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Degradation Rate (degradation + rate)
Selected AbstractsBiodegradable Polymer Crosslinker: Independent Control of Stiffness, Toughness, and Hydrogel Degradation RateADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Chaenyung Cha Abstract Hydrogels are being increasingly studied for use in various biomedical applications including drug delivery and tissue engineering. The successful use of a hydrogel in these applications greatly relies on a refined control of the mechanical properties including stiffness, toughness, and the degradation rate. However, it is still challenging to control the hydrogel properties in an independent manner due to the interdependency between hydrogel properties. Here it is hypothesized that a biodegradable polymeric crosslinker would allow for decoupling of the dependency between the properties of various hydrogel materials. This hypothesis is examined using oxidized methacrylic alginate (OMA). The OMA is synthesized by partially oxidizing alginate to generate hydrolytically labile units and conjugating methacrylic groups. It is used to crosslink poly(ethylene glycol) methacrylate and poly(N -hydroxymethyl acrylamide) to form three-dimensional hydrogel systems. OMA significantly improves rigidity and toughness of both hydrogels as compared with a small molecule crosslinker, and also controls the degradation rate of hydrogels depending on the oxidation degree, without altering their initial mechanical properties. The protein-release rate from a hydrogel and subsequent angiogenesis in vivo are thus regulated with the chemical structure of OMA. Overall, the results of this study suggests that the use of OMA as a crosslinker will allow the implantation of a hydrogel in tissue subject to an external mechanical loading with a desired protein-release profile. The OMA synthesized in this study will be, therefore, highly useful to independently control the mechanical properties and degradation rate of a wide array of hydrogels. [source] Estimation of Degradation Rates by Satisfying Mass Balance at the InletGROUND WATER, Issue 4 2010Vedat Batu Using a steady-state mass conservative solute transport analytical solution that is based on the third-type (or flux-type or Cauchy) source condition, a method is developed to estimate the degradation parameters of solutes in groundwater. Then, the inadequacy of the methods based on the first-type source-based analytical solute transport solution is presented both theoretically and through an example. It is shown that the third-type source analytical solution exactly satisfies the mass balance constraint at the inlet location. It is also shown that the first-type source (or constant source concentration or Dirichlet) solution fails to satisfy the mass balance constraint at the inlet location and the degree of the failure depends on the value of the degradation as well as the flow and solute transport parameters. The error in the first-type source solution is determined with dimensionless parameters by comparing its results with the third-type source solution. Methods for estimating the degradation parameter values that are based on the first-type steady-state solute transport solution may significantly overestimate the degradation parameter values depending on the values of flow and solute transport parameters. It is recommended that the third-type source solution be used in estimating degradation parameters using measured concentrations instead of the first-type source solution. [source] Potential for octylphenol to biodegrade in some english riversENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2000Andrew C. Johnson Abstract To study octylphenol biodegradation, samples of river water and sediments were taken from the Aire and Calderr vers in the United Kingdom, running through urban/industrial areas, as well as the Thames River running through a more rural area. Using laboratory microcosms, half-lives of 7 to 50 d were obtained for the water samples, with most curves fitting a zero-order reaction. The Calder River was sampled at four separate points along a 45-km length, encompassing rural to increasingly urban/industrial reaches. Little degradation was observed in the sample from the upland/rural reach, while half-lives of 8 to 13 d were seen in the more urban/industrial reaches. Mineralization of the phenyl ring, detected by evolution of 14CO2 from ring-labeled octylphenol, was only observed in water from the Calder River sample. Degradation rate was similar for a range of concentrations from 0.3 to 100 ,,g/L when tested with river water from the Thames River. No degradation was observed over 83 d when bed sediments were spiked with octylphenol and incubated under anaerobic conditions. [source] Effect of different levels of Quebracho tannin on nitrogen utilization and growth performance of Najdi sheep fed alfalfa (Medicago sativa) hay as a sole dietANIMAL SCIENCE JOURNAL, Issue 5 2009Soliman N. AL-DOBAIB ABSTRACT A commercial tannin source (Quebracho tannin, QT), containing 75% condensed tannins (CT) in dry matter (DM) was used to evaluate the effects of addition of different levels of QT to alfalfa hay on the in vitro degradation kinetics of organic matter (OM) and nitrogen (N) in experiment 1 (Exp. 1), N utilization and microbial N synthesis (MNS) in experiment 2 (Exp. 2) and growth performance of growing Najdi lambs in experiment 3 (Exp. 3). Alfalfa hay was treated with QT at the levels of 0, 1, 2 and 3% of DM to form four treatments of QT0, QT1, QT2 and QT3 to have actual levels of CT being 0, 0.75, 1.5 and 2.25% of DM, respectively. Degradation rate and the effective degradability of N were significantly decreased (P < 0.05) for QT2 and QT3 as compared with the QT0. In Exp. 2, digestibility coefficients for OM, neutral detergent fiber and acid detergent fiber were significantly decreased (P < 0.05) at QT3, whereas QT1 and QT2 showed no difference toQT0. In the metabolism trial (Exp. 2), digested N (DN) and urinary N (UN) excretion for QT2 and QT3 were significantly decreased (P < 0.05) compared to QT0 and QT1. The DN and UN as percentage of