of key device features through all stages of clinical translation must be engineered intentionally. Therefore, in this study we tested feasibility of obtaining structural information in pre-clinical systems and high-resolution micro-CT (μCT) under physiological conditions. To overcome the low CT contrast of polymers in hydrated environments, radiopaque nanoparticle contrast agent was incorporated into porous devices. The size of resolved features in porous structures is highly dependent on the resolution (voxel size) of the scan. As the voxel size of the CT scan increased (lower resolution) from 5 to 50 μm, the measured pore size was overestimated, and percentage porosity was underestimated by nearly 50%. With the homogeneous introduction of nanoparticles, changes to device structure could be quantified in the hydrated state, including at high-resolution. Biopolymers had significant structural changes post-hydration, including a mean increase of 130% in pore wall thickness that could potentially impact biological response. By incorporating imaging capabilities into polymeric devices, CT can be a facile way to monitor devices from initial design stages through to clinical translation.

A multiscale model to predict the equation of state of a saturated cement paste

An advanced multiscale analytical approach for predicting the Equation of State (EOS) of fully saturated cement pastes is presented. This approach models the matrix as an elastic–plastic material with linear hardening that includes capillary pores filled with water. The model takes into account both the stochastic variation of pore sizes and their spatial distribution. The microscale level is represented by a spherical medium having the mechanical properties of the cement paste matrix. A single spherical pore that is filled with compressible water is located at the center of the micro-domain. The behavior of the compressible water is modeled by the nonlinear Tait equation of state. The EOS at the macro level is obtained by averaging the micro level domain strains over the pore sizes and pore wall thicknesses. It is shown that the solution depends only on the ratio between the minimum pore wall thickness and the lower limit of capillary pore radius and is independent of each of these parameters separately. The EOS obtained by the proposed model shows good agreement with experimental data for cement paste with water/cement ratio w/c = 0.50. The performed parametric study shows that the bulk modulus and yield stress of undisturbed cement gel matrix significantly affect the EOS, while the variation of Poison ratio, plastic hardening parameter and minimum limit pore size and wall thickness (within physically accepted range) slightly affect the cement paste bulk behavior.

Structural changes of flaxseed protein modified by fermentation and the gel properties and swallowing characteristics of its composite system with mung bean starch

The fermentation modification of plant-based proteins has attracted extensive attention recently. This study was to investigate the effect of fermentation on molecular structures of flaxseed protein (FP), and evaluate the gel properties and swallowing characteristics of the composite gel composed of mung bean starch (MBS) and fermented FP (FFP). After 10 h of fermentation, the content of free amino acids in FFP increased ∼14.3 times over that of the unfermented FP, while the proportion of small peptides increased by ∼37.2%. Fermentation reduced the α-helical conformation in FFP. After heating, FFP was easier to cross-link with MBS to form strengthened composite gel network with denser and larger pores as well as thicker pore wall, in which the maximum gel hardness increased by 2.6 times. MBS-FFP composite gels also exhibited increase in viscoelastic moduli, cohesiveness, thermal stability, and water-holding capacity (WHC) than the control gel. The WHC was increased from 63.4% to 92.3% when composite gel contained 10 h fermented FP. Furthermore, international dysphagia diet standardization initiative (IDDSI) tests indicated that all MBS-FFP composite gels could be categorized as level 7 dysphagia food. These findings provide new insights into the structural nature and potential application of plant protein-based fermentation-induced gel systems.

High porosity hafnia ceramics by freeze casting

Highly porous hafnia ceramics are prepared by freeze casting. The major challenge resides in the high density of the hafnia particles typically leading to settling in the slurry. To address this, we optimized the suspension formulation to achieve structures with porosities of 68–74 %. Our approach includes a reduction in additive quantities and an adjustment of the pH value for suspension stabilization and prevention of particle settling. The use of PVA and PEG ensures a green body strength during the process yielding in cellular microstructure with pore channels aligned in the freezing direction throughout the sample. With increasing solid loading, the scaffolds become denser and the pore wall thickness increases. Compressive strength tests confirm the enhanced stiffness of the samples with 15 vol% hafnia. Samples with 10 vol% hafnia show a buckling-dominated failure behavior. Our results provide valuable insights to the preparation of suspensions containing high density materials.

