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Thaw Cycles (thaw + cycle)
Selected AbstractsTEXTURE STABILITY OF HYDROGEL COMPLEX CONTAINING CURDLAN GUM OVER MULTIPLE FREEZE,THAW CYCLESJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 1 2009PATRICK D. WILLIAMS ABSTRACT The texture stability of hydrogel complexes containing curdlan gum over multiple freeze,thaw cycles (FTCs) was investigated. The hydrogels formed by curdlan and xanthan gum, locust bean gum, carrageenan or guar gum at various combinations were stored at 4C for 24 h before subjected to five FTCs alternating between,16 (18 h) and 25C (6 h). Xanthan/curdlan hydrogels showed the highest freeze,thaw stability in terms of syneresis, heat stability and adhesiveness. The viscosity of xanthan/curdlan combination was the lowest among all samples studied yet the most stable over the five FTCs, whereas significant changes were observed with locust bean/curdlan hydrogels. The guar/curdlan combination before freeze,thaw treatments exhibited predominant elasticity; however, as the cycles progressed the elasticity decreased. The most stable gel strength was achieved when curdlan was combined with guar or xanthan at 2% (w/v) total concentration, while carrageenan/curdlan gels were the least stable. PRACTICAL APPLICATIONS Texture instability remains the most significant challenge for frozen food products, especially with inevitable post-production temperature fluctuations. Loss of moisture and changes in textural attributes often results in significant reduction of product quality. Precise control of hydrogel complexes that provide texture stabilization over multiple freeze,thaw cycles will enhance the quality of existing products while enabling the development of new ones. [source] Detection of Konjac glucomannan by immunoassayINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 7 2010Ian P. Hurley Summary Konjac glucomannan is a hydrocolloid that has been used in food applications. The European ban on the use of Konjac glucomannan means that the detection and analysis has potential applications in the food industry, particularly detection of food adulteration. The aim of this work was to develop an assay capable of detecting Konjac glucomannan as an isolated sample and within food matrices. An indirect competitive ELISA was developed utilising a polyclonal antibody raised against Konjac glucomannan. The ELISA was found to be specific for Konjac glucomannan and sensitive, with a detection limit of 0.1 ng mL,1. Increasing salt concentration and freeze/thaw cycles did not affect the performance of the assay. The ELISA was able to detect Konjac glucomannan in admixtures with other gums and also in confectionery that had been spiked with Konjac glucomannan. The ELISA has potential as a kit for the differentiation of Konjac glucomannan from other hydrocolloids and detection in food. [source] Preparation and properties of physically crosslinked sodium carboxymethylcellulose/poly(vinyl alcohol) complex hydrogelsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2008Congming Xiao Abstract A series of physically crosslinked complex hydrogels of poly(vinyl alcohol) (PVA) and sodium carboxymethylcellulose (CMC) were prepared via physical mixing and a freeze/thaw technique. The morphology of the CMC/PVA complex gels was analyzed with differential scanning calorimetry and wide-angle X-ray diffraction. It was found that the crystallinity and melting temperature of the complex gels decreased, whereas the glass-transition temperature increased, with an increase in the content of CMC. The reswelling of the complex gels was pH-responsive and relied on the content of CMC and the freeze/thaw cycles. A network structure model of the complex gel was presented. PVA crystalline regions served as physical crosslinks; the interaction between CMC and PVA resulted in intramolecular entanglements. It was also found that the model drug hemoglobin was released completely from the complex hydrogels in 4 h, and its release rate increased with an increase in the content of CMC. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Investigation of freezing- and thawing-induced biological, chemical, and physical changes to enoxaparin solutionJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2009Rahul P. Patel Abstract This study investigated the effect of freezing and thawing on the biological, physical, and chemical properties of enoxaparin solution. Solutions were frozen and thawed under different conditions, in the presence or absence of dimethyl sulfoxide (DMSO) or 1,2-propanediol (1,2-PD), and the antifactor Xa (AFXa) activity was determined. Enoxaparin solution lost more than 60% of its AFXa activity when thawed rapidly after freezing at ,196°C. The loss of AFXa activity was less with higher freezing temperatures and increased with the number of freeze/thaw cycles, but was independent of the duration of freezing. Slow freezing to ,196°C with rapid thawing, or rapid freezing with slow thawing, resulted in negligible loss of AFXa activity. The loss of AFXa activity did not involve the loss of N -sulfate groups, the breakdown of glycosidic bonds or the glassy state transition. Controlling the freezing or thawing conditions, dilution with water or addition of a small percentage of DMSO ameliorated the loss of enoxaparin AFXa activity. The loss in AFXa activity was found by size exclusion chromatography to be primarily due to aggregation and was reversed by sonication in the presence of DMSO. These results may provide insight into solutions for the long-term storage of concentrated or diluted enoxaparin. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:1118,1128, 2009 [source] Biochemical and analytical development of the CIME cocktail for drug fate assessment in humansRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 16 2010Orianne Videau Phenotyping based on drug metabolism activity appears to be informative regarding mechanism-based interactions during drug development. We report here the first steps of the development of the innovative CIME cocktail. This cocktail is designed not only for the major cytochrome P450, with caffeine, amodiaquine, tolbutamide, omeprazole, dextromethorphan and midazolam as substrates of CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6 and CYP3A, respectively, but also phase II enzymes UGT 1A1/6/9 with acetaminophen, P-gp and OATP1B1 with digoxin and rosuvastatin, and renal function with memantine. An assay combining ultra-performance liquid chromatography using a 1.7,µm particle size column with tandem mass spectrometry (UPLC/MS/MS) was set up for the simultaneous quantification of the 20 substrates and metabolites after extraction from human plasma using solid-phase extraction. The method was validated in the spirit of the FDA guidelines. Mean accuracy ranged from 87.7 to 115%, the coefficient of variance (CV%) of intra- and inter-run from 1.7 to 16.4% and from 1.6 to 14.9%, respectively, and for the limit of quantification (LOQ) with ten lots of plasma, accuracy ranged from 84 to 115% and CV% precision was <16%. Short-term stability was evaluated in eluate (4,h, room temperature), plasma (24,h, room temperature), the autosampler (24,h, 4°C) and in three freeze/thaw cycles in plasma. All except three analytes were stable under these conditions. For the three others a specific process can be followed. This robust, fast and sensitive assay in human plasma provides an analytical tool for ten-probe drugs of the CIME cocktail. Clinical samples will be assayed in the near future using this new assay method. Copyright © 2010 John Wiley & Sons, Ltd. [source] Simultaneous quantitative determination of cyclosporine A and its three main metabolites (AM1, AM4N and AM9) in human blood by liquid chromatography/mass spectrometry using a rapid sample processing methodRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2006Nozomu Koseki We have developed a sensitive and specific liquid chromatography/mass spectrometry (LC/MS) method for the simultaneous determination of cyclosporine A (CsA) and its three main metabolites (AM1, AM4N and AM9) in human blood. Following protein precipitation, supernatant was directly injected into the LC/MS system. Chromatographic separation was accomplished on a Symmetry C8 (4.6,×,75,mm, 3.5,µm) column with a linear gradient elution prior to detection by atmospheric pressure chemical ionization (APCI) MS using selected ion monitoring (SIM) in positive mode. This method can be applied to single mass equipment. The analytical range for each analyte was set at 1,2500,ng/mL using 100,µL of blood sample. The analytical method was fully validated according to FDA guidance. Intra-day mean accuracy and precision were 95.2,113.5% and 0.9,8.9%, respectively. Inter-day mean accuracy and precision were 95.8,107.0% and 1.5,10.7%, respectively. In blood all analytes were stable during three freeze/thaw cycles, for 24,h at room temperature and for 12 months at or below ,15°C. Stability was also confirmed in processed samples for 24,h at 10°C and for 6 months at 4°C in methanol. In addition, we confirmed the method could avoid matrix effects from transplant subjects' samples. This LC/MS technique provided an excellent method for simultaneous quantitative determination of CsA and its three metabolites for evaluation of their pharmacokinetic profiles. Copyright © 2006 John Wiley & Sons, Ltd. [source] Testing extraction and storage parameters for a fecal hormone methodAMERICAN JOURNAL OF PRIMATOLOGY, Issue 11 2010David J. Pappano Abstract Four experiments were conducted to test different aspects of a "field-friendly" fecal hormone extraction method that utilizes methanol extraction in the field followed by storage on C18 solid-phase extraction cartridges. Fecal samples were collected from geladas (Theropithecus gelada) housed at the Bronx Zoo, and the experiments were conducted in a laboratory setting to ensure maximum control. The experiments were designed to either simulate the conditions to which fecal samples are subjected during fieldwork or improve on an existing protocol. The experiments tested the relationship between fecal hormone metabolite preservation/recovery and: (1) the amount of time a sample is stored at ambient temperature; (2) the number of freeze/thaw cycles a sample undergoes; (3) the effectiveness of different extraction solutions; and (4) the effectiveness of different cartridge washes. For each experiment, samples were assayed by radioimmunoassay for fecal glucocorticoid (GC) and testosterone (T) metabolites. Results for each of the experiments were as follows. First, storage at ambient temperature did not affect hormone levels until 4 weeks of storage, with significant increases for both GC and T metabolites at 4 weeks. Second, hormone levels significantly decreased in samples after two freeze/thaw cycles for GCs and six freeze/thaws cycles for T. Third, for both GCs and T, hormone extraction using various methanol solutions was significantly higher than using 100% ethanol. Finally, using a 20% methanol solution to wash cartridges significantly increased GC levels but had no effect on T levels. These results suggest that, when utilizing C18 cartridges for fecal steroid storage, researchers should consider several methodological options to optimize hormone preservation and recovery from fecal samples. Am. J. Primatol. 72:934,941, 2010. © 2010 Wiley-Liss, Inc. [source] Validation of a simple HPLC method for DRF-4848, a novel COX-2 inhibitor suitable for pharmacokinetic application in rats,BIOMEDICAL CHROMATOGRAPHY, Issue 12 2006Raja Reddy Kallem Abstract For pharmacokinetic and toxicokinetic purpose a simple HPLC-UV method has been developed and validated for the estimation of DRF-4848, a novel COX-2 inhibitor in rat plasma. A liquid,liquid extraction was used to extract DRF-4848 and internal standard (IS, DRF-4367) from rat plasma. The analysis was performed on a C18 column with UV detection at 285 nm. The isocratic mobile phase, 0.01 m potassium dihydrogen ortho phosphate (pH 3.2) and acetonitrile (50:50, v/v) was run at a flow rate of 1 mL/min. The retention times of DRF-4848 and IS were 6.8 and 11.2 min, respectively. Absolute recovery for analyte and IS was >80% from rat plasma. A linear response was observed over a concentration range 0.1,20 mg/mL. The lower limit of quantification (LLOQ) of