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At least 145 records · Page 8Linked to original sources
PubMed2002

Effect of sodium content on the crystallization behavior of fluoramphibole glass-ceramics.

The purpose of this study was to evaluate the effect of sodium content on the crystallization behavior of glass-ceramics in the system SiO(2)-MgO-CaO-Na(2)O-K(2)O-F. Five glass compositions were prepared with increasing sodium content. The compositions were melted at 1400 degrees C for 2 h and cast into 60 x 12-mm ingots. Differential thermal analyses were performed on the glasses up to 1400 degrees C. Discs (1.5 x 12 mm) were cut from the ingots, nucleated in the temperature range 600-650 degrees C for 1-2 h, and crystallized in the temperature range 900-1000 degrees C for 0.5-4 h. The crystalline phases were analyzed by x-ray diffraction. The microstructure was investigated by scanning electron microscopy. Differential thermal analyses showed that the crystallization exotherm occurred in the temperature range 600-750 degrees C. There was a linear relationship between the amount of sodium and the transformation temperatures. X-ray diffraction revealed the presence of mica and diopside as major crystalline phases in the sodium-free composition. Mica, diopside, and fluorrichterite were present in all other glass-ceramics. The microstructure of the sodium-free glass-ceramic was characterized by the presence of hexagonal mica crystals and prismatic diopside crystals. All other compositions exhibited needle-shaped fluorrichterite crystals (2-5 microm in length) in addition to mica and diopside crystals.

Aluminum Silicates↗
PubMed1980

Piezoelectric ceramic implants: a feasibility study.

A piezoelectric ceramic has been investigated as a direct substitute for hard tissues. Barium titanate (BaTiOz) power was slipcast and fired at 1430 degrees C for 2 hr, then made piezoelectric by polarizing. After 16 and 86 days of implantation in the cortex of the femoral midshafts, the femora with test specimens were sectioned into about 4-cm lengths. Their voltage outputs were measured under cyclic load at 1 Hz. The present results show that the voltage gradient at the implant surface is 0.15 mV/mm for the 16-day implantation with a 445-N (100-lbs.) load. This in turn can give rise to about 0.01 microA current flow in the adjacent area of the 16-day implant. The 86-day implant showed an order of magnitude higher voltage output compared to the 16-day implant with the same magnitude of loads. This is probably due to the "load-transfer" efficiency through the implants, since the voltage output is directly proportional to the actual load transferred to the implant. The more bone implant interface matures, the better the load transfer occurs through the implant, resulting in higher voltage output.

Animals↗
PubMed1981

Piezoelectric ceramic implants: in vivo results.

The suitability of barium titanate (BaTiO3) ceramic for direct substitution of hard tissues was evaluated using both electrically stimulated (piezoelectric) and inactive (nonpolarized) test implants. Textured cylindrical specimens, half of them made piezoelectric by polarization in a high electric field, were implanted into the cortex of the midshaft region of the femora of dogs for various periods of time. Interfacial healing and bio-compatibility of the implant material were studied using mechanical, microradiographical, and histological techniques. Our results indicate that barium titanate ceramic shows a very high degree of biocompatibility as evidenced by the absence of inflammatory or foreign body reactions at the implant-tissue interface. Furthermore, the material and its surface porosity allowed a high degree of bone ingrowth as evidenced by microradiography and a high degree of interfacial tensile strength. No difference was found between the piezoelectric and the electrically neutral implant-tissue interfaces. Possible reasons for this are discussed. The excellent mechanical properties of barium titanate, its superior biocompatibility, and the ability of bone to form a strong mechanical interfacial bond with it, makes this material a new candidate for further tests for hard tissue replacement.

Animals↗
PubMed2006

In vitro biocompatibility of a novel membrane of the composite poly(vinylidene-trifluoroethylene)/barium titanate.

