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At least 1,153 records · Page 64Linked to original sources
PubMed2001

Primary tissue failure of bioprostheses: new evidence from in vitro tests.

BACKGROUND: Primary tissue failure, which is mainly caused by calcification, is still the limiting factor in the long-term outcome of heart valve bioprostheses. Even though the precise nature of this process is not fully understood, in vitro tests have been developed to reproduce and predict calcification for individual bioprostheses. METHODS: In vitro calcification testing was performed by using an accelerated pulsatile valve tester which was adapted for testing stented as well as stentless bioprostheses with physiological fluid dynamics. A total of 84 bioprostheses (porcine, pericardial and stentless porcine of different manufacturers) were cyclically loaded at a test rate of 300/min at 37 degrees C within a rapid calcification fluid with CaxP = 130(mg/dl)2 at pH 7.4. Calcification was assessed by microradiography after 12 x 10(6) cycles. In a previous step, holographic interferometry was performed to identify irregularities of valve leaflets in order to predict later calcification. Selected specimens of calcified bioprostheses underwent histology, transmission (TEM) and scanning (SEM) electron microscopy. Tissue mineralization was investigated by coupling SEM, electron microprobe analysis (EMPA) and X-ray powder diffraction (XRPD) methods. RESULTS: For all tested bioprostheses, a significant calcification was achieved within 4 to 6 weeks of ongoing testing, and the degree of calcification increased with time. A significant correlation between calcification and leaflet irregularities (detected by holographic interferometry) was found (r = 0.80, p = 0.001). Calcification varied between individual bioprostheses, and significant differences were detected for different groups (calculated as percentage of total leaflet area, mean +/- SD): porcine stented (37.3 +/- 12.0%), bovine stented (23.0 +/- 8.9%), porcine stentless (16.2 +/- 7.6%). Histological and ultrastructural investigation showed intrinsic calcification involving both the spongiosa and fibrosa with collagen fibrils, interfibrillar spaces and cells as early sites of calcification. There was clear evidence of apatite crystallization, and observations made with in vitro calcification were quite similar to those occurring with in vivo implanted bioprostheses. CONCLUSION: In vitro tests can reproduce intrinsic calcification of bioprostheses even in the absence of viable biologic host factors. Moreover, degree and sites of calcification have become predictable. This enables the development and evaluation of bioprostheses with reduction of animal experiments. From our results obtained with a broad range of available bioprostheses, stented bovine and stentless porcine valves seem to be superior to conventional stented porcine bioprostheses with regard to leaflet calcification.

Animals↗
PubMed2006

Crystallization on heating and complex phase behavior of alpha-cyclodextrin solutions.

Solutions composed of alpha-cyclodextrin (alpha-CD), water, and various methylpyridines, in particular, 4-methylpyridine (4MP), undergo reversible liquid-solid transitions upon heating, the crystalline solid phases undergoing further phase transformations at higher temperatures. This unusual behavior has been characterized by an ensemble of measurements, including solubility, differential scanning calorimetry, quasielastic neutron scattering, as well as x-ray powder diffraction. For the alpha-CD/4MP system five crystalline phases have been identified. The unit cell parameters and corresponding changes with temperature indicate a scenario for the crystallization process. A simple model is proposed that mimics the observed disorder-order transition.

Journal Article↗
PubMed1969

Crystallization of DNA from dilute solution.

Hexagonal platelet crystals about 1 mu across and about 150 A thick have been precipitated by the addition of ethanol to solutions of ultrasonically degraded, salmon sperm DNA in sodium cacodylate buffer. X-ray powder diffraction patterns from concentrated slurries of these crystals in mother liquor show intense rings at 23.9 A and at about 3.4 A; the former arise from lateral packing and the latter from an axial periodicity of the DNA helix. Evidence is presented to indicate that native DNA helices crystallize by chain folding and that no irreversible denaturation results from the crystallization process.