N intake were 79.2, 76.9, 75.5 and 69.8%; and 24.4, 22.6, 19.9 and 19.6% for QT0, QT1, QT2 and QT3, respectively. QT2 had the highest MNS and the lowest value was in QT3, the MNS of the treatments were 18.1, 18.7, 19.2 and 15.8 g/day for QT0, QT1, QT2 and QT3, respectively. In the growth trial of 56 days duration (Exp. 3, n = 24 lambs), the addition of QT at the level of QT2 enhanced (P < 0.05) the average daily gain and feed conversion rate compared with the QT0, while, QT1 and QT3 had intermediate values. It is concluded that alfalfa hay treated with QT at the level of 2% of DM could be used to protect alfalfa N from ruminal degradation that would lead to improve growth performance of lambs. [source] Degradation kinetics of ptaquiloside in soil and soil solutionENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2008Rikke Gleerup Ovesen Abstract Ptaquiloside (PTA) is a carcinogenic norsesquiterpene glycoside produced in bracken (Pteridium aquilinum (L.) Kuhn), a widespread, aggressive weed. Transfer of PTA to soil and soil solution eventually may contaminate groundwater and surface water. Degradation rates of PTA were quantified in soil and soil solutions in sandy and clayey soils subjected to high natural PTA loads from bracken stands. Degradation kinetics in moist soil could be fitted with the sum of a fast and a slow first-order reaction; the fast reaction contributed 20 to 50% of the total degradation of PTA. The fast reaction was similar in all horizons, with the rate constant k1F ranging between 0.23 and 1.5/h. The slow degradation, with the rate constant k1S ranging between 0.00067 and 0.029/h, was more than twice as fast in topsoils compared to subsoils, which is attributable to higher microbial activity in topsoils. Experiments with sterile controls confirmed that nonmicrobial degradation processes constituted more than 90% of the fast degradation and 50% of the slow degradation. The lower nonmicrobial degradation rate observed in the clayey compared with the sandy soil is attributed to a stabilizing effect of PTA by clay silicates. Ptaquiloside appeared to be stable in all soil solutions, in which no degradation was observed within a period of 28 d, in strong contrast to previous studies of hydrolysis rates in artificial aqueous electrolytes. The present study predicts that the risk of PTA leaching is controlled mainly by the residence time of pore water in soil, soil microbial activity, and content of organic matter and clay silicates. [source] A novel reactor for exploring the effect of water content on biofilter degradation ratesENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 2 2003Milinda A. Ranasinghe A novel batch recycle reactor was developed to investigate the effect of water content changes on the biological degradation rate of gas phase contaminants in low water content systems, such as biofilters. The reactor tightly controlled the water content of the unsaturated packing material using the principle of a suction cell. Matric potential in the compost was controlled between ,6 and ,36 cm H2O. A soil water retention curve relating matric potential to gravimetric water content was generated for the compost. Periodic dry weight analyses of reactor samples, together with the water retention curve, verified moisture content control. Runs were performed with toluene as the contaminant using unamended compost at a constant temperature of 30°C. Degradation results indicated a linear, biologically limited degradation region, followed by a non-linear region at lower concentrations. Elimination capacities were calculated for the linear region for different matric potentials along both the wetting and drying curves, and both changes in the water content and direction of approach affected the removal rates in the linear region. The elimination capacity ranged from 155 g/m3 hr to 24 g/m3 hr for toluene over the matric potential range investigated. Repeatability studies indicated that moisture content was most likely the parameter that influenced changes in performance. [source] Factors affecting the degradation of pharmaceuticals in agricultural soils,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2009Sara C. Monteiro Abstract Pharmaceuticals may be released to the soil environment through the application of biosolids to land. To understand those factors affecting the persistence of pharmaceuticals in the soil environment, the present study was performed to assess the effects of soil type, the presence of biosolids, and the impact of chemical mixture interactions on the degradation of three pharmaceuticals: naproxen, carbamazepine, and fluoxetine. Single-compound studies showed that naproxen degraded in a range of soils with half-lives ranging from 3.1 to 6.9 d and in biosolids with a half-life of 10.2 d. No relationships were observed between degradation rate and soil physicochemical properties and soil bioactivity. For naproxen, addition of biosolids to soils reduced the degradation rate observed in the soil-only studies, with half-lives in the soil-biosolid systems ranging from 3.9 to 15.1 d. Carbamazepine and fluoxetine were found to be persistent in soils, biosolids, and soil-biosolid mixtures. When degradation was assessed using a mixture of the three study compounds and the sulfonamide antibiotic sulfamethazine, the degradation behavior of fluoxetine and carbamazepine was similar to that observed in the single compound studies (i.e., no degradation). However, the degradation rate of naproxen in soils, biosolids, and soil-biosolid systems spiked with the mixture was significantly slower than in the single-compound studies. As degradation studies for risk assessment purposes are performed using single substances in soil-only studies, it is possible that current risk assessment procedures will underestimate environmental impacts. Further work is therefore warranted on a larger range of substances, soils, biosolid types, and chemical mixtures to better understand the fate of pharmaceuticals in terrestrial systems. [source] Laboratory persistence and fate of fluoxetine in aquatic environmentsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2006Jeong-Wook