DRF-4848 was 0.1 mg/mL. The inter- and intra-day precisions in the measurement of quality control (QC) samples, 0.1, 0.3, 8.0 and 15.0 mg/mL, were in the range 1.74,8.70% relative standard deviation (RSD) and 0.75,8.43% RSD, respectively. Accuracy in the measurement of QC samples was in the range 93.29,116.51% of the nominal values. Analyte and IS were stable in the battery of stability studies viz., benchtop, autosampler, long-term and freeze/thaw cycles. Copyright © 2006 John Wiley & Sons, Ltd. [source] High performance liquid chromatographic,mass spectrometric assay for the quantitation of BMS-204352 in dog K3EDTA plasmaBIOMEDICAL CHROMATOGRAPHY, Issue 3 2002Ming Yao A high performance liquid chromatographic-mass spectrometric (LC/MS) assay was developed and validated for the determination of BMS-204352 in dog K3EDTA plasma. A 0.5,mL aliquot of control plasma was spiked with BMS-204352 and internal standard (IS) and buffered with 1,mL of 5,mM ammonium acetate. The mixture was then extracted with 3,mL of toluene. After separation and evaporation of the organic phase to dryness using nitrogen at 40°C, the residue was reconstituted in the mobile phase and 25,µL of the sample were injected onto a Hypersil C18 column (2,×,50,mm; 3,µm) at a flow rate of 0.5,mL/min. The mobile phase was consisted of two solvent mixtures (A and B). Solvent A was composed of 5,mM ammonium acetate and 0.1% triethylamine in 75:25 v/v water:methanol, pH adjusted to 5.5 with glacial acetic acid, and solvent B was 5,mM ammonium acetate in methanol. A linear gradient system was used to elute the analytes. The mass spectrometer was programmed to admit the de-protonated molecules at m/z 352.7 (IS) and m/z 357.9 (BMS-204352). Standard curves of BMS-204352 were linear (r2,,,0.998) over the concentration range of 0.5,1000,ng/mL. The mean predicted quality control (QC) concentrations deviated less than 5.1% from the corresponding nominal values (ie 4, 80, 400 and 2000,ng/mL); the within- and between-assay precision of the assay were within 5.5% relative standard deviation. Stability of BMS-204352 was confirmed after at least three freeze/thaw cycles and BMS-204532 was stable in dog plasma when stored frozen at or below ,20°C for at least 16 weeks in spiked QC samples and for at least 4 1/2 weeks for in vivo study samples. BMS-204352 and IS were stable in the injection solvent at room temperature for at least 24,h. The assay was applied to delineate the pharmacokinetic disposition of BMS-204352 in dogs following a single intravenous dose administration. In conclusion, the assay is accurate, precise, specific, sensitive and reproducible for the pharmacokinetic analysis of BMS-204532 in dog plasma. Copyright © 2002 John Wiley & Sons, Ltd. [source] Gelifluction: viscous flow or plastic creep?EARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2003Charles Harris Abstract This paper reports results from two scaled centrifuge modelling experiments, designed to simulate thaw-related geli,uction. A planar 12° prototype slope was modelled in each experiment, using the same natural ,ne sandy silt soil. However two different scales were used. In Experiment 1, the model scale was 1/10, tested in the centrifuge at 10 gravities (g) and in Experiment 2, the scale was 1/30, tested at 30 g. Centrifuge scaling laws indicate that the time scaling factor for thaw consolidation between model and prototype is N2, where N is the number of gravities under which the model was tested. However, the equivalent time scaling for viscous ,ow is 1/1. If geli,uction is a viscosity-controlled ,ow process, scaling con,icts will therefore arise during centrifuge modelling of thawing slopes, and rates of displacement will not scale accurately to the prototype. If, however, no such scaling con,icts are observed, we may conclude that geli,uction is not controlled by viscosity, but rather by elasto-plastic soil deformation in which frictional shear strength depends on effective stress, itself a function of the thaw consolidation process. Models were saturated, consolidated and frozen from the surface downwards on the laboratory ,oor. The frozen models were then placed in the geotechnical centrifuge and thawed from the surface down. Each model was subjected to four freeze,thaw cycles. Soil temperatures and pore water pressures were monitored, and frost heave, thaw settlement and downslope displacements measured. Pore water pressures, displacement rates and displacement pro,les re,ecting accumulated shear strain, were all similar at the two model scales and volumetric soil transport per freeze,thaw cycle, when scaled to prototype, were virtually identical. Displacement rates and pro,les were also similar to those observed in earlier full-scale laboratory ,oor experiments. It is concluded therefore that the modelled geli,uction was not a time-dependent viscosity-controlled ,ow phenomenon, but rather elasto-plastic in nature. A ,rst approximation ,,ow' law is proposed, based on the ,Cam Clay' constitutive model for soils. Copyright © 2003 John Wiley & Sons, Ltd. [source] Taphonomic Changes to Blunt Force Trauma: A Preliminary Study,JOURNAL OF FORENSIC SCIENCES, Issue 3 2007Stephanie E. Calce B.Sc. Abstract: This study examines the effects of taphonomic processes on blunt force trauma (BFT) through an experimental study involving pig heads. Of particular concern is the possibility that taphonomic changes can create pseudo-trauma and/or conceal evidence of actual trauma. BFT was inflicted on 10 pig skulls using a hammer. The skulls were subsequently exposed to the environment for 12 months. Seven taphonomic changes were evaluated: the freeze,thaw cycle; rodent gnawing; carnivore scavenging; presence/weight of soil; presence/weight of rain and snow; movement/displacement of bones; and discoloration due to sun bleaching and grass staining. Taphonomic effects varied between cancellous, compact, fresh, and degreased bone. Freezing and thawing, exposure to rain and snow, movement of the skulls, and soil erosion altered and, in some cases disguised, pre-existing trauma. Rodent and carnivore activity did not obliterate evidence of BFT. Recommendations for evaluating BFT on remains