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PubMed1988

The effect of porosity and mineral content on the Young's modulus of elasticity of compact bone.

The Young's modulus of elasticity, the calcium content and the volume fraction (1-porosity) of 23 tension specimens and 80 bending specimens, taken from compact bone of 18 species of mammal, bird and reptile, were determined. There was a strong positive relationship between Young's modulus and both calcium content and volume fraction. A power law model fits the data better than a linear model. Young's modulus has a roughly cubic relationship with both calcium content and volume fraction. Over 80% of the total variation in Young's modulus in this data set is explained by these two variables.

Animals↗
PubMed1996

Bonded cellulose-derived high-performance liquid chromatography chiral stationary phases. II. Influence of the porosity of the silica gel matrix on performance.

Two cellulose derivatives bearing simultaneously 10-undecenoyl and 3,5-dimethylphenylaminocarbonyl groups in different ratios were chemically bonded on allylsilica gels of different porosity. The systematic study of the effect of the silica gel pore size on the bonding of the polysaccharide derivative and on the performance of the resulting chiral supports is presented.

Cellulose↗
PubMed1989

Effect of preclotting on the porosity and thrombogenicity of knitted Dacron grafts.

The effects of single- and four-stage preclotting methods on graft porosity and thrombogenicity were compared in two types of Dacron prosthesis. The single-stage method significantly reduced leakage of blood (P less than 0.001), but did not seal the grafts. The four-stage method rendered the grafts impermeable at the second step. Thrombogenicity was compared by perfusing preclotted grafts with fresh heparinized blood (containing 111In-labelled platelets) in an artificial circulation. Platelet deposition and consumption were significantly less in the four-stage method whilst platelet function remained unchanged during perfusion. We conclude that the four-stage technique is superior to standard preclotting methods by rendering knitted Dacron grafts impermeable and hypothrombogenic.

Blood Coagulation↗
PubMed1990

The influence of stress treatment on femur cortical bone porosity and medullary bone status in Japanese quail selected for high and low blood corticosterone response to stress.

1. Femurs taken from Japanese quail (Coturnix coturnix japonica) genetically selected for either exaggerated (HS; high-stress) or reduced (LS; low-stress) blood corticosterone (B) response to unfamiliar environments were examined to determine their cortical bone porosity (CBP; degree of osteoporosis) and medullary bone (MB) status following treatment with or without stress. 2. Femur CBP was elevated in both sexes of stressed, HS-line quail and was attributed directly to the presumably exaggerated blood B responses known to occur in this line as a consequence of the stress treatments used. 3. The increase in CBP in stressed, HS-line birds occurred independently of changes in the numbers of osteoclast cells (CLASTS) associated with cortical bone. 4. Stress treatment was associated with lower CLAST numbers/mm2 of MB and with increased MB accretion. 5. These stress-induced effects were considered to be the consequence of a reduced rate of lay found in stressed quail hens. 6. There was only marginal evidence for a direct effect of B in stimulating MB resorption.

Analysis of Variance↗
PubMed2005

Estimation of diffusion parameters in functionalized silicas with modulated porosity. Part I: chromatographic studies.

The diffusion parameters of binary gas mixture He (tracer gas)-N2 (carrier gas) in hybrid organic-inorganic SiO2-X porous solids which have suffered gradual functionalization with functional groups X of increasing length (X = psi, [triple bond]Si-H, [triple bond]Si-CH2OH, [triple bond]Si-(CH2)3OH, [triple bond]Si-(CH2)11CH3) are reported. The effective diffusivities Deff, the Henry law constants K as well as the tortuosity factors tau for the examined solids were estimated by a typical pulse gas chromatographic method. Analysis of the experimental results was carried out by the well-known method of linearization of moments. The moments s analysis provides a powerful means for extracting diffusion parameters from the experimental response curves The proposed methodology is simple compared to other similar studies and provides rapidly reliable data. The results of this work indicate that the effective diffusivity Deff in porous networks drops markedly as the initial porosity of the parent SiO2 sample is blocked by the functionalization of the pore surfaces with functional groups of increasing size, [triple bond]Si-H, [triple bond]Si-CH2OH, [triple bond]Si-(CH2)3OH and [triple bond]Si-(CH2)11CH3. The low values of the Henry law constants K found indicate that the adsorption of He on the porous surfaces for all the solids is weak. Also, the tortuosity factor r is proportionally correlated to the pore blocking effects and the percolation phenomena of gases flowing into the porous network.

