Concave Pores Research Articles

Porous titanium/hydroxyapatite interpenetrating phase composites with optimal mechanical and biological properties for personalized bone repair

This study introduces the first fabrication of porous titanium/hydroxyapatite interpenetrating phase composites through an innovative processing method. The approach combines additive manufacturing of a customized titanium skeleton with the infiltration of an injectable hydroxyapatite foam, followed by in situ foam hardening at physiological temperature. This biomimetic process circumvents ceramic sintering and metal casting, effectively avoiding the formation of secondary phases that can impair mechanical performance. Hydroxyapatite foams, prepared using two foaming agents (polysorbate 80 and gelatine), significantly reinforce the titanium skeleton while preserving the microstructural characteristics essential for osteoinductive properties. The strengthening mechanisms rely on the conformation of the foams to the titanium surface, thereby enabling stable mechanical interlocking and effective interfacial stress transfer. This, combined with the mechanical constriction of phases, enhances damage tolerance and mechanical reliability of the interpenetrating phase composites. In addition, the interpenetrating phase composites feature a network of concave pores with an optimal size for bone repair, support human osteoblast proliferation, and exhibit mechanical properties compatible with bone, offering a promising solution for the efficient and personalized reconstruction of large bone defects. The results demonstrate a significant advancement in composite fabrication, integrating the benefits of additive manufacturing for bone repair with the osteogenic capacity of calcium phosphate ceramics.

Synergetic effects of S, N co-doping and surface concave-pores rich in lotus-leaf-like carbon nanosheets enabled threefold lithium storage mechanisms

Carbon-based materials based on structural and dimensional optimization are appealing as anode materials in lithium-ion batteries (LIBs). However rational design of high-efficiency low-dimensional carbon-based electrodes is still challenging. Therefore, a synthesis strategy based on Schiff base reaction has been devised for S, N co-doped and surface-enriched concave pores coupled with two-dimensional lotus-leaf-like carbon nanosheets (S, N-SCP/LCN). Experimental and theoretical results disclose that the synergetic effect of S, N co-doping and surface concave pores synergistically contribute to the improved lithium storage efficiency. The numerous concave pores within the defective carbon substrates significantly enhance the specific surface area and boost the quantity of active sites. Furthermore, S, N co-doping induces additional surface and structural defects and widens the crystallographic spacing. Herein, the formed threefold lithium storage mechanisms work synergistically to increase the active lithium storage sites and ion diffusion channels, promoting ion diffusion and charge transfer during lithium storage. As expected, the S, N-SCP/LCN exhibits remarkably high lithium storage capacity (1250 mAh/g at 0.1 A/g) and exceptional rate performance (445.65 mAh/g at a high rate of 10 A/g).

Elastic properties and microstructure evolution of Zn2SnO4-spinel-containing composite ceramics based on tin oxide and zinc oxide

Ceramics based on tin oxide (SnO2) and zinc oxide (ZnO) were sintered at temperatures up to 1400 °C. Except for the end members, all these ceramics are two- or three-phase composites containing spinel phase (Zn2SnO4). Similar to pure SnO2 ceramics, also the spinel-rich composite (50:50 mixture) does not exhibit densification after sintering at 1400 °C. Spinel Zn2SnO4 is formed in all composites, with a major increase of spinel content at around 1000 °C. Young’s modulus values, determined via impulse excitation, are between the exponential relation for convex pores and a benchmark relation for concave pores (or a percolation relation). The evolution of Young’s modulus during sintering reveals significant differences between SnO2 (weak increase above 1000 °C), ZnO (significant increase above 800 °C) and the composites (intermediate). Spinel formation is revealed during heating by a distinct peak (elastic anomaly) at around 1000 °C.

