Growth In Pores Research Articles

New computational tools and experiments reveal how geometry affects tissue growth in 3D printed scaffolds

Understanding how tissue growth in porous scaffolds is influenced by geometry is a fundamental challenge in the field of tissue engineering. We investigate the influence of pore geometry on tissue growth using osteoblastic cells in 3D printed melt electrowritten scaffolds with square-shaped pores and non-square pores with wave-shaped boundaries. Using a reaction–diffusion model together with a likelihood-based uncertainty quantification framework, we quantify how the cellular mechanisms of cell migration and cell proliferation drive tissue growth for each pore geometry. Our results show that the rates of cell migration and cell proliferation appear to be largely independent of the pore geometries considered, suggesting that observed curvature effects on local rates of tissue growth are due to space availability rather than directly affecting cell behaviour. This result allows for simple squared-shaped pores to be used for estimating parameters and making predictions about tissue growth in more realistic pores with more realistic, complicated shapes. Our findings have important implications for the development of predictive tools for tissue engineering and experimental design, highlighting new avenues for future research.

A hybrid machine-learning approach for analysis of methane hydrate formation dynamics in porous media with synchrotron CT imaging.

Fast multi-phase processes in methane hydrate bearing samples pose a challenge for quantitative micro-computed tomography study and experiment steering due to complex tomographic data analysis involving time-consuming segmentation procedures. This is because of the sample's multi-scale structure, which changes over time, low contrast between solid and fluid materials, and the large amount of data acquired during dynamic processes. Here, a hybrid approach is proposed for the automatic segmentation of tomographic data from time-resolved imaging of methane gas-hydrate formation in sandy granular media, which includes a deep-learning 3D U-Net model. To prepare a training dataset for the 3D U-Net, a technique to automate data labeling based on sample-specific information about the mineral matrix immobility and occasional fluid movement in pores is proposed. Automatic segmentation allowed for studying properties of the hydrate growth in pores, as well as dynamic processes such as incremental flow and redistribution of pore brine. Results of the quantitative analysis showed that for typical gas-hydrate stability parameters (100 bar methane pressure, 7°C temperature) the rate of formation is slow (less than 1% per hour), after which the surface area of contact between brine and gas increases, resulting in faster formation (2.5% per hour). Hydrate growth reaches the saturation point after 11 h of the experiment. Finally, the efficacy of the proposed segmentation scheme in on-the-fly automatic data analysis and experiment steering with zooming to regions of interest is demonstrated.

In Situ Growing CuO/ZIF-8 into Nickel Foam to Fabricate a Binder-Free Self-Supported Glucose Biosensor

A binder-free self-supported CuO/ZIF-8@NiF electrode is fabricated with CuO/ZIF-8 particles in situ growth in nickel foam pores. ZIF-8 is first assembled inside the nickel foam pores and then Cu2+ is adsorbed around the surface of ZIF-8 crystal, and finally reduced and oxidized to form CuO. Scanning electron microscopy indicates CuO is uniformly distributed on the surface of ZIF-8. The Cu element is significantly increased from 1.16 to 30.91 mg·g–1 under the existence of ZIF-8 from inductively coupled plasma results. The electrochemical analyses show that the electrochemical active surface area of the CuO/ZIF-8@NiF electrode can be increased two times while its electronic transport resistance can be reduced to one-seventh compared with the CuO/ZIF-8/NiF electrode with CuO/ZIF-8 binding on the substrate. The detection tests exhibit enhanced electrochemical properties with a sensitivity of 5640 μA·mM–1·cm–2, a low detection limitation of 0.1 μM, and a linear detection range from 0.5 to 120 μM. The biosensor presents good anti-interference property, stability, and a 101.08–104.53% recovery rate.