Effect of process parameters on the synthesis and lead ions removal performance of novel porous hydroxyapatite sheets prepared via non-aqueous precipitation method

Herein, porous hydroxyapatite sheets with high lead ions removal performance are synthesized via self-assembly non-aqueous precipitation method, and the effects of process parameters on the synthesis and lead ions removal performance are systematically investigated. The optimized precursors concentration, the molar ratio of calcium to phosphorus and the calcination temperature are 0.25 mol/L, 1.67 and 650 °C, respectively. The refinement XRD, FE-SEM and EDS tests of the optimized samples show that the samples have a porous sheet structure with uniform pore size and wall thickness. The lead ions removal rate of hydroxyapatite sheets has the maximum value of 99.6% when the hydroxyapatite addition amount is 1 g/L. The lead ions removal content is the maximum of 1303.6 mg/g when the initial lead ions concentration is 9 mmol/L. The removal mechanism of lead ions by porous hydroxyapatite sheets prepared in this work is the composite mechanisms of surface adsorption, surface complexation and ions exchange. The hydroxyapatite porous sheet material prepared by optimizing the process parameters in this study has the advantages of high removal capacity and wide adaptability, so it is expected to become a novel adsorbent to solve lead-containing wastewater.

Sustainable versatile chitin aerogels: facile synthesis, structural control and high-efficiency acoustic absorption.

Bio-based materials with excellent acoustic absorption properties are in great demand in architecture, interior, and human settlement applications for efficient noise control. In this study, crayfish shells, a form of kitchen waste, are utilized as the primary material to produce ultralight and multifunctional chitin aerogels, which effectively eliminate noise. Different replacement solvents and freezing rates were employed to regulate the porous structures of chitin aerogels, and their resulting acoustic absorption performance was investigated. Results demonstrate that employing deionized water as the replacement solvent and utilizing a common-freeze mode (frozen via refrigerator at -26 °C) can produce chitin aerogels with larger porosity (96.26%) and apertures, as well as thicker pore walls. This results in superior broadband acoustic absorption performance (with a maximum absorption coefficient reaching 0.99) and higher Young's modulus (28 kPa). Conversely, chitin aerogels solvent-exchanged with tert-butyl alcohol or subjected to quick-freeze mode (frozen via liquid nitrogen) exhibit smaller porosity (92.32% and 94.84%) and apertures, thereby possessing stronger diffuse reflection of visible light (average reflectance of 94.30% and 88.18%), and enhanced low-frequency (500 to 1600 Hz) acoustic absorption properties. Additionally, the acoustic absorption mechanism of fabricated chitin aerogels was predicted using a simple three-parameter analysis Johnson-Champoux-Allard-Lafarge (JCAL) model. This study presents a novel approach to developing multifunctional biomass materials with excellent acoustic absorption properties, which could have a wide range of potential applications.

Giant piezoresponse in nanoporous (Ba,Ca)(Ti,Zr)O3 thin film.

Lattice strain effects on the piezoelectric properties of crystalline ferroelectrics have been extensively studied for decades; however, the strain dependence of the piezoelectric properties at nano-level has yet to be investigated. Herein, a new overview of the super-strain of nanoporous polycrystalline ferroelectrics is reported for the first time using a nanoengineered barium calcium zirconium titanate composition (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 (BCZT). Atomic-level investigations show that the controlled pore wall thickness contributes to highly strained lattice structures that also retain the crystal size at the optimal value (<30 nm), which is the primary contributor to high piezoelectricity. The strain field derived from geometric phase analysis at the atomic level and aberration-corrected high-resolution scanning transmission electron microscopy (STEM) yields of over 30% clearly show theoretical agreement with high piezoelectric properties. The uniqueness of this work is the simplicity of the synthesis; moreover the piezoresponse d 33 becomes giant, at around 7500 pm V-1. This response is an order of magnitude greater than that of lead zirconate titanate (PZT), which is known to be the most successful ferroelectric over the past 50 years. This concept utilizing nanoporous BCZT will be highly useful for a promising high-density electrolyte-free dielectric capacitor and generator for energy harvesting in the future.