Animals↗
PubMed2000

Physical properties of the transmembrane signal molecule, sn-1-stearoyl 2-arachidonoylglycerol. Acyl chain segregation and its biochemical implications.

sn-1,2-diacylglycerol (DAG), a key intermediate in lipid metabolism, activates protein kinase C and is a fusogen. Phosphoinositides, the main sources of DAG in cell signaling, contain mostly stearoyl and arachidonoyl in the sn-1 and -2 positions, respectively. The polymorphic behavior of sn-1-stearoyl-2-arachidonoylglycerol (SAG) was studied by differential scanning calorimetry, x-ray powder diffraction, and solid state magic angle spinning (MAS) (13)C NMR. Three alpha phases were found in the dry state. X-ray diffraction indicated that the acyl chains packed in a hexagonal array in the alpha phase, and the two sub-alpha phases packed with pseudo-hexagonal symmetry. In the narrow angle range strong diffractions of approximately 31 and approximately 62 A were present. High power proton-decoupled MAS (13)C NMR of isotropic SAG gave 16 distinct resonances of the 20 arachidonoyl carbons and 5 distinct resonances of the 18 stearoyl carbons. Upon cooling, all resonances of stearoyl weakened and vanished in the sub-alpha(2) phase, whereas arachidonoyl carbons from 8/9 to 20 gave distinct resonances in the frozen phases. Remarkably, the omega-carbon of the two acyl chains had different chemical shifts in alpha, sub-alpha(1), and sub-alpha(2) phases. Large differences in spin lattice relaxation of the stearoyl and arachidonoyl methene and methyl groups were demonstrated by contact time (cross-polarization) MAS (13)C NMR experiments in the solid phases alpha, sub-alpha(1), and sub-alpha(2). This shows that stearoyl and arachidonoyl in SAG have different environments in the solid states (alpha, sub-alpha(1), and sub-alpha(2) phases) and may segregate during cooling. The NMR and long spacing x-ray diffraction results suggest that SAG does not pack in a conventional double layer with the two acyls in a hairpin fashion. Our findings thus provide a physicochemical basis for DAG hexagonal phase domain separation within membrane bilayers.

Calorimetry, Differential Scanning↗
PubMed2004

Fluconazole encapsulation in PLGA microspheres by spray-drying.

Fluconazole-loaded PLGA microspheres were prepared by the spray-drying process. The influence of some process parameters on the physical characteristics of the microspheres was evaluated. Neither type nor polymer concentration influenced significantly the mean diameter of the microspheres, their size distribution and encapsulation efficiency of the drug. However, the drug loading greatly affected their size and the physical state in which fluconazole can exist in the matrix of the carriers, and, thus, affected the release rate of the drug. Results obtained by differential thermal analysis and X-ray powder diffraction revealed that at low nominal drug loading, fluconazole was incorporated in an amorphous state or in a molecular dispersion in the matrix of the microspheres and at high nominal drug loading part of the drug was in a crystalline form. Release profiles of fluconazole from the microspheres displayed a biphasic shape. The duration and extent of each phase were affected mainly by polymer nature, drug loading and physical state in which fluconazole existed in the polymeric matrix.

Antifungal Agents↗
PubMed2005

Characterization and dissolution properties of ketoprofen in binary and ternary solid dispersions with polyethylene glycol and surfactants.

The effect of incorporation of an anionic [sodium dodecyl sulfate (SDS) or dioctylsulfosuccinate (DSS)] or nonionic [Tween 60 (TW60)] surfactant on the properties of ketoprofen solid dispersions in polyethylene glycol 15000 (PEG) has been investigated. Physicochemical and morphological properties of the various solid systems were determined by differential scanning calorimetry, hot stage microscopy, X-ray powder diffraction analysis, and scanning electron microscopy. The results from dissolution studies, performed according to the USP 24 basket method, indicated that all ternary dispersed systems were significantly (p < 0.001) more efficacious than the corresponding binary ones, by virtue of the additive wetting and solubilizing effect due to the presence of the surfactant. The relative effectiveness of the incorporated surfactant was in the same order as found in phase-solubility studies (i.e., SDS > DSS > TW60). With regard to the solid dispersion preparation method, coevaporated products always gave better results than the corresponding cofused ones; however, this effect was statistically significant (p < 0.001) only in the initial phase of the dissolution process. The most effective solid dispersion was the 10-80-10 w/w drug-PEG-SDS ternary coevaporate, which allowed dissolution of 50% drug after only 6 min (in comparison with > 120 min for drug alone and 17 min for the binary coevaporate) and dissolution of about 100% drug after 30 min (in comparison with > 120 min for the binary coevaporate).

