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PubMed1989

The effect of placement technique upon the compressive strength and porosity of a composite resin.

This paper examines the effect of two placement techniques upon the compressive strength and level of porosity of specimens of a composite resin. Those specimens prepared by a condensation technique had a significantly lower mean compressive strength (P less than 0.05) and value of Weibull modulus (P less than 0.05) than specimens prepared using a smearing technique. No significant differences in the overall mean percentage area occupied by porosity and mean number of pores were demonstrated (P greater than 0.05) between the two placement techniques. Specimens prepared using the smearing technique, however, had significantly smaller mean maximum pore diameters (P less than 0.05) than those prepared using the condensation technique. It is therefore desirable when placing composite resins to reduce to a minimum handling procedures that are likely to influence the levels of porosity within the material.

Composite Resins↗
PubMed2004

Influence of polymer membrane porosity on C3A hepatoblastoma cell adhesive interaction and function.

The effect of the porosity of acrylonitrile-N-vinylpyrrolidone copolymer membranes on human C3A hepatoblastoma cell adhesive interaction and functioning is investigated on four membranes with an average pore size ranging between 6 and 12 nm. Adhesion of C3A cells was quantified and characterized by studying overall cell morphology and focal adhesion formation. Cell-cell interactions were characterized by E-cadherin expression and organization. Cell growth, fibronectin synthesis and cytochrome P450 activity were estimated as criteria of functional cell activity. The results suggest that membrane porosity influences the initial cell-surface interactions since an increasing pore size augmented cell adhesion and aggregate formation. Cell growth after 7 d was diminished on membranes with an average pore size of 12 nm. The activity of P450 measured by 7-ethoxycoumarin conversion at day 7 was influenced by membrane topography representing a clear optimum in the range of 7-10 nm pore size. These results indicate that membrane porosity is a determinant for the function of hepatocytes in extracorporal liver assist devices.

Cell Adhesion↗
PubMed2007

Age-dependent change in the 3D structure of cortical porosity at the human femoral midshaft.

Microstructural change associated with cortical bone remodeling has been extensively explored with 2D techniques. However, relatively little is known regarding the 3D dynamic microstructure of cortical bone. Therefore, we employed micro-CT imaging to investigate 3D remodeling-related change in the structure of cortical bone porosity across the human lifespan. Anterior femoral midshaft specimens (n=51 male, 28 female) spanning 18 to 92 years of age were scanned with 7 mum nominal isotropic resolution. Canal volume fraction (Ca.V/TV), mean diameter (Ca.Dm), mean separation (Ca.Sp), degree of anisotropy (DA), connectivity density (Ca.ConnD), and number (Ca.N) were calculated for subperiosteal cylindrical regions of interest. Ca.N was calculated in 2D (Ca.N(2D)) and 3D (Ca.N(3D)). Regression was used to examine the relation between the structural parameters and age. Additionally, the impact of sex, height, and weight were investigated collectively (MANCOVA) and individually (ANCOVA). For all analyses, Ca.V/TV and Ca.Dm were inverted (Ca.V/TV(-1), Ca.Dm(-1)) to establish normality and linear relations with age. Ca.N values (2D and 3D) were non-linearly (quadratic) related to age, increasing until the 6th decade then decreasing. This relation was only significant for the pooled sexes Ca.N(3D) values (p=0.012). Ca.ConnD was positively related to age (p<0.05), while all remaining 3D parameters, except DA for males (p=0.070), were negatively related (p<0.05). In all cases, the relation with age was strongest for females. MANCOVA revealed that age was the only significant (p<0.001) covariate overall. Univariate ANCOVA indicated significant differences between the sexes for Ca.V/TV(-1) and Ca.Dm(-1) (p=0.018 and 0.010, respectively). Relative to males, females had lower values for these parameters, translating into larger mean canal diameter and overall porosity. Body weight had a significant (p=0.043) positive relation with Ca.Dm(-1), indicating lower weight was also associated with increased mean canal diameter. Therefore, while age was the most important factor, sex and body size were found to play a role in parameters related to canal size and the overall level of porosity. This study is unique in that changes in cortical bone microstructure were examined across the adult human lifespan in three rather than two dimensions.

Adolescent↗
PubMed2006

Porosity estimation of aged mortar using a micromechanical model.

Degradation of concrete structures located in high humidity atmospheres or under flowing water is a very important problem. In this study, a method for ultrasonic non-destructive characterization in aged mortar is presented. The proposed method makes a prediction of the behaviour of aged mortar accomplished with a three phase micromechanical model using ultrasonic measurements. Aging mortar was accelerated by immersing the probes in ammonium nitrate solution. Both destructive and non-destructive characterization of mortar was performed. Destructive tests of porosity were performed using a vacuum saturation method and non-destructive characterization was carried out using ultrasonic velocities. Aging experiments show that mortar degradation not only involves a porosity increase, but also microstructural changes in the cement matrix. Experimental results show that the estimated porosity using the proposed non-destructive methodology had a comparable performance to classical destructive techniques.