Evolution of Young’s modulus and damping of Czech kaolins during sintering monitored via impulse excitation

The evolution of Young’s modulus and damping is investigated for Czech kaolins in situ via the impulse excitation technique (IET) from room temperature to 1250 and 1400 °C. During heating the processes of drying, dehydroxylation, spinel formation, mullitization, silica release and glass melting are clearly discernible. During cooling Young’s modulus increases, exhibiting a flat maximum around 800 °C and a steep decrease below 200 °C when the cristobalite content is high. Differential IET curves are introduced as a new representation of IET results, and damping curves are shown to provide additional information. The phase composition is determined via XRD, including the glass phase. Based on the densities, Young’s moduli and volume fractions of the individual phases, the densities and Young’s moduli of the kaolin-based ceramics are calculated and compared to theoretical predictions, showing that Young’s modulus is nicely predicted by a benchmark relation for partially sintered ceramics with concave pores.

Young’s modulus and damping of partially sintered potassium sodium niobate (KNN) ceramics and its temperature dependence determined via the impulse excitation technique (IET)

Potassium sodium niobate (KNN) is suitable for the preparation of lead-free piezoelectric ceramics, and thus the elastic properties and damping behavior should be reliably known for practical applications. In this work we compare partially sintered KNN ceramics prepared by uniaxial and conventional sintering from three different KNN powders and show that the impulse excitation technique (IET) is perfectly suited to determine Young’s modulus at room temperature as well as the temperature dependence of Young’s modulus and damping (heating-cooling cycles with maximum temperature 800 °C). Room temperature values of the effective Young’s modulus of partially sintered KNN ceramics are below the predictions for convex pores and above a recently published numerical benchmark relation for concave pores. The phase transition temperatures determined by the IET are 160–190 °C for the low-temperature orthorhombic-tetragonal / tetragonal-orthorhombic transition and 388–412 °C for the high-temperature tetragonal-cubic / cubic-tetragonal transition, with hysteresis 12–25 K.

Study on the scale-forming mechanism of magnesium phosphate by polyepoxysuccinic acid based on solution conductivity method

PurposeThis study aims to investigate the influence of polyepoxysuccinic acid sodium (PESA), a green antiscalant, on the nucleation, crystallization and precipitation of magnesium phosphate.Design/methodology/approachThe conductivity method was used to investigate the maximum relative supersaturation of magnesium phosphate across various PESA dosages. Subsequently, a magnesium phosphate scale was prepared using the static scale inhibition method (GB/T16632-1996) and then analyzed via scanning electron microscopy.FindingsThe findings showed that PESA extends the induction period of magnesium phosphate crystallization, reduces crystal growth rate and elevates the solution’s relative supersaturation. Notably, PESA exerts a low dosage effect on inhibition of the magnesium phosphate scale, with the optimal dosage identified at 10 mL. Scanning electron microscopy revealed that PESA dispenses a dispersing effect on the magnesium phosphate scale, generating numerous concave, convex and deeper pores on the scale particles’ surface, and thereby significantly enhancing the surface area, especially when using an antiscalant with variable dosages.Originality/valueThis study sheds new light on the impact of PESA, a green antiscalant, on the crystallization and precipitation of magnesium phosphate, thus paving the way for the development of enhanced and eco-friendly scale inhibition strategies in future applications.

Porosity dependence of sound velocities in partially sintered alumina, zirconia, ATZ, and mullite ceramics

AbstractYoung's modulus and sound velocities of partially sintered alumina, zirconia, ATZ, and mullite ceramics with a broad range of porosities determined via the impulse excitation technique (IET) and the ultrasonic wave propagation pulse‐echo technique (UPT) are found to be in good agreement and exhibit sigmoidal curves as a function of the sintering temperature. The porosity dependence of the relative values of Young's modulus and sound velocities is either close to or below (but never above) the prediction based on an exponential relation, and none of them is significantly below the prediction based on a percolation relation or a recently proposed numerical benchmark relation for overlapping monosized spheres. Values are lower when concave pores or irregular anisometric grains are dominating. The correlation of the normalized longitudinal wave velocities and relative transverse wave velocities, with VL/VT ratios ranging from 0.50 to 1.91, is well predicted by models for Poisson's ratios between 0.35 and 0.2.

