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At least 379 records · Page 21Linked to original sources
PubMed2005

Cu(II)-loaded iminodiacetic acid-silica particles for protein profiling of human serum samples using surface-enhanced affinity capture: support porosity effects.

Silica particles of different porosity were functionalised with iminodiacetic acid (IDA) and loaded with Cu(II) ions to yield Cu(II)-IDA-silica. These immobilised metal affinity chromatography (IMAC) materials were subjected to a comprehensive characterisation study. The Cu(II) content--determined via UV/Vis spectroscopy and atomic absorption spectroscopy (AAS)--was found to be linearly dependent on the specific surface area of the silica particles. The evaluation of protein adsorption isotherms provided information on binding properties towards biomolecules. The data fitted Langmuir's adsorption theory. Binding capacity of hen egg white lysozyme (HEWL) was highest for Cu(II)-IDA-silica with mean pore diameter of 120 A, reaching nearly 350 mg/g. All derivatised materials were applied to the fractionation of human serum samples and subsequent mass spectrometric analysis (m/z: 2000-10,000) according to a surface-enhanced affinity capture (SEAC) protocol. Pore size of the support material affected the appearance of the mass spectra to a great extent, showing that surface morphology is another parameter that has to be considered in addition to surface chemistry. Signal intensity as well as the number of detected masses were strongly dependent on the pore diameter, indicating that the carrier material has to be carefully chosen to assure best results.

Blood Chemical Analysis↗
PubMed2004

Diffusivity of ions in agarose gels and intervertebral disc: effect of porosity.

The effect of tissue porosity on ion (sodium, potassium, and chloride) diffusivity in agarose gels and porcine intervertebral disc tissues was investigated using an electrical conductivity method. An empirical, constitutive model for diffusivity (D) of solutes in porous fibrous media was proposed: D/Do = exp[-alpha(r(s)/k(1/2))beta] where r(s) is the Stokes radius of a solute, kappa is the Darcy permeability of the porous medium, Do is the diffusivity in free solution, alpha and beta are two positive parameters whose values depend on material structure. It is found that alpha = 1.25 +/- 0.138, beta = 0.681 +/- 0.059 (95% confidence interval, R2 = 0.92, n = 72) for agarose gels and alpha = 1.29 +/- 0.171 and beta = 0.372 +/- 0.088 (95% confidence interval, R2 = 0.88, n = 86) for porcine annulus fibrosus. The functional relationship between solute diffusivity and tissue deformation was derived. Comparisons of our model prediction with experimental data on diffusion coefficients of macromolecules (proteins, dextrans, polymer beads) in agarose gels in the literature were made. Our results were also compared to the data on ion diffusivity in charged gels and in cartilaginous tissues reported in the literature. There was a good agreement between our model prediction and the data in the literature. The present study provides additional information on solute diffusivity in uncharged gels and charged tissues, and is important for understanding nutritional transport in avascular cartilaginous tissues under different mechanical loading conditions.

Animals↗
PubMed1992

High-performance affinity chromatography of DNA. II. Porosity effects.

A DNA-silica, (dT)18-silica, was prepared and used in a study of the chromatography of the oligonucleotide, (dA)18, based upon base pairing. It was shown that hybridization efficiency did not depend upon flow-rates up to 2 ml/min for the small columns (22 x 2 mm) used. As increasing amounts of (dA)18 were loaded onto the columns, the columns were found to saturate at a well defined capacity that was always less than the amount that theoretically could have been bound. Maximum capacity was achieved whenever the loading temperature was at least 20-25 degrees C below the temperature at which the loaded oligonucleotide would elute. The effects of porosity on both coupling efficiency and capacity were measured and suggest that pore sizes in the 300-500 A range are most appropriate for this form of chromatography.

Chromatography, Affinity↗
PubMed1993

Radiographic and metallographic evaluation of porosity defects and grain structure of cast chromium cobalt removable partial dentures.