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2006

Formulation of a fast-dissolving ketoprofen tablet using freeze-drying in blisters technique.

The aim of this work was to develop a ketoprofen tablet which dissolve-rapidly in the mouth, therefore, needing not be swallowed. The solubility and dissolution rate of poorly water-soluble ketoprofen was improved by preparing a lyophilized tablet (LT) of ketoprofen using freeze-drying technique. The LT was prepared by dispersing the drug in an aqueous solution of highly water-soluble carrier materials consisting of gelatin, glycine, and sorbitol. The mixture was dosed into the pockets of blister packs and then was subjected to freezing and lyophilization. The saturation solubility and dissolution characteristics of ketoprofen from the LT were investigated and compared to the plain drug and the physical mixture (PM). Results obtained showed that the increase in solubility of ketoprofen from LT matrix, nearly three times greater than the solubility of the plain drug, was due to supersaturation generated by amorphous form of the drug. Results obtained from dissolution studies showed that LT of ketoprofen significantly improved the dissolution rate of the drug compared with the PM and the plain drug. More than 95% of ketoprofen in LT dissolved within 5 min compared to only 45% of ketoprofen plain drug dissolved during 60 min. Initial dissolution rate of ketoprofen in LT was almost tenfold higher than that of ketoprofen powder alone. Crystalline state evaluation of ketoprofen in LT was conducted through differential scanning calorimetry (DCS) and x-ray powder diffraction (XRPD) to denote eventual transformation to amorphous state during the process. Scanning electron microscopic (SEM) analysis was performed and results suggest reduction in ketoprofen particle size.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2006

Characterization of calcium alginate beads containing structurally similar drugs.

The aim of this study was to investigate the characteristics of alginate beads prepared by ionotropic gelation in which structurally similar drugs were incorporated. For this purpose theophylline and theobromine were selected as model drugs. The influence of incorporated drugs on bead characteristics such as size, shape, and morphology, as well as encapsulation efficiency, was examined. It was found that theobromine as well as theophylline content in beads significantly decreased with increasing hardening time due to drug diffusion into the hardening media. In theobromine beads the drug content was extremely improved by dropping the alginate and drug solution into an acidic calcium chloride solution, while theophylline content was to some extent improved by the hardening of beads in a calcium chloride solution saturated with the drug. The most evident difference between theophylline and theobromine beads was in their shape and morphology. Theobromine beads were round, while theophylline ones had an irregular shape with an extremely wrinkled surface. The distinction in shape was highly dependent on drug content. Additionally, it was demonstrated that beads' shape was dependent on preparation conditions as well. On the basis of x-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC) analyses and scanning electron microscope (SEM) photographs it was found that the most of the drug in bead was present in an amorphous state. Therefore, it is suggested that some drug-alginate interactions could be present in beads and might be responsible for the different shape of theophylline and theobromine beads. Thus it can be concluded that the preparation of beads by ionotropic gelation cannot be generalized even though structurally similar drugs are incorporated.

Alginates↗
PubMed1990

Interaction of deoxyguanylic acid with alkaline earth metal ions. Evidence for the deoxyribose C3'-endo/anti, O4'-endo/anti and C2'-endo/anti conformational transitions.

The interaction of 2'-deoxyguanosine-5'-monophosphoric acid (H2-dGMP) with the alkaline earth metal ions has been investigated in aqueous solution at neutral pH. The solid salts of the type Mg-dGMP.5H2O Ca-dGMP.6H2O, Sr-dGMP.7H2O and Ba-dGMP.7H2O were isolated and characterized by FT-IR, proton-NMR and X-ray powder diffraction measurements. Two types of metal-nucleotide interactions have been identified: (a) the indirect metal-base and the direct metal-phosphate bindings (outer- and inner-sphere interaction), for the Mg(II) and Sr(II) ions and (b) the direct metal-base and direct metal-phosphate bindings (inner-sphere interaction), for the Ca(II) and Ba(II) ions. In aqueous solution, a dynamic equilibrium of the type base-metal-H2O. . .PO3 in equilibrium base. . .H2O-metal-PO3 is present. The deoxyribose moiety exhibits C3'-endo/anti conformation, in the Mg(II)-, Ca(II)-, Sr(II)- and Ba(II)-dGMP salts.