affected by taphonomic processes are presented. As each taphonomic process outlined by this study has the potential to disguise antemortem injury, the authors propose that one must carefully examine large, circular openings in the skull that may represent the remnant evidence of BFT. [source] Specific gravity as an alternative to creatinine for estimating urine concentration in captive and wild chimpanzee (Pan troglodytes) SamplesAMERICAN JOURNAL OF PRIMATOLOGY, Issue 2 2009Stephanie F. Anestis Abstract The measurement of hormones in urine has become a widely used technique in primatology. Because urine concentration varies according to fluid intake, concentration must be measured in each sample collected, and hormone values are always expressed per unit of concentration. Traditionally, creatinine has been used as a concentration index, but some studies in humans have shown that creatinine varies among populations and even within and between individuals within a population, and that it begins to degrade after just one freeze,thaw cycle. In addition, creatinine measurement is relatively time-consuming and expensive and creates hazardous waste. In this study, we tested the hypothesis that specific gravity, or the ratio of the density of a sample to that of water, is highly correlated with creatinine measurement in urine samples collected from captive chimpanzees at the New Iberia Research Center in Louisiana and wild chimpanzees at the Ngogo study site in the Kibale National Park, Uganda. We found that specific gravity and creatinine were highly correlated in both captive (N=124) and wild (N=13) chimpanzee samples, and that specific gravity measurement was robust to actual and simulated transport conditions and repeated freeze,thaw cycles. We recommend that researchers consider specific gravity measurement as a preferable alternative to creatinine measurement in their studies of primate endocrinology. Am. J. Primatol. 71:130,135, 2009. © 2008 Wiley-Liss, Inc. [source] Physical modelling of fault scarp degradation under freeze,thaw cyclesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 14 2006M. Font Abstract Physical modelling has been developed in order to simulate the effects of periglacial erosion processes on the degradation of slopes and scarps. Data from 41 experimental freeze,thaw cycles are presented. They attest to the efficiency of periglacial processes that control both erosion and changes in scarp morphology: (i) cryoexpulsion leads to an increase of scarp surface roughness and modifies significantly the internal structure of the active layer; (ii) combined effects of frost creep and gelifluction lead to slow and gradual downslope displacements of the active layer (0·3 cm/cycle); (iii) debris flows are associated with the most significant changes in scarp morphology and are responsible for the highest rate of scarp erosion; (iv) quantification of the erosion rate gives values close to 1 cm3 cm,2 for 41 freeze,thaw cycles. These experimental results are consistent with field data acquired along the La Hague fault scarp (Normandy, France) where an erosion rate of 4·6 ± 1 m3 m,2 per glacial stage has been computed from the volume of natural slope deposits stored during the Weichselian glacial stage. These results show that moist periglacial erosion processes could lead to an underestimation of Plio-Quaternary deformation in the mid-latitudes. Copyright © 2006 John Wiley & Sons, Ltd. [source] Gelifluction: viscous flow or plastic creep?EARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2003Charles Harris Abstract This paper reports results from two scaled centrifuge modelling experiments, designed to simulate thaw-related geli,uction. A planar 12° prototype slope was modelled in each experiment, using the same natural ,ne sandy silt soil. However two different scales were used. In Experiment 1, the model scale was 1/10, tested in the centrifuge at 10 gravities (g) and in Experiment 2, the scale was 1/30, tested at 30 g. Centrifuge scaling laws indicate that the time scaling factor for thaw consolidation between model and prototype is N2, where N is the number of gravities under which the model was tested. However, the equivalent time scaling for viscous ,ow is 1/1. If geli,uction is a viscosity-controlled ,ow process, scaling con,icts will therefore arise during centrifuge modelling of thawing slopes, and rates of displacement will not scale accurately to the prototype. If, however, no such scaling con,icts are observed, we may conclude that geli,uction is not controlled by viscosity, but rather by elasto-plastic soil deformation in which frictional shear strength depends on effective stress, itself a function of the thaw consolidation process. Models were saturated, consolidated and frozen from the surface downwards on the laboratory ,oor. The frozen models were then placed in the geotechnical centrifuge and thawed from the surface down. Each model was subjected to four freeze,thaw cycles. Soil temperatures and pore water pressures were monitored, and frost heave, thaw settlement and downslope displacements measured. Pore water pressures, displacement rates and displacement pro,les re,ecting accumulated shear strain, were all similar at the two model scales and volumetric soil transport per freeze,thaw cycle, when scaled to prototype, were virtually identical. Displacement rates and pro,les were also similar to those observed in earlier full-scale laboratory ,oor experiments. It is concluded therefore that the modelled geli,uction was not a time-dependent viscosity-controlled ,ow phenomenon, but rather elasto-plastic in nature. A ,rst approximation ,,ow' law is proposed, based on the ,Cam Clay' constitutive model for soils. Copyright © 2003 John Wiley & Sons, Ltd. [source] Direct observation of frost wedging in alpine bedrockEARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2001Norikazu Matsuoka Abstract Width and temperature of rock joints were automatically monitored in the Japanese Alps. Three years of monitoring on a sandstone rock face shows two seasonal peaks of joint widening in autumn and spring. The autumn events are associated with short-term freeze,thaw cycles, and the