Adsorption↗
PubMed2005

Estimation of diffusion parameters in functionalized silicas with modulated porosity. Part II: pore network modeling.

In this work, the pore structure of those five (5) silicas SiO2-X (see Part I) which have suffered gradual functionalization with functional groups X of increasing length (X = psi, [triple bond]Si-H, [triple bond]Si-CH2OH, [triple bond]Si-(CH2)3OH, [triple bond]Si-(CH2)11CH3), is modeled as a three-dimensional cubic network of cylindrical pores. Those hybrids organic-inorganic SiO2-X samples are characterized by different extent of pore blocking effects. The pores of samples are represented in a 9 x 9 x 9 lattice by the nodes as well the bonds that are interconnected in a so-called dual site-bond model, DSBM, network. The pore network is developed using a Monte Carlo statistical method where the cylindrical pores (nodes and bonds) are randomly assigned into the lattice, until matching of the theoretical results to the experimental data of N2 adsorption-desorption measurements. Thus, a visual picture of the porous solid is possible. This realistic network is used next in order to study the steady-state gas transport (Knudsen gas-phase and viscous diffusion) properties for the examined materials and how flow processes depend on the morphology of the pore structure. The pore diffusivity Dp and total permeability P of each porous medium is determined based on theoretical calculations and the structural statistical parameters, such as porosity epsilonp, tortuosity factor tau and connectivity c of pores is discussed with the corresponding experimental data described in Part I of this work. The results indicate clearly that the diffusion model made it possible to predict pore effective diffusivity in these porous media in very good agreement with the corresponding experimental results for all the examined solids (Part I). The pore diffusivity increases significantly as the value of the pore connectivity increases but the transport properties of the network are influenced strongly at lowest connectivity. Also the predicted tortuosity factor is related inversely to the extent of interconnection of pores in these solids, which indicates that the influence of pore branching to the tortuosity factor of the pore network decreases, as connectivity increases.

2-Propanol↗
PubMed1989

Variable porosity of the mitochondrial inner membrane induced by energization.

The empirically observed relationship between the activity of membrane-bound enzyme systems and transporters and the external osmotic pressure offered a direct method to assess the reflection coefficients to polyols in respiring mitochondria. These osmotically modulated reaction rates varied with the molecular mass of the external polyol similar to volume and solute fluxes across dialysis membranes. The equivalent pore radii of mitochondria were shown to increase with respiration (and temperature) and decrease on addition of the uncoupler, 2,4-dinitrophenol. The magnitude of the induced porosity in the inner membrane was large enough to render the chemiosmotic mechanism inoperable in well-coupled rat liver mitochondria.

2,4-Dinitrophenol↗
PubMed2001

Visualization of solute migration in chromatographic columns influence of the frit porosity.

The dual-perspective, on-column detection method previously described was used to observe the effects of the inlet frit on the profiles of chromatographic bands. Visualization of bands of iodine was achieved by injecting its dilute solutions in carbon tetrachloride into a glass column packed with a C18-bonded silica and eluted with carbon tetrachloride, which has the same refractive index as the packing material. The bands were photographed on-column with two standard 35-mm SLR cameras oriented at right angle. The photographs were scanned and the digitized images of the sample bands analyzed with proper software. A number of columns, as similar as possible, were fitted with different 2- and 10-microm porosity stainless steel frits. Subsequent analysis of the digitized band images revealed irregularities in the band shape resulting from frit contributions to band dispersion. The 2-microm frits produced more dramatic effects overall than the coarser frits. Local axial dispersion coefficient values, expressed as local reduced plate height, were calculated. The results demonstrate the possibly damaging effects of the frit on the band shape.

Chromatography, Liquid↗
PubMed2001

Novel monolithic columns with templated porosity.

