An osmotic micro-pump integrated on a microfluidic chip for perfusion cell culture

A novel microfluidic chip integrating an osmosis-based micro-pump was developed and used for perfusion cell culture. The micro-pump includes two sealed chambers, i.e., the inner osmotic reagent chamber and the outer water chamber, sandwiching a semi-permeable membrane. The water in the outer chamber was forced to flow through the membrane into the inner chamber via osmosis, facilitating continuous flow of fluidic zone in the channel. An average flow rate of 0.33 μL min⁻¹ was obtained within 50 h along with a precision of 4.3% RSD (n = 51) by using a 100 mg mL⁻¹ polyvinylpyrrolidone (PVP) solution as the osmotic driving reagent and a flow passage area of 0.98 cm² of the semi-permeable membrane. The power-free micro-pump has been demonstrated to be pulse-free offering stable flow rates during long-term operation. The present microfluidic chip has been successfully applied for the perfusion culture of human colorectal carcinoma cell by continuously refreshing the culture medium with the osmotic micro-pump. In addition, in situ cell immunostaining was also performed on the microchip by driving all the reagent zones with the integrated micro-pump.     

A model for methanol transport through Nafion membrane in diffusion cell

The transport of methanol through Nafion^® membrane in diffusion cell is investigated using the open circuit potential method at different initial methanol concentration solutions. A simple mathematical model based on quasi-steady-state diffusion for the transport of methanol across the membrane in a diffusion cell is developed to simulate the experimental data in order to measure the methanol permeability. The influence of the diffusion cell parameters and thickness of the membrane on the methanol permeability measurement has been evaluated and analyzed. By means of Maclaurin expansion technique, this model can be used to predict the deviation of methanol permeability determined by steady-state diffusion model.     

Dehumidification and humidification of air by surface-soaked liquid membrane module with triethylene glycol

A novel liquid membrane system, a surface-soaked liquid membrane, with triethylene glycol (TEG) on the hydrophilic-treated surface of the hydrophobic microporous membrane was developed and used for the dehumidification and humidification of air. The selectivity of the TEG liquid membrane for water vapor with respect to air was over 2000, which was derived from the selective absorption of the TEG liquid. A flat-type liquid membrane module with a dual membrane surface was designed, of which the TEG liquid membrane thickness was 18 μm and the permeation area was 0.13 m². The liquid membrane humidifier and dehumidifier consisted of the membrane module and a vacuum pump. As a dehumidifier, the membrane system recovered water vapor at 4.1 g/h from 70%RH room air at 298 K. For use as a humidifier, the air flow was effectively humidified by the permeated water vapor through the membrane module. The effects of the air humidity and sweep air flow rate were studied and discussed. Simple model calculations based on the permeability of the water vapor well predicted the experimental results.     

Water transport coefficient distribution through the membrane in a polymer electrolyte fuel cell

The net water transport coefficient through the membrane, defined as the ratio of the net water flux from the anode to cathode to the protonic flux, is used as a quantitative measure of water management in a polymer electrolyte fuel cell (PEFC). In this paper we report on experimental measurements of the net water transport coefficient distribution for the first time. This is accomplished by making simultaneous current and species distribution measurements along the flow channel of an instrumented PEFC via a multi-channel potentiostat and two micro gas chromatographs. The net water transport coefficient profile along the flow channels is then determined by a control-volume analysis under various anode and cathode inlet relative humidity (RH) at 80 °C and 2 atm. It is found that the local current density is dominated by the membrane hydration and that the gas RH has a large effect on water transport through the membrane. Very small or negative water transport coefficients are obtained, indicating strong water back diffusion through the 30 μm Gore-Select^® membrane used in this study.     

Effect of thickness of the PPO membranes on the surface morphology

The effect of membrane thickness on surface morphology has been studied for the case of polyphenylene oxide (PPO) membranes cast from solutions of PPO in trichloroethylene (TCE). Both roughness and nodule size decrease with increasing membrane thickness up to a certain point after which they begin to increase. Minima in roughness and nodule size are observed for 9–11 μm thick films. These minima depend on initial polymer concentration in the casting solution. At a membrane thickness greater than 11 μm, super nodular aggregates are formed. A mechanism based on Marangoni and Rayleigh number is presented.     