magnitude of widening reflects the freezing intensity and water availability. The short-term freezing can produce wedging to a depth of at least 20,cm. The spring events follow a rise in the rock surface temperature to 0,°C beneath the seasonal snowcover, and likely originate from refreezing of meltwater entering the joint. Some of these events contribute to permanent enlargement of the joint. Two other joints on nearby rock faces experience only sporadic widening accompanying freeze,thaw cycles and insignificant permanent enlargement. Observations indicate that no single thermal criterion can explain frost weathering. The temperature range at which wedging occurs varies with the bedrock conditions, water availability and duration of freezing. Copyright © 2001 John Wiley & Sons, Ltd. [source] Near,surface ground temperature regime variability in selected microenvironments, Kärkevagge, Swedish LaplandGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 3-4 2002Colin E. Thorn The importance of topographic microvariability in influencing shallow (10,50 cm depths) soil temperature regimes in arctic,alpine Kärkevagge, northern Sweden, from August 1999 to July 2000 is demonstrated using six sites. The ground microclimate on the tops of very large boulders forming an extensive boulder field in the central valley bottom is more comparable to that at an alpine ridge,crest site 300 m higher than it is to the microclimate at the base of one of the boulders. The boulder crests also differ substantially from the more generalized valley,bottom conditions outside the boulder field. Assuming that chemical processes may be active at temperatures at or above 0°C, sites in the valley experience favorable conditions from 159 to 324 days of the year. Aside from the annual cycle, freeze,thaw cycles are infrequent within Kärkevagge. [source] Physically crosslinked composite hydrogels of PVA with natural macromolecules: Structure, mechanical properties, and endothelial cell compatibilityJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2009Y. Liu Abstract Polyvinyl alcohol (PVA) hydrogels have been considered potentially suitable for applications as engineered blood vessels because of their structure and mechanical properties. However, PVA's hydrophilicity hinders its capacity to act as a substrate for cell attachment. As a remedy, PVA was blended with chitosan, gelatin, or starch, and hydrogels were formed by subjecting the solutions to freeze-thaw cycles followed by coagulation bath immersion. The structure-property relationships for these hydrogels were examined by measurement of their swelling, rehydration, degradation, and mechanical properties. For the case of pure PVA hydrogels, the equilibrium swelling ratio was used to predict the effect of freeze thaw cycles and coagulation bath on average molecular weights between crosslinks and on mesh size. For all hydrogels, trends for the reswelling ratio, which is indicative of the crosslinked polymer fraction, were consistent with relative tensile properties. The coagulation bath treatment increased the degradation resistance of the hydrogels significantly. The suitability of each hydrogel for cell attachment and proliferation was examined by protein adsorption and bovine vascular endothelial cell culture experiments. Protein adsorption and cell proliferation was highest on the PVA/gelatin hydrogels. This study demonstrates that the potential of PVA hydrogels for artificial blood vessel applications can be improved by the addition of natural polymers, and that freeze-thawing and coagulation bath treatment can be utilized for fine adjustment of the physical characteristics. © 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009 [source] Effects of Temporal Application Parameters on Lesion Dimensions During Transvenous Catheter CryoablationJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 2 2005HUNG-FAT TSE M.D. Background: Transvenous catheter cryoablation is a novel technique for treating cardiac arrhythmias. However, the relative importance of temporal application parameters on lesion dimension and clinical efficacy has not been studied. Methods and Results: We investigated the effects of (1) application duration: single 2.5 (2.5 × 1) versus single 5 versus double 2.5 (2.5 × 2) versus double 5 (5 × 2) minutes, (2) number of freeze,thaw cycles: single versus double, and (3) electrode contact area: horizontal versus vertical orientation, on the lesion diameter and depth during catheter cryoablation (10F, 6.5-mm tip-electrode, CryoCorŌ, San Diego) in a thigh muscle preparation. A total of 175 lesions (horizontal = 90, vertical = 85) were created in thigh muscle preparations on 10 swine. The lesion diameter and depth were significantly greater using 2.5 × 2 and 5 × 2 application modes as compared with 2.5 × 1 applications (P < 0.05). Horizontal tip-electrode orientation produced larger lesion diameter (P < 0.05), but not lesion depth as compared with vertical orientation. Multivariate analysis demonstrated that both tip-electrode orientation and duration of freeze >2.5 minutes were independent predictors for lesion diameter (P < 0.001). However, only duration of freeze >2.5 minutes was an independent predictor for lesion depth (P < 0.001). Conclusions: The dimensions of lesions created by catheter cryoablation are affected by mode of cryoablation application and electrode orientation. Increasing the duration of application, employing multiple freeze,thaw cycles at shorter cycle durations, and orienting the catheter to enhance/increase tissue contact can create a larger lesion. [source] TEXTURE STABILITY OF HYDROGEL COMPLEX CONTAINING CURDLAN GUM OVER MULTIPLE FREEZE,THAW CYCLESJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 1 2009PATRICK D. WILLIAMS ABSTRACT The texture stability of hydrogel complexes containing curdlan gum over multiple freeze,thaw cycles (FTCs) was investigated. The hydrogels formed by curdlan and xanthan gum, locust bean gum, carrageenan or guar gum at various combinations were stored at 4C for 24 h before subjected to five FTCs alternating between,16 (18 h) and 25C (6 h). Xanthan/curdlan hydrogels showed the highest freeze,thaw stability