Kwon Abstract The persistence and fate of fluoxetine, a selective serotonin reuptake inhibitor, has been investigated in laboratory-scale experiments, including studies with various aqueous solutions, water/sediment systems, and activated sludge-amended medium. The samples were placed in the dark and/or in a growth chamber fitted with fluorescent lamps simulating the ultraviolet output of sunlight. Over a period of 30 d, fluoxetine was hydrolytically and photolytically stable in all aqueous solutions except synthetic humic water (pH 7), in which the degradation rate was increased by approximately 13-fold in comparison with buffered solutions at the same pH. Fluoxetine rapidly dissipated from the aqueous phase in water/sediment systems, primarily because of distribution to sediments. The dissipation rate from the aqueous phase was similar between light and dark systems, indicating a low contribution of photodegradation to the dissipation of fluoxetine in this system. The potential impact of fluoxetine in aquatic environments would be decreased because of adsorption to sediments. Based on results of ready-biodegradability investigations, fluoxetine would not be expected to rapidly biodegrade in wastewater treatment plants. A photoproduct was detected only in a sample of synthetic humic water and was identified as norfluoxetine formed by demethylation. Results indicate that fluoxetine is relatively recalcitrant to hydrolysis, photolysis, and microbial degradation and that it is rapidly removed from surface waters by adsorption to sediment, where it appears to be persistent. [source] Degradation of chlorpyrifos, fenamiphos, and chlorothalonil alone and in combination and their effects on soil microbial activityENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2002Brajesh Kumar Singh Abstract The effects of repeated application and of combinations of pesticides on their degradation rates in soil and on some soil microbial properties were studied. Repeated application of chlorpyrifos did not modify its degradation rate, whereas repeated applications of fenamiphos and chlorothalonil suppressed their own rates of degradation. When applied in combination, the presence of chlorothalonil reduced the degradation rate of both chlorpyrifos and fenamiphos, and the half-life of chlorothalonil was extended in the presence of chlorpyrifos. The dynamics of residues of the major metabolites of the different compounds were also affected by the pesticide combinations and, particularly, by the presence of chlorothalonil. The measured soil microbial parameters (enzyme activities and total microbial biomass) were stable in the pesticide-free control soils throughout the 90-d incubation period, but they were all adversely affected by the presence of chlorothalonil in the soil. The effects from fenamiphos or chlorpyrifos on the soil microbial characteristics were either very small or insignificant. [source] Effect of sorption and desorption resistance on aerobic trichloroethylene biodegradation in soilsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2002Sangjin Lee Abstract Biodegradation of trichloroethylene(TCE) by toluene-degrading bacteria was measured under aerobic conditions in aqueous and soil-slurry batch microcosms. For soil-phase experiments, a freshly contaminated soil and a soil containing only the desorption-resistant fraction of TCE were tested. In both cases, presence of soil resulted in biodegradation rates substantially lower than those determined in the absence of soil. In aqueous-phase experiments, an appreciable increase in the rate and extent of TCE biodegradation was observed in microcosms when toluene was added multiple times. The TCE degradation rates were clearly correlated with toluene dioxygenase (TOD) enzyme activity over time, thus providing an indication of the cometabolic pathway employed by the microbial population. In soil-slurry experiments containing freshly contaminated soil, a TCE degradation rate of approximately 150 ,g TCE/kg/h was observed during the first 39-h period, and then the TCE degradation rate slowed considerably to 0.59 and 0.84 ,g TCE/kg/h for microcosms receiving one and two additions of toluene, respectively. The TCE degradation rates in soil-slurry microcosms containing the desorption-resistant fraction of TCE-contaminated soil were approximately 0.27 and 0.32 ,g TCE/kg/h in microcosms receiving one and two additions of toluene, respectively. It is clear from these results that mass transfer into the aqueous phase limited bioavailability of TCE in the contaminated soil. [source] Biodegradable Polymer Crosslinker: Independent Control of Stiffness, Toughness, and Hydrogel Degradation RateADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Chaenyung Cha Abstract Hydrogels are being increasingly studied for use in various biomedical applications including drug delivery and tissue engineering. The successful use of a hydrogel in these applications greatly relies on a refined control of the mechanical properties including stiffness, toughness, and the degradation rate. However, it is still challenging to control the hydrogel properties in an independent manner due to the interdependency between hydrogel properties. Here it is hypothesized that a biodegradable polymeric crosslinker would allow for decoupling of the dependency between the properties of various hydrogel materials. This hypothesis is examined using oxidized methacrylic alginate (OMA). The OMA is synthesized by partially oxidizing alginate to generate hydrolytically labile units and conjugating methacrylic groups. It is used to crosslink poly(ethylene glycol) methacrylate and poly(N -hydroxymethyl acrylamide) to form three-dimensional hydrogel systems. OMA significantly improves rigidity and toughness of both hydrogels as compared with a small molecule crosslinker, and also controls the degradation rate of hydrogels depending on the oxidation degree, without altering their initial mechanical properties. The protein-release rate from a hydrogel and subsequent angiogenesis in vivo are thus regulated with the chemical structure of OMA. Overall, the results of