Biomarkers↗
PubMed1994

Reversible crystal transition of guanosine between the dihydrate and anhydrous states coupled with adsorption-desorption process.

Relative humidity induces the reversible crystal transition of guanosine between the dihydrate and the anhydrous state. The characteristics of the transition was investigated by means of X-ray powder diffraction analysis and high-resolution solid-state 13C NMR spectroscopy. Adsorption-desorption hysteresis was observed. Guanosine dihydrate (the H-state) which is crystallized from an aqueous solution rapidly loses crystal water below 10% relative humidity (rh), and is anhydrous at 0% rh (the A-state). The crystals gradually recover the H-state at approximate 20% rh. In the adsorption process between 10-20% rh, there exists one intermediate state, M, with 1.2-1.3 moles water per mole guanosine. The lattice of the M-state was determined to be orthorhombic with the cell parameters of a = 16.248(1), b = 11.603(1), and c = 13.643(2) A. The base-stacking structure is retained throughout the transition. On the other hand, conformational changes of the riboses and break of the hydrogen-bonding network between the bases would be induced in the A-state in conformity with lack of crystal water.

Adsorption↗
PubMed2004

Composition of eye cosmetics (kohls) used in Cairo.

A total of 18 kohl samples were analysed using X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM). All the samples were purchased in Cairo and eleven of them originated in Egypt. The main component of six samples was found to be galena (PbS); where four of these samples originated in Egypt and two in India. For a further ten samples the main component was found to be one of the following: amorphous carbon, calcite (CaCO(3)), cuprite (Cu(2)O), goethite (FeO(OH)), elemental silicon or talc (Mg(3)Si(4)O(10)(OH)(2)). For the last two samples the main component of each was an unknown amorphous organic compound.

Carbon↗
PubMed2002

The utilization of catalyst sorbent in scrubbing acid gases from incineration flue gas.

Catalyst sorbents based on alumina-supported CuO, CeO2, and CuO-CeO2 were applied to a dry scrubber to clean up the SO2/HCl/NO simultaneously from pilot-scale fluidized-bed incineration flue gas. In the presence of organic compounds, CO and the submicron particles SO2 and HCI removed by the fresh catalyst sorbents and NO reduced to N2 by NH3 under the catalysis of fresh and spent desulfurization/dechloridization (DeSO2/DeHCl) catalyst sorbents (copper compounds, Cu, CuO, and CuSO4) were evaluated in this paper. The fresh and spent catalyst sorbents were characterized by the Brunner-Emmett-Teller method (BET), X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), inductively coupled plasma-mass spectrometry (ICP-MS), and the elemental analyzer (EA). The study showed that the performances of CuO, CeO2, and CuO-CeO2/gamma-Al2O3 were better than that of Ca(OH)2. The removal efficiency of SO2 and HCl was 80-95% in the dry scrubber system. Under NH3/NO = 1, NO could not be reduced to N2 because it was difficult to control the ratio of air/fuel in the flue gas. For estimating the feasibility of regenerating the spent catalyst sorbents, BET and EA analyses were used. They indicated that the pore structures were nearly maintained and a small amount of carbon accumulated on their surface.

Absorption↗
PubMed1989

Occupational exposure and analysis of microcrystalline cristobalite in mullite operations.