Journal Article↗
PubMed1994

Studies of cell pellets: I. Electrical properties and porosity.

Cell pellets formed by centrifugation provided a good system to study the osmotic behavior, electroporation, and interaction between cells. Rabbit erythrocyte pellets were used in this study because they were simpler than nucleated cells to model analytically. Structurally, cell pellets possessed properties of porous solid bodies and gels. Electrically, cell pellets were shown to behave as a parallel set of resistance, Rp, and capacitance, Cp. Information on pellet structures was obtained from electric measurements. The pellet resistance reflected the intercellular conductivity (porosity and gap conductivity), whereas the pellet capacitance depended mostly on membrane capacitance. The pellet resistance was more sensitive to experimental conditions. The intercellular gap distance can be derived from pellet porosity measurements, providing the cell volume and surface area were known. Rp increased and relaxed exponentially with time when centrifugation started and stopped; the cycles were reversible. When supernatants were exchanged with solutions containing hypotonic electrolytes or macromolecules (such as PEG) after the pellets were formed, complicated responses to different colloidal osmotic effects were observed. A transient decrease followed by a large increase of Rp was observed after the application of a porating electric pulse, as expected from a momentary membrane breakdown, followed by a limited colloidal-osmotic swelling of pelleted cells. The equilibrium values of Rp, Cp, pellet porosity, and intercellular distances were measured and calculated as functions of cell number, centrifugation force, and ionic strength of the exchanged supernatant. Thus, the structure and properties of cell pellets can be completely characterized by electrical measurements.

Animals↗
PubMed1986

Porosity of the basement membrane overlying Peyer's patches in rats and monkeys.

The porosity of the epithelial basement membrane (basal lamina) overlying lymphoid follicles within Peyer's patches was studied in rats and monkeys by scanning electron microscopy. Basement membranes of lymphoid follicles are markedly porous, more conspicuously so than those of adjacent villus cores. The porosity increases centrifugally from the apex of the follicle to its periphery, where the basement membrane continues into the cul-de-sacs of the crypts. Such porosity may facilitate bidirectional passage of lymphocytes during an immune response. The unique structure of the basement membrane overlying lymphoid follicles suggests a biologic adaptation of this tissue boundary to a specific physiologic activity of the organism.

Animals↗
PubMed1978

Radiographic evaluation of porosities in removable partial denture castings.

Most of the removable partial denture castings examined showed radiographic evidence of internal porosity. In general the porosity ocurred in characteristic regions associated with abrupt changes in cross-sectional thickness. These were located either within the partial denture framework or at the casting-sprue junctions. The porosity is due to metal shrinkage caused by a premature solidification at some point, which in turn interferes with a controlled unidirectional soldification of the casting.

Dental Alloys↗
PubMed2000

Porosity estimation of concrete by ultrasonic NDE

The increasing number of concrete structures with symptoms of premature deterioration due to environmental action demands procedures to estimate the durability of this type of component. Concrete durability is related to porosity, which determines the intensity of interactions of the material with aggressive agents. The pores and capillaries inside the structure facilitate the destructive processes that generally begin in the surface. In this work, an ultrasonic NDE technique to estimate the porosity of concrete is developed. The method is based on the analysis of the mechanical behaviour of mortar probes built with calibrated sand, in which the concentration of water-cement mixture has been varied. In this sense, data of sound velocity are correlated with data of porosity, which have been previously measured by destructive measurements.

Journal Article↗
PubMed2002

Contaminant transport in dual-porosity media with dissolved organic matter and bacteria present as mobile colloids.

In riverbank filtration, contaminant transport is affected by colloidal particles such as dissolved organic matter (DOM) and bacterial particles. In addition, the subsurface heterogeneity influences the behavior of contaminant transport in riverbank filtration. A mathematical model is developed to describe the contaminant transport in dual-porosity media in the presence of DOM and bacteria as mobile colloids. In the model development, a porous medium is divided into the mobile and immobile regions to consider the presence of ineffective micropores in physically heterogeneous riverbanks. We assume that the contaminant transport in the mobile region is controlled by the advection and dispersion while the contaminant transport in the immobile region occurs due to the molecular diffusion. The contaminant transfer between the mobile and immobile regions takes place by diffusive mass transfer. The mobile region is conceptualized as a four-phase system: two mobile colloidal phases, an aqueous phase, and a solid matrix. The complete set of governing equations is solved numerically with a fully implicit finite difference method. The model results show that in riverbank filtration, the contaminant can migrate further than expected due to the presence of DOM and bacteria. In addition, the contaminant mobility increases further in the presence of the immobile region in aquifers. A sensitivity analysis shows that in dual-porosity media, earlier breakthrough of the contaminant takes place as the volumetric fraction of the mobile region decreases. It is also demonstrated that as the contaminant mass transfer rate coefficient between the mobile and immobile regions increases, the contaminant concentration gradient between the two regions reverses at earlier pore volumes. The contaminant mass transfer coefficient between the mobile and immobile regions mainly controls the tailing effect of the contaminant breakthrough. The contaminant breakthrough curves are sensitive to changes in contaminant adsorption and desorption rate coefficients on DOM and bacteria. In situations where the contaminant is released in the presence of DOM and bacteria in dual-porosity media, the early breakthrough and tailing occur due to the colloidal facilitation and presence of immobile regions.