this study suggests that the use of OMA as a crosslinker will allow the implantation of a hydrogel in tissue subject to an external mechanical loading with a desired protein-release profile. The OMA synthesized in this study will be, therefore, highly useful to independently control the mechanical properties and degradation rate of a wide array of hydrogels. [source] Biomedical Materials: Nanoporous Biodegradable Elastomers (Adv. Mater.ADVANCED MATERIALS, Issue 2 20092/2009) The mechanical properties and degradation rate of elastomers can be tailored with nanoporosity. The elastomers described in this study by Guillermo Ameer and co-workers (p. 188) are based on citric acid and are biocompatible. The nanopores also facilitate the entrapment and slow release of macromolecular therapeutics. The inside cover depicts the nano- and microarchitecture of the elastomer prior to pore collapse. [source] An oil-degrading bacterium: Rhodococcus erythropolis strain 3C-9 and its biosurfactantsJOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2007F. Peng Abstract Aims:, To isolate a biosurfactant-producing bacterium and find new products within its culture. Methods and Results:, A biosurfactant-producing bacterium identified as Rhodococcus erythropolis (3C-9 strain) was isolated from seaside soil. When n -hexadecane was supplied as the sole carbon source, two types of biosurfactants (free fatty acids and glycolipids) were detected in the supernatant of the bacterial culture by use of thin layer chromatography (TLC). Gas chromatography,mass spectrometry (GC,MS) analysis revealed that the former consisted of at least 12 free fatty acids of chain lengths from C9 to C22; and the latter contained 2 kinds of glycolipids (a glucolipid and a trehalose lipid), which were detected by use of TLC, as well as GC,MS. The hydrophobic moieties of both glycolipids consisted of seven types of straight-chain fatty acids of varying compositions, with chain lengths ranging from C10 to C18. It was also noted that biosurfactants of strain 3C-9 were produced in a manner that was growth-related and cannot be synthesized from water-soluble substrates. The effects to enhance the solubility of polycyclic aromatic hydrocarbons and the degradation rate of hexadecane were also tested. Conclusions:, The biosurfactants produced by strain 3C-9 of R. erythropolis included two kinds of glycolipids, as well as free fatty acids. These biosurfactants were notably different from those of previously reported Rhodococcus species, both in terms of their structure and chemical composition. Significance and Impact of the Study:, Strain 3C-9 of R. erythropolis is a competitive candidate for use in oil spill cleanup operations, or in new biosurfactant exploration. The findings in this report show that Rhodococcus is a natural reservoir of new biosurfactants. [source] Kinetics of the arginine metabolism of malolactic wine lactic acid bacteria Lactobacillus buchneri CUC-3 and Oenococcus oeni Lo111JOURNAL OF APPLIED MICROBIOLOGY, Issue 3 2000R. Mira de Orduña The excretion of citrulline, a precursor of carcinogenic ethyl carbamate, formed from arginine degradation by malolactic bacteria in wine is of toxicological concern. The arginine metabolism of resting cells of Lactobacillus buchneri CUC-3 and Oenococcus oeni Lo111 was examined. The citrulline excretion rate was found to be linearly correlated to the arginine degradation rate. It was possible to calculate an arginine to citrulline conversion ratio which could be used to predict the amount of citrulline expected after the degradation of a known quantity of arginine. The conversion ratios determined in this study were similar to data calculated from other authors for fermentations in wine and ranged between 4·0% and 7·7%. Ribose, fructose and glucose inhibited the degradation of arginine in Lact. buchneri CUC-3, and inhibition of arginine degradation by glucose correlated with higher arginine to citrulline conversion ratios. The work presents new results of arginine metabolism in malolactic bacteria and gives starting points for investigations in wine. [source] Facile method to manipulate the molecular weight and practical mass production of chitosan by mechanical shearing and concurrent ultrafiltration treatmentJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010Min Lang Tsai Abstract The objective of this study was to propose a facile method to manipulate the molecular weight and practical mass production of chitosan by mechanical shearing and concurrent ultrafiltration (UF) treatment. The proposed method was based on the degradation rate and rate constant of various process variables, such as: solution temperature, reaction time, concentration of chitosan solution, with or without concurrent removal of degraded fragments during mechanical shearing. The result obtained was that the degradation rate constant was 1.8,6.0 times higher for those using UF to remove smaller degraded molecules concurrently during treatment, than that without UF treatment. The degradation rate constant increased with increasing solution temperature; however, the solution temperature should not exceed than 50°C to prevent the undesired color changes of the resulting product. A method combining mechanical shearing/UF treatment at 50°C and ultrasonic radiation or microfluidization/UF treatment at 30°C is proposed here for a facile method to manipulate the molecular weight of the resultant chitosan with an energy saving, efficient and practical mass production. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Comparative study of the hydrolytic degradation of glycolide/L -lactide/,-caprolactone terpolymers initiated by zirconium(IV) acetylacetonate or stannous octoateJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Janusz Kasperczyk Abstract A series of copolymers have been synthesized by the ring-opening polymerization of glycolide, L -lactide, and ,-caprolactone with zirconium(IV) acetylacetonate [Zr(Acac)4] or stannous octoate [Sn(Oct)2] as the catalyst. The resulting terpolymers have been characterized by analytical techniques such as proton nuclear magnetic resonance, size exclusion chromatography, and differential scanning calorimetry. Data have confirmed that Sn(Oct)2 leads to less transesterification of polymer chains than Zr(Acac)4 under similar conditions. The various copolymers have been compression-molded and allowed to degrade in a pH 7.4 phosphate buffer at 37°C. The results show that the degradation rate depends not only on the copolymer composition but also on the chain microstructure, the Sn(Oct)2 -initiated copolymers degrading less rapidly than Zr(Acac)4 -initiated ones with more random chain structures. The caproyl component appears the most resistant to degradation as its content increases in almost all cases. Moreover, caproyl units exhibit a protecting effect on neighboring lactyl or glycolyl units. The glycolyl content exhibits different features: it decreases because of faster degradation of glycolyl units, which are more hydrophilic than caproyl and lactyl ones, remains stable in the case of abundant CGC sequences, which are very resistant to degradation, or even increases because of the formation of polyglycolide crystallites. Terpolymers can crystallize during degradation if the block length of one of the components is sufficiently long, even though they are amorphous initially. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Thermal properties of extruded/injection-molded poly(lactic acid) and biobased composites,,JOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008Abdellatif A. Mohamed Abstract To determine the degree of compatibility between poly(lactic acid) and different biomaterials (fibers), poly(lactic acid) was compounded with sugar beet pulp and apple fibers. The fibers were added in 85 : 15 and 70 : 30 poly(lactic acid)/fiber ratios. The composites were blended by extrusion followed by injection molding. Differential scanning calorimetry and thermogravimetric analysis were used to analyze the extruded and extruded/injection-molded composites. After melting in sealed differential scanning calorimetry pans, the composites were cooled through immersion in liquid nitrogen and aged (stored) at room temperature for 0, 7, 15, and 30 days. After storage, the samples were heated from 25 to 180°C at 10°C/min. The neat poly(lactic acid) showed a glass-transition transition at 59°C with a change in heat capacity (,Cp) value of 0.464. The glass transition was followed by crystallization and melting transitions. The enthalpic relaxation of the poly(lactic acid) and composites steadily increased as a function of the storage time. Although the presence of fibers had little effect on the enthalpic relaxation, injection molding reduced the enthalpic relaxation. The crystallinity percentage of the unprocessed neat poly(lactic acid) dropped by 95% after extrusion and by 80% for the extruded/injection-molded composites. The degradation was performed in air and nitrogen environments. The degradation activation energy of neat poly(lactic acid) exhibited a significant drop in the nitrogen environment, although it increased in air. This meant that the poly(lactic acid) was more resistant to degradation in the presence of oxygen. Overall, injection molding appeared to reduce the activation energy for all the composites. Sugar beet pulp significantly reduced the activation energy in a nitrogen environment. In an air environment, both sugar beet pulp and apple fibers increased the activation energy. The enzymatic degradation of the composites showed a higher degradation rate for the extruded samples versus the extruded/injection-molded composites, whereas the apple composites exhibited higher weight loss. The thermogravimetric analysis data showed that the degradation of unprocessed and extruded neat poly(lactic acid) followed a one-step mechanism, whereas extruded/injection-molded composites showed two-step degradation. A higher fiber content resulted in up to three-step degradation mechanisms. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source] Kinetic study of the thermal degradation of poly(aryl ether ketone)s containing 2,7-naphthalene moietiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008Si-Jie Liu Abstract The degradation of poly(aryl ether ketone) containing 2,7-naphthalene moieties was subjected to dynamic and isothermal thermogravimetry in nitrogen and air. The dynamic experiments showed that the initial degradation temperature, temperature for 5% weight loss, and temperature corresponding to the maximum degradation rate of poly(aryl ether ketone) containing 2,7-naphthalene moieties were a little higher than those of poly(ether ether ketone) and almost independent of the 2,7-naphthalene moiety content. The thermal stability of poly(aryl ether ketone) containing 2,7-naphthalene moieties in air was substantially less than that in nitrogen, and the degradation mechanism was more complex. The results obtained under the isothermal conditions were in agreement with the corresponding results obtained in nitrogen and air under the dynamic conditions. In the dynamic experiments, the apparent activation energies for the degradation processes were 240 and 218 kJ/mol in nitrogen and air for the second reaction stage as the heating rate was higher than 5°C/min. In the isothermal experiments, the apparent activation energies for the degradation processes were 222 and 190 kJ/mol in nitrogen and air, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Biodegradable blend films based on two polysaccharide derivatives and their use as ibuprofen-releasing matricesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007Ju-Zhen Yi Abstract Differential scanning calorimetry (DSC), FTIR, X-ray diffraction (XRD), and viscosity methods were used to examine the miscibility, interaction, and degradability of cationic guar gum (GG) and sodium carboxymethylcellulose (NaCMC) in their blend films. The experiment results prove that there exist electrostatic interactions and hydrogen bonding between GG and NaCMC. Blend films degrade quicker than pure GG or NaCMC film. Furthermore, the degradation rate of blend films is related to the interactions between GG and NaCMC. Based on the research of blend films as the drug carriers for Ibuprofen, it is found that the blend composition, initial drug concentration, and pH value affect the drug release and the GG/NaCMC blend films have good sustained release performance. