Polydimethylsiloxane modified chitosan. Part III: Preparation and characterization of hybrid membranes

The paper deals with the synthesis of organic–inorganic hybrid membranes, Hy, obtained by simultaneous grafting and crosslinking of chitosan with epoxy-terminated polydimethylsiloxane and γ-glycidoxypropyltrimethoxysilane. Porous membranes, HyP, were also obtained by acid decomposition, at different temperatures (25 and 50 °C), of calcium carbonate porogenic agent trapped inside the material. As proved by electron and atomic force microscopy, the non-porous membrane is a phase segregated material with spherical domains (10–40 μm) of silica core covered by hydrophobic siloxane in a hydrophilic chitosan matrix. The porous membranes showed different morphologies with irregular circular pores of 10–30 μm diameters for the membranes obtained at lower temperature, while the membranes prepared at 50 °C tend to adopt a plan-parallel porosity. The water contact angles of hybrid membranes (78°) and pure chitosan membranes (72°) indicated a lower hydrophilic character of modified chitosan. As a result of the crosslinking and of increased hydrophobicity, the hybrid membranes were characterized by a smaller water swelling degree (about 30%) as compared to pure chitosan membrane (700%). However, the presence of the pores in HyP membranes determined an increase of the water adsorption (maximum swelling degree, about 100%). The hybrid membranes possess a slightly higher thermal stability as compared to chitosan (first initial decomposition temperature, 147 and 175 °C for chitosan and hybrid membranes, respectively), but a lower one as compared to pure polydimethylsiloxane. The high storage modulus of chitosan (about 5.1 × 10⁹ Pa at 20 °C) is decreased by about one order of magnitude by the introduction of the highly flexible polysiloxane and the hybrid membranes are more flexible.     

Speciation of platinum in blood plasma and urine by micelle-mediated extraction and graphite furnace atomic absorption spectrometry

A highly sensitive and selective technique for the speciation of platinum by cloud point extraction prior to determination by graphite furnace atomic absorption spectrometry (GFAAS) was described. The separation of Pt(II) from Pt(IV) was performed in the presence of 4-(p-chlorophenyl)-1-(pyridin-2-yl)thiosemicarbazide (HCPTS) as chelating agent and Triton X-114 as a non-ionic surfactant. The extraction of Pt(II)–HCPTS complex needs temperature higher than the cloud point temperature of Triton X-114 and pH = 7, while Pt(IV) remains in the aqueous phase. The Pt(II) in the surfactant phase was analyzed by GFAAS, and the concentration of Pt(IV) was calculated by subtraction of Pt(II) from total platinum which was directly determined by GFAAS. The effect of pH, concentration of chelating agent, surfactant, and equilibration temperature were investigated. An enrichment factor of 42 was obtained for the preconcentration of Pt(II) with 50 mL solution. Under the optimum experimental conditions, the calibration curve was linear up to 30 μg L^?1 with detection limit of 0.08 μg L^?1 and the relative standard deviation was 1.8%. No considerable interference was observed due to the presence of coexisting anions and cations. The accuracy of the results was verified by analyzing different spiked samples (tap water, blood plasma and urine). The proposed method was applied to the speciation analysis of Pt in blood plasma and urine with satisfactory results.     

Serum selenium levels of the very low birth weight premature newborn infants with bronchopulmonary dysplasia

BackgroundThe selenium (Se) is an essential trace element that has a critical role in synthesis and activity of a number of selenoproteins with protective properties against free radical damage. This study was conducted to detect the serum Se concentration in very low birth weight (VLBW) preterm infants and its association with bronchopulmonary dysplasia (BPD).Materials and methodsCord blood Se concentration was determined in 54 neonates with gestation age 30 week or less. Another sample was obtained from these infants at day 28 of birth and serum Se levels were measured by atomic absorption spectrophotometer. All neonates were followed for oxygen dependency at 28 day after birth and 36 week postmenstrual age.ResultsThe mean cord blood Se concentration in studied neonates was 64.78 ± 20.73 μg L^?1. Serum Se concentration was 60.33 ± 26.62 μg L^?1 at age 28-day. No significant correlation was observed for serum Se concentration at birth and at one month after birth (r = ?0.04, p = 0.72). BPD was diagnosed in 25 neonates (46%). The mean serum Se concentration at one month was 57.16 ± 29.68 μg L^?1 in patients with BPD (25 cases) and 63.27 ± 23.6 μg L^?1 in 29 patients without BPD (p = 0.40).ConclusionIn our study, serum Se concentration at 28 day of birth was lower than cord blood levels in preterm neonates, but we have not found significant difference among patients who had BPD or not with respect to serum Se concentrations at this age.     