Synthesis of Ni@Au core-shell magnetic nanotubes for bioapplication and SERS detection

[email protected] core-shell nanotubes were synthesized using a two-stage method including Ni nanotubes growth in pores of PET template and their electroless wet-chemical functionalizing with gold. The structure, morphology, chemical composition, surface condition and magnetic properties of [email protected] nanotubes were comprehensively studied. Cellular cytotoxicity of Ni and [email protected] nanotubes was evaluated demonstrating its strong reduction when nanotubes were coated with Au layer. The gold layer had a granular structure with some agglomerations resulting in surface irregularities which is advantageous for surface-enhanced Raman spectroscopy (SERS). The fundamental possibility of using the functionalized [email protected] nanotubes as SERS substrates was demonstrated by the example of methylene blue detection for concentrations down to 10−6 M. The average enhancement factor was 104, which is sufficient for use in chemo- and biosensorics.

Naturally Occurring Hydrate Formation and Dissociation in Marine Sediment: Experimental Validation

Fundamental understanding of gas hydrate as a natural storehouse of carbon and a potential energy resource found in permafrost layers and marine sediments is crucial in extracting hydrocarbon fuel from hydrate reservoirs. With this, a theoretical framework is grounded involving the complicated physics of naturally occurring hydrate formation and dissociation with pure and mixed guest gases in the unconsolidated silica sand and seawater. The proposed formulation addresses various practical concerns, including the collective influence of pure water, salt ion, and porous medium; surface renewal at the interface between bulk guest and aqueous phase; pore irregularity in heterogeneous porous materials; hydrate growth and decay in those nanometer-sized pores along with interstitial spaces; and influence of surface tension, among others. To show its versatility, the dynamic model framework is tested under various experimental conditions that mimic the actual field conditions in terms of the type of guest gases (i.e., methane, and pure and mixed carbon dioxide); the concentration of salt ions in the liquid phase; the size, shape, and amount of porous silica sand; and the operating temperature and pressure. Under every aforementioned condition, the proposed model outperforms the existing models, which is quantified in terms of the percentage of average absolute relative deviation (AARD). For gas hydrate formation cases, the proposed model keeps AARD in the range of 1.23–9.57%, which is 5.46–19.58% for the existing models. On the other hand, for gas hydrate decomposition, the AARD of the proposed formulation varies from 2.73 to 9.78%, which is reasonably high (11.89–22.26%) for the existing model.

Structure and Electronic Properties of InSb Nanowires Grown in Flexible Polycarbonate Membranes.

A dense array of vertically aligned indium antimonide (InSb) nanowires with high aspect ratio (diameter 150 nm, length 20 m) were grown in the pores of a track-etched polycarbonate membrane via a one-step electrochemical method. There are several reports on InSb nanowire growth in the pores of a mechanically rigid, nano-channel alumina template (NCA), where nanowire growth occurs in the pores of the NCA. This work on InSb nanowire growth in pores of track-etched polycarbonate (PC) membrane sheds light on the various factors that affect nucleation and nanowire growth. The average length and diameter of the as-grown nanowires was about 10 m and 150 nm, respectively. Two possible mechanisms accounting for two different morphologies of the as-grown nanowires are proposed. The polycrystallinity observed in some of the nanowires is explained using the 3D ‘nucleation-coalescence’ mechanism. On the other hand, single crystal nanowires with a high density of twin defects and stacking faults grow epitaxially by a two-dimensional (2D) nucleation/growth mechanism. To assess the electrical quality of the nanowires, two- and four-terminal devices were fabricated using a single InSb nanowire contacted by two Ni electrodes. It was found that, at low bias, the ohmic current is controlled by charge diffusion from the bulk contacts. On the other hand, at high bias, the effects of space charge limited current (SCLC) are evident in the current–voltage behavior, characteristic of transport through structures with reduced electrostatic screening. A cross-over from ohmic to SCLC occurs at about 0.14 V, yielding a free carrier concentration of the order of cm.