A new type of monolithic stationary phase was prepared within the confines of fused-silica tubing by in situ polymerization of divinylbenzene or ethylene dimethacrylate either with styrene or butyl methacrylate. The porosity of the monolith was dictated by silica beads packed in the capillary prior to flushing the column with the monomeric solution. Subsequent washing of the polymeric rod with sodium hydroxide rendered a porous monolith that was used for both micro-LC and capillary electrochromatography. The novelty of the approach presented herein lies in preparing the polymer within the confines of a fused-silica capillary. The challenges posed in this new context and their resolution are presented in detail. In addition, this study proposes that in addition to tailoring the pore size, the silica beads, through their surface chemistry, can influence the surface characteristics of the finished polymer monolith. For example, the data suggests that octadecyl modified silica particles interacted with hydrophobic moieties of monomers before initiation of polymerization, thus dictating their orientation in the resulting polymer.

Amino Acid Sequence↗
PubMed2001

Size exclusion behavior of hydroxypropylcellulose beads with temperature-dependent porosity.

Beads prepared from a thermosensitive polymer, hydroxypropylcellulose, exhibit temperature-dependent porosity. At temperatures below 40 degrees C the beads are swollen having large pores, while at temperatures above 45 degrees C the beads are in a shrunken state having smaller pores. In the presence of 1 M NaCl the transition temperature decreased to about 30 degrees C. In a swollen state the size of pore is large enough to accommodate lysozyme (mol. mass 14400) and alpha-chymotrypsin (mol. mass 21600) but not bovine serum albumin (mol. mass 67000). When the beads are shrunken, all the proteins are eluted from the column packed with hydroxypropylcellulose beads in the volume close to the void volume of the column.

Chromatography, Gel↗
PubMed2001

Porosity-graded hydroxyapatite ceramics to replace natural bone.

Porous hydroxyapatite HA bodies were prepared with an aim to simulate bone tissue morphology. By varying the characteristics of starting HA powders and the impregnation strategy of cellulosic sponges with rheologically optimized slurries, a wide range of physico-chemical and mechanical properties of the porous ceramics can be obtained. The samples were characterized microstructurally, by density and porosimetry and by mechanical strength. Cylindrical specimens exhibiting a porosity gradient showed a promising behaviour after implantation in rabbits' femur: newly formed bone grew in tight contact with the ceramic in a very short time, no modified cells are induced and bone tissue fills even the inner pores.

Animals↗
PubMed2003

Acrylonitrile-sodium methallylsulfonate copolymer. DSC approach to membrane porosity of foam and hollow fibers.

The porosity of membranes formed from acrylonitrile-sodium methallylsulfonate copolymer was characterized from the analysis of the depression of the melting point of absorbed water. Membranes were obtained either as a foam or as a hollow fiber; the foam consisted of interconnected macrocavities (mean diameter about equal to 1 mm) while the hollow fiber was a symmetric membrane used for blood ultrafiltration. Differential scanning calorimetry (DSC) of water revealed both the Gaussian distribution of pore sizes and correspondingly, their mean size: 5.2 nm for the pores through the walls separating macrocavities in the foam and 5.6 and 10.6 nm associated with two distributions representing nearly equal amounts of absorbed water, for the hollow fiber. In addition to DSC, the water magnetic relaxation showed that the isothermal dehydration of the foam was due to the deswelling of macrocavities while the increasing amount of absorbed water in pores reflects its strong interaction with the polymer.

Acrylic Resins↗
PubMed2000

Histomorphometric evidence for increased bone turnover without change in cortical thickness or porosity after 2 years of cyclical hPTH(1-34) therapy in women with severe osteoporosis.