Equilibria and kinetics of protein transfer to and from affinity-based reverse micelles of Span 85 modified with Cibacron Blue F-3GA

Sorbitan trioleate was modified with Cibacron Blue F-3GA (CB) to create an affinity surfactant and to form affinity-based reverse micelles in n-hexane. The partitioning equilibria and the extraction kinetics of lysozyme and bovine serum albumin (BSA) were then examined. The solubilization capacity of the reverse micellar system for lysozyme increased linearly with increasing the CB concentration from 0.1 to 0.5 mmol L⁻¹. In contrast, the capacity for BSA at 0.5 mmol L⁻¹ of coupled CB was only about one-fifth that for lysozyme. It indicates a strong steric hindrance effect of the micelles for the high molecular mass protein. The overall volumetric mass transfer coefficient of lysozyme in the forward extraction increased from 0.43 × 10⁻³ to 1.25 × 10⁻³ s⁻¹ with increasing CB concentration from 0.1 to 0.5 mmol L⁻¹. Due to the high molecular mass of BSA, its volumetric mass transfer coefficient in the forward extraction was only one-sixth that of lysozyme. The ratio of the coefficient in the back extraction to that in the forward extraction was less than 0.03, much lower than those in other micellar systems. It indicates that the interfacial resistance in this system was severer than in others.     

Behavioral thermoregulation and critical thermal limits of giant keyhole limpet Megathura crenulata (Sowerby 1825) (Mollusca; Vetigastropoda)

The thermoregulatory behavior of the giant keyhole limpet Megathura crenulata was determined in a horizontal thermal gradient during the day at 18.9 °C and 18.3 °C for the night. The final preferendum determined for giant keyhole limpets was of 18.6±1.2 °C.Limpets' displacement velocity was 10.0±3.9 cm h⁻¹ during the light phase and 8.4±1.6 cm h⁻¹ during the dark phase. The thermotolerance (measured as CTMax at 50%) was determined in a keyhole limpet in three acclimation temperatures 17, 20, and 23 °C. Limpets were subjected to water increasing temperatures at a rate of 1 °C every 30 min, until they detached from the substrate. The critical thermal maximum at 50% was 27.2, 27.9 and 28.3 °C respectively.     

Characterization of methylated azopyridine as a potential electron transfer mediator for electroenzymatic systems

N,N'-dimethyl-4,4'-azopyridinium methyl sulfate (MAZP) was characterized as an electron transfer mediator for oxidation reactions catalyzed by NAD⁺- and pyrroloquinoline quinone (PQQ)-dependent alcohol dehydrogenases. The bimolecular rate constant of NADH reactivity with MAZP was defined as (2.2 ± 0.1) × 10⁵ M⁻¹ s⁻¹, whereas the bimolecular rate constant of reactivity of the reduced form of PQQ-dependent alcohol dehydrogenase with MAZP was determined to be (4.7 ± 0.1) × 10⁴ M⁻¹ s⁻¹. The use of MAZP for the regeneration of the cofactors was investigated by applying the electrochemical oxidation of the mediator. The total turnover numbers of mediator MAZP and cofactor NADH for ethanol oxidation catalyzed by NAD⁺-dependent alcohol dehydrogenase depended on the concentration of the substrate and the duration of the electrolysis, and the yield of the reaction was limited by the enzyme inactivation and the electrochemical process. The PQQ-dependent alcohol dehydrogenase was more stable, and the turnover number of the enzyme reached a value of 2.3 × 10³. In addition, oxidation of 1,2-propanediol catalyzed by the PQQ-dependent alcohol dehydrogenase proceeded enantioselectively to yield l-lactic acid.     