Morphological Analysis of Archetypal Calcite Cement

Archetypal cements from their deposition to the time they are sampled preserve a record of subsurface fluid evolution that can cover many millions of years. Their morphological development after nucleating on fissure walls is simulated by graphical models showing maturation from isolated to competitive to parallel growth. Graphical models are not available for the cementation of pores that are more complex and diverse. The reconstruction of cement growth in pores is accomplished here using multiple cathodoluminescent (CL) growth zones. Sediment pores are filled in two stages separated by a cementation threshold associated with a rapid drop in permeability. Pre-threshold cement is centripetal ordered, regularly distributed, and nurtured by a megapore network. Post-threshold cement is disordered, sporadically distributed, and nurtured by labile micropore connections. The crystallographic form of euhedral crystals at cement's growing front has environmental significance while the anhedral shape of aggregate crystals it leaves behind is controlled by geometrical selection. Growth of seeded cement is divided into epitaxial and mantle stages; syntaxial when these two are not identified. The epitaxial stage begins with a seed at multiple points then coalesces, simplifies, and morphs towards the Wulff or equilibrium surface. The extent of epitaxial growth is correlated with the size of crystals forming pore walls. Increments of mantle growth can be initiated over the whole surface of a pre-existing crystal, or can be restricted to its edges and/or corners. Restricted seeding is often linked with changes of crystal habit resulting in the reorientation of the crystal's fastest growth direction and the direction of maturation. Some impingement intercrystalline boundaries have offset growth zones explained by dissolution; such a self-cannibalization process is new. The existing explanation that some enfacial junctions are due to pauses in growth is confirmed by the arrangement of growth zones around triple points, but a new type is recorded formed from continuously growing crystals whose intercrystalline boundaries become modified. The presence of the cement's internal growth surfaces allow its development to be reconstructed, providing the foundation for further cement studies; however, one example is presented where the disproportionate filling of pores in adjacent millimeter-thick layers is obscure because its crystals lack internal growth surfaces.

On (sub)mesoscopic scale peculiarities of diffusion driven growth in an active matter confined space, and related (bio)material realizations

Diffusion in a confined space becomes an extremely important problem with many versatile applications, ranging from biomedical to biotechnological, and involving functional and smart (bio)materials. In this study, we have shown that the well-known Mullins-Sekerka approach to morphological stability of the diffusional non-ideal sphere’s growth, for which a confinement factor disappears, is a firm starting point for further questions. It has two modifications and/or extensions for which the confinement factor is involved readily and becomes (in)finite firstly for microscale (or micrometer scale) involving biomatter packing phenomena. They are also applicable for nanoscopic biomaterial arrangements for which very tightly packed material and active-matter including outcomes of subdiffusive proveniency would manifest, as it has already been observed for the protein crystal growth in pores and globule-to-coil crossover phenomena.

Osseointegration of porous apatite-wollastonite and poly(lactic acid) composite structures created using 3D printing techniques

A novel apatite-wollastonite/poly(lactic acid) (AW/PLA) composite structure, which matches cortical and cancellous bone properties has been produced and evaluated in vitro and in vivo. The composites structure has been produced using an innovative combination of 3D printed polymer and ceramic macrostructures, thermally bonded to create a hybrid composite structure. In vitro cell assays demonstrated that the AW structure alone, PLA structure alone, and AW/PLA composite were all biocompatible, with the AW structure supporting the proliferation and osteogenic differentiation of rat bone marrow stromal cells. Within a rat calvarial defect model the AW material showed excellent osseointegration with the formation of new bone, and vascularisation of the porous AW structure, both when the AW was implanted alone and when it was part of the AW/PLA composite structure. However, the AW/PLA structure showed the largest amount of the newly formed bone in vivo, an effect which is considered to be a result of the presence of the osteoinductive AW structure stimulating bone growth in the larger pores of the adjacent PLA structure. The layered AW/PLA structure showed no signs of delamination in any of the in vitro or in vivo studies, a result which is attributed to good initial bonding between polymer and ceramic, slow resorption rates of the two materials, and excellent osseointegration. It is concluded that macro-scale composites offer an alternative route to the fabrication of bioactive bone implants which can provide a match to both cortical and cancellous bone properties over millimetre length scales.