The porosity dependence of sound velocities in ceramic materials

The porosity dependence of transverse and longitudinal sound wave velocities is studied in statistically isotropic porous ceramics. Based on the model relations for elastic moduli six model relations are constructed for the prediction of the porosity dependence of these velocities. All of them predict a decrease of sound wave velocities with increasing porosity, but the Maxwell / Mori-Tanaka / MMT model leads to unrealistic predictions for high porosity. A velocity ratio function is defined which contains the porosity dependence of the effective Poisson ratio and enables the prediction of longitudinal wave velocities. A comparison with literature data shows that most data lie below the exponential prediction and above the numerical prediction for concave pores. The correlation of the normalized longitudinal wave velocities and relative transverse wave velocities shows that essentially all values are above the highest lower bound and are reasonably predicted by the differential, exponential and self-consistent models.

Enhancing visible-light photocatalytic activity of hard-biotemplated TiO2: From macrostructural morphology replication to microstructural building units design

Biotemplating technique using hard templates is an effective strategy to prepare visible light-activated TiO2 inherited macrostructural morphologies and self-doping elements from templates. However, conventional hard biotemplating method for preparing TiO2 focused only on replicating the macrostructural morphology of templates via the sol-gel method, and neglected the effect of microstructural building units for artificial macrostructure assembly. Generally, the microstructural building units of the final macrostructural morphology are tightly packed nanoparticles. This paper presents a newly designed solvothermal method to replace the microstructural building units from tightly packed nanoparticles to convex nanowires or concave pores. This strategy can achieve the leap of conventional hard biotemplating method from macrostructure replication to microstructural building units design. The hard-biotemplated TiO2 with designed microstructure exhibited significantly further enhanced visible-light photocatalytic efficiency in tetracycline degradation due to the increase of active sites, high separation efficiency of photo-generated electrons and reducing the charge-transfer resistance. Biotemplated TiO2 with concave porous microstructural building units is 22.0, 5.5 and 4.4 times higher than those of pure TiO2 and the two biotemplated TiO2 samples prepared via conventional sol-gel method and solvothermal method without glycerol or HF added, respectively. The enhanced visible-light photocatalytic efficiency by microstructure design was also demonstrated by using ciprofloxacin.

Porosity variation of elastic wave velocities in clean sandstones

ABSTRACTThe mechanical properties of sandstones, including porosity, density and elastic moduli, can be estimated non‐destructively through elastic wave‐velocity measurements. Here, the variation of elastic wave velocity with porosity in sandstones is modelled using Maxwell's effective field theory, extended to the elasticity of heterogeneous media by Sevostianov and coworkers. Comparing measured and predicted elastic wave velocities shows that on deposition, pores in sandstones are less stiff than spherical pores, but that their stiffness increases as porosity decreases. This suggests that concavity of pores in sandstone decreases with decreasing porosity. This interpretation is confirmed by the simple model of Sevostianov and Giraud in which concave pores are represented as superspherical pores, defined by a shape parameter that allows the effect of pore concavity on elastic wave velocities to be investigated. Inversion of measured velocities for this parameter indicates that pore concavity decreases with decreasing porosity. Moreover, values of the shape parameter obtained by inverting measured P‐velocities alone are found to give a good prediction of both P‐ and S‐wave velocities, confirming the applicability of the model.

3D printing of hierarchical porous biomimetic hydroxyapatite scaffolds: Adding concavities to the convex filaments