This study was aimed at investigating the in vitro biocompatibility of a novel membrane of the composite poly(vinylidene-trifluoroethylene)/barium titanate (P(VDF-TrFE)/BT). Osteoblastic cells were obtained from human alveolar bone fragments and cultured under standard osteogenic condition until subconfluence. First passaged cells were cultured on P(VDF-TrFE)/BT and expanded polytetrafluoroethylene (e-PTFE--control) membranes in 24-well plates. Cell adhesion and spreading were evaluated at 30 min, and 4 and 24 h. For proliferation assay, cells were cultured for 1, 7, and 10 days. Cell viability was detected by trypan blue at 7 and 10 days. Total protein content and alkaline phosphatase (ALP) activity were measured at 7, 14, and 21 days. Cultures were stained with Alizarin red at 21 days, for detection of mineralized matrix. Data were compared by ANOVA and Student t test. Cell attachment (p = 0.001), cell number (p = 0.001), and ALP activity (p = 0.0001) were greater on P(VDF-TrFE)/BT. Additionally, doubling time was greater on P(VDF-TrFE)/BT (p = 0.03), indicating a decreased proliferation rate. Bone-like nodule formation took place only on P(VDF-TrFE)/BT. The present results showed that both membranes are biocompatible. However, P(VDF-TrFE)/BT presented a better in vitro biocompatibility and allowed bone-like nodule formation. Therefore, P(VDF-TrFE)/BT could be an alternative membrane to be used in guided tissue regeneration.

Alkaline Phosphatase↗
PubMed2004

Injectable acrylic bone cements for vertebroplasty with improved properties.

Currently commercially available acrylic bone cements lack adequate radiopacity and viscosity when they are used in percutaneous vertebroplasty (PVP). In this work improved formulations of radiopaque and injectable poly(methyl methacrylate) bone cements were prepared with different amounts (10-50 wt.%) of BaTiO3 or SrTiO3 particles as the radiopaque agent. Two sets of cements were prepared by using untreated or silanated radiopaque particles, respectively. The influence of the content and nature of the radiopaque agent as well as its silanation with 3-(trimethoxysilyl) propyl methacrylate (gamma-MPS), on the curing parameters, residual monomer content, radiopacity, mechanical properties, and injectability of the resulting materials, was examined. Doughing and setting times, maximum temperature, and compressive strength of all formulations fulfilled the requirements of standard specifications, with values of peak temperature in the range 57-72 degrees C and those of compressive strength between 114 and 135 MPa. Formulations containing at least 20 wt.% BaTiO3 or SrTiO3 had radiopacities equal to or greater than that corresponding to 2 mm of Al as required for surgical plastics. Injectability of any of the formulations provided 75-80 wt.% of the total mass manually injected through a conventional biopsy needle 4 min after mixing. Silanation of the BaTiO3 or SrTiO3 particles led to formulations with improved mechanical properties and injectability compared to those obtained with the untreated fillers.

Barium Compounds↗
PubMed2007

The effect of nanofiller on the opacity of experimental composites.

The purpose of this study was to evaluate the effect of the nanofiller in experimental composites on opacity (contrast ratio). Thirteen experimental composites were prepared with three different sizes of fillers: barium glass minifiller (1 microm; 69-76 wt %), silica microfiller (0.04 microm; 0-6 wt %), and silica nanofiller (7 nm; 0-7 wt %). After disk-type specimens were irradiated with a halogen light curing unit at 500 mW/cm(2) for 30 s, the specimens were aged for 6 h at room conditions and were stored in deionized water for 1, 7, 14, 21, 28, 56, and 84 days. The contrast ratios of the specimens were measured as a function of aging period using a spectrophotometer. The distribution morphology of the filler particles in the resin matrix was also examined using energy-filtering transmission electron microscopy. The experimental composites that contained more than 3% nanofiller had significantly lower contrast ratios (p < 0.05). The composites that contained 6 wt % nanofiller had contrast ratios 34-65% lower than the composite that did not contain nanofiller. The values of the contrast ratio from the composites that excluded microfiller were lower than the values from the composites that included microfiller. From the comparison with the 3 different sizes of filler, the contrast ratio of the composite that contained 70 wt % minifiller and 6 wt % microfiller was the highest, the contrast ratio of the composite that contained only 76 wt % minifiller was the median value, and the contrast ratio of the composite that contained 70 wt % minifiller and 6 wt % nanofiller was the lowest. When the microfiller content was decreased from 6 wt % to 0 wt %, the contrast ratio decreased 6-9%. Energy-filtering transmission electron microscopy images indicated that the contrast ratio of experimental composites is related to the distribution morphology of the filler particles in the resin matrix.