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3553,3559, 2007 [source] Effects of a peripheral enamel bond on the long-term effectiveness of dentin bonding agents exposed to water in vitroJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2008Andre F. Reis Abstract This study evaluated the effects of water exposure on the in vitro microtensile bond strength (,TBS) of etch-and-rinse and self-etching adhesives to human dentin over a 1-year storage period. Five adhesive systems used were as follows: a one-step self-etching adhesive (One-up Bond F-OB), two two-step self-etching primers (Clearfil SE Bond-SE and Clearfil Protect Bond-CP), and two etch-and-rinse adhesives (Single Bond-SB and Prime&Bond NT-PB). Dentin surfaces were bonded, restored, and assigned to four subgroups, according to the degree of water exposure: 24 h of peripheral water exposure (24 h-PE) (having circumferential enamel); and 1 year of peripheral exposure (1 yr-PE), direct exposure (1 yr-DE) (dentin directly water-exposed), or directly exposed to oil only (no water exposure) (1 yr-DOE). A composite-enamel bond adjacent to the restoration is determined if the water exposure was peripheral or direct. After storage periods, specimens were serially sectioned, trimmed to an hourglass shape with a cross-sectional area of 1 mm2 at the interface, and tested in tension. Results were analyzed by two-way ANOVA and Tukey test (, = 0.05). No difference was found between 24 h-PE and 1 yr-PE for OB, CP, SB, and PB. However, ,TBS values significantly dropped after 1 yr-DE for SE, CP, SB, and PB. A decreased ,TBS was seen in SE after 1 yr-PE, but no differences existed between 1 yr-PE and 1 yr-DE. Similar or increased ,TBS values were noted in 1 yr-DOE for all adhesives. Water-storage for 1 year significantly decreased ,TBS for all adhesives. However, except for SE, the presence of a peripheral composite-enamel bond seemed to reduce the degradation rate in resin-dentin interfaces for all materials. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008 [source] Chitosan scaffolds for in vitro buffalo embryonic stem-like cell culture: An approach to tissue engineeringJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2007Wah W. Thein-Han Abstract Three-dimensional (3D) porous chitosan scaffolds are attractive candidates for tissue engineering applications. Chitosan scaffolds of 70, 88, and 95% degree of deacetylation (% DD) with the same molecular weight were developed and their properties with buffalo embryonic stem-like (ES-like) cells were investigated in vitro. Scaffolds were fabricated by freezing and lyophilization. They showed open pore structure with interconnecting pores under scanning electron microscopy (SEM). Higher % DD chitosan scaffolds had greater mechanical strength, slower degradation rate, lower water uptake ability, but similar water retention ability, when compared to lower % DD chitosan. As a strategy to tissue engineering, buffalo ES-like cells were cultured on scaffolds for 28 days. It appeared that chitosan was cytocompatible and cells proliferated well on 88 and 95% DD scaffolds. In addition, the buffalo ES-like cells maintained their pluripotency during the culture period. Furthermore, the SEM and histological study showed that the polygonal buffalo ES-like cells proliferated well and attached to the pores. This study proved that 3D biodegradable highly deacetylated chitosan scaffolds are promising candidates for ES-like cell based tissue engineering and this chitosan scaffold and ES cell based system can be used as in vitro model for subsequent clinical applications. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2007 [source] Ozonation of 1,3,6-naphthalenetrisulfonic acid in presence of heavy metalsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2004M Sánchez-Polo Abstract A study was conducted of the mechanisms by which heavy metals, commonly present in industrial effluents, increase the purification effectiveness of ozone in the removal of organic contaminants of low biodegradability. For this purpose, the ozonation of 1,3,6-naphthalenetrisulfonic acid (NTS) in the presence of Ni(II), Fe(II), Mn(II), Zn(II), Sr(II), Cr(III), Cd(II), Hg(II), and Cu(II) was examined. The presence of small amounts of Mn(II), Fe(II), Ni(II), Zn(II), and Cr(III) was observed in the system, increasing the degradation rate of the NTS and transforming the dissolved organic matter into CO2. The mineralization of the organic matter was highly favored, especially in the first minutes of treatment. The results obtained appear to indicate that the activity of the metals in the NTS ozonation process is related to their reduction potential. Thus, metals susceptible to oxidation by ozone are potential promoters of NTS ozonation. The presence of Fe(II) or Mn(II) during NTS ozonation increased its degradation rate by 79% and 72% respectively. Moreover, the reaction kinetics of metal oxidation with ozone controls the increase in the purification effectiveness of these systems. The presence of radical scavengers (tert -butanol or bicarbonate) in the medium during the promoted ozonation of NTS showed a negative effect on this process, and the NTS degradation rate decreased with an increasing concentration of these inhibitors in the system. These results confirm that the degradation of NTS by ozone in the presence of heavy metals occurs by a radical mechanism. O3/Zn(II) and O3/Fe(II) systems were applied to the decontamination of urban waste waters. The presence of Zn(II) or Fe(II) during the ozonation produced a reduction during the first 5 min of treatment of 20% or 44%, respectively, in the concentration of dissolved organic matter present in the system. These results show that ozonation in the presence of heavy metals is a highly promising system for the purification of waste waters and industrial effluents. Copyright © 2004 Society of Chemical Industry [source] Anthocyanin Degradation of Blueberry,Aronia Nectar in Glass Compared