A study was undertaken to determine the defects in the internal microstructure of clasps of cast chromium cobalt removable partial denture frameworks. Ninety cast frameworks were radiographically evaluated for porosity with an industrial radiographic machine. The grain structure of the clasps was analyzed with an optical photomicroscope before and after various heat treatments. The radiographic study showed a large number of internal defects in various parts of removable partial denture frameworks. The grain structure study revealed microporosities randomly distributed within the matrix. Various heat treatments were performed and resulted in no change in the grain structure of the original castings.

Chromium Alloys↗
PubMed1994

Granulates based on calcium phosphate with controlled morphology and porosity for medical applications: physico-chemical parameters and production technique.

Since the pore size distribution of a material in contact with bone is decisive for its type of link with the tissue, many granules are commercially available as fillers and as bone reconstructing materials. We propose a new technological procedure. The optimum architectural design for obtaining the most suitable link in vivo is investigated. Particular attention is attached to the granulate texture: micropores, macropores, total volume of pores, pore size distribution, and the morphology and shape of the pores. These characteristics are studied in order to obtain the best porosity for hydroxyapatite granulates now applied in vivo, with interesting results in mechanical and hard tissue linkage terms.

Biocompatible Materials↗
PubMed1995

Animal models of cortical porosity.

Increased cortical porosity (Ct.Po) has been observed as a consequence of aging, disease (hyperparathyroidism, osteoporosis), and pharmacologic intervention (thyroid hormone, fluoride, parathyroid hormone, prostaglandins). Whether this is permanent or transient in humans has not been established nor has the impact of Ct.Po on bone strength or fracture incidence been determined. There is a need to understand the causes and consequences of increased Ct.Po and how it relates to disease states and osteoporosis therapies. The mechanism of increased Ct.Po is thought to be an increased activation of Haversian remodeling systems accompanied by increased Haversian canal diameter. Increased activation at the endocortical surface and subsequent trabecularization may also contribute to loss of cortical bone. Ct.Po has been observed in several animal models which can be used to further study the phenomenon. Ct.Po is seen in normal dogs and is increased by treatment with PTH and prostaglandins. In the dog it has also been shown that increased Ct.Po is reversible after anabolic therapy is discontinued. Furthermore, in dogs an antiresorptive agent (risedronate) will block PTH-induced increases in Ct.Po (control 1.6% +/- 0.7; PTH 3.0% +/- 1.1, PTH plus risedronate 1.8% +/- 1.2) without interfering with anabolic effects. In rats, increased Ct.Po occurs following treatment with anabolic agents such as PTH, prostaglandin, and insulin-like growth factor 1 (IGF-1). For instance, with IGF-1, Ct.Po increased from 0.4% +/- 0.4 to 5.4% +/- 1.8. Other species in which Ct.Po is observed include primates and ferrets.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

The mechanical properties and osteoconductivity of hydroxyapatite bone scaffolds with multi-scale porosity.

The relative osteoconductivity and the change in the mechanical properties of hydroxyapatite (HA) scaffolds with multi-scale porosity were compared to scaffolds with a single pore size. Non-microporous (NMP) scaffolds contained only macroporosity (250-350 microm) and microporous (MP) scaffolds contained both macroporosity and microporosity (2-8 microm). Recombinant human bone morphogenetic protein-2 (rhBMP-2) was incorporated into all scaffolds via gelatin microspheres prior to implantation into the latissimus dorsi muscle of Yorkshire pigs. After 8 weeks, only the MP scaffolds contained bone. The result demonstrates the efficacy of the MP scaffolds as drug carriers. Implanted and as-fabricated scaffolds were compared using histology, microcomputed tomography, scanning electron microscopy, and compression testing. Implanted scaffolds exhibited a stress-strain response similar to that of cancellous bone with strengths between those of cancellous and cortical bone. The strength and stiffness of implanted NMP scaffolds decreased by 15% and 46%, respectively. Implanted MP scaffolds lost 30% of their strength and 31% of their stiffness. Bone arrested crack propagation effectively in MP scaffolds. The change in mechanical behavior is discussed and the study demonstrates the importance of scaffold microporosity on bone ingrowth and on the mechanical behavior of HA implant materials.

Animals↗
PubMed2004

Applicability of (SBE)7m-beta-CD in controlled-porosity osmotic pump tablets (OPTs).