Adsorption↗
PubMed1998

Dependence between dissolution rate and porosity of compressed erythromycin acistrate tablets.

The correlation between dissolution rate and porosity of compressed erythromycin acistrate tablets was studied. The total porosity of the tablets, the pore size distribution and the specific surface area of the pores were determined using high-pressure mercury porosimetry. The particle size and specific surface area of the raw material and of the dry granulated mass of the tablets were also determined. The results show that the pore size distribution, showing the differences in pore structure, is more informative than total intruded volume of mercury. However, it is very difficult to explain the dissolution behaviour of erythromycin acistrate tablets only by porosity results of the tablets, and more work is still needed in this field.

Erythromycin↗
PubMed2001

Alendronate increases degree and uniformity of mineralization in cancellous bone and decreases the porosity in cortical bone of osteoporotic women.

The strength of bone is correlated with bone mass but is also influenced significantly by other factors such as structural properties of the matrix (e.g., collagen mutations) and the mineral. Changes at all levels of this organization could contribute to fracture risk. We investigated the effects of alendronate (Aln) treatment on the density of mineralization and the ultrastructure of the mineral/collagen composite, size and habitus of mineral particles in iliac cancellous bone, as well as on the porosity of iliac cortical bone from postmenopausal osteoporotic women. Twenty-four transiliac bone biopsies from Phase III Aln (10 mg/day) trials (placebo and Aln after 2 and 3 years of treatment, n = 6 per group) were studied. The mineral structure was investigated by quantitative backscattered electron imaging (qBEI) and by scanning small-angle X-ray scattering (scanning-SAXS). qBEI histograms reflect the bone mineralization density distribution (BMDD), whereas SAXS patterns characterize the size and arrangement of the mineral particles in bone. We found that: (i) the relative calcium content of osteoporotic bone was significantly lower than that of data-base controls; (ii) mineralization was significantly higher and more uniform after Aln treatment; (iii) size and habitus of the mineral particles was not different between placebo and Aln-treated groups; and (iv) the porosity of cortical bone was reduced significantly by Aln treatment. We conclude that Aln treatment increases the degree and uniformity of bone matrix mineralization without affecting the size and habitus of the mineral crystals. It also decreases the porosity of the corticalis. Together these effects may contribute to the observed reduction in fractures.

Alendronate↗
PubMed2006

Development of porosity in a char during reaction with steam or supercritical water.

Two series of activated carbon have been prepared by reaction of a char (from olive stones) with supercritical water (SCW) with the objective of studying the effect of temperature and residence time on the development of porosity. The results have been compared with those obtained using the same char but with classical activation with steam. Both procedures develop porosity, but (i) the reaction rate is critical in the development of porosity for steam but not for SCW activation, and (ii) SCW activation produces a larger development of microporosity at low degrees of burnoff, whereas steam produces more meso- and macroporosity. The differences have been explained by assuming that the mechanism for the carbon-water reaction is common but the transport properties of water in the supercritical state are more favorable to facilitate the access of water to the interior of the char particles. In contrast, when steam is used for the activation of the char, the diffusion of the molecules cannot keep up with the chemical rate and, consequently, the reaction is preferentially taking place at the most accessible surface sites, thus facilitating the development of larger pores and the widening of microporosity.

Journal Article↗
PubMed1999

Porosity control of hydroxyapatite implants.

Conformation of hydroxyapatite (HAp) bodies was carried out using a multiple slip-casting technique, in order to obtain dual-layer samples with differential sized porosities. The external layer, because of its porosity, controlled by the addition of organic compounds (polyvinyl polyacrylate, PVC), will promote bone ingrowth. The internal denser layer, due to the addition of lithium phosphate (Li3PO4) as sintering additive, will give mechanical resistance to the implant. HAp aqueous suspensions were characterized by rheological measurements. Scanning electron microscopy (SEM) and intrusion mercury porosimetry (MP) were used to characterize sintered bodies. It can be concluded that it is possible to introduce gross porosity in HAp bodies by the addition of organic compounds. The results show that a compatible shrinking of the layers during the sintering process and a good frequency of pores with an appropriate size in the external layer can be achieved with the use of organic additives.