Research on the development of green foaming fluid and the improvement in the performance of foamed cement

The promotion of green foamed cement in engineering aligns with the double carbon strategy and sustainable development goals. The impacts of different foaming materials, their concentrations, the water–binder ratio, the foam–grout ratio, and the mineral powder on the slurry performance of foamed cement were investigated. Orthogonal and comprehensive tests were conducted to examine these factors. The results demonstrated that surface active agent molecules formed an interfacial film with mechanical strength, significantly enhancing the strength and uniformity of green foam. Although the density of green foamed cement was similar to that of commercial foamed cement, its compressive strength at 28 d was three times higher, reaching 8.07 MPa. Scanning electron microscopy observations revealed that the green foamed cement mainly featured 0–0.2-mm-diameter pores with independent pore spaces and thick pore walls, which could be improved by using surface active agents. Moreover, the production price per cubic meter of green foamed cement was 79.56 RMB lower than that of ordinary cement. In brief, the research indicated that the application prospects for green foamed cement are promising due to its performance and economic benefits.

Limiting Thickness of Pore Walls Formed in Processes of Anode Etching of Heavily Doped Semiconductors

Limiting Thickness of Pore Walls Formed in Processes of Anode Etching of Heavily Doped Semiconductors

Protein-stabilized Pickering emulsion interacting with inulin, xanthan gum and chitosan: Rheological behavior and 3D printing

Physical stability and lipid digestion of protein-stabilized Pickering emulsions interacting with polysaccharides have been emphasized in our previous investigation. However, the polysaccharide coating and micelle protection of protein-based stable Pickering emulsion and its three-dimensional (3D) printing properties have not been thoroughly studied. The rheological properties and 3D printing properties of gelatin-catechin nanoparticles (GCNPs) stabilized Pickering emulsion were studied by using different charged polysaccharides, such as inulin (neutral), Xanthan gum (XG, anion), and chitosan (cation) as stable materials. The microstructure analysis of polysaccharide-stabilized Pickering emulsion (PSPE) showed that the order of pore wall thickness was GC-Chitosan > GC-XG > GC-Inulin. The network structure of GC-Chitosan was thickened, allowing the 3D printed product to have a good surface texture and adequate support. Rheological analysis showed that PSPEs in extrusion (shear thinning), self-support (rigid structure), and recovery (the outstanding thixotropy) of the three stages exhibited good potential of 3D printing. 3D printing results also showed that GC-Chitosan had the best printing performance. Therefore, polysaccharide-stabilized Pickering emulsions can provide a basis for the development of 3D printed food products.

Morphology and Crystallinity Effects of Nanochanneled Niobium Oxide Electrodes for Na-Ion Batteries.

Niobium pentoxide (Nb2O5) is a promising negative electrode for sodium ion batteries (SIBs). By engineering the morphology and crystallinity of nanochanneled niobium oxides (NCNOs), the kinetic behavior and charge storage mechanism of Nb2O5 electrodes were investigated. Amorphous and crystalline NCNO samples were made by modulating anodization conditions (20-40 V and 140-180 °C) to synthesize nanostructures of varying pore sizes and wall thicknesses with identical chemical composition. The electrochemical energy storage properties of the NCNOs were studied, with the amorphous samples showing better overall rate performance than the crystalline samples. The enhanced rate performance of the amorphous samples is attributed to the higher capacitive contributions and Na-ion diffusivity analyzed from cyclic voltammetry (CV) and the galvanostatic intermittent titration technique (GITT). It was found that the amorphous samples with smaller wall thicknesses facilitated improved kinetics. Among samples with similar pore size and wall thickness, the difference in their power performance stems from the crystallinity effect, which plays a more significant role in the resulting kinetics of the materials for Na-ion batteries.