The purpose of this study was to investigate the general application of a controlled-porosity osmotic pump tablet (OPT) utilizing (SBE)7m-beta-CD as both a solubilizer and an osmotic agent for drugs with varying physical properties. OPTs utilizing (SBE)7m-beta-CD were prepared for five poorly soluble and two highly water-soluble drugs. The Japanese Pharmacopoeia dissolution method was used to study the drug and (SBE)7m-beta-CD release from the OPTs. The drug concentration in the OPT core after the OPT was placed in the release medium for two hours was assayed gravimetrically and by HPLC. An appropriate composition ratio (ACR) of (SBE)7m-beta-CD to drug at which drug release from the OPT was complete and pH-independent within the physiological pH range of the GI tract was determined for each drug. The ACR values correlate to the drug concentration in the OPT core when the OPTs were placed in the release medium for two hours. The release profiles of prednisolone (a poorly water-soluble drug) and sodium chloride (a water-soluble compound) from the OPTs were almost the same as that of (SBE)7m-beta-CD. Also, the release rate of each drug per unit membrane surface area from the OPTs was similar, regardless of the differences in drug solubility. The present results confirmed that (SBE)7m-beta-CD serves as both a solubility modulator and as an osmotic pumping agent for OPTs, from which the release rate of both water-soluble and poorly water-soluble drugs can be controlled.

Adjuvants, Pharmaceutic↗
PubMed2006

How porosity and size affect the drug release mechanisms from PLGA-based microparticles.

Porous, poly(lactic-co-glycolic acid) (PLGA)-based microparticles were prepared using a water-in-oil-in-water (W/O/W) solvent extraction/evaporation technique. Lidocaine was used as a model drug and different-sized particle fractions were obtained by sieving. The physicochemical properties of the devices and changes thereof upon exposure to phosphate buffer pH 7.4 were studied using optical and scanning electron microscopy, size exclusion chromatography (SEC), differential scanning calorimetry (DSC), gravimetric analysis and in vitro drug release measurements. In contrast to non-porous microparticles of identical composition, the relative drug release rate was found to decrease with increasing system size. SEC, DSC and gravimetric analysis showed that the degradation rate of the polymer increased with increasing microparticle dimension, indicating that autocatalytic effects play an important role even in small and highly porous PLGA-based microparticles. However, these effects were much less pronounced than in non-porous devices. Importantly, they were overcompensated by the effects of the increasing diffusion pathway lengths with increasing system dimension. Thus, high initial microparticle porosities do not only lead to increased drug mobilities, but can also fundamentally alter the underlying mass transport mechanisms.

Catalysis↗
PubMed2005

Porosity and tortuosity relations as revealed by a mathematical model of biofilm structure.

A biofilm is assumed to be submerged in a fluid with given viscosity and low Reynolds number. The interaction between fluid and bacteria is modeled through streamlines. We use finite-difference and boundary element numerical schemes to predict streamlines within the biofilm. The results show that this approach can provide information about prior distribution and geometry of the biofilm structure. Theoretical values of porosity and tortuosity are computed and compared with published data.

Animals↗
PubMed2005

Determination of porosity and flow distribution in packed beds by magnetic resonance imaging.

Magnetic resonance methods have been used to investigate the porosity and flow distributions in packed beds. The motivation of our study is to understand the behaviour of multiphase flow in fixed bed reactors, especially in trickle bed reactors. The results of this study should be included in a model for predicting the influence of hydrodynamics on hydrodesulfurization process in bench-scale reactors.

Imaging, Three-Dimensional↗
PubMed2005

Analysis of porosity in porous silicon using hyperpolarized 129Xe two-dimensional exchange experiments.

The porosity in porous silicon was characterized using hyperpolarized (HP) xenon as a probe. HP xenon under conditions of continuous flow allows for the rapid acquisition of xenon NMR spectra that can be used to characterize a variety of materials. Two-dimensional exchange spectroscopy (EXSY) (129)Xe NMR experiments using HP xenon were performed to obtain exchange pathways and rates of xenon mobility between pores of different dimensions within the structure of porous silicon and to the gas phase above the sample. Pore sizes are estimated from chemical shift information and a model for pore geometry is presented.

