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PubMed2006

Influence of the porosity of hydroxyapatite ceramics on in vitro and in vivo bone formation by cultured rat bone marrow stromal cells.

The in vitro and in vivo osteoblastic differentiation of rat bone marrow stromal cells (MSCs) was assessed on hydroxyapatite disks with 3 different porosities: 30%, 50%, and 70% (HA30, HA50, and HA70, respectively). MSCs obtained by 10-day culture of fresh bone marrow cells were subcultured for 2 weeks on 3 kinds of porous HA disks in the presence and absence of dexamethasone (Dex). After 2 weeks of subculture, alkaline phosphatase (ALP) activity and osteocalcin production of MSCs/HA composites with Dex were higher than those without, and increased with increasing porosity. The resultant bone tissue grafts "cultured-bone/HA constructs" were implanted subcutaneously into the backs of syngeneic rats, and harvested 1, 2, and 4 weeks after implantation. At 1 week, only cultured-bone/HA70 constructs exhibited expanded bone formation. At 2 and 4 weeks, active osteoblasts and progressive bone formation were observed morphologically in both cultured-bone/HA50 and HA70 constructs. At 4 weeks, bone tissue was observed even in cultured-bone/HA30 constructs. ALP activity and osteocalcin production also increased with increasing porosity and time after implantation. In this in vivo model, different scaffold porosity with similar crystal morphology of the apatite phase demonstrated marked differences in ability to support osteogenesis by implanted rat MSCs.

Animals↗

PubMed2004

Non-destructive porosity profile measurement of amorphous materials by gamma-ray transmission.

This work presents measurements of the total porosity of TRe soil, sandstone rocks and porous ceramic samples. For determination of the total porosity, the gamma-ray transmission method and the Archimedes method (conventional) were employed. The porosity measurement using the gamma-ray methodology has a significant advantage with respect to the conventional method due to fast and non-destructive determination, and also for supplying results with a greater spatial resolution, in relation to the heterogeneity of the porosity. The conventional methodologies provide good results only for homogeneous samples. The experimental setup for the gamma-ray transmission technique consisted of a 241Am source (5953 keV), a NaI(Tl) scintillation detector, collimators, a XYZ micrometric table and standard gamma spectrometry electronics connected to a multichannel analyzer.

Ceramics↗

PubMed2006

Future of high pressure liquid chromatography: do we need porosity or do we need pressure?

Making a theoretical study supported by experiments of the kinetic advantages of increased inlet pressures versus increased external porosity using impedance plots of analysis time versus required plate number, it is found that both approaches more or less have the same effect on the kinetic performance. The need to change a given system to one with an increased inlet pressure or with an increased external porosity can best be assessed from the optimal plate number (N(opt)) of the system. When the pursued application requires a plate number that is larger than N(opt), any increase in inlet pressure and external porosity is beneficial. When the required plate number is smaller than N(opt), any increase in inlet pressure and external porosity should preferentially be accompanied by an overall reduction of the feature sizes of the support. The degree to which this feature size reduction can be realized in practice will to a large extent determine which of the two approaches will be the dominant system of the future.

Chromatography, High Pressure Liquid↗

PubMed2006

Porosity of different dental luting cements.

OBJECTIVE: The aim of this in vitro study was to compare open porosity and pore size distribution of different types of luting cements (zinc phosphate and polycarboxylate produced by Harvard Cement, Great Britain, glass-ionomer product GC Fuji I, GC Corporation, Japan, and Panavia F, resin based composite cement, Kurraray Co. Ltd. Japan) using mercury intrusion porosimetry and use it as an additional parameter for ranging the quality of cements used in prosthetics. METHOD: Samples were hand mixed in accordance with the manufacturer's instructions and formed in cylindrical test specimens. Density of samples was determined using a pycnometer while porous structure was estimated using high pressure mercury intrusion porosimeter enabling estimation of pore diameters in interval 7.5-15,000 nm. RESULTS: The polycarboxylate cement posses the highest porosity and specific pore volume among investigated cements. By comparison of the results obtained for zinc phosphate and glass-ionomer cement, it can be observed that according to some textural properties zinc phosphate cement is better choice (smaller specific pore volume and absence of macropores larger than 1 microm) while according to other textural properties the glass-ionomer has advantage (smaller porosity). The resin based composite cement poses the most desired porous structure for prosthetic application among the investigated cements (the lowest porosity and specific pore volume and all identified pores are smaller than 20 nm). SIGNIFICANCE: Based on results of this study, it is possible to estimate the efficiency of luting cements to protect the interior of tooth from penetration of oral fluids, bacteria and bacterial toxins into unprotected dentine.