Three analytical methods currently used for crystalline free silica determination in occupational exposure samples were evaluated for their applicability to ceramic materials containing synthetic mullite. X-ray powder diffraction is the only method that can be used with sufficient precision and potentially adequate accuracy for occupational exposure monitoring. Personal respirable dust exposure samples were collected in two foundries. The results of exposure evaluations in Plant A showed overexposure to the dust, particularly in the shakeout area. The cristobalite concentration in the respirable dust exceeded that in the original material for this particular area. This may be related to the preheating of molds to more than 1100 degrees C for the pouring of stainless steel castings, causing conversion of some of the colloidal silica binder to cristobalite, and related to high vibration fracture of the material during removal of castings from molds. In Plant B, quartz was sometimes present along with cristobalite in personal samples. Respirable dust levels exceeded the Occupational Safety and Health Administration's (OSHA) permissible exposure limit (PEL) and the National Institute for Occupational Safety and Health's (NIOSH) recommended time-weighted average (TWA) for crystalline free silica, indicating a need for better engineering controls to reduce dust levels. The inadequacy of reference standards currently available for cristobalite analysis in these types of materials is cited. The need for more toxicological research is emphasized.

Aluminum Silicates↗
PubMedDate not supplied

Specific toxicity and crystallinity of alpha-quartz in respirable dust samples.

alpha-Quartz dust of respirable size--on inhalation--deposits in the lung, where it may remain for long duration and be a risk factor in the development of silicosis and (with increasing weight of evidence) lung cancer in humans. The risk assessment for these end points is fundamentally based on those properties of alpha-quartz that allow it to persist over time in the lung. For individual samples of respirable alpha-quartz it is likely that the specific toxicity of the alpha-quartz in the sample is related to this residence time, which, in turn, will be a function of its crystallinity because of the latter's potential influence on alpha-quartz's cytotoxicity and solubility. Current X-ray powder diffraction technology allows for the routine assessment of diffraction line broadening by measuring the full-width-at-half-maximum (FWHM) of a diffraction line. The FWHM for any accessible alpha-quartz diffraction line in a sample can then be used to directly assess Murata and Norman's Crystallinity Index for the alpha-quartz. This method greatly enhances the practicability of determining alpha-quartz crystallinity on individual respirable dust microsamples collected by personal sampling. It is likely that the Crystallinity Index will prove to be a useful measure of the specific toxicity of alpha-quartz and, hence, find incorporation into the risk assessment for alpha-quartz exposure.

Crystallization↗
PubMed1999

Ibuprofen agglomerates preparation by phase separation.

The compression ability and dissolution rate of ibuprofen are poor. There are many processes to optimize these properties through adapted formulations. However, it would be more satisfactory to obtain directly during the crystallization step crystalline particles that can be directly compressed and quickly dissolved. This was the aim of this work. Ibuprofen spherical agglomerates were obtained using a very simple method based on the difference of solubility of ibuprofen in ethanol and in water. By cooling down an ibuprofen-saturated solution in an ethanol/water 50/50 mixture from 60 degrees C to room temperature under stirring, a phase separation occurs. Ibuprofen crystallizes in separated water droplets. After separation by sieving and drying, spherical agglomerates were obtained. A study of the physical properties of ibuprofen agglomerates was carried out using electron scanning microscopy and X-ray powder diffraction. The compression ability was tested using an instrumented tablet machine, and the dissolution rate was measured using continuous flow cells. An improvement in compression and dissolution properties of the spherical agglomerates produced was observed. The process of crystallization in a separated dispersed phase could be envisaged each time a drug exhibits opposite solubilities in two miscible solvents.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2001

Preformulation studies on the S-isomer of oxybutynin hydrochloride, an Improved Chemical Entity (ICE).

