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Increased Porosity (increased + porosity)
Selected AbstractsPropagation of a shear band in sandstoneINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2007J. J. Riedel Abstract Closed-loop, servo-controlled experiments were conducted to investigate the development of a shear band in Berea sandstone at various confining pressures. The tests were performed with the University of Minnesota Plane-Strain Apparatus, which was designed to allow the shear band to develop in an unrestricted manner. Measured load and displacements provided estimates of the stress and deformation states whereby dilatancy and friction were evaluated prior to localization. Experiments were stopped at various stages of shear-band development within the strain-softening regime. The specimens displayed a progression of deformation from inception, where the shear band was characterized by a high density of intragranular microcracks and crushed grains, to the tip where the intragranular microcracks were significantly less dense and separated by intact grains. Decreased slip deformation towards the tip of the shear band indicated that localization developed and propagated in plane. Thin-section microscopy showed porosity increase within the shear band was 3,4 grain diameters wide. Increased porosity did not extend beyond the tip of the shear band. A cohesive zone model of shear fracture, used to examine the stress field near the tip, showed similarities to principal compressive stress orientations interpreted from intragranular microcracks. Thus, propagation of the shear band could be associated with in-plane mode II fracture. Copyright © 2006 John Wiley & Sons, Ltd. [source] Lyophilization to improve drug delivery for chitosan-calcium phosphate bone scaffold construct: A preliminary investigationJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2009Benjamin T. Reves Abstract Lyophilization was evaluated in chitosan-calcium phosphate microspheres and scaffolds to improve drug delivery of growth factors and antibiotics for orthopedic applications. The dual delivery of an antibiotic and a growth factor from a composite scaffold would be beneficial for treatment of complex fracture sites, such as comminuted fractures and segmental bone defects. The aim of this investigation was to increase the loading capacity of the composite by taking advantage of the increased porosity, due to lyophilization, and to produce an extended elution profile using a secondary chitosan-bead coating. The physiochemical properties of the composite were investigated, and loading and elution studies were performed with alkaline phosphatase (ALP), bone morphogenetic protein-2 (BMP-2), and amikacin. Lyophilization was found to increase the surface area of scaffolds by over 400% and the porosity of scaffolds by 50%. Using ALP as a model protein, the loading capacity was increased by lyophilization from 4.3 ± 2.5 to 24.6 ± 3.6 ,g ALP/mg microspheres, and the elution profile was extended by a supplemental chitosan coating. The loading capacity of BMP-2 for composite microspheres was increased from 74.4 ± 3.7 to 102.1 ± 8.0 ,g BMP-2/g microspheres with lyophilization compared with nonlyophilized microspheres. The elution profiles of BMP-2 and the antibiotic amikacin were not extended with the supplemental coating. Additional investigations are planned to improve these elution characteristics for growth factors and antibiotics. © 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009 [source] Intermittently Administered Human Parathyroid Hormone(1,34) Treatment Increases Intracortical Bone Turnover and Porosity Without Reducing Bone Strength in the Humerus of Ovariectomized Cynomolgus MonkeysJOURNAL OF BONE AND MINERAL RESEARCH, Issue 1 2001David B. Burr Abstract Cortical porosity in patients with hyperparathyroidism has raised the concern that intermittent parathyroid hormone (PTH) given to treat osteoporotic patients may weaken cortical bone by increasing its porosity. We hypothesized that treatment of ovariectomized (OVX) cynomolgus monkeys for up to 18 months with recombinant human PTH(1,34) [hPTH(1,34)] LY333334 would significantly increase porosity in the midshaft of the humerus but would not have a significant effect on the strength or stiffness of the humerus. We also hypothesized that withdrawal of PTH for 6 months after a 12-month treatment period would return porosity to control OVX values. OVX female cynomolgus monkeys were given once daily subcutaneous (sc) injections of recombinant hPTH(1,34) LY333334 at 1.0 ,g/kg (PTH1), 5.0 ,g/kg (PTH5), or 0.1 ml/kg per day of phosphate-buffered saline (OVX). Sham OVX animals (sham) were also given vehicle. After 12 months, PTH treatment was withdrawn from half of the monkeys in each treatment group (PTH1-W and PTH5-W), and they were treated for the remaining 6 months with vehicle. Double calcein labels were given before death at 18 months. After death, static and dynamic histomorphometric measurements were made intracortically and on periosteal and endocortical surfaces of sections from the middiaphysis of the left humerus. Bone mechanical properties were measured in the right humeral middiaphysis. PTH dose dependently increased intracortical porosity. However, the increased porosity did not have a significant detrimental effect on the mechanical properties of the bone. Most porosity was concentrated near the endocortical surface where its mechanical effect is small. In PTH5 monkeys, cortical area (Ct.Ar) and cortical thickness (Ct.Th) increased because of a significantly increased endocortical mineralizing surface. After withdrawal of treatment, porosity in PTH1-W animals declined to sham values, but porosity in PTH5-W animals remained significantly elevated compared with OVX and sham. We conclude that intermittently administered PTH(1,34) increases intracortical porosity in a dose-dependent manner but does not reduce the strength or stiffness of cortical bone. [source] Combined effects of wetting, drying, and microcrystalline cellulose type on the mechanical strength and disintegration of pelletsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2009Maria Balaxi Abstract Effects of wetting and drying conditions on micromeritic, mechanical