Dental Cements↗

PubMed2004

PAMPA--a drug absorption in vitro model 8. Apparent filter porosity and the unstirred water layer.

In the parallel artificial membrane permeability assay (PAMPA), if more lipid is used than needed to fill all the pores of a microfilter, the excess lipid layer on both sides of the lipophilic filter increases the "apparent" porosity, epsilon(a), of the filter. The specific resistance of the artificial membrane barrier is lowered with increasing lipid excess. If this effect is not recognized, and the uncorrected value of filter porosity, epsilon, is used, then the calculated intrinsic permeability and the unstirred water layer (UWL) permeability coefficient of the permeating molecule can be significantly overestimated, resulting in underestimates of the thickness of the unstirred water layer. Unstirred water layer corrections are important in pharmaceutical research for in vitro-in vivo correlations aimed at predicting oral absorption and blood-brain barrier penetration characteristics of lead candidate compounds. The novel concept of the apparent porosity is introduced, described, and its utility demonstrated with the drugs diclofenac, desipramine, caffeine, and piroxicam. The PAMPA data of Wohnsland and Faller [J. Med. Chem. 44 (2001) 923] is taken as an example, where the reported extraordinarily efficient stirring is thought to be better explained in terms of normal stirring when apparent porosity is taken into account in the calculation of the effective permeability coefficient.

Adsorption↗

PubMed2004

A novel method for biomaterial scaffold internal architecture design to match bone elastic properties with desired porosity.

An often-proposed tissue engineering design hypothesis is that the scaffold should provide a biomimetic mechanical environment for initial function and appropriate remodeling of regenerating tissue while concurrently providing sufficient porosity for cell migration and cell/gene delivery. To provide a systematic study of this hypothesis, the ability to precisely design and manufacture biomaterial scaffolds is needed. Traditional methods for scaffold design and fabrication cannot provide the control over scaffold architecture design to achieve specified properties within fixed limits on porosity. The purpose of this paper was to develop a general design optimization scheme for 3D internal scaffold architecture to match desired elastic properties and porosity simultaneously, by introducing the homogenization-based topology optimization algorithm (also known as general layout optimization). With an initial target for bone tissue engineering, we demonstrate that the method can produce highly porous structures that match human trabecular bone anisotropic stiffness using accepted biomaterials. In addition, we show that anisotropic bone stiffness may be matched with scaffolds of widely different porosity. Finally, we also demonstrate that prototypes of the designed structures can be fabricated using solid free-form fabrication (SFF) techniques.

Animals↗

PubMed2005

Antero-postero differences in cortical thickness and cortical porosity of T12 to L5 vertebral bodies.

OBJECTIVE: This study will investigate interrelationships between the cortical shell and cancellous bone trabecular thickness, in vertebral bodies. METHODS: One hundred and sixty vertebral bodies from T12 to L5 were obtained at autopsy. The average age of the cohort was 59.3+/-22.1 years (range = 20-94 years). Cortical thickness, cortical porosity and trabecular thickness from the adjacent cancellous bone were measured. RESULTS: At the mid-vertebral body anterior cortical thickness was significantly greater than posterior cortical thickness (524 +/- 352 vs. 370 +/- 283 microm, respectively, P < 0.0001) and mid-anterior cortical porosity was significantly less than mid-posterior cortical porosity (24 +/- 14% vs. 32 +/- 16%, respectively, P < 0.0001). There were no anterior/posterior differences in trabecular thickness of the cancellous bone adjacent to the cortical walls. CONCLUSION: This study provides a novel perspective of T12 to L5 vertebral body bone, where measurement of cortical thickness and cortical porosity in a cohort of skeletally normal individuals revealed structural differences between load bearing anterior and posterior cortical walls. The data suggest that modulators of change to vertebral body bone may affect the cortical and trabecular bone differently. The relationships between cortical and cancellous bone suggest that the middle sectors of the vertebral body play a critical role in load bearing.