in terms of syneresis, heat stability and adhesiveness. The viscosity of xanthan/curdlan combination was the lowest among all samples studied yet the most stable over the five FTCs, whereas significant changes were observed with locust bean/curdlan hydrogels. The guar/curdlan combination before freeze,thaw treatments exhibited predominant elasticity; however, as the cycles progressed the elasticity decreased. The most stable gel strength was achieved when curdlan was combined with guar or xanthan at 2% (w/v) total concentration, while carrageenan/curdlan gels were the least stable. PRACTICAL APPLICATIONS Texture instability remains the most significant challenge for frozen food products, especially with inevitable post-production temperature fluctuations. Loss of moisture and changes in textural attributes often results in significant reduction of product quality. Precise control of hydrogel complexes that provide texture stabilization over multiple freeze,thaw cycles will enhance the quality of existing products while enabling the development of new ones. [source] Development and validation of a liquid chromatographic/tandem mass spectrometric assay for the quantitation of nucleoside HIV reverse transcriptase inhibitors in biological matricesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 1 2005Séverine Compain Abstract Besides liquid chromatographic (LC)/UV methods adapted to therapeutic drug monitoring, there is still a need for more powerful techniques that can be used for pharmacological research and clinical purposes. We developed an LC method coupled with tandem mass spectrometry (MS/MS) to separate, detect and quantify with high sensitivity the nucleoside analogues used in multitherapies (zidovudine, stavudine, zalcitabine, didanosine, lamivudine and abacavir) in plasma and in the intracellular medium. We worked on two essential issues: (i) the need to use two ionization modes in order to achieve the best sensitivity, which leads to the optimization of the chromatographic separation of drugs detected in the positive ionization mode and drugs detected in the negative ionization mode, and (ii) the need to optimize the extraction step in order to enhance sample recovery. The peripheral blood mononuclear cells were lysed in Tris buffer,MeOH. A clean-up procedure was performed by solid-phase extraction only for plasma samples. The LC separation was carried out on a Zorbax Stable Bond C18 column followed by MS/MS analysis after electrospray ionization in either the negative or positive mode. The positive ionization mode was applied at the beginning of the run to detect zalcitabine and lamivudine, then the ionization mode was changed to negative for the detection of didanosine, stavudine, internal standard and zidovudine. The calibration range for all the analytes was 0.5,200 ng ml,1. The recoveries were between 64 and 90%, with coefficients of variation (CVs) lower than 15%. The inaccuracy (bias) was ±15% with CVs always lower than 12%. The analytes were stable at room temperature and in the extraction solvent for at least 24 h, after storage at ,80 °C for 3 months, after three freeze,thaw cycles and in the injection solvent after 48 h at 4 °C. Together with the measurement of intracellular triphosphorylated metabolites thanks to the powerful plasma and intracellular assay method for intact drugs, it is possible to describe the behaviour of nucleoside analogues against HIV through plasma pharmacokinetics, cell membrane diffusion including drug transport involvement, and also the intracellular metabolism. Copyright © 2005 John Wiley & Sons, Ltd. [source] Simple, sensitive and rapid liquid chromatographic/electrospray ionization tandem mass spectrometric method for the quantification of lacidipine in human plasmaJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 7 2004N. V. S. Ramakrishna Abstract A simple, sensitive and rapid liquid chromatographic/electrospray ionization tandem mass spectrometric method was developed and validated for the quantification of lacidipine in human plasma using its structural analogue, amlodipine, as internal standard (IS). The method involves a simple single-step liquid,liquid extraction with tert -butyl methyl ether. The analyte was chromatographed on an Xterra MS C18 reversed-phase chromatographic column by isocratic elution with 20 mM ammonium acetate buffer,acetonitrile (10 : 90, v/v; pH 6) and analyzed by mass spectrometry in the multiple reaction monitoring mode. The precursor to product ion transitions of m/z 456.4 , 354.4 and m/z 409.3 , 238.3 were used to measure the analyte and the I.S., respectively. The chromatographic run time was 1.5 min and the weighted (1/x2) calibration curves were linear over the range 0.1,25 ng ml,1. Lacidipine was sensitive to temperature in addition to light. The method was validated in terms of accuracy, precision, absolute recovery, freeze,thaw stability, bench-top stability and re-injection reproducibility. The limit of detection and lower limit of quantification in human plasma were 50 and 100 pg ml,1, respectively. The within- and between-batch accuracy and precision were found to be well within acceptable limits (<15%). The analyte was stable after three freeze,thaw cycles (deviation <15%). The average absolute recoveries of lacidipine and amlodipine (IS) from spiked plasma samples were 51.1 ± 1.3 and 50.3 ± 4.9%, respectively. The assay method described here could be applied to study the pharmacokinetics of lacidipine. Copyright © 2004 John Wiley & Sons, Ltd. [source] Development and validation of an HPLC method for the determination of seven penicillin antibiotics in veterinary drugs and bovine blood plasmaJOURNAL OF SEPARATION SCIENCE, JSS, Issue 9 2009Victoria F. Samanidou Abstract Herein a quantitative method for the determination of seven penicillins in bovine plasma and veterinary drugs has been developed. Amoxicillin (AMO), ampicillin (AMP), penicillin G (PENG), penicillin V (PENV), oxacillin (OXA), cloxacillin (CLO) and dicloxacillin (DICLO) were separated on a Perfectsil ODS-2 (250×4 mm, 5 ,m) column, using gradient elution, with a mobile phase of 0.1% v/v TFA and ACN,methanol (90:10 v/v). PDA detection