Glass transition temperatures and water sorption isotherms of cassava starch

The effect of water content on the glass transition temperatures of cassava starch was determined by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). Samples were transformed to the amorphous state by compression molding at high temperature (as demonstrated by wide angle X-ray diffraction, WAXS), and then the samples were moisture conditioned. Both DSC and DMTA showed that water anti-plasticized cassava starch at lower moisture contents, and plasticized it at higher water contents. Samples with higher moisture contents stored at room temperature, 45 °C and 80 °C underwent retrogradation as indicated by WAXS. Sorption isotherms of cassava starch showed that for a_w values lower than around 0.85, the sorption capacity decreased with increasing temperature; while the opposite behavior was observed at a_w > 0.85. This inversion point (a_w = 0.85) was attributed to the fact that more active sites were exposed to the adsorption processes, due to the enhanced molecular mobility promoted in the amorphous regions by starch crystallization.     

Amperometric acetylthiocholine sensor based on acetylcholinesterase immobilized on nanostructured polymer membrane containing gold nanoparticles

Poly(acrylonitrile-methylmethacrylate-sodium vinylsulfonate) membranes were chemically modified and loaded with gold nanoparticles. Acetylcholinesterase was immobilized on the prepared membranes in accordance with two distinctive procedures, the first of which involved immobilization of the enzyme by convection, and the other by diffusion. The prepared enzyme carriers were used for the construction of amperometric biosensors for detection of acetylthiocholine.Two sets of experiments were carried out. The first set was designed so that to evaluate the effects of the gold nanoparticle deployment and the immobilization procedures over the biosensor effectiveness. The other set of experiments was conducted in order to determine the influence of the individual components of the enzyme mixture, containing gold nanoparticles, acetylcholinesterase, bovine serum albumin and glutaraldehyde, over the current output of the constructed acetylthiocholine biosensors. The optimum composition of the mixture was determined to be as follows: enzyme, 0.1 U ml^?1; gold nanoparticles, 0.50 ml (per 1 ml enzyme mixture); albumin, 0.5% and glutaraldehyde, 0.7%.On the basis of the experimental results, the most efficient enzyme membrane was selected and used for the preparation of an acetylthiocholine biosensor. Its basic amperometric characteristics were investigated. A calibration plot was obtained for ATCh concentration ranging from 10 to 400 μM. A linear interval was detected along the calibration curve from 10 to 170 μM. The sensitivity of the constructed biosensor was calculated to be 0.066 μA μM^?1 cm^?2. The correlation coefficient for this concentration range was 0.996. The detection limit with regard to ATCh was calculated to be 1.80 μM.The potential application of the biosensor for detection and quantification of organophosphate pesticides was investigated as well. It was tested against sample solutions of Paraoxon. The biosensor detection limit for Paraoxon was determined, 7.39 × 10^?11 g l^?1, as well as the concentration interval (10^?10 to 10^?7 g l^?1) within which the biosensor response was linearly dependant on Paraoxon concentration.Finally the storage stability of the enzyme carrier was traced for a period of 50 days. After storage for 20 days the sensor retained 75% of its initial current response and after 30 days ?25%.     

A novel approach to the measurement of surfactant parameters in arthropod digestive juices

In arthropods, the determination of two important parameters of digestive juices, i.e. the total surfactant concentration and the critical micelle concentration (CMC), is challenging due to small sample volumes and low surfactant concentrations. In this work, we report a successful implementation of potentiometric titrations using the surfactant ion-selective electrode (SISE) and the pyrene fluorescence method (PFM) for the determination of the total surfactant concentration and CMC in the digestive juice of terrestrial isopod crustaceans Porcellio scaber. Pooled digestive juice extracts of four (SISE) or two (PFM) animals were used per measurement run. In both cases, digestive juice extracts in 100 μL of deionized water were sufficient for one measurement run. The total surfactant concentration of P. scaber digestive juice was determined to be 9.2 ± 3.5 mM and the CMC was approximately 90 μM. Our work presents an important improvement towards easy CMC determination in small volume samples in comparison with the commonly used stalagmometric technique, where much larger sample volumes are usually needed. To date, the total surfactant concentration was not measured in the digestive juices of arthropods other than Homarus vulgaris, Astacus leptodactylus and Cancer pagurus, for which complex separation and analytical techniques were required. Our results obtained by SISE and PFM therefore present the first successful quantification of surfactants and their CMC in small volumes of arthropod digestive juice without prior separation or purification techniques.     