Effects of Gamma Irradiation on the Properties of Hydroxyapatite-Collagen-Chitosan-Mg-ZnO Scaffolds for Bone Tissue Engineering

Bone tissue engineering aims to repair diseased or damaged bone that cannot be regenerated naturally. This study is designed to develop biodegradable porous scaffolds as bone substitutes and evaluate the effect of gamma irradiation on these scaffolds for the restoration of defected bone. Here, composite scaffolds (HA-COL-CS-Mg-ZnO) were prepared by the thermally induced phase separation (TIPS) technique using collagen (COL) and chitosan (CS), hydroxyapatite (HA), magnesium (Mg), and zinc oxide (ZnO) at different mass ratios. Thereafter, the scaffolds were subjected to 10 KGy γ-radiation for physical cross-linking and sterilization. The physicochemical and biological properties of the scaffolds were evaluated by Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR), field emission scanning electron microscopy (FESEM), physical stability (biodegradability, swelling rate, porosity, and density), mechanical properties, biocompatibility, cytotoxicity, and antimicrobial activity against Escherichia coli (ATCC-25922) and Staphylococcus aureus (ATCC-25923). We found that the irradiated scaffold showed enhanced tensile strength and antimicrobial activities which are desirable characteristics of bone-mimicking scaffolds. FESEM revealed that the average pore size decreased from 192.3 to 104.5 μm due to radiation. FTIR-ATR spectra showed that γ-radiation triggered cross-linking in the polymer matrix which improved mechanical strength (0.82 N/mm2 to 1.86 N/mm2) by increasing pore wall thickness. Moreover, the irradiated and nonirradiated scaffolds were biocompatible and noncytotoxic toward the Vero cell line which ensured their suitability for use in vivo. These results demonstrate that sterilization of HA-COL-CS-Mg-ZnO scaffolds with gamma-irradiation substantially improves the physicochemical and morphological features which aid bone tissue regeneration and could be supportive for new bone formation.

3D printed triply periodic minimal surfaces calcium phosphate bone substitute: The effect of porosity design on mechanical properties

Triply periodic minimal surfaces (TPMSs) are relevant structures for building synthetic bone grafts due to their tortuosity and interconnected pores. In order to investigate their porosity and mechanical properties, three different hydroxyapatite-based TPMSs were printed by vat polymerization: the Schwartz diamond, Schwartz primitive, and gyroid scaffolds. Each structure was designed with three levels of porosity, two different pore sizes, and two different wall thicknesses so as to gain an understanding of the effect of pore size and wall thickness on the mechanical properties. The results highlighted the importance of cleaning in the manufacturing process and its impact on the final porosity, especially for small pore sizes. This article intends to be among the first to discuss mechanical testing with macro spherical indentation. Bending and macro spherical indentation resistance tests revealed differences in the mechanical properties between the different structures, with a strong sensitivity of bending strength to the presence of cracks after thermal treatment. Notably, increasing the wall thickness was shown to increase the risk of damage to the solid parts of the scaffolds, therefore lowering the bending strength.

Melt Electrowriting of Nylon-12 Microfibers with an Open-Source 3D Printer.

This study demonstrates how either a heated flat or cylindrical collector enables defect-free melt electrowriting (MEW) of complex geometries from high melting temperature polymers. The open-source "MEWron" printer uses nylon-12 filament and combined with a heated flat or cylindrical collector, produces well-defined fibers with diameters ranging from 33±4 to 95±3µm. Processing parameters for stable jet formation and minimal defects based on COMSOL thermal modeling for hardware design are optimized. The balance of processing temperature and collector temperature is achieved to achieve auxetic patterns, while showing that annealing nylon-12 tubes significantly alters their mechanical properties. The samples exhibit varied pore sizes and wall thicknesses influenced by jet dynamics and fiber bridging. Tensile testing shows nylon-12 tubes are notably stronger than poly(ε-caprolactone) ones and while annealing has limited impact on tensile strength, yield, and elastic modulus, it dramatically reduces elongation. The equipment described and material used broadens MEW applications for high melting point polymers and highlights the importance of cooling dynamics for reproducible samples.