Journal Article↗
PubMed2003

Controllable porosity hydroxyapatite ceramics as spine cage: fabrication and properties evaluation.

A procedure was designed to prepare porosity-graded hydroxyapatite (HA) ceramics simulating the bimodal structure of natural bone, which could be used to build a cage that would promote the reconstruction of the anterior column after vertebrectomy or corpectomy in tumor and trauma surgery. HA ceramics with controllable pore size distribution and porosity were developed by using chitosan and Poly(vinyl alcohol) (PVA) as the pore-forming agents. HA ceramics with worthwhile properties such as a wide range of volume porosity (10-50%) and pore size (nanometer to 400 microm) can be obtained from this method, which allows the fabrication of HA ceramics with desirable porous characteristics simulating the bimodal natural bone architecture expected to provide advantages for bony fusion in the intervertebral foramina. When coated with chitosan-gelatin network, the bending strength of the porous HA ceramics significantly improved. The polymer network coated porous HA have potential application in the construction of cages for spinal operations.

Journal Article↗
PubMed1981

The use of fibrin glue for sealing vascular prostheses of high porosity.

Vascular prostheses of different porosity (Cooley Very Soft; Miliknit Lo-Por; Microvel; Sparks Mandril) were pretreated with fibrin glue and the permeability was assessed both in vitro and in 12 dog experiments by descending aorta replacement under full systemic heparinization. It was found that all types of prostheses were completely sealed after the pretreatment. In 28 patients undergoing descending or abdominal aorta replacement under systemic heparinization high porosity knitted Dacron grafts were pretreated with the fibrin glue only. There was no blood loss across the prosthetic wall. It is concluded that graft-pretreatment with fibrin glue allows for combining full heparinization and the use of high porosity vascular grafts.

Animals↗
PubMed2006

Modeling electroosmotic and pressure-driven flows in porous microfluidic devices: zeta potential and porosity changes near the channel walls.

This work presents analytical solutions for both pressure-driven and electroosmotic flows in microchannels incorporating porous media. Solutions are based on a volume-averaged flow model using a scaling of the Navier-Stokes equations for fluid flow. The general model allows analysis of fluid flow in channels with porous regions bordering open regions and includes viscous forces, permitting consideration of porosity and zeta potential variations near channel walls. To obtain analytical solutions problems are constrained to the linearized Poisson-Boltzmann equation and a variation of Brinkman's equation [Appl. Sci. Res., Sect. A 1, 27 (1947); 1, 81 (1947)]. Cases include one continuous porous medium, two adjacent regions of different porosities, or one open channel adjacent to a porous region, and the porous material may have a different zeta potential than that of the channel walls. Solutions are described for two geometries, including flow between two parallel plates or in a cylinder. The model illustrates the relative importance of porosity and zeta potential in different regions of each channel.

Journal Article↗
PubMed2006

Mechano-active scaffold design based on microporous poly(L-lactide-co-epsilon-caprolactone) for articular cartilage tissue engineering: dependence of porosity on compression force-applied mechanical behaviors.

An essential component of functional articular cartilage tissue engineering is a mechano-active scaffold, which responds to applied compression stress and causes little permanent deformation. As the first paper of a series on mechano-active scaffold-based cartilage tissue engineering, this study focused on mechanical responses to various modes of loading of compression forces and subsequent selection of mechano-active scaffolds from the biomechanical viewpoint. Scaffolds made of elastomeric microporous poly(L-lactide-co-epsilon-caprolactone) (PLCL) with open-cell structured pores (300 approximately 500 microm) and with different porosities ranging from 71 to 86% were used. The PLCL sponges and rabbit articular cartilage tissue were subjected to compression/unloading tests (0.1 and 0.005 Hz) at 5 kPa, and stress relaxation tests at 10, 30, and 50% strain. The measurements of the maximum strain under loading and residual strain under unloading for compression tests and the maximum stress and equilibrium stress in the stress relaxation test showed that the lower the porosity, the closer the mechanical properties are to those of native cartilage tissue. Among the PLCL sponges, the sponge with 71% porosity appears to be a suitable cartilage scaffold.

Animals↗
PubMed1986

Porosity in posterior composite resins.

The percent pore area and the mean pore size were measured in specimens made of nine brands of composite resin restorative materials. The overall percent porosity ranged from 0.01 to 4.5%. The specimens for the study were prepared in two ways; by condensation or by pressure. Most of the materials, including all those chemically activated, showed more porosity in the condensed than in the pressure specimens. Reversed results emerged for two of the materials, and for another two, the specimens were similar in this respect. The mean pore sizes were smaller in the condensed than in the pressure specimens. Neither mean pore size nor total amount of porosities could be correlated to the curing method of the materials.

Composite Resins↗