Optimization and immobilization of amylase obtained from halotolerant bacteria isolated from solar salterns

The objective of the present study was to isolate halotolerant bacteria from the sediment sample collected from Marakanam Solar Salterns, Tamil Nadu, India using NaCl supplemented media and screened for amylase production. Among the 22 isolates recovered, two strains that had immense potential were selected for amylase production and designated as P1 and P2. The phylogenetic analysis revealed that P1 and P2 have highest homology with Pontibacillus chungwhensis (99%) and Bacillus barbaricus (100%). Their amylase activity was optimized to obtain high yield under various temperature, pH and NaCl concentration. P1 and P2 strain showed respective, amylase activity maximum at 35 °C and 40 °C; pH 7.0 and 8.0; 1.5 M and 1.0 M NaCl concentration. Further under optimized conditions, the amylase activity of P1 strain (49.6 U mL^?1) was higher than P2 strain. Therefore, the amylase enzyme isolated from P. chungwhensis P1 was immobilized in sodium alginate beads. Compared to the free enzyme form (49.6 U mL^?1), the immobilized enzyme showed higher amylase activity as 90.3 U mL^?1. The enzyme was further purified partially and the molecular mass was determined as 40 kDa by SDS–PAGE. Thus, high activity of amylase even under increased NaCl concentration would render immense benefits in food processing industries.     

Influence of operating conditions on the degradation kinetics of an azo-dye in a vertical flow constructed wetland using a simple mechanistic model

A simple mechanistic model of a pulse-fed vertical flow constructed wetland is presented. In this work, the model is shown to accurately reproduce measurements of outlet flow and outlet concentration obtained while treating a synthetic wastewater containing the azo-dye, Acid Orange 7 (AO7). Application of the model to results obtained in summer and winter gave a unique apparent first-order kinetic constant (4.1 × 10^?7 s^?1), indicating that the activation energy is low. The treatment efficiencies determined while operating in a pseudo-stationary state for a high AO7 inlet concentration of 692 ± 92 mg L^?1 were 68 ± 5 and 70 ± 21% in summer and winter, respectively, for a flooding level of 21% and a pulse feeding of 13 min each 3 h. At the end of these trials (lasting more than 1 year), the system clogged. This occurrence was accurately modelled by including a variation in the free surface area with the liquid height above the bed surface. The model was then applied to design a robust dye wastewater treatment system producing water suitable for discharge to aquatic bodies. Model sensitivity to positive and negative evapotranspiration, that mimic variations in rainfall and temperature, and to variations in the rate constant, accounting for different azo-dyes biodegradability, was analyzed.     

A Kazal-type serine proteinase inhibitor from chicken liver (clTI-1): Purification,primary structure,and inhibitory properties

Low-molecular-mass trypsin inhibitor (clTI-1; chicken liver Trypsin Inhibitor-1) was purified from chicken liver by extraction with perchloric acid, ammonium sulfate precipitation, a combination of ethanol-acetone fractionation followed by gel filtration, ion-exchange chromatography and RP-HPLC on a C18 column. The inhibitor occurs in two isoforms with molecular masses of 5938.56 and 6026.29 Da (determined by MALDI TOFF mass spectrometry). The complete amino acid sequences of both isoforms were determined (UniProtKB/Swiss-Prot P85000; ISK1L_CHICK). The inhibitor shows a high homology to Kazal-type family inhibitors, especially to trypsin/acrosin inhibitors and pancreatic secretory trypsin inhibitors. clTI-1 inhibits both bovine and porcine trypsin (K_a = 1.1 × 10⁹ M^?1 and 2.5 × 10⁹ M^?1, respectively). Significant differences were shown in the inhibition of the anionic and cationic forms of chicken trypsin (K_a = 4.5 × 10⁸ M^?1 and 1.2 × 10¹⁰ M^?1). Weak interaction with human plasmin (K_a = 1.2 × 10⁷ M^?1) was also revealed.     