Adult↗

PubMed2005

Redistribution of contaminants by a fluctuating water table in a micro-porous, double-porosity aquifer: field observations and model simulations.

Large seasonal fluctuations of the water table are characteristic of aquifers with a low specific yield, including those fractured, double-porosity aquifers that have significant matrix porosity containing virtually immobile porewater, such as the Chalk of northern Europe. Where these aquifers are contaminated, a strong relationship between water table elevation and contaminant concentration in groundwater is commonly observed, of significance to the assessment, monitoring, and remediation of contaminated groundwater. To examine the processes governing contaminant redistribution by a fluctuating water table within the 'seasonally unsaturated zone', or SUZ, profiles of porewater solute concentrations have been established at a contaminated site in southern England. These profiles document the contaminant distribution in porewater of the Chalk matrix over the SUZ at a greater level of detail than recorded previously. A novel double-porosity solute transport code has been developed to simulate the evolution of the SUZ matrix porewater contaminant profiles, given a fluctuating water table, when the groundwater is initially contaminated and the SUZ is initially free of contamination. The model is simply characterised by: the matrix-fracture porosity ratio, the matrix block geometry, and a characteristic diffusion time. De-saturation and re-saturation of fractures is handled by a new approximation method. Contaminant accumulates in the upper levels of the SUZ, where it is less accessible to mobile groundwater, and acts as a persistent secondary source of contamination once the original source of contamination has been removed or has become depleted. The 'SUZ process' first attenuates the progress of contaminants in groundwater, and subsequently controls the slow release of contamination back to the mobile groundwater, thus prolonging the duration of groundwater contamination by many years. The SUZ process should operate in any fractured, micro-porous lithology e.g. fractured clays and mudstones, making this approach widely applicable.

Diffusion↗

PubMed2005

Modelling the migration of contaminants through variably saturated dual-porosity, dual-permeability chalk.

In the Hesbaye region in Belgium, tracer tests performed in variably saturated fissured chalk rocks presented very contrasting results in terms of transit times, according to artificially controlled water recharge conditions prevailing during the experiments. Under intense recharge conditions, tracers migrated across the partially or fully saturated fissure network, at high velocity in accordance with the high hydraulic conductivity and low effective porosity (fracture porosity). At the same time, a portion of the tracer was temporarily retarded in the almost immobile water located in the matrix. Under natural infiltration conditions, the fissure network remained inactive. Tracers migrated downward through the matrix, at low velocity in relation with the low hydraulic conductivity and the large porosity of the matrix. Based on these observations, Brouyère et al. (2004a) [Brouyère, S., Dassargues, A., Hallet, V., 2004a. Migration of contaminants through the unsaturated zone overlying the Hesbaye chalky aquifer in Belgium: a field investigation, J. Contam. Hydrol., 72 (1-4), 135-164, doi: 10.1016/j.conhyd.2003.10.009] proposed a conceptual model in order to explain the migration of solutes in variably saturated, dual-porosity, dual-permeability chalk. Here, mathematical and numerical modelling of tracer and contaminant migration in variably saturated fissured chalk is presented, considering the aforementioned conceptual model. A new mathematical formulation is proposed to represent the unsaturated properties of the fissured chalk in a more dynamic and appropriate way. At the same time, the rock water content is partitioned between mobile and immobile water phases, as a function of the water saturation of the chalk rock. The groundwater flow and contaminant transport in the variably saturated chalk is solved using the control volume finite element method. Modelling the field tracer experiments performed in the variably saturated chalk shows the adequacy and usefulness of the new conceptual, mathematical and numerical model.

Adsorption↗

PubMed2005

Evolution of porosity in geotechnical composites.