Acrylic Resins↗
PubMed1991

A fast image simulation technique for high resolution electron microscopy with multicomponent atomic species.

A new method has been developed for simulating high resolution electron microscope images of weak phase objects via a digital television frame store system and fast Fourier transforms of a graphical representation of structures containing several atomic species. Here masks are constructed which consist of circular disk regions whose areas are proportional to the scattering power of the different atom types. These masks represent the object transmission function. The method extends the previous work on image computations of monatomic species objects using small point-like model representations of atom positions. Several examples will be given to verify the relative scattering power from masks corresponding to different atomic species such as Y, Ba, Cu, and O, as well as the limitations of this method for representing objects. Image simulations, which are in agreement with experiments, will also be presented for superconducting oxide materials of the form YBa2Cu3O7 using the circular disk method.

Barium↗
PubMed1995

Significant discrepancies between van't Hoff and calorimetric enthalpies. II.

Isothermal calorimetric titration of 18-crown-6 ether with BaCl2 in pure aqueous solution over the temperature range 7-40 degrees C gives precise binding constants and enthalpy changes. Nonlinear least-squares fitting of the binding constants to the integrated van't Hoff equation, including a temperature-independent change in heat capacity, leads to van't Hoff enthalpies that differ significantly from the observed calorimetric enthalpies. This perplexing discrepancy appears at present to be very widely occurring.

Barium Compounds↗
PubMed1994

Palladium(II), magnesium(II), and barium(II) nitrate combinations for matrix modification in electrothermal atomic absorption measurement of total selenium in human urine.

Electrothermal atomic absorption spectrometry with a temperature-stabilizing platform and palladium(II) nitrate-magnesium nitrate-barium nitrate matrix modifier combination was used to measure total selenium concentrations in 0.5-ml samples of human urine. The method was validated by analysis of desiccated, standard urine samples (SRM 2670) from NIST. The peak height response was linear from 0 to 150 micrograms Se/liter urine with a sensitivity of 0.001 absorbance unit/micrograms Se/liter and a detection limit of 6 micrograms Se/liter (P = 0.05) for a single measurement. Total urinary selenium concentrations and urine volumes of 24-h samples from 28 healthy adult subjects on self-selected diets and living in San Angelo, Texas were measured. Daily total urinary excretions of 16 male and 12 female subjects (mean +/- SD) were 28 +/- 26 and 34 +/- 25 micrograms Se/day, respectively. A single subject taking 300 micrograms Se/day in the form of aqueous SeO2 as a dietary supplement excreted 232 micrograms Se/day. The unsupplemented subjects' daily selenium excretions correspond to a mean dietary intake of approximately 60 micrograms/day.

Adult↗
PubMed1994

IP3-activated calcium-permeable channels in the inside-out patches of cultured cerebellar Purkinje cells.

Inositol-1,4,5-trisphosphate (IP3)-activated calcium-permeable channels were recorded from inside-out patches of cultured cerebellar Purkinje cells. When 2-5 microM of IP3 was applied to the internal surface of the inside-out patches, inward Ba2+ currents were activated within 10 sec following the application in 11 out of 24 patches. In the presence of heparin (100 micrograms/ml), activation of Ba2+ currents by IP3 was inhibited. Unitary currents with different amplitudes and kinetics were observed; small and large unitary currents, and rapid fluctuations with various amplitudes. The small unitary currents (single channel conductance; 5.6 pS) were most frequent. Addition of inositol 1,3,4-trisphosphate (2-5 microM) slightly activated Ba2+ currents in 2 out of 10 patches, but the amount of the increment was much smaller than that produced by IP3. These results suggest a possibility that IP3 directly activates Ca(2+)-permeable channels in the plasma membrane of cerebellar Purkinje cells.