Isotopes↗
PubMed2002

A method for evaluating the influence of porosity on the early reactions of blood with materials.

A method is presented for evaluating the influence of porosity on the early reactions of blood with polymer membranes of cellulose acetate and polyethersulfone with two different pore sizes, 0.1-0.2 microm and 0.8 microm. A system of two phases consisting of capillary blood and Dulbecco's phosphate buffered saline was constructed. Platelet adhesion and exposure of thrombospondin was examined by immunofluorescence. Platelet adhesion was higher on the membrane with 0.8 microm pore size. Leukocyte adhesion and viability was measured by fluorescein diacetate/propidium iodide staining, and the respiratory burst response to PMA and opsonized zymosan was measured by chemiluminescence. Leukocyte viability was higher on the membranes with 0.8 microm pore size and higher on the cellulose membrane for exposures upto 2 h. After 3 h the leukocyte viability was highest on the polyethersulfone membrane with a pore size of 0.8 microm. The respiratory burst response of membrane-adhering leukocytes could not be triggered by opsonized zymosan on any of the tested membranes. A response was seen after stimulation with PMA of cells adhering to the cellulose membrane with a pore size of 0.8 microm.

Biocompatible Materials↗
PubMed2003

Drug release kinetics and fronts movement studies from methyl methacrylate (MMA) copolymer matrix tablets: effect of copolymer type and matrix porosity.

Several methyl methacrylate (MMA) copolymers have recently been proposed as an alternative for the formulation of controlled-release matrix tablets. Copolymers were synthesised by free radical copolymerisation of methyl methacrylate with starch or cellulose derivatives and were alternatively dried by oven or freeze-drying techniques. Both the chemical composition and the drying technique were demonstrated to have a considerable influence on the physical properties of the copolymers. The present investigation was focused on the elucidation of the drug release mechanism from MMA copolymer matrices, using anhydrous theophylline as model drug. Drug release experiments were performed from free tablets. Radial drug release and fronts movement were also evaluated using special devices consisting of two Plexiglass discs joined by means of four stainless steel screws. Mathematical analysis of release data was performed using Higuchi, Korsmeyer and Peppas equations and fronts movement was investigated using a colorimetric technique. The drug release rate and the relative positions of the fronts were studied as functions of the type of copolymer and the initial porosity of the tablets. Drug release was controlled mainly by diffusion and the release rate was found to be affected by the drying method and related to the area exposed to the dissolution medium. Three distinct fronts (water uptake, complete wetting, erosion) were observed during the release process and the dynamics of fronts movement confirmed the diffusional mechanism.

Methylmethacrylate↗
PubMed2004

Effect of Er:YAG laser and organic matrix on porosity changes in human enamel.

OBJECTIVES: Cariostatic effects of lasers have been well documented in the past few decades; however, the mechanisms remain unclear. Our previous study revealed the statistically significant effect of organic matrix (OM) in the laser-induced caries prevention. The aim of the present study is to further investigate the role of organic matters in the laser-induced porosity changes. METHODS: Enamel powder from five sound molars was randomly divided into two samples. One sample was treated with approximately 10% NaClO solution to remove OM and the other was left untreated. Both groups were then subjected to irradiation by an Er:YAG laser. The samples were characterized by thermogravimetric analysis (TGA) and N(2) physico-adsorption. RESULTS: TGA results confirmed that the NaClO treatment had at least partially removed the OM in enamel powder. The surface area and pore volume of normal enamel powder decreased significantly after laser treatment. In contrast, in the NaClO-treated enamel powder, laser treatment did not significantly decrease the surface area and the pore volume remained almost unchanged. The substantial difference between the normal enamel powder and the NaClO-treated enamel powder after laser treatment confirmed the laser-induced blocking of OM in the micro-diffusion pathway in enamel. CONCLUSION: The findings in this study seemed to substantiate the "organic blocking theory" as one of the mechanisms in the laser-induced caries prevention.