Porosity plays a key role on the osteogenic performance of bone scaffolds. Direct Ink Writing (DIW) allows the design of customized synthetic bone grafts with patient-specific architecture and controlled macroporosity. Being an extrusion-based technique, the scaffolds obtained are formed by arrays of cylindrical filaments, and therefore have convex surfaces. This may represent a serious limitation, as the role of surface curvature and more specifically the stimulating role of concave surfaces in osteoinduction and bone growth has been recently highlighted. Hence the need to design strategies that allow the introduction of concave pores in DIW scaffolds. In the current study, we propose to add gelatin microspheres as a sacrificial material in a self-setting calcium phosphate ink. Neither the phase transformation responsible for the hardening of the scaffold nor the formation of characteristic network of needle-like hydroxyapatite crystals was affected by the addition of gelatin microspheres. The partial dissolution of the gelatin resulted in the creation of spherical pores throughout the filaments and exposed on the surface, increasing filament porosity from 0.2 % to 67.9 %. Moreover, the presence of retained gelatin proved to have a significant effect on the mechanical properties, reducing the strength but simultaneously giving the scaffolds an elastic behavior, despite the high content of ceramic as a continuous phase. Notwithstanding the inherent difficulty of in vitro cultures with this highly reactive material an enhancement of MG-63 cell proliferation, as well as better spreading of hMSCs was recorded on the developed scaffolds. Statement of significanceRecent studies have stressed the role that concave surfaces play in tissue regeneration and, more specifically, in osteoinduction and osteogenesis. Direct ink writing enables the production of patient-specific bone grafts with controlled architecture. However, besides many advantages, it has the serious limitation that the surfaces obtained are convex. In this article, for the first time we develop a strategy to introduce concave pores in the printed filaments of biomimetic hydroxyapatite by incorporation and partial dissolution of gelatin microspheres. The retention of part of the gelatin results in a more elastic behavior compared to the brittleness of hydroxyapatite scaffolds, while the needle-shaped nanostructure of biomimetic hydroxyapatite is maintained and gelatin-coated concave pores on the surface of the filaments enhance cell spreading.

Random Walks of a Cell With Correlated Speed and Persistence Influenced by the Extracellular Topography

Cell migration through extracellular matrices is critical to many physiological processes, such as tissue development, immunological response and cancer metastasis. Previous models including persistent random walk (PRW) and Lévy walk only explain the migratory dynamics of some cell types in a homogeneous environment. Recently, it was discovered that the intracellular actin flow can robustly ensure a universal coupling between cell migratory speed and persistence for a variety of cell types migrating in the in vitro assays and live tissues. However, effects of the correlation between speed and persistence on the macroscopic cell migration dynamics and patterns in complex environments are largely unknown. In this study, we developed a Monte Carlo random walk simulation to investigate the motility, the search ability and the search efficiency of a cell moving in both homogeneous and porous environments. The cell is simplified as a dimensionless particle, moving according to PRW, Lévy walk, random walk with linear speed-persistence correlation (linear RWSP) and random walk with nonlinear speed-persistence correlation (nonlinear RWSP). The coarse-grained analysis showed that the nonlinear RWSP achieved the largest motility in both homogeneous and porous environments. When a particle searches for targets, the nonlinear coupling of speed and persistence improves the search ability (i.e. find more targets in a fixed time period), but sacrifices the search efficiency (i.e. find less targets per unit distance). Moreover, both the convex and concave pores restrict particle motion, especially for the nonlinear RWSP and Lévy walk. Overall, our results demonstrate that the nonlinear correlation of speed and persistence has the potential to enhance the motility and searching properties in complex environments, and could serve as a starting point for more detailed studies of active particles in biological, engineering and social science fields.

Octanuclear Cobalt(II) Cluster-Based Metal-Organic Framework with Caged Structure Exhibiting the Selective Adsorption of Ethane over Ethylene.

A novel metal-organic framework (MOF) of [Co8(OH)4(TCA)4(H2O)4]n (abbreviation: JXNU-9) based on the unique octanuclear Co8(μ3-OH)4 clusters linked by 4,4',4″-nitrilotribenzoate (TCA3-) ligands featuring small caged structures and one-dimensional channels was prepared and characterized. JXNU-9 shows a high C2H6 uptake capacity of 3.60 mmol g-1 (4.46 mmol cm-3) at 298 K and 1 atm with a small isosteric heat of adsorption (23.6 kJ mol-1) and a moderate C2H6/C2H4 adsorption selectivity of 1.7, resulting in excellent C2H6/C2H4 separation performance. The pore walls decorated by plenty of aromatic rings provide π-electron-cloud-surrounding environments to accommodate the large polarizable C2H6 molecules. The calculations demonstrate that the rich π-systems in JXNU-9 facilitate an adsorption affinity for large C2H6 molecules through multiple C-H···π interactions. Additionally, the open metal sites located in the concave pores with a close Co···Co separation (4.21 Å) in octanuclear Co8(μ3-OH)4 clusters make the open metal sites inaccessible for the C2H4 molecule with a kinetic diameter of 4.163 Å. Thus, the annihilation of open metal sites in this structure is achieved, which further facilitates the C2H6-selective C2H6/C2H4 separation.