with Carton during StorageJOURNAL OF FOOD SCIENCE, Issue 8 2008K. Tro ABSTRACT:, Blueberry,aronia nectar is known as a rich source of anthocyanins, which are mostly destroyed during commercial storage of the product. The factors influencing the rate of degradation are connected to the oxygen protection offered by the packaging, as well as the type of anthocyanidin and the amount of glycosylated sugar. The current study was aimed to compare the stability of total anthocyanin between glass and carton packaging as well as to determine the stability of individual anthocyanin with respect to aglycone and glycosylated sugar. The degradation rate of total anthocyanin degradation rate was 22% higher in carton packaging than glass bottle. The ranking order of the stability of individual anthocyanin with respect to aglycone was as follows (from the most to least stable): cyanindin > peonidin > petunidin > malvidin = delphinidin. The ranking order of the stability of anthocyanins with respect to glycosylated sugars was as follows (from the most to least stable): glucose > galactose > arabinose. As individual anthocyanins have different degradation rates this study can be used to determine the most stable natural colorant and the most sensitive antioxidant among the anthocyanins tested. [source] Interleukin-4 and interleukin-10 modulate nuclear factor ,B activity and nitric oxide synthase-2 expression in Theiler's virus-infected brain astrocytesJOURNAL OF NEUROCHEMISTRY, Issue 6 2002Eduardo Molina-Holgado Abstract In brain astrocytes, nuclear factor ,B (NF-,B) is activated by stimuli that produce cellular stress causing the expression of genes involved in defence, including the inducible nitric oxide synthase (NOS-2). Theiler's murine encephalomyelitis virus (TMEV) induces a persistent CNS infection and chronic immune-mediated demyelination, similar to human multiple sclerosis. The cytokines interleukin (IL)-4 and IL-10 inhibit the expression of proinflammatory cytokines, counteracting the inflammatory process. Our study reports that infection of cultured astrocytes with TMEV resulted in a time-dependent phosphorylation of I,B,, degradation of I,B, and I,B,, activation of NF-,B and expression of NOS-2. The proteasome inhibitor MG-132 blocked TMEV-induced nitrite accumulation, NOS-2 mRNA expression and phospho-I,B, degradation, suggesting NF-,B-dependent NOS-2 expression. Pretreatment of astrocytes with IL-4 or IL-10 decreased p65 nuclear translocation, NF-,B binding activity and NOS-2 transcription. IL-4 and IL-10 caused an accumulation of I,B, in TMEV-infected astrocytes without affecting I,B, levels. The I,B kinase activity and the degradation rate of both I,Bs were not modified by either cytokine, suggesting de novo synthesis of I,B,. Indeed, IL-4 or IL-10 up-regulated I,B, mRNA levels after TMEV infection. Therefore, the accumulation of I,B, might impair the translocation of the NF-,B to the nucleus, mediating the inhibition of NF-,B activity. Overall, these data suggest a novel mechanism of action of IL-4 and IL-10, which abrogates NOS-2 expression in viral-infected glial cells. [source] Increased biofilm activity in BGAC reactorsAICHE JOURNAL, Issue 3 2005Moshe Herzberg Abstract In bioreactors systems granulated activated carbon (GAC) was proven to be an advantageous biofilm carrier over inert media with similar physical properties (nonadsorbing carbon) under conditions of pollutant partial penetration in the biofilm. Results from laboratory experiments using atrazine degrading bacteria (Pseudomonas ADP) and modeling assuming GAC adsorption/desorption mechanism, showed higher atrazine degradation rate resulting in better effluent quality in the biofilm granulated activated carbon (BGAC) reactor. Increased biofilm activity due to the double flux of substrate from the bulk liquid and from the GAC can explain the better performance of the BGAC reactor. © 2005 American Institute of Chemical Engineers AIChE J, 51: 1042,1047, 2005 [source] The effect of bulking agents on the chemical stability of acid-sensitive compounds in freeze-dried formulations: Sucrose inversion studyJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2009Enxian Lu Abstract The goal of the study was to evaluate the impact of amorphous bulking agents on the chemical stability of freeze-dried materials. Polyvinylpyrrolidone and dextran of different molecular weights and lactose were used as bulking agents, and sucrose was used as an example of an acid-sensitive compound. Lyophiles containing bulking agent and sucrose at 10:1 (w/w) ratio, citrate buffer, and optionally bromophenol blue (pH indicator) were tested by X-ray powder diffractometry, differential scanning calorimetry, and Karl Fischer titrimetry. Diffuse reflectance UV,vis spectroscopy was used to obtain the concentration ratio of the deprotonated (In2,) to the protonated (HIn,) indicator species, from which the Hammett acidity function (H2,) was calculated. The extent of sucrose inversion in lyophiles stored at 60°C was quantified by HPLC. The bulking agent had a major impact on both the apparent solid-state acidity (H2,) and the degradation rate, with the degradation rate constants value highest for dextran lyophiles (most "acidic", lower H2,) followed by lactose and polyvinylpyrrolidone lyophile (least "acidic", higher H2,). The Hammett acidity function can be used as an empirical solid-state acidity scale, to predict the rank-order stability of acid-sensitive compounds in lyophiles prepared with different bulking agents. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:3387,3396, 2009 [source] Analysis of the Stability and Degradation Products of TriptolideJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 1 2000YAN PING MAO Triptolide is the major active ingredient of the Chinese herbal remedy Tripterygium wilfordii Hook F. (TwHF). As triptolide content is used to estimate the potency of preparations of TwHF, assessment of its stability is warranted. The accelerated stability of triptolide was investigated in 5% ethanol solution in a light-protected environment at pH 6.9, within a temperature range of 60,90°C. The observed degradation rate followed first-order kinetics. The degradation rate constant (K25°C) obtained by trending line analysis of Arrhenius plots of triptolide was 1.4125 times 10,4 h,1. The times to degrade 10% (t1/10) and 50% (t1/2) at 25°C were 31 and 204 days, respectively. Stability tests of triptolide in different solvents and different pH conditions (pH 4,10) in a light-protected environment at room temperature demonstrated that basic medium and a hydrophilic solvent were the major factors that accelerated the degradation of triptolide. Triptolide exhibited the fastest degradation rate at pH 10 and the slowest rate at pH 6. In a solvent comparison, triptolide was found to be very stable in chloroform. The stability of triptolide in organic polar solvents tested at both 100% and 90% concentration was greater in ethanol than in methanol than in dimethylsulphoxide. Stability was also greater in a mixture of solvent: pH 6 buffer (9:1) than in 100% solvent alone. An exception was ethyl acetate, which is less polar than the other solvents tested, but permitted more rapid degradation of triptolide. Two of the degradation products of triptolide were isolated and identified by HPLC and mass spectroscopy as triptriolide and triptonide. This suggested that the decomposition of triptolide occurred at the C12 and C13 epoxy group and the C14 hydroxyl. The opening of the C12 and C13 epoxy is an irreversible reaction, but the reaction occurring on the C14 hydroxyl is reversible. These results show that the major degradation pathway of triptolide involves decomposition of the C12 and C13 epoxy group. Since this reaction is very slow at 4°C at pH 6, stability is enhanced under these conditions. [source] An efficient approach to synthesize polysaccharides- graft -poly(p -dioxanone) copolymers as potential drug carriersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2009Fang Lu Abstract Starch and poly(p -dioxanone) (PPDO) are the natural and synthetic biodegradable and biocompatible polymers, respectively. Their copolymers can find extensive applications in biomedical materials. However, it is very difficult to synthesize starch- graft -PPDO copolymers in common organic solvents with very good solubility. In this article, well-defined polysaccharides- graft -poly(p -dioxanone) (SAn -PPDO) copolymers were successfully synthesized via the ring-opening polymerization of p -dioxanone (PDO) with an acetylated starch (SA) initiator and a Sn(Oct)2 catalyst in bulk. The copolymers were characterized via Fourier transform infrared spectroscopy, 1H NMR, gel permeation chromatography, thermogravimetric analysis (TG), differential scanning calorimetry, and wide angle x-ray diffraction. The in vitro degradation results showed that the introduction of SA segments into the backbone chains of the copolymers led to an enhancement of the degradation rate, and the degradation rate of SAn -PPDO increased with the increase of SA wt %. Microspheres with an average volume diameter of 20 ,m, which will have potential applications in controlled release of drugs, were successfully prepared by using these new copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5344,5353, 2009 [source] Synthesis and characterization of multiblock copolymers based on L -lactic acid, citric acid, and poly(ethylene glycol)JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2003Fanglian Yao Abstract Because poly(L -lactic acid) (PLLA) is a biodegradable polyester with low immunogenicity and good biocompatibility, it is used as a biomaterial. However, hydrophobic PLLA does not have any reactive groups. Thus, its application is limited. To increase the hydrophilicity of PLLA and accelerate its degradation rate, functionalized pendant groups and blocks were introduced through copolymerization with citric acid and poly(ethylene glycol) (PEG), respectively. This article describes the synthesis and characterization of poly(L -lactic- co -citric acid) (PLCA)-PLLA and PLCA-PEG multiblock copolymers. The results indicated that the hydrolysis rate was enhanced, and the hydrophilicity was improved because of the incorporation of carboxyl groups in PLCA-PLLA. The joining of the PEG block led to improved hydrophilicity of PLCA, and the degradation rate of PLCA-PEG accelerated as compared with that of PLCA-PLLA. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2073,2081, 2003 [source] Evaluation of heat and oxidative damage during storage of processed tomato products.JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 9 2003Abstract Tomato products (pulp, puree and paste) submitted to accelerated aging (30, 40 and 50 °C for 3 months) were studied to evaluate variations in the kinetics of the degradation of antioxidants and antioxidant activity. The carotenoids lycopene and ,-carotene, ascorbic acid, rutin and total phenolics were analysed. The antioxidant activity was measured using (a) the xanthine oxidase (XOD)/xanthine system, which generates superoxide radicals and hydrogen peroxide, and (b) the linoleic acid/CuSO4 system, which promotes lipid peroxidation. The ascorbic acid content decreased even at 30 °C, following pseudo-first-order kinetics, with an activation energy of 105 200 J mol,1 for tomato pulp and 23 600 J mol,1 for tomato paste. The lower the initial ascorbic acid content, the higher was the degradation rate. Variations in phenolic compounds occurred at 40 °C and higher, following pseudo-zero order kinetics. The antioxidant activity of the hydrophilic fraction of the tomato products depended on both antioxidant degradation and the Maillard reaction and could not be described by a kinetic model. The ,-carotene content decreased even at 30 °C, whereas the lycopene content was stable in all samples. The antioxidant activity of the lipophilic fraction of the tomato products decreased following pseudo-first order kinetics, with an activation energy of 22 200 J mol,1 for tomato pulp and 20 200 J mol,1 for tomato paste. It is concluded that significant ,oxidative damage' can occur in tomato products during their commercial shelf-life. Copyright © 2003 Society of Chemical Industry [source] | ||||||||||||||||||||||||||||||||||||||||