Animals↗
PubMed1994

Mechanosensitive single channel calcium currents in rat mesangial cells.

Mechanical stimulation of mesangial cells enhances expression of early response protooncogenes in an extracellular Ca(2+)-dependent manner. This has lead investigators to postulate that a mechanosensitive Ca2+ channel may exist in these cells. At the present time, however, very little is known about single channel Ca2+ currents in mesangial cells. To examine this question, cell-attached patches of rat mesangial cells in early passages were studied with 100 mM BaCl2 patch-clamp pipets. Our studies identified a 21 pS, Co(2+)-sensitive channel that responded with an increase in open probability to mechanical stretch, applied through the patch pipet. The channel was also activated by a reduction in extracellular osmolarity. In both instances, channel responses underwent spontaneous adaptation despite continuous stimulation. This Ca2+ channel exhibited electrophysiological and kinetic properties that distinguished it from other cation-selective channels previously reported by us and other investigators on rat mesangial cell membranes.

Animals↗
PubMed1999

Sorting of a constitutive secretory protein to the regulated secretory pathway of exocrine cells.

Exocrine cells secrete granule proteins by regulated or constitutive-like secretory pathways. It is thought that all secretory proteins can enter immature secretory granules in exocrine cells. To test this hypothesis, we expressed the constitutive secretory protein secreted alkaline phosphatase (SEAP) in the exocrine cell line AR42J and compared its secretion to that of amylase, an endogenous regulated secretory protein. Secretion of SEAP and amylase were stimulated about 1.5-fold by substance P and 2-fold by barium chloride. In dexamethasone-treated cells, SEAP and amylase secretion were stimulated about 1.8-fold by substance P, 5-fold by barium chloride, and 4-fold by cholecystokinin-8. Cycloheximide reduced basal secretion of SEAP and amylase by 50%, increasing cholecystokinin-stimulated secretion to about 10-fold. Sodium butyrate induced expression of SEAP 2-fold but had no effect on stimulated secretion. These results suggest that SEAP is stored in secretory granules in AR42J cells.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1999

Intracellular calcium puffs in osteoclasts.

We studied intracellular calcium ([Ca(2+)](i)) in acid-secreting bone-attached osteoclasts, which produce a high-calcium acidic extracellular compartment. Acid secretion and [Ca(2+)](i) were followed using H(+)-restricted dyes and fura-2 or fluo-3. Whole cell calcium of acid-secreting osteoclasts was approximately 100 nM, similar to cells on inert substrate that do not secrete acid. However, measurements in restricted areas of the cell showed [Ca(2+)](i) transients to 500-1000 nM consistent with calcium puffs, transient (millisecond) localized calcium elevations reported in other cells. Spot measurements at 50-ms intervals indicated that puffs were typically less than 400 ms. Transients did not propagate in waves across the cell in scanning confocal measurements. Calcium puffs occurred mainly over regions of acid secretion as determined using lysotracker red DND99 and occurred at irregular periods averaging 5-15 s in acid secreting cells, but were rare in lysotracker-negative nonsecretory cells. The calmodulin antagonist trifluoperazine, cell-surface calcium transport inhibitors lanthanum or barium, and the endoplasmic reticulum ATPase inhibitor thapsigargin had variable acute effects on the mean [Ca(2+)](i) and puff frequency. However, none of these agents prevented calcium puff activity, suggesting that the mechanism producing the puffs is independent of these processes. We conclude that [Ca(2+)](i) transients in osteoclasts are increased in acid-secreting osteoclasts, and that the puffs occur mainly near the acid-transporting membrane. Cell membrane acid transport requires calcium, suggesting that calcium puffs function to maintain acid secretion. However, membrane H(+)-ATPase activity was insensitive to calcium in the 100 nM-1 microM range. Thus, any effects of calcium puffs on osteoclastic acid transport must be indirect.