and disintegration properties of microcrystalline cellulose (MCC) pellets were evaluated. Extrusion/spheronization and three drying methods (fluidized bed, microwaves, and freeze drying) were applied using two wetting liquids (water or water-isopropanol 60:40 w/w) and three MCC types: (standard, silicified, and modified). Additionally, the effects of drying method were compared on highly porous pellets prepared by the incorporation and extraction of pore former (NaCl). It was found that the drying method has the greatest effect on the pellet size and porosity followed by the wetting liquid. The modification of MCC resulted in reduced water retention ability, implying hornification, increased porosity, reduced resistance to deformation and tensile strength of pellets. The disintegration time also decreased markedly due to the modification but only in the low porosity range <37%. Silicification increased greatly the disintegration time of the low porosity pellets (<14%). Combination of water-isopropanol, freeze drying and modified MCC gave the greatest increase in pellet size and porosity. The increase in pellet porosity caused exponential reduction in the resistance to deformation, tensile strength and disintegration time, as expected. Compared to fluidized bed, the freeze drying resulted in 20,30% higher porosity for pellets prepared without pore former and 6% for those with pore former, indicating the possibility of preparing highly porous pellets by employing freeze drying. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:676,689, 2009 [source] In vitro transdermal iontophoretic delivery of leuprolide,mechanisms under constant voltage applicationJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 1 2003Charu Kochhar Abstract The transdermal iontophoretic delivery of Leuprolide, a nonapeptide LHRH agonist was studied with the aim of understanding the mechanisms of iontophoresis. Permeation studies were carried out at pH 4.5 and 7.2, at which the average ionic valence of the drug molecule was roughly 2 and 1, respectively. Heat-separated human epidermal membrane was subjected to constant voltage within the range of 250 to 1000 mV during the iontophoretic phase. Iontophoretic enhancement at pH 7.2 was greated than at 4.5. A model for iontophoretic enhancement was developed that takes into consideration the membrane alterations caused by iontophoresis depicted as increased porosity and the permeation through lipid pathways of the stratum corneum. Model-based evaluation yielded that first, the porosity increased with the applied voltage to as much as three times the original at 1000 mV. Second, the lipid pathways contributed approx. 20% to the total permeation during the passive phase. Third, the electro-osmotic flow contributed significantly to the enhancement and its direction was from anode to cathode at pH 7.2 and the opposite at pH 4.5. The magnitude of the electro-osmotic flow was at pH 4.5 somewhat lower than at pH 7.2. Addition of a negatively charged water soluble peptide, Acetyl leucine leucinolyl phosphate as an adjuvant led to twofold increase in the enhancement factor at pH 4.5 and a decrease in the magnitude of the electro-osmotic flow from cathode to anode. Repeated iontophoretic applications of 250 mV on the same skin specimen resulted in same enhancement every time and did not cause any barrier alterations when applied for 1 h every 24 h, which was not the case if the duration between the two iontophoretic applications was only 3 h. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 92:84,96, 2003 [source] Paleomagnetism and petrophysics of the Jänisjärvi impact structure, Russian KareliaMETEORITICS & PLANETARY SCIENCE, Issue 12 2006J. Salminen The impactites (tagamites, suevites, and lithic breccias) are characterized by increased porosity and magnetization, which is in agreement with observations performed at other impact structures. Thermomagnetic, hysteresis, and scanning electron microscope (SEM) analysis document the presence of primary multidomain titanomagnetite with additional secondary titanomaghemite and ilmenohematite. The characteristic impact-related remanent magnetization (ChRM) direction (D = 101.5°, I = 73.1°, ,95 = 6.2°) yields a pole (Lat. = 45.0°N, Long. = 76.9°E, dp = 9.9°, dm = 11.0°). Additionally, the same component is observed as an overprint on some rocks located in the vicinity of the structure, which provides proofs of its primary origin. An attempt was made to determine the ancient geomagnetic field intensity. Seven reliable results were obtained, yielding an ancient intensity of 68.7 ± 7.6 ,T (corresponding to VDM of 10.3 ± 1.1 times 1022 Am2). The intensity, however, appears to be biased toward high values mainly because of the concave shape of the Arai diagrams. The new paleomagnetic data and published isotopic ages for the structure are in disagreement. According to well-defined paleomagnetic data, two possible ages for magnetization of Jänisjärvi rocks exist: 1) Late Sveconorwegian age (900,850 Myr) or 2) Late Cambrian age (,500 Myr). However, published isotopic ages are 718 ± 5 Myr (K-Ar) and 698 ± 22 Myr (39Ar- 40Ar), but such isotopic dating methods are often ambiguous for the impactites. [source] Ag,Ag0.08V2O5·nH2O composite films as host materials for Li+ intercalationPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2005Ying Wang Abstract We have prepared Ag,Ag0.08V2O5·nH2O composite films by dispersing Ag nanowires into V2O5·nH2O sol and have investigated electrochemical properties of the films for Li+ -ion intercalation applications. With the molar ratio of Ag nanowires to V2O5·nH2O as 0.1, such prepared films are composed of metallic Ag nanowires embedded in the matrix of Ag0.08V2O5·nH2O, due to partial Ag reacted with V2O5·nH2O. At a current density of 85 mA/g, such Ag,Ag0.08V2O5·nH2O film can intercalate about two equivalents of Li ions and delivers twice the capacity of the V2O5·nH2O xerogel film. Such improved electrochemical performance is ascribed to the changes in the microstructure and crystallinity of the Ag,Ag0.08V2O5·nH2O films including (i) further amorphization of V2O5·nH2O, (ii) increased porosity, and (iii) enhancement of electrical conductivity. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||