Preparation and characterization of cockle shell aragonite nanocomposite porous 3D scaffolds for bone repair

The demands for applicable tissue-engineered scaffolds that can be used to repair load-bearing segmental bone defects (SBDs) is vital and in increasing demand. In this study, seven different combinations of 3 dimensional (3D) novel nanocomposite porous structured scaffolds were fabricated to rebuild SBDs using an extraordinary blend of cockle shells (CaCo₃) nanoparticles (CCN), gelatin, dextran and dextrin to structure an ideal bone scaffold with adequate degradation rate using the Freeze Drying Method (FDM) and labeled as 5211, 5400, 6211, 6300, 7101, 7200 and 8100. The micron sized cockle shells powder obtained (75 µm) was made into nanoparticles using mechano-chemical, top-down method of nanoparticles synthesis with the presence of the surfactant BS-12 (dodecyl dimethyl bataine). The phase purity and crystallographic structures, the chemical functionality and the thermal characterization of the scaffolds’ powder were recognized using X-Ray Diffractometer (XRD), Fourier transform infrared (FTIR) spectrophotometer and Differential Scanning Calorimetry (DSC) respectively. Characterizations of the scaffolds were assessed by Scanning Electron Microscopy (SEM), Degradation Manner, Water Absorption Test, Swelling Test, Mechanical Test and Porosity Test. Top-down method produced cockle shell nanoparticles having averagely range 37.8±3–55.2±9 nm in size, which were determined using Transmission Electron Microscope (TEM). A mainly aragonite form of calcium carbonate was identified in both XRD and FTIR for all scaffolds, while the melting (Tm) and transition (Tg) temperatures were identified using DSC with the range of Tm 62.4–75.5 °C and of Tg 230.6–232.5 °C. The newly prepared scaffolds were with the following characteristics: (i) good biocompatibility and biodegradability, (ii) appropriate surface chemistry and (iii) highly porous, with interconnected pore network. Engineering analyses showed that scaffold 5211 possessed 3D interconnected homogenous porous structure with a porosity of about 49%, pore sizes ranging from 8.97 to 337 µm, mechanical strength 20.3 MPa, Young's Modulus 271±63 MPa and enzymatic degradation rate 22.7 within 14 days.     

Comparison of two methods of synchronization of estrus in brown brocket deer (Mazama gouazoubira)

This study aimed to establish a protocol for synchronization of estrus in brown brocket deer (Mazama gouazoubira). Two groups of hinds (n = 3) were submitted to two different protocols: Treatment 1 received an intravaginal progesterone (CIDR^®) device for 8 days, followed by 265 μg injection of cloprostenol at the time of removal; and Treatment 2 received two injections of 265 μg of cloprostenol 11 days apart. After 30 days, each group of three hinds received the other treatment. Treatment efficacy was evaluated by reproductive behavior, fecal progestin and estrogen concentration and the observation of CL by laparoscopy 6 days after the end of estrus. All the hinds (100%) had estrous behavior upon the completion of treatment, but a significant difference occurred between the time of onset, 70.5 ± 5.0 h for Treatment 1 and 52.3 ± 5.6 h for Treatment 2. The mean estrus duration time (34.7 ± 4.50 and 37.0 ± 8.11 h), ovulation rates (5/6 and 4/6), mean CL size (4.85 ± 0.74 and 3.21 ± 0.19 mm) and mean fecal progestin concentration at 6 days after the end of estrus (865.53 ± 76.59 and 1073.35 ± 106.82 ng/g feces) were not significantly different between treatments. There was no difference in fecal estrogen concentrations throughout the treatment and the greatest values of the estrogen:progestin ratio coincided with estrous behavior. Although fertility was not evaluated directly, both treatments were effective in synchronizing estrus in the species M. gouazoubira, with the formation of functional corpora lutea.     