Nuclear magnetic resonance (NMR) (H1) transverse relaxation measurements were carried out on 37x70-mm cylindrical mineral/organic composites to determine and monitor the porosity evolution. Porosity is related, in principle, to the stability of such materials in geotechnical applications, for example, engineering foundations. The specimens represented novel formulations of mixed "wastes" containing coarse screened mineral, digested sewage sludge, quicklime, and pulverized fuel ash mixed and compacted together to form mechanically competent material. The measurements on a selected formulation indicated initially low porosity (<12%) that becomes lower over 6 months ( approximately 8%) due to pozzolanic reactions occurring. A relaxation time cutoff of 1.5 ms between "bound" and 'mobile' pore water much lower than sandstones (33 ms) was observed. The results confirmed that the NMR method allows a more reliable assessment of porosity and pore-size evolution.

Biotechnology↗

PubMed1998

Effect of filler porosity on the abrasion resistance of nanoporous silica gel/polymer composites.

OBJECTIVES: This laboratory study was designed to investigate the effect of controlled nanoporosity on the wear resistance of polymeric composites reinforced with silica gel powders and to determine the mechanisms controlling the abrasive wear properties of these unique nanostructured materials. METHODS: Silica gels were prepared by hydrolysis and condensation of tetraethylorthosilicate (TEOS) using four different catalysts to modify the porous structure of the resulting polysilicate silanation, an organic monomer (TEGDMA) containing various initiators was introduced into the gel powders to form a paste. The various pastes were then polymerized inside a glass mold. A pin-on-disk apparatus was then used to record the specimen length and number of revolutions. Abrasive wear rates were determined by regression analysis and statistical differences were determined by analysis of variance and multiple comparisons. BET was used to characterize the filler pore structure and scanning electron microscopy was used used to visually examine the abraded surfaces. RESULTS: Significant differences (p < 0.05) in the wear rates of the experimental composites were noted. Within the range of filler porosities examined, wear resistance was found to be linearly dependent (R2 = 0.983) on filler pore volume. The wear rates decreased with increasing filler porosity. HCl-catalyzed gels having low porosity produced composites having relatively limited abrasion resistance. In contrast, high porosity HF-catalyzed gels produced more wear-resistant composites. The abrasive wear resistance of these nanocomposites was not significantly affected by the level of silane coupling used in these experiments. SEM evaluation suggested that better wear resistance was associated with fine-scale plastic deformation of the wear surface and the absence of filler particle pullout. SIGNIFICANCE: Porous particles prepared via sol-gel show some promise as fillers that improve the wear resistance of photopolymerized resins. The wear resistance of the fillers appears to be directly related to nanoporous structure of the gel particles. Unlike conventional dental composites, these materials rely primarily on nanomechanical coupling for improved wear resistance. This new principle should benefit subsequent investigations.

Ceramics↗

PubMed2002

Tissue ingrowth and degradation of two biodegradable porous polymers with different porosities and pore sizes.

Commonly, spontaneous repair of lesions in the avascular zone of the knee meniscus does not occur. By implanting a porous polymer scaffold in a knee meniscus defect, the lesion is connected with the abundantly vascularized knee capsule and healing can be realized. Ingrowth of fibrovascular tissue and thus healing capacity depended on porosity, pore sizes and compression modulus of the implant. To study the lesion healing potential, two series of porous polyurethanes based on 50/50 epsilon-caprolactone/L-lactide with different porosities and pore sizes were implanted subcutaneously in rats. Also, in vitro degradation of the polymer was evaluated. The porous polymers with the higher porosity, more interconnected macropores, and interconnecting micropores of at least 30 microm showed complete ingrowth of tissue before degradation had started. In implants with the lower macro-porosity and micropores of 10-15 microm degradation of the polymer occurred before ingrowth was completed. Directly after implantation and later during degradation of the polymer, PMN cells infiltrated the implant. In between these phases the foreign body reaction remained restricted to macrophages and giant cells. We can conclude that both foams seemed not suited for implantation in meniscal reconstruction while either full ingrowth of tissue was not realized before polymer degradation started or the compression modulus was too low. Therefore, foams must be developed with a higher compression modulus and more connections with sufficient diameter between the macropores.

Animals↗

PubMed2002

The effect of water in inorganic microsponges of calcium phosphates on the porosity and permeability of composites made with polymethylmethacrylate.