The dynamic nature of crystal growth in pores.

The kinetics of crystal growth in porous media controls a variety of natural processes such as ore genesis and crystallization induced fracturing that can trigger earthquakes and weathering, as well as, sequestration of CO2 and toxic metals into geological formations. Progress on understanding those processes has been limited by experimental difficulties of dynamically studying the reactive surface area and permeability during pore occlusion. Here, we show that these variables cause a time-dependency of barite growth rates in microporous silica. The rate is approximately constant and similar to that observed on free surfaces if fast flow velocities predominate and if the time-dependent reactive surface area is accounted for. As the narrower flow paths clog, local flow velocities decrease, which causes the progressive slowing of growth rates. We conclude that mineral growth in a microporous media can be estimated based on free surface studies when a) the growth rate is normalized to the time-dependent surface area of the growing crystals, and b) the local flow velocities are above the limit at which growth is transport-limited. Accounting for the dynamic relation between microstructure, flow velocity and growth rate is shown to be crucial towards understanding and predicting precipitation in porous rocks.

A Hypothesis for Salt Frost Scaling in Cementitious Materials

In this study freezing characteristics was investigated experimentally on adequately air-entrained cementitious materials (Powers’ spacing factor is between 60-160 µm) with variables including water-binder (w/b) ratio, slag cement addition and a wide range of air content. Results confirm cryogenic suction as the primary transport mode of the external moisture into the surface region to amplify continuous ice growth in capillary pores therein. This leads to pore pressure build-up and eventually surface scaling. Three key factors are identified to govern this cryogenic suction mechanism: (I) the initial ice nucleation in capillary pores and (II) the presence of unfrozen moisture transported through (III) the capillary network. Air entrainment, although needed for protecting internal frost damage, yields no added gain in improving scaling resistance in concrete and is consistent with the capillary suction dominated scaling mechanism. Addition of salt in the pore solution suppresses the ice nucleation and subsequent growth which may explain the pessimum effect.

Immobilization of Candida rugosa lipase on ZnO nanowires/macroporous silica composites for biocatalytic synthesis of phytosterol esters

ZnO nanowires were successfully introduced into a macroporous SiO2 by in-situ hydrothermal growth in 3D pores. The obtained composites were characterized by SEM and XRD, and used as supports to immobilize Candida rugosa lipase (CRL) through adsorption. The high specific surface area (233m2/g) and strong electrostatic interaction resulted that the average loading amount of the composite supports reached 287.2mg/g. Both adsorption capacity and the activity of the CRL immobilized on the composite supports almost kept unchanged as the samples were soaked in buffer solution for 48h. The immobilized CRL exhibited better thermal stability, reusability and pH adaptability in comparison to free CRL. The immobilized CRL was used as biocatalyst for the preparation of phytosterol esters by the esterification of phytosterol and oleic acid. A maximum molar conversion of 96.5% was achieved under the optimal condition. After twelve recycles the immobilized lipase could retain 89.9% of its initial activity.

Pore-Scale Controls on Reaction-Driven Fracturing

In this article we attempt to shed some light on the factors that determine whether volume-increasing reactions and growth in pores will reduce or increase permeability. We will start by describing fi eld-scale examples of reaction-driven fracturing, and use a Discrete Element Model (DEM) to analyze how the resulting pattern and the rate and progress of reaction depend on the initial porosity of the rock. Ultimately, however, stress generation is related to growth processes taking place at the pore scale. We will therefore zoom in and describe pore-scale growth processes and how these are associated with fracturing and the production of new reactive surface area and new transport channelways for migrating fl uids. Stress generation by growth in pores requires that crystals continue to grow even after having ‘hit’ the pore wall. This implies that the fl uid from which the crystals precipitate is not squeezed out from the reactive interface by the normal stress generated by the growth, but can be kept in place as a thin fi lm by opposing forces that operate at very small scales. To understand the dynamics of crystal growth against confi ning pore walls, we need to zoom in even further and examine interface processes taking place at the nanometer scale. Hence, the last part of this chapter focuses on the nanometer-scale morphology of the reacting interface and the mechanical and transport properties of the fl uids confi ned along reactive grain boundaries.