(S)-Oxybutynin HCl (S-OXY) is a white crystalline solid powder with an acicular particle morphology. Differential scanning calorimetry (DSC) thermograms revealed one characteristic endotherm at 116.2 degrees C. On rescanning a sample heated to 120 degrees C, no thermal events were distinguished in the temperature range 25 degrees C to 150 degrees C. Weight loss curves determined by thermogravimetric analysis showed a continuous, gradual weight loss of about 0.15% over the temperature range 30 degrees C to 110 degrees C, followed by a change in slope and more rapid weight loss beginning at 150 degrees C. Observation by hot-stage microscopy confirmed the melting endotherm observed by DSC. Equilibrium moisture uptake studies indicated low water vapor uptake at low relative humidities (<52.8%). At relative humidities of 75.3% and 84.3%, S-OXY first deliquesced and then converted to a lower melting point crystal form. X-ray powder diffraction (XRPD) data supported the DSC findings. S-OXY underwent degradation by ester hydrolysis at alkaline pHs. The kinetics of this reaction were studied at 25 degrees C in carbonate-bicarbonate buffers. Observed rate constants of 0.008 h(-1) and 0.0552 h(-1) were determined at pH 9.69 and 10.25, respectively. The pKa of S-OXY was 7.75. The aqueous solubility of S-OXY was described as a function of pH and the free-base solubility. The mean partition coefficient log P was 3.33 using 1-octanol. The surface tensions of aqueous solutions of S-OXY decreased with increasing concentration, but no concentration-independent region was observed, indicating that S-OXY does notform micelles in aqueous solution. The dissolution rate of S-OXY from a compressed disk in 0.1 N HCl was rapid, whereas it was considerably slower at pH 7.4. Addition of 1% hexadecyltrimethylammonium bromide (CTAB) at pH 7.4 significantly improved the dissolution rate. S-OXY displayed very poor flow properties when compared to standard pharmaceutical excipients. XRPD results indicated that S-OXY exhibited a loss in crystallinity following ball milling. Hiestand tableting indices indicated that S-OXY has good bonding properties andforms strong compacts, but is likely to be susceptible to capping on ejection from the die. This indicated the needfor a plastically deformable excipient such as Avicel PH-101 in tablet formulations.

Calorimetry, Differential Scanning↗
PubMed2001

Molecular properties of propranolol hydrochloride prepared as drug-resin complexes.

Drug-resin complexes, as well as physical dispersions, containing varying contents of propranolol were prepared. The molecular properties of samples were investigated by differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), and infrared (IR) spectroscopy. In addition, the USP paddle method was used to determine the release behavior of drug from various formulations prepared from the samples. The data from DSC and XRPD indicated that the molecular state of drug in the complexes was amorphous, whereas that in the physical dispersions exhibited the crystalline state of pure drug. These results suggested that the molecule of drug prepared as drug-resin complexes was monomolecularly dispersed in the resin bead. The IR study provided evidence that demonstrated the interaction between the drug and resin in the complexes. The release behavior of drug from the complexes was governed by the cross-linkage structure and equilibrium treatment of drug exchange of resin.

Anti-Anxiety Agents↗
PubMed2001

The potential of small-scale fusion experiments and the Gordon-Taylor equation to predict the suitability of drug/polymer blends for melt extrusion.

The aim of this study was to investigate the use of small-scale fusion experiments and the Gordon-Taylor (GT) equation to predict whether melt extrusion of a drug with an amorphous polymer produces a stable amorphous dispersion with increased drug dissolution. Indomethacin, lacidipine, nifedipine, piroxicam, and tolbutamide were used as poorly soluble drugs. Drug/polyvinylpyrrolidone (PVP) blends were prepared at a 1:1 mass ratio. Small-scale fusion experiments were performed in a differential scanning calorimeter (DSC) and in stainless steel beakers. Extrusion was performed in a Brabender Plasti-corder. The glass transition temperatures Tg were determined by DSC. Taking an average Tg from the DSC melt, beaker melt, and GT equation accurately predicted the extrudate Tg. Physical stability of beaker melt and extrudate samples was tested by X-ray powder diffraction (XRPD) and DSC after storage at 30 degrees C (beaker melt) or 25 degrees C (extrudate) and less than 10%, 60%, and 75% relative humidity, (RH). Beaker melts were amorphous, apart from some residual crystallinity. Extrudates were amorphous after preparation. Except for indomethacin/PVP, which remained amorphous, the crystallinity of beaker melts and extrudates increased only at 75% RH. Recrystallization occurred even when the Tg of the sample was well above the storage temperature. Chemical stability of the beaker melts and extrudates was tested by capillary electrophoresis and high-performance liquid chromatography (HPLC). Stability was slightly improved in the extrudate compared to the beaker melt. In general, the order for rate of dissolution was crystalline drug was less than the physical mixture, which was less than the drug/PVP beaker melt, which was approximately equal to the extrudate. The use of beaker melts allows a conservative estimate of the potential to melt extrude a drug. To predict physical stability, analysis of the Tg must be combined with physical stability experiments.

Algorithms↗