A comparative calorimetric and spectroscopic study of the effects of cholesterol and of the plant sterols β-sitosterol and stigmasterol on the thermotropic phase behavior and organization of dipalmitoylphosphatidylcholine bilayer membranes

We performed comparative DSC and FTIR spectroscopic measurements of the effects of β-sitosterol (Sito) and stigmasterol (Stig) on the thermotropic phase behavior and organization of DPPC bilayers. Sito and Stig are the major sterols in the biological membranes of higher plants, whereas cholesterol (Chol) is the major sterol in mammalian membranes. Sito differs in structure from Chol in having an ethyl group at C24 of the alkyl side-chain, and Stig in having both the C24 ethyl group and trans-double bond at C22. Our DSC studies indicate that the progressive incorporation of Sito and Stig decrease the temperature and cooperativity of the pretransition of DPPC to a slightly lesser and greater extent than Chol, respectively, but the pretransition persists to 10 mol % sterol concentration in all cases. All three sterols produce essentially identical effects on the thermodynamic parameters of the sharp component of the DPPC main phase transition. However, the ability to increase the temperature and decrease the cooperativity and enthalpy of the broad component decreases in the order Chol > Sito > Stig. Nevertheless, at higher Sito/Stig concentrations, there is no evidence of sterol crystallites. Our FTIR spectroscopic studies demonstrate that Sito and especially Stig incorporation produces a smaller ordering of the hydrocarbon chains of fluid DPPC bilayers than does Chol. In general, the presence of a C24 ethyl group in the alkyl side-chain reduces the characteristic effects of Chol on the thermotropic phase behavior and organization of DPPC bilayer membranes, and a trans-double bond at C22 magnifies this effect.     

Immobilization of lipase on epoxy-activated Purolite® A109 and its post-immobilization stabilization

In this study, Purolite^® A109, polystyrenic macroporous resin, was used as immobilization support due to its good mechanical properties and high particle diameter (400 μm), which enables efficient application in enzyme reactors due to lower pressure drops. The surface of support had been modified with epichlorhydrine and was tested in lipase immobilization. Optimized procedure for support modification proved to be more efficient than conventional procedure for hydroxy groups (at 22 °C for 18 h), since duration of procedure was shortened to 40 min by performing modification at 52 °C resulting with almost doubled concentration of epoxy groups (563 μmol g⁻¹). Lipase immobilized on epoxy-modified support showed significantly improved thermal stability comparing to both, free form and commercial immobilized preparation (Novozym^® 435). The highest activity (47.5 IU g⁻¹) and thermal stability (2.5 times higher half-life than at low ionic strength) were obtained with lipase immobilized in high ionic strength. Thermal stability of immobilized lipase was further improved by blocking unreacted epoxy groups on supports surface with amino acids. The most efficient was treatment with phenylalanine, since in such a way blocked immobilized enzyme retained 65% of initial activity after 8 h incubation at 65 °C, while non-blocked derivative retained 12%.     

Synthesis,radiosynthesis and first in vitro evaluation of novel PET-tracers for the dopamine transporter: [11C]IPCIT and [18F]FE@IPCIT

IntroductionPresent data indicate that merging beneficial structural elements from previously published DAT-ligands highest DAT affinity, selectivity and a suitable metabolic profile should be achieved. This combination led to the development of IPCIT and FE@IPCIT.MethodsPrecursor synthesis was done starting from cocaine in a six step reaction. O-[¹¹C]-methylation was established using [¹¹C]methyl iodide, optimized and subsequently automated. Small scale ¹⁸F-fluroroethylation as well as optimization of reaction parameters and automation were performed. Affinity and selectivity of the candidate substances were tested in standard binding experiments on human membranes. Metabolic stability and blood–brain-barrier (BBB) penetration were determined.ResultsPrecursor compound, IPCITacid, and reference compounds, IPCIT and FE@IPCIT, were obtained in 4.9%, 12.7% and 4.1% yield, respectively. Automated radiosynthesis of [¹¹C]IPCIT yielded 1.9 ± 0.7 GBq (12.5 ± 4%, corrected for decay). Optimum parameters for ¹⁸F-fluoroethylation were 110 °C for 15 min under TBAH catalysis, yielding 67 ± 16% radiochemical incorporation. Affinity was determined as 1.7 ± 0.6 nM for IPCIT, 1.3 ± 0.2 nM for FE@IPCIT and 37 ± 13 nM for the precursor molecule, IPCIT-acid. Results from in vitro and in silico evaluations revealed high stability but also high lipophilicity.ConclusionPresent data indicate high affinity and stability of both IPCIT and FE@IPCIT. Radiolabelling, optimization of reaction parameters and automation succeeded. On the other hand, data concerning BBB-penetration are not promising.     