Effect of Nanopore Geometry in the Conformation and Vibrational Dynamics of a Highly Confined Molecular Glass.

The effect of nanoporous confinement on the glass transition temperature (Tg) strongly depends on the type of porous media. Here, we study the molecular origins of this effect in a molecular glass, N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD), highly confined in concave and convex geometries. When confined in controlled pore glass (CPG) with convex pores, TPD's vibrational spectra remained unchanged and two Tg's were observed, consistent with previous studies. In contrast, when confined in silica nanoparticle packings with concave pores, the vibrational peaks were shifted due to more planar conformations and Tg increased, as the pore size was decreased. The strong Tg increases in concave pores indicate significantly slower relaxation dynamics compared to CPG. Given TPD's weak interaction with silica, these effects are entropic in nature and are due to conformational changes at molecular level. The results highlight the role of intramolecular degrees of freedom in the glass transition, which have not been extensively explored.

Effective elastic properties of transversely isotropic materials with concave pores

The aim of this paper is to extend recent works devoted to the study of the effect of 3D pores of concave shape embedded in isotropic matrix to the case of transversely isotropic (TI) matrix. In the first part of the paper, approximate relations for the compliance contribution tensor of pores of two reference shapes, supersphere and axisymmetrical superspheroid, are developed on the basis of 3D Finite Element Modelling, recently presented in a companion paper, and known exact solutions for the limiting cases of spherical pores and circular crack. In the second part application to effective elastic coefficients of transversely isotropic materials such as clay rocks, in the frame of homogenization theory is presented to illustrate the impact of concavity parameter on overall properties.

Effect of pore shapes on the overall electrical conductivity of cathode material in Li-ion batteries

The paper focuses on the development and verification of a quantitative micromechanical model for evaluation of the overall electrical conductivity of electrodes in Li-ion batteries. Based on microstructural observations, the cathode is modeled as a multiphase composite consisting of PVDF/C matrix, spherical particles made of the active component Li(Ni1/3Co1/3Mn1/3)O2, oblate spheroidal graphite particles and concave pores. Effective electrical conductivity of such a multiphase material is evaluated using Maxwell homogenization techniques and compared with the experimental data available in literature. The agreement is generally very good and allow extraction of information about porous space geometry required for evaluation of other physical properties of the material.

SERS-Active Substrate with Collective Amplification Design for Trace Analysis of Pesticides.

Health risks posed by the exposure to trace amounts of pesticide residue in agricultural products have gained a lot of concerns, due to their neurotoxic nature. The applications of surface-enhanced Raman Scattering (SERS) as a detection technique have consistently shown its potential as a rapid and sensitive means with minimal sample preparation. In this study, gold nanoparticles (Au NPs) in elliptical shapes were collected into a layer of ordered zirconia concave pores. The porous zirconia layer (pZrO2) was then deposited with Au NPs, denoted as Au NPs (x)/pZrO2, where x indicates the deposition thickness of Au NPs in nm. In the concave structure of pZrO2, Au-ZrO2 and Au-Au interactions provide a synergistic and physical mechanism of SERS, which is anticipated to collect and amplify SERS signals and thereafter improve the enhancement factor (EF) of Au NPs/pZrO2. By taking Rhodamine 6G (R6G) as the test molecule, EF of Au NPs/pZrO2 might reach to 7.0 × 107. Au NPs (3.0)/pZrO2 was then optimized and competent to detect pesticides, e.g., phosmet and carbaryl at very low concentrations, corresponding to the maximum residue limits of each, i.e., 0.3 ppm and 0.2 ppm, respectively. Au NPs (3.0)/pZrO2 also showed the effectiveness of distinguishing between phosmet and carbaryl under mixed conditions. Due to the strong affinities of the phosphoric groups and sulfur in phosmet to the Au NPs (3.0)/pZrO2, the substrate exhibited selective detection to this particular pesticide. In this study, Au NPs (3.0)/pZrO2 has thus demonstrated trace detection of residual pesticides, due to the substrate design that intended to provide collective amplification of SERS.