Parathyroid hormone (PTH) increases trabecular but may decrease cortical bone mass during treatment of postmenopausal osteoporosis. In a 2-year trial, PTH, with or without sequential calcitonin (CT), was given to 29 osteoporotic women (mean age 67 +/- 7 years), in 3-month cycles [28 days hPTH(1-34), 50 microg/day, +/-42 days CT, 75 units/day, 20 days "free"]. Over 2 years, lumbar spine bone mineral density measurements increased an average of 10%. Paired iliac crest biopsies were obtained 28 days and 2 years after starting the trial. The addition of CT made no difference to changes seen with cyclical PTH alone. Thus, the histomorphometric analyses for all 29 treated patients were compared with a separate group of biopsies from untreated osteoporotic control patients (n = 15). No significant increments in total bone volume or trabecular architecture were seen over 2 years of cyclical PTH treatment, although the light microscopic appearance of bone was normal. At the level of the bone remodeling unit, a twofold increase in total trabecular erosion surface over the control measurements was observed within the first 28 days of PTH treatment (10 +/- 5 vs. 5 +/- 3% trabecular surface, p < 0.01), which was sustained over 2 years. Trabecular bone formation rates (surface referent) were 11 +/- 7 microm(3)/microm(2)/year in control patients and threefold higher in treated patients both acutely (31 +/- 31 microm(3)/microm(2)/year, p < 0.01) and after 2 years (33 +/- 43 microm(3)/microm(2)/year, p < 0. 05). The activation frequency of trabecular remodeling was threefold higher than controls through 2 years of treatment (p < 0.05). The mean wall thickness of completed osteons after 2 years of treatment was significantly larger than controls (28 +/- 7 vs. 22 +/- 5 microm, p < 0.01), suggesting a positive remodeling balance, as well as the histomorphometric evidence of increased bone turnover and the increased resorption surfaces. Over 2 years of cyclical PTH therapy, cortical thickness remained significantly higher than controls (680 +/- 202 vs 552 +/- 218 microm, p < 0.05), without significant changes in cortical porosity. Thus, the histomorphometric changes during cyclical PTH therapy in patients with severe osteoporosis are consistent with increased trabecular bone turnover and a positive remodeling balance, with no evidence for detrimental changes in cortical bone.

Aged↗
PubMed2002

Measurement of packing tortuosity and porosity in capillary electrochromatography.

The application of conductivity measurements for packing structure characterization has been extended to a column consisting of a packed section and an open section as typically used in capillary electrochromatography (CEC). Because of the difference in electric conductivity between the packed and open sections, the electric fields applied across the two sections vary, depending on the length of the packed section relative to that of the total column. On the basis of mass conservation law, it can be shown that the ratio of the electric current measured in such a duplex column to that without packing is a function of the length and the geometric structure of the packing bed. Thus, knowing the lengths of the packed section and the whole column, we can readily calculate the obstructive factors, such as the porosity and the tortuosity factor, from the measured conductivity ratio. An example is given to demonstrate the application of this method, with experimental data taken from published work.

Journal Article↗
PubMed2006

Synthesis, crystal structure, and porosity estimation of hydrated erbium terephthalate coordination polymers.

The reaction of the Er3+ ion with polycarboxylate ligands in gel media leads to coordination polymers exhibiting various structural types and dimensionalities. Five Er3+/1,4-benzenedicarboxylate-based coordination polymers have been obtained in such conditions. Four out of the five are new. Their crystal structures are reported and compared herein. Compound 1, namely, Er2Ter3(H2O)6, where H2Ter symbolizes the terephthalic acid, crystallizes in the space group P1 (No. 2) with a = 7.8373(10) A, b = 9.5854(2) A, c = 10.6931(2) A, alpha = 68.7770(8) degrees, beta = 70.8710(8) degrees, and gamma = 75.3330(12) degrees. It has already been reported elsewhere. The last four compounds are new. Compound 2, namely, Er2Ter3(H2O)6 x 2 H2O, crystallizes in the space group P121/a1 (No. 14) with a = 6.7429(2) A, b = 22.4913(7) A, c = 9.6575(3) A, and beta = 91.6400(18) degrees. Compound 3, namely Er2Ter3(H2O)8 x 2 H2O crystallizes in the space group P1 (No. 2) with a = 7.5391(2) A, b = 10.0533(3) A, c = 10.4578(3) A, alpha = 87.7870(10) degrees, beta = 82.5510(11) degrees, and gamma = 86.2800(16) degrees. Compound 4, namely, Er2Ter3(H2O)6 x 2 H2O crystallizes in the space group C2/c (No. 15) with a = 38.5123(13) A, b = 11.1241(4) A, c = 7.0122(2) A, and beta = 98.634(2) degrees. Compound 5, namely, Er2Ter3(H2O)6 x H2O, crystallizes in the space group P1 (No. 2) with a = 6.8776(10) A, b = 11.0420(2) A, c = 18.5675(3) A, alpha = 84.7240(6) degrees, beta = 81.8380(6) degrees, and gamma = 84.1770(8) degrees. A computational method has also been developed to evaluate the potential porosity of the coordination polymers. This method is described and then applied to the different Er2Ter3(H2O)n coordination polymers previously described.