Challenging biological limits with microfluidic single cell analysis.

Challenging biological limits with microfluidic single cell analysis.

Immobilized Candida antarctica lipase B on ZnO nanowires/macroporous silica composites for catalyzing chiral resolution of (R,S)-2-octanol

ZnO nanowires were successfully introduced into a macroporous SiO2 by in situ hydrothermal growth in 3D pores. The obtained composites were characterized by SEM and XRD, and used as supports to immobilize Candida antarctica lipase B (CALB) through adsorption. The high specific surface area (233m2/g) and strong electrostatic interaction resulted that the average loading amount of the composite supports (196.8mg/g) was 3–4 times of that of macroporous SiO2 and approximate to that of a silica-based mesoporous material. Both adsorption capacity and the activity of the CALB immobilized on the composite supports almost kept unchanged as the samples were soaked in buffer solution for 48h. The chiral resolution of 2-octanol was catalyzed by immobilized CALB. A maximum molar conversion of 49.1% was achieved with 99% enantiomeric excess of (R)-2-octanol acetate under the optimal condition: a reaction using 1.0mol/L (R,S)-2-octanol, 2.0mol/L vinyl acetate and 4.0wt.% water content at 60°C for 8h. After fifteen recycles the immobilized lipase could retain 96.9% of relative activity and 93.8% of relative enantioselectivity.

Theoretical analysis of impurity precipitation in nanopores in crystals. II: Kinetics of impurity cluster growth in pores

The kinetics of the formation of impurity clusters in subsurface nanopores in crystals is studied theoretically. A physical model of precipitation of the impurity phase in nanopores in a sample with sinks of various types is developed. This model forms the basis for the calculation of the annealing kinetics of copper containing subsurface pores and cobalt impurity atoms. The optimal annealing conditions are determined in which cobalt atoms diffuse predominantly into pores and form impurity clusters in them.

Simple model of mass transfer in template synthesis of metal ordered nanowire arrays

A simple model of electrochemical growth of nanowires in the pores of anodic aluminum oxide (AAO) template is developed. The metal deposition is considered at various overpotentials. The model takes into consideration the ionic transfer both in the varying diffusion layer in the pores and in the diffusion layer above the template, which is determined by the external hydrodynamic conditions. The model takes into account the kinetics of electrochemical reaction by means of the Tafel equation and the diffusion transfer of metal cations both in the pores and in the outer diffusion layer. The analytical solution of the problem with several simplifications yields the equations for calculating the time dependence of current, the pore filling time, and other parameters of the process. An example of the application of the model for the analysis of nanowire growth in the template pores is compared with the experimental data showing good agreement.

Greater scaffold permeability promotes growth of osteoblastic cells in a perfused bioreactor

Pore size and porosity have been widely acknowledged as important structural factors in tissue-engineered scaffolds. In fact, scaffolds with similar pore size and porosity can provide important and varied permeability due to different pore shape, interconnectivity and tortuosity. However, the effects of scaffold permeability on seeded cells remains largely unknown during tissue regeneration in vitro. In this study, we measured the Darcy permeability (K) of tri-calcium phosphate scaffolds by distributed them into three groups: Low, Medium and High. As a result, the effects of scaffold permeability on cell proliferation, cellular activity and growth in the inner pores were investigated in perfused and static cultures in vitro. Results demonstrated that higher permeable scaffolds exhibited superior performance during bone regeneration in vitro and the advantages of higher scaffold permeability were amplified in perfused culture. Based on these findings, scaffold permeability should be considered in future scaffold fabrications.