Microfiltration membrane performance in two-chamber microbial fuel cells

Proton exchange membranes (PEMs) are typically used in two-chamber microbial fuel cells (MFCs) to separate the anode and cathode chambers while allowing protons to pass between the chambers. However, PEMs such as Nafion are not cost-effective. To reduce the cost of MFCs, we examined the performances of cellulose acetate microfiltration membranes in a two-chamber microbial fuel cell using acetate. The internal resistance, the maximum power density and the coulombic efficiency (CE) of the microfiltration membrane MFC (MMMFC) were 263 Ω, 0.831 ± 0.016 W/m² and 38.5 ± 3.5%, respectively, in a fed-batch mode, while the corresponding values of the MFC using a PEM were 267 Ω, 0.872 ± 0.021 W/m² and 74.7 ± 4.6%, respectively. We further used the MMMFC for poultry wastewater treatment. The maximum power density of 0.746 ± 0.024 W/m² and CE of 35.3 ± 3.2% were achieved when the poultry wastewater containing 566 mg/L COD was used, removing 81.6 ± 6.6% of the COD. These results demonstrate microfiltration membranes, compared with PEMs, have a similar internal resistance and reduce pH gradient across the membrane. They parallel PEMs in maximum power density, while CE is much lower due to the oxygen and substrate diffusion. The MMMFC was effective for poultry wastewater treatment with high COD removal.     

Exenatide-loaded PLGA microspheres with improved glycemic control: In vitro bioactivity and in vivo pharmacokinetic profiles after subcutaneous administration to SD rats

A subcutaneous exenatide delivery system was developed and characterized in vitro and in vivo. The results clearly showed that the exenatide loaded PLGA microspheres prepared by using a non-aqueous processing medium had low burst release and high drug encapsulation efficiency. Exenatide loaded in the microspheres preserved its bioactivity. The pharmacokinetics parameters were determined after subcutaneous administration of microspheres to SD rats. The plasma concentration of the single dose of the sustained-release microspheres attained C_max of 108.19 ± 14.92 ng/ml at t_max of 1.33 ± 0.58 h and the t_1/2 was 120.65 ± 44.18 h. There was a linear correlation between the in vitro and in vivo release behavior (R² = 0.888). Exenatide loaded microspheres may prove to have great potential for clinical use.     

Oxygen regulates the effective diffusion distance of nitric oxide in the aortic wall

Endothelium-derived nitric oxide (NO) is critical in maintaining vascular tone. Accumulating evidence shows that NO bioavailability is regulated by oxygen concentration. However, it is unclear to what extent the oxygen concentration regulates NO bioavailability in the vascular wall. In this study, a recently developed experimental setup was used to measure the NO diffusion flux across the aortic wall at various oxygen concentrations. It was observed that for a constant NO concentration at the endothelial surface, the measured NO diffusion flux out of the adventitial surface at [O₂] = 0 μM is around fivefold greater than at [O₂] = 150 μM, indicating that NO is consumed in the aortic wall in an oxygen-dependent manner. Analysis of experimental data shows that the rate of NO consumption in the aortic wall is first order with respect to [NO] and first order with respect to [O₂], and the rate constant k₁ was determined as (4.0 ± 0.3) × 10³ M^?1 s^?1. Computer simulations demonstrate that NO concentration distribution significantly changes with oxygen concentration and the effective NO diffusion distance at low oxygen level ([O₂] ≤ 25 μM) is significantly longer than that at high oxygen level ([O₂] = 200 μM). These results suggest that oxygen-dependent NO consumption may play an important role in dilating blood vessels during hypoxia by increasing the effective NO diffusion distance.