Bone-substitute compounds were obtained by mixing pre-polymerised powders of polymethylmethacrylate and liquid methylmethacrylate monomer with two aqueous dispersions of alpha-tricalcium phosphate (alpha-TCP) grains and calcium-deficient hydroxyapatite (CDHA) powders. The final composites appeared to be porous. The total open porosity was a function of the amount of water added. The water, which was the pore-forming agent, vapourised after the polymerisation process, leaving behind empty spaces in the polymeric matrix. The inorganic powders placed inside the polymeric matrix were shown to act as local microsponges. The water capacity of these microsponges can be determined by a centrifugation step carried out on aqueous dispersion of alpha-TCP and/or CDHA powders that occur before any reaction with the organic compound. The relationship between the total open porosity of the composites and the amount of water trapped inside the inorganic agglomerates proved to be almost linear. The effect of the chemical composition of the powder on the total open porosity is not too great, provided that the two kinds of pellets are prepared with the same amount of water. Both the permeability and shape of the pores proved to be a function of the total open porosity. An increase of the latter parameter produces an increase in permeability and a decrease in tortuosity. Osteoconductivity and osteoinductivity of the final composites were tested in vivo by implantation in rabbits. Formation of new trabecular bone was observed inside the pores where the inorganic powders had been placed.

Animals↗

PubMed2003

Effect of sequestration on PAH degradability with Fenton's reagent: roles of total organic carbon, humin, and soil porosity.

The phenomenon of contaminant sequestration-and the physicochemical soil parameters which drive this process-has recently been studied by several authors with regard to microbial contaminant degradation. Very little work has been done to determine the effects of contaminant sequestration on the chemical treatability (oxidizability) of soil contaminants; the current study was conducted to address this data gap. A suite of six model soils, ranging in organic matter content from 2.32 to 24.28%, were extensively characterized. Measured parameters included: (1) levels of total organic carbon (TOC); (2) contents of humic acid (HA); fulvic acid (FA) and humin; and (3) total porosity and surface area. Each soil was then spiked with coal tar and, after varying periods of aging/sequestration, subjected to slurry-phase Fenton's reagent oxidation. Percent recoveries of 12 PAHs, ranging from 3 to 6 aromatic rings, were determined. Results indicated that the susceptibility of each PAH to chemical oxidation was a function of TOC in four of the soils (those with TOC greater than approximately 5%), but was strongly dependent on soil porosity for low-TOC soils. The importance of these two parameters changed with increasing sequestration time, with the relative contribution of porosity-mediated sequestration becoming more important over time. Porosity-mediated effects were more rapid and significant with lower-molecular-weight PAHs (e.g. those with three or four aromatic rings) than with higher-molecular-weight, more hydrophobic compounds. These observations are discussed in light of current physicochemical models of the contaminant sequestration process.

Benzopyrans↗

PubMed1996

Quantitative determination of porosity: a local assessment by NMR imaging techniques.

The local determination of porosity is an extremely valuable target because of different applications in petrophysics. In fact, obtaining a reliable profile of porosity or saturations could considerably improve the evaluation of transport properties of porous media, especially if applied to multiphase flow test (i.e., for relative permeability characterisation). However, the best procedure to adopt for these kind of studies is currently under debate, involving different experimental choices both for acquisition and hardware solutions. The choice of a reliable procedure could be particularly important especially if heterogeneous samples (i.e., vugular or fractured carbonates) are approached. We have investigated selected carbonate cores, characterised by fractures and large vugs, using different instrumental solutions in order to assess usefulness of application of NMR imaging methods as a porosity measurement tool for heterogeneous samples. Local porosity data have been obtained and discussed relative to conventional measurements and petrographical aspects of rock samples.

Carbonates↗

PubMed1999

Tabletting behaviour of pellets of a series of porosities--a comparisonbetween pellets of two different compositions.