was used at 240 nm. Penicillins were isolated from bovine plasma by SPE on Lichrolut RP-18 cartridges with mean recoveries from 85.7 to 113.5%. Colchicine (3 ng/,L) was used as an internal standard. The developed method was validated in terms of selectivity, linearity, accuracy, precision, stability and sensitivity. Repeatability (n = 5) and between-day precision (n = 5) revealed RSD < 12%. The detection limits in the bovine plasma were estimated as 18 ng for AMO and AMP, 25 for PENG, PENV and OXA, 3 ng for CLO and 12 ng for DICLO. Spiked plasma samples were stable for 1 wk, except for AMP and CLO, which were stable for 3 wk and OXA for 4 wk. AMO, PENG and PENV were stable for two freeze,thaw cycles, OXA, CLO and DICLO for four, while AMP only for one. [source] Freeze,thaw-induced embolism in Pinus contorta: centrifuge experiments validate the ,thaw-expansion hypothesis' but conflict with ultrasonic emission dataNEW PHYTOLOGIST, Issue 4 2010Stefan Mayr Summary ,The ,thaw-expansion hypothesis' postulates that xylem embolism is caused by the formation of gas bubbles on freezing and their expansion on thawing. We evaluated the hypothesis using centrifuge experiments and ultrasonic emission monitoring in Pinus contorta. ,Stem samples were exposed to freeze,thaw cycles at varying xylem pressure (P) in a centrifuge before the percentage loss of hydraulic conductivity (PLC) was measured. Ultrasonic acoustic emissions were registered on samples exposed to freeze,thaw cycles in a temperature chamber. ,Freeze,thaw exposure of samples spun at ,3 MPa induced a PLC of 32% (one frost cycle) and 50% (two cycles). An increase in P to ,0.5 MPa during freezing had no PLC effect, whereas increased P during thaw lowered PLC to 7%. Ultrasonic acoustic emissions were observed during freezing and thawing at ,3 MPa, but not in air-dried or water-saturated samples. A decrease in minimum temperature caused additional ultrasonic acoustic emissions, but had no effect on PLC. ,The centrifuge experiments indicate that the ,thaw-expansion hypothesis' correctly describes the embolization process. Possible explanations for the increase in PLC on repeated frost cycles and for the ultrasonic acoustic emissions observed during freezing and with decreasing ice temperature are discussed. [source] Involutions resulting from annual freeze,thaw cycles: a laboratory simulation based on observations in northeastern JapanPERMAFROST AND PERIGLACIAL PROCESSES, Issue 4 2007Yoshiko Ogino Abstract A pilot laboratory experiment using a reversed two-layer soil model simulated small-scale involutions formed in a seasonal frost environment during the last glacial period. At the modelled site, the interface between the upper aeolian sandy loam and the lower volcanic pumice constitutes small-scale involutions that display upward-extending tapered projections and downward-extending round hollows. Two scale-reduced laboratory models were subjected to three accelerated annual freeze,thaw cycles with monitoring of frost heave, soil temperature, moisture and pressure. Ice segregation near the layer interface induces upheaving of coarse pumice grains on freezing and earlier settlement of mobilised loam on thawing, resulting in deformation of the interface. A reconstructed 3-D interface displays mounds and depressions with a diameter of 15,20,cm and a height increasing with freeze, thaw alternations. The experimental results imply that the repetition of differential heave and soft-loam settlement promotes decimetre-scale involutions in near-saturated soils subject to deep seasonal frost penetration. Copyright © 2007 John Wiley & Sons, Ltd. [source] Preparation and characterization of biocompatible spongy cryogels of poly(vinyl alcohol),gelatin and study of water sorption behaviourPOLYMER INTERNATIONAL, Issue 9 2005Dr AK Bajpai Abstract Porous biocompatible spongy hydrogels of poly(vinyl alcohol) (PVA),gelatin were prepared by the freezing,thawing method and characterized by infrared and differential scanning calorimetry. The prepared so-called ,cryogels' were evaluated for their water-uptake potential and the influence of various factors, such as the chemical architecture of the spongy hydrogels, pH and the temperature of the swelling bath, on the degree of water sorption by the cryogels was investigated. It was found that the water sorption capacity constantly decreased with increasing concentration of PVA while initially an increase and thereafter a decrease in swelling was obtained with increasing amounts of gelatin in the cryogel. The water sorption capacity decreased with an increase in the number of freeze,thaw cycles. The hydrogels were also swollen in salt solutions and various simulated biological fluids and a fall in swelling ratio was noticed. The effect of the drying temperature of the cryogel on its water sorption capacity was also investigated, and a decrease in swelling was obtained with increasing temperature of drying. The biocompatibility of the prepared materials was assessed by in vitro methods of blood-clot formation, platelet adhesion, and per cent haemolysis. It was noticed that with increasing concentration of PVA and gelatin the biocompatibility increased, while a reduced biocompatibility was noted with an increasing number of freeze,thaw cycles. Copyright © 2005 Society of Chemical Industry [source] PP13 stability in first trimester maternal serum and whole bloodPRENATAL DIAGNOSIS, Issue 6 2010N. J. Cowans Abstract Background Maternal serum placental protein 13 (PP13) has been proposed as a marker for prenatal screening of pre-eclampsia (PE) and other adverse pregnancy outcomes. This study aims to examine the stability of PP13 at different routine temperatures. Methods Maternal serum pools and whole blood samples were stored at ,30 °C', room temperature or refrigerator temperature. Further, serum pools were also subjected to repeated freeze,thaw cycles. PP13 was measured at set time points using an AutoDELFIA® research assay. Results Levels of PP13 are stable, defined as less than 10% change in concentration, in serum for 17.4 h at ,30 °C', 3.4 days at room temperature and for at least 34 days at refrigerator temperature. PP13 concentration