Dental Enamel↗
PubMedDate not supplied

MRI velocimetry and lattice-Boltzmann simulations of viscous flow of a Newtonian liquid through a dual porosity fibre array.

Viscous flow through fibrous porous media has considerable importance in a number of industrial processes including, in particular, resin transfer molding. In this paper magnetic resonance flow imaging techniques are used to visualize flow of a Newtonian liquid through a dual porosity structure. Of particular interest in these studies is the transition in the flow as the liquid moves from the open region into the fiber array. The ability of lattice-Boltzmann simulations to predict the visualized flow fields is presented and discussed.

Computer Simulation↗
PubMedDate not supplied

Morphology control in co-continuous poly(L-lactide)/polystyrene blends: a route towards highly structured and interconnected porosity in poly(L-lactide) materials.

Poly(L-lactide) is a biodegradable polymer primarily used in biomedical applications. In this paper, both the microstructure and the region of dual-phase continuity are examined for binary and compatibilized poly(L-lactide)/polystyrene blends (PLLA/PS) prepared by melt mixing. The blends are shown to be completely immiscible with an interfacial tension of 6.1 mN/m. The PS-b-PLLA (24,000-b-28,000) diblock copolymer compatibilizer has an asymmetric effect on the blend. It is effective at compatibilizing 50/50 PLLA/PS blends but is only a marginal emulsifier for blends where PLLA is the dominant matrix. Percent continuity, as estimated by solvent extraction/gravimetry and also torque/composition diagrams clearly indicate an onset of the region of dual-phase continuity at 40-45%PS. It is demonstrated that highly percolated blends of the above materials exist from 40 to 75% PS and 40 to 60% PS for the binary and compatibilized blends, respectively. The scale of the microstructure of the continuous morphology is measured using BET and mercury intrusion porosimetry techniques, after extraction of the PS phase. Both the pore size and extent of continuity can be controlled through composition and interfacial modification. Static annealing of the blend after melt mixing can also be used to substantially increase the pore size of the system. Extraction of the PS phase in the blend, carried out after the above preparation protocols, is a route to generating completely interconnected porosity of highly controlled morphologies (pore size, void volume) in poly(L-lactide) materials. In this study, the pore diameter was controlled from 0.9 to 72 microm for a constant void volume of 45-47%, and the void volume was modified from 35 to 74% depending on the blend composition.

Biocompatible Materials↗
PubMed2005

Determination of interstitial water chemistry and porosity in consolidated aquifer materials by diffusion equilibrium-exchange.

Diffusion equilibrium exchange (DEE) is presented as a novel, practical alternative to centrifugation for the recovery and chemical analysis of interstitial water in contaminated core samples from consolidated rocks and aquifers. The methodology is suitable for sampling organic and inorganic compounds, including redox sensitive species such as SO4(2-), NO3-, NO2-, Mn(II), Fe(II), and sulfide (HS-). DEE also permits analyte extraction from kilogram quantities of core, which avoids extended centrifugation or sample amalgamation and provides analyte masses appropriate for stable isotope analysis. The procedure involves simple and rapid on-site sectioning of representative core samples, which are preserved in the field by storage in airtight bottles filled with deoxygenated deionized water containing a conservative tracer (Br-). Equilibration times for individual solutes can be estimated in advance to reduce the need for time-series analysis; for an effective diffusion coefficient of 2.5 x 10(-10) m2 s(-1) (Br- in chalk rock) equilibration was >90% completed after 30 h, consistent with the predicted equilibration time. The DEE method presented minimizes sampling errors from temperature changes, oxidation of reduced chemical species, and loss of volatile compounds, which can occur with other interstitial water sampling techniques. It also gives superior resolution of in situ solute distributions and geochemical processes in consolidated sediments than centrifugation and can provide estimates of aquifer porosity in core samples. Laboratory experiments using chalk rock core and simulated extraction procedures confirm the superior performance of the DEE method over centrifugation for a range of solutes. The method has been used to generate detailed interstitial water profiles of electron acceptor and contaminant concentrations along the flow path of a petroleum hydrocarbon plume in the U.K. Upper Chalk aquifer as part of a natural attenuation assessment.

Environmental Monitoring↗