The tabletting behaviour of pellets prepared from a 4:1 mixture of dicalcium phosphate dihydrate (DCP) and microcrystalline cellulose (MCC) was studied and compared with the tabletting behaviour of pellets made solely from microcrystalline cellulose (results from an earlier study by Johansson et al.). A series of pellets with porosities in the range 26-55% were prepared and tabletted at applied pressures of 25-200 MPa. Tablets were also formed from lubricated pellets. The degree of compression during compaction was calculated, and the porosity and tensile strength of the tablets and their permeability to air flow were determined. The porosity of the pellets was found to significantly affect the tabletting behaviour of the DCP/MCC pellets. However, the relationship between pellet porosity and tablet data for the DCP/MCC pellets was different from that for the MCC pellets. The DCP/MCC pellets were generally less prone to a reduction in volume during tabletting, and the pore structure of the DCP/MCC tablets was more closed. It was concluded that the DCP/MCC pellets were more rigid and underwent a different mode of deformation during tabletting than the MCC pellets. This mode of deformation was characterised by a more limited bulk deformation and a more extensive surface deformation at the pellet surfaces. The DCP/MCC pellets tended to give tablets of a lower mechanical strength. They were also less sensitive to lubrication in terms of their compactability, which may be explained either by less surface coverage by the lubricant before compression or rupture of the lubricant film during compression caused by the more extensive surface deformation of DCP/MCC pellets.

Calcium Phosphates↗

PubMed2002

Increasing paracellular porosity by E-cadherin peptides: discovery of bulge and groove regions in the EC1-domain of E-cadherin.

PURPOSE: The objective of this work is to evaluate the ability of peptides derived from the bulge (HAV-peptides) and groove (ADT-peptides) regions of E-cadherin EC1-domain to increase the paracellular porosity of the intercellular junctions of Madin-Darby canine kidney (MDCK) cell monolayers. METHODS: Peptides were synthesized using a solid-phase method and were purified using semi-preparative HPLC. MDCK monolayers were used to evaluate the ability of cadherin peptides to modulate cadherin-cadherin interactions in the intercellular junctions. The increase in intercellular junction porosity was determined by the change in transepithelial electrical resistance (TEER) values and the paracellular transport of 14C-mannitol. RESULTS: HAV- and ADT-peptides can lower the TEER value of MDCK cell monolayers and enhance the paracellular permeation of 14C-mannitol. HAV- and ADT-decapeptides can modulate the intercellular junctions when they are added from the basolateral side but not from the apical side; on the other hand. HAV- and ADT-hexapeptides increase the paracellular porosity of the monolayers when added from either side. Conjugation of HAV- and ADT-peptides using omega-aminocaproic acid can only work to modulate the paracellular porosity when ADT-peptide is at the N-terminus and HAV-peptide is at the C-terminus; because of its size, the conjugate can only modulate the intercellular junction when added from the basolateral side. CONCLUSIONS: Peptides from the bulge and groove regions of the EC1 domain of E-cadherin can inhibit cadherin-cadherin interactions, resulting in the opening of the paracellular junctions. These peptides may be used to improve paracellular permeation of peptides and proteins. Furthermore, this work suggests that both groove and bulge regions of EC-domain are important for cadherin-cadherin interactions.

Animals↗

PubMed2005

New replication technique for the fabrication of thin polymeric microfluidic devices with tunable porosity.

In this article we present a new versatile replication method to produce thin polymeric microfluidic devices with tunable porosity. This method is based on phase separation of a polymer solution on a microstructured mold. Compared to existing microfabrication techniques, such as etching and hot embossing, our technique offers four advantages: (a) simple and cheap process that can be performed at room temperature outside clean room facilities; (b) very broad range of applicable materials (including materials that could not be processed before); (c) ability to make thin flexible chips; (d) ability to introduce and tune porosity in the chip. By introducing porosity, the channel walls can be used for selective transport of gasses, liquids and solutes. A proof-of-concept will be given, by showing fast CO2 transport through the channel walls of a porous polymer chip. Furthermore, it will be demonstrated that the gas permeation performance of chips can be enhanced dramatically by a decrease in chip thickness and incorporation of porosity. We expect that the development of porous chips can lead to the on-chip integration of multiple unit operations, such as reaction, separation, gas liquid contacting and membrane emulsification.

Carbon Dioxide↗