Adenosine Triphosphate↗
PubMed1997

Acetylcholine modulates I(f) and IK(ACh) via different pathways in rabbit sino-atrial node cells.

The aim of the present study was to examine whether a direct G-protein pathway was necessary to explain the depression of the cardiac pacemaker current (I(f)) by acetylcholine (ACh). Pacemaker current and spontaneous fluctuations of muscarinic K+ current (IK(ACh)) were simultaneously measured in sino-atrial (SA) node cells isolated from rabbit hearts, using cell-attached and outside-out macro-patches. The effects of 1 microM ACh, added to the bathing solution, were compared on I(f) and on IK(ACh), known to be activated via a direct G-protein mechanism. In a cell-attached configuration where cytoplasmic substrates were present, ACh depressed I(f) by a negatively directed shift of the open probability curve of 7.6 +/- 0.3 mV. ACh never induced modifications in spontaneous openings of muscarinic K+ channels. These results indicate that ACh added to the external solution is unable to modulate IK(ACh) recorded in the membrane-delimited mode, via a G-protein pathway. The ACh depressing effect on I(f) is related to changes in second messenger activity. In outside-out conditions, with guanosine triphosphate (GTP) added to the pipette solution. ACh increased the variance of IK(ACh) fluctuations from 1.66 +/- 0.50 pA2 to 6.60 +/- 2.05 pA2 (at -120 mV). indicating direct G-protein action. ACh had no effect on I(f). It is concluded that in SA node cells, the regulation of I(f) by muscarinic receptors does not involve a direct G-protein pathway. ACh depresses I(f) by a mechanism that probably implicates reduction of intracellular cAMP production.

Acetylcholine↗
PubMed1998

Action potential prolongation and potassium currents in left-ventricular myocytes isolated from hypertrophied rabbit hearts.

We have studied the action potential characteristics and potassium currents in single left ventricular myocytes isolated from control and hypertrophied rabbit hearts. Left-ventricular hypertrophy (LVH) was induced following perinephritis-induced hypertension. Control animals underwent a sham operation. Animals were killed at 10 weeks post-operation. Left-ventricular myocytes were isolated by an enzyme dissociation technique. Action potential duration (APD) at 50 and 90% repolarisation was prolonged in myocytes obtained from hypertrophied compared to control hearts over the range of stimulation frequencies (0.1-1.5 Hz). This prolongation in APD was more pronounced in epicardial compared to endocardial myocytes. Steady-state ionic current, measured at the end of voltage clamp steps of 3-s duration, stepping at intervals of 10 mV, from a holding potential of -40 mV, was similar in control and hypertrophied myocytes. However, when normalised for capacitative cell surface area, steady-state current was significantly smaller in hypertrophied myocytes over the voltage range -40 to -60 mV and at potentials greater than +10 mV. Inward rectifier potassium current (IKl), identified as the barium chloride (0.1 mM)-sensitive current, contributed to the steady state current at negative potentials. Normalised IKl was significantly smaller in hypertrophied compared to control myocytes at potentials negative to -60 mV. Peak transient outward potassium current (Ito) density was reduced in hypertrophied compared to control myocytes at 0 and +10 mV, from a holding potential -80 mV (12.9 +/- 2.3 v 24.9 +/- 3.9 microA cm2, at +10 mV, P < 0.05). Steady-state inactivation of Ito was similar in control and hypertrophied myocytes. In conclusion, LVH induced by perinephritis hypertension in the rabbit is associated with a prolongation in APD. Reductions in IKl, sustained outward current and Ito may contribute to the prolongation in APD.

Action Potentials↗