Ion-Specific Confined Water Dynamics in Convex Nanopores of Gemini Surfactant Lyotropic Liquid Crystals.

The impact of pore geometry and functionality on the dynamics of water nanoconfined in porous media are the subject of some debate. We report the synthesis and small-angle X-ray scattering (SAXS) characterization of a series of perdeuterated gemini surfactant lyotropic liquid crystals (LLCs), in which convex, water-filled nanopores of well-defined dimensions are lined with carboxylate functionalities. Quasielastic neutron scattering (QENS) measurements of the translational water dynamics in these dicarboxylate LLC nanopores as functions of the surfactant hydration state and the charge compensating counterion (Na+, K+, NMe4+) reveal that the measured dynamics depend primarily on surfactant hydration, with an unexpected counterion dependence that varies with hydration number. We rationalize these trends in terms of a balance between counterion-water attractions and the nanopore volume excluded by the counterions. On the basis of electron density maps derived from SAXS analyses of these LLCs, we directly show that the volume excluded by the counterions depends on both their size and spatial distribution in the water-filled channels. The translational water dynamics in the convex pores of these LLCs are also slower than those reported in the concave pores of AOT reverse micelles, implying that water dynamics also depend on the nanopore curvature.

Efficient lithium storage of concave graphitic anode embedded with nanoconfined silicon

This study reports the use of engineering nanocarbon film with confined silicon nanoparticles as an anode material for lithium-ion batteries. The unique “concave” graphitic nanostructure, prepared in porous templates with morphology of interconnected arrays, makes nanocarbon electrodes a good lithium-ion intercalation medium and, more importantly, robust nanocontainers to effectively confine high-capacity silicon nanoparticles for lithium-ion storage. Open structures of the concave nanocarbon increase the accessibility of Li ions, and allow Li ions to diffuse active materials. In addition, the highly textured concave pores allow the volume expansion of the silicon nanoparticles to be confined to the nanospace during lithium-ion insertion/extraction. The specific capacity of the nanoconfined silicon/nanocarbon anode reaches up to 2500 mAh/g at 0.5 A/g. After long cycling, the anode materials becomes even more stable, showing the invariant lithium-ion storage capacity as the charge-discharge rate is increased by 10 times from 2–20 A/g. The capacity is retained constantly after 200 charge-discharge cycles.

Shear and bulk moduli of isotropic porous and cellular alumina ceramics predicted from thermal conductivity via cross-property relations

Based on alumina as a paradigmatic example, shear and bulk moduli have been numerically calculated on computer-generated digital random microstructures representing isotropic porous materials with convex or concave pores and for cellular materials with closed or open cells. On the other hand, the relative elastic moduli cross-property relations (CPRs) have been predicted from the numerically calculated relative thermal conductivities. It has been shown that the Pabst-Gregorová cross-property relation (PG-CPR) with constant CPR exponent 4/3 or its generalized version with the correct Poisson-ratio-dependent CPR exponents (for alumina 1.316 and 1.426, respectively, for the shear and bulk modulus) provides the best prediction currently available, although its accuracy is significantly worse for the bulk modulus (maximum differences between predicted and calculated values ranging from – 0.05 to + 0.09 relative property units/RPU) than for the shear modulus, where the accuracy is excellent for all microstructures (maximum difference smaller than ± 0.02 RPU).