is not altered following three ,20 °C to room temperature freeze,thaw cycles. PP13 is stable in whole blood for at least 3 days at all three temperatures studied. Conclusions PP13 is a suitably stable molecule and can be treated under routine laboratory and normal transport temperatures. Copyright © 2010 John Wiley & Sons, Ltd. [source] Specific gravity as an alternative to creatinine for estimating urine concentration in captive and wild chimpanzee (Pan troglodytes) SamplesAMERICAN JOURNAL OF PRIMATOLOGY, Issue 2 2009Stephanie F. Anestis Abstract The measurement of hormones in urine has become a widely used technique in primatology. Because urine concentration varies according to fluid intake, concentration must be measured in each sample collected, and hormone values are always expressed per unit of concentration. Traditionally, creatinine has been used as a concentration index, but some studies in humans have shown that creatinine varies among populations and even within and between individuals within a population, and that it begins to degrade after just one freeze,thaw cycle. In addition, creatinine measurement is relatively time-consuming and expensive and creates hazardous waste. In this study, we tested the hypothesis that specific gravity, or the ratio of the density of a sample to that of water, is highly correlated with creatinine measurement in urine samples collected from captive chimpanzees at the New Iberia Research Center in Louisiana and wild chimpanzees at the Ngogo study site in the Kibale National Park, Uganda. We found that specific gravity and creatinine were highly correlated in both captive (N=124) and wild (N=13) chimpanzee samples, and that specific gravity measurement was robust to actual and simulated transport conditions and repeated freeze,thaw cycles. We recommend that researchers consider specific gravity measurement as a preferable alternative to creatinine measurement in their studies of primate endocrinology. Am. J. Primatol. 71:130,135, 2009. © 2008 Wiley-Liss, Inc. [source] Sensitive and selective liquid chromatography,tandem mass spectrometry method for the determination of metoclopramide in human plasma: application to a bioequivalence studyBIOMEDICAL CHROMATOGRAPHY, Issue 9 2010Jaswanth Kumar Inamadugu Abstract A simple, sensitive and rapid method has been developed and validated for determination of the metoclopramide (MCP) in 100,,L human plasma. The analytical procedure involves a liquid,liquid extraction method using tramadol as an internal standard (IS). Chromatographic separation was carried out on a HyPURITY ADVANCE column using a mobile phase consisting of acetonitrile and 10,mm ammonium acetate buffer in the ratio of 80:20 (v/v) at a flow rate of 0.3,mL/min. The total run time of analysis was 2.5,min and elution of MCP and IS occurred at 0.9 and 1.3,min, respectively. A linear response function was established for the range of concentrations 0.53,42.07,ng/mL (r > 0.99). The intra- and inter-day precision values for MCP met the acceptance as per FDA guidelines. MCP was stable in a battery of stability studies viz., bench-top, auto-sampler and freeze,thaw cycles. The developed assay method was successfully applied to an oral bioequivalence study in humans. Copyright © 2010 John Wiley & Sons, Ltd. [source] Liquid chromatographic,tandem mass spectrometry assay for quantitation of a novel antidiabetic S002-853 in rat plasma and its application to pharmacokinetic study,BIOMEDICAL CHROMATOGRAPHY, Issue 7 2010N. Gautam Abstract A sensitive and selective LC-MS/MS method has been developed and validated for the estimation of novel antidiabetic synthetic flavonoid S002-853 in rat plasma using centchroman as an internal standard. The method involves a simple two-step liquid,liquid extraction with diethyl ether. The analyte was chromatographed on a Pierce Spheri-5, guard cyano column (30 × 4.6,,mm i.d., 5,,µm) with isocratic mobile phase consisting of methanol,ammonium acetate buffer (pH 4.6, 10,,mm; 90,:,10, v/v) at a flow rate of 0.75,,mL/min. The API 4000 triple-quadrupole LC,MS/MS system was operated under multiple reaction-monitoring mode. The ionization was performed by electrospray ionization technique in positive ion mode. The chromatographic run time was 6,,min and the weighted (1/x2) calibration curves were linear over the range 0.78,400,,ng/mL. The limit of detection and lower limit of quantification were 0.195 and 0.78,,ng/mL, respectively. The intra- and inter-batch accuracy (%bias) and precision (%RSD) were found to be less than 8.47 and 11.6% respectively. The average absolute recoveries of S002-853 and internal standard from spiked plasma samples were >90%. S002-853 was stable for 8,,h at ambient temperature, 4 weeks at ,60°C and after three freeze,thaw cycles. The assay was successfully applied to determine the pharmacokinetic parameters in male Sprague,Dawley rats after an oral dose administration at 25,,mg/kg. Copyright © 2009 John Wiley & Sons, Ltd. [source] Development and validation of a rapid and sensitive HPLC method for the quantification of 5-fluorocytosine and its metabolitesBIOMEDICAL CHROMATOGRAPHY, Issue 5 2010Kinta M. Serve Abstract To study the intracellular metabolism of the prodrug 5-fluorocytosine (5FC), we developed a novel reverse-phase high-performance liquid chromatography method to simultaneously detect 5FC and its four major anabolic metabolites: 5-fluorouracil, 5-fluorouridine, 5-fluorouridine-monophosphate and 5-fluoro-2,deoxyuridine-5,-monophosphate. Separation of each compound was accomplished under isocratic conditions using a C18 column and mobile phase of formic acid,water (1,:,99,v/v). The method was validated for both accuracy and reproducibility in cell culture media. Additionally, metabolites were assessed for stability at ambient temperatures and following freeze,thaw cycles. Calibration curves were linear over a range of 1,200,,g/mL. Limit of quantification for four of the five compounds was 1,,g/mL in cell culture media (RSD < 11%). This method was successfully used to monitor intracellular conversion of 5FC to its metabolic products over a 24h period. 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