Journal Article↗
PubMed2006

Stability and porosity enhancement through concurrent ligand extension and secondary building unit stabilization.

A trigonal nanosized carboxylate ligand, 1,3,5-tris[4'-carboxy(1,1'-biphenyl-4-yl)]benzene (TCBPB), has been synthesized and applied in the construction of porous metal-organic frameworks (MOFs). A solvothermal reaction of TCBPB and a zinc salt in the presence of pyridine produces 1, an unstable MOF consisting of a tetrazinc secondary building unit (SBU) with labile terminal ligands. Changing pyridine to a noncoordinating base in the assembly procedure affords 2, a stable MOF with permanent porosity containing an octazinc SBU without labile terminal ligands.

Journal Article↗
PubMed2005

Tailoring of nanoscale porosity in carbide-derived carbons for hydrogen storage.

The poor performance of hydrogen storage materials continues to hinder development of fuel cell-powered automobiles. Nanoscale carbons, in particular (activated carbon, exfoliated graphite, fullerenes, nanotubes, nanofibers, and nanohorns), have not fulfilled their initial promise. Here we show that carbon materials can be rationally designed for H2 storage. Carbide-derived carbons (CDC), a largely unknown class of porous carbons, are produced by high-temperature chlorination of carbides. Metals and metalloids are removed as chlorides, leaving behind a collapsed noncrystalline carbon with up to 80% open pore volume. The detailed nature of the porosity-average size and size distribution, shape, and total specific surface area (SSA)-can be tuned with high sensitivity by selection of precursor carbide (composition, lattice type) and chlorination temperature. The optimum temperature is bounded from below by thermodynamics and kinetics of chlorination reactions and from above by graphitization, which decreases SSA and introduces H2-sorbing surfaces with binding energies too low to be useful. Intuitively, pores of different size and shape should not contribute equally to hydrogen storage. By correlating pore properties with 77 K H2 isotherms from a wide variety of CDCs, we experimentally confirm that gravimetric hydrogen storage capacity normalized to total pore volume is optimized in materials with primarily micropores ( approximately 1 nm) rather than mesopores. Thus, in agreement with theoretical predictions, a narrow size distribution of small pores is desirable for storing hydrogen, while large pores merely degrade the volumetric storage capacity.

Journal Article↗
PubMed2006

Structure and growth of thin films of aniline on silver: nucleation and premelting of nanocrystallites, porosity, and crystallization.

The structure and growth of thin films of aniline vapor deposited on Ag(111) and Ag(110) surfaces have been examined using optical second harmonic generation (SHG) and linear optical differential reflectivity (DR). Aniline thin films deposited at 90 K give a detectable SH signal that arises from small polycrystallites with orientation anisotropy in the film. Upon annealing, the SH signal decreases, first due to premelting (at approximately 145 K) of the polycrystallites and then sublimation (at approximately 180 K) of the film. Quantitative analysis of the SH intensity change by a premelting model [J. Phys. Chem. 1988, 92, 7241] allows the determination of the average size of the crystallites as 1.1 nm in diameter and containing approximately 45 aniline molecules. The existence of the nanocrystalline structure and its premelting are confirmed by DR experiments. The DR signal around 145 K exhibits change corresponding to an order-disorder transition. Quantitative analysis of the DR data results in the same nanocrystallite size. Experimental observations indicate that films deposited at 90 K contain not only nanocrystallites but also approximately 30% porosity, which can be reduced by annealing. At temperatures above 195 K, micron-size crystallites start to form within the amorphous film, causing a large amount of light scattering while the film sublimates. It appears that, for molecules such as aniline with stronger intermolecular interactions, more enthalpy is released, upon adsorption to the local surrounding molecules, causing them to reorient into crystalline form. The low deposition temperature, on the other hand, prevents diffusion for further crystallization beyond nanocrystallites. The refractive index of the amorphous aniline solid can be determined as 1.68 +/- 0.03.

Journal Article↗