Effect of the magnetic field on the hydrodynamic permeability of a membrane

The present paper concerns the influence of the magnetic field on the permeability of a membrane of solid cylindrical particles covered with porous layer. Here, we have considered the flow along the axis of cylinder and the alignment of uniform magnetic field is assumed to be perpendicular to the axis. The Brinkman equation is used for flow through porous region and Stokes equation is used for flow through clear fluid region. To model flow through assemblage of particles, cell model technique has been used i.e. the porous cylindrical shell is assumed to be confined within a hypothetical cell of same geometry. The stress jump condition has been employed at the fluid-porous interface and all four alternative conditions Happel, Kuwabara, Kvashnin and Mehta-Morse/Cunningham are used at the hypothetical cell. Effect of the Hartmann number on the hydrodynamic permeability of the membrane is discussed.     

Direct visual observation of yeast deposition and removal during microfiltration

Periodic reverse flow through membranes is an effective technique to remove foulants from microfiltration (MF) membrane surfaces. This work explored direct visual observation (DVO) of yeast deposition and subsequent removal via backwashing and single backpulses using microvideo photography with cellulose-acetate (CA) and Anopore anodised-alumina (AN) MF membranes. Foulant deposited less uniformly on the surfaces of the CA membranes than on the AN membrane surfaces during forward filtration. Foulant cake layers of approximately 30 μm thickness formed on both membranes after forward filtration for 1–2 h, leading to fouled-membrane fluxes of only 15–25% of the clean-membrane fluxes.Foulant was removed by reverse flow from the CA membrane surfaces in clumps. The time constant for foulant removal was determined from photomicrographs to be approximately 0.2 s, and 95% of the membrane surface was cleaned within 1 s of backpulsing, resulting in 95% recovery of the initial flux. The foulant cake was also removed from the AN membranes in clumps, though much of the membrane remained covered in a monolayer of yeast. The flux through the membrane covered with a full monolayer was determined during forward filtration to be about 70% of the clean membrane flux.A model for flux recovery is proposed which takes into account the fraction of the membrane surface which is completely cleaned as well as the fraction which remains covered in a foulant monolayer. The predicted and experimentally-determined recovered fluxes as a function of backpulse duration are in very good agreement.     

The effect of polymer swelling and resistance to flow on solvent diffusion and permeability

The main purpose of this paper is to test the model of molecular sorption [Vesely D. Polymer 2001;42:4417-22] for Case II type diffusion by measuring the effect of sorption/swelling and resistance to flow through the swollen region on the mass transport of solvents in glassy amorphous polymer. The system of methanol and polymethylmethacrylate (PMMA) has been selected for easy comparison with the existing literature data.The weight loss of penetrant permeating through the polymer has been monitored using a permeability cell placed on a balance (gravimetry). The rate of diffusion and swelling has been measured using light microscopy on samples cut after different elapsed time exposure to the solvent.The contribution of polymer swelling and resistance to flow has been evaluated by comparing the mass transport during diffusion and permeation processes. It is shown that for thin films the thickness independent component of the mass transport process (swelling) makes a significant contribution to the diffusion rate. For thicker samples the thickness dependent component (the resistance to flow through the swollen polymer) dominates both, diffusion and permeation.     

Improving real-time measurement of H/D exchange using a FTIR biospectroscopic probe

We describe the improvement of a novel approach to investigating hydrogen/deuterium (H/D) exchange kinetics in biomolecules using transmission infrared spectroscopy. The method makes use of a Fourier transform infrared spectrometer coupled with a microdialysis flow cell to determine exchange rates of labile hydrogens. With this cell system, the monitoring of exchange reactions has been studied here as a function of some cell characteristics such as: (a) dialysis membrane surface contacting both the H₂O and D₂O compartments; (b) molecular cutoff of dialysis membrane; and (c) distance between the cell-filling holes. The best improvement has been obtained by increasing the dialysis membrane surface followed by increase of molecular cutoff. However, not significant differences were found using various distances between filling holes. The fastest exchange rate which can be measured with the cell system used here is found to be k = 0.41 ± 0.02 min⁻¹, that is, about threefold greater than the one got in a previous work. This microdialysis flow cell has been used here for the study of H/D exchange in nucleic acids with subsequent structural analysis by 2D correlation spectroscopy.     

The effect of oscillatory flow on crossflow microfiltration of beer in a tubular mineral membrane system – Membrane fouling resistance decrease and