Effect of H2/H2O ratio on thermally grown chromia scales formed on Ni25Cr alloy in Ar–H2–H2O atmospheres at 1000°C

The oxidation behaviour of a NiCr-base model alloy with a 25% chromium content is investigated at 1000°C in different low p(O2) environments (Ar –H2–H2O) with the emphasis of how hydrogen andyor water vapour affects the oxidation behaviour of chromia forming alloys \\in low p(O2) environments containing H2 and H2O. After equilibrium conditions are achieved, chromia growth on Ni25Cr in low p(O2) type test gases containing H2 and H2O is ruled by the concentration of Cr interstitials available for Cr outward transport. The chromia microstructure, therefore, consists largely of columnar shaped oxide grains. The chromia scales are growing predominantly from oxygen coming from the water vapour in the test gas. H-species may facilitate oxide growth in pores at the metal – oxide interface. H-defects affect the transport properties of chromia scales formed on Ni25Cr. At low p(O2) the H-defects in the chromia scale are compensated by a lower concentration of Cr interstitials. Depending on the nature of the test gas, i.e. p(O2), p(H2) and p(H2O), as well as on the Cr activity in the metal substrate, the growth of chromia scales on NiCr alloys may be featured and shaped differently.

Sculpting of Rocks by Reactive Fluids

Interactions between rocks and reactive fluids produce a plethora of patterns, often visible to the naked eye, both at the Earth’s surface and at depth. Patterns arise from the coupling between chemical reactions, transport and sometimes, mechanical processes in systems where fluids and solids are at least initially sufficiently far from thermodynamic equilibrium for non-linear processes to operate. Surprisingly often, similar patterns are formed at different scales under very different conditions in systems with different chemical compositions. For example, many of the patterns formed by growth and dissolution processes mediated by reactive fluids at or near the Earth’s surface can also be seen in ice. This independence of details, or universality , has inspired us to organise this issue in a way that might appear to be unusual in a geochemistry context, by emphasising the similarities and differences in shapes rather than compositions. After introducing the principles of pattern formation and reviewing the reaction path approach to reactive transport modelling, which requires a full and explicit account of homogeneous and heterogeneous chemical reactions, we begin a pattern focused discourse with a discussion of simple, surface normal growth. From the spheroidal shapes that result from surface normal growth, we continue toward the branched and dendritic patterns arising from growth in a diffusive field. Then, the symmetry breaking effects of fluid flow, demonstrated by growth and dissolution processes on free surfaces, are introduced. The effects of confinement in subsurface environments add another level of complexity because growth is often tightly coupled to dissolution under these conditions and volume changing reactions generate local stresses. Consequently, reactive transport in porous and/or fractured rocks is, in general, coupled with mechanical processes. To avoid the additional challenges of time dependent deformation processes such as creep, only elastic deformation and fracturing are discussed, with a focus on fracturing because many of the most spectacular patterns observed in reactive fluid-rock systems are strongly influenced by fracturing. Deformation that is slowly driven by stresses that are continuously generated by heterogeneous reactions between rocks and fluids often leads to hierarchical fracturing, which divides rock or mineral volumes into successively smaller pieces by smaller and smaller fractures. Hierarchical fracturing occurs during both serpentinisation and spheroidal weathering and it provides first order controls on the evolution of reactive surfaces area and thus overall reaction rates. Then, we explicitly describe how stresses are generated by growth in pores and again point to the lessons that can be learnt by comparing fluid rock systems to the chemically simpler situation represented by the growth of ice in soils or rocks and the similarities between them. The potential implications of reaction driven fracturing for in situ carbon sequestration are also emphasised. Finally, we discuss the significance of the scaling behaviour of patterns and, in particular, the connections between patterns and processes. > Water is fluid, soft and yielding. > > But water will wear away rock, which is rigid and cannot yield. > > As a rule, whatever is fluid, soft and yielding, > > will overcome whatever is rigid and hard. > > This is another paradox: what is soft is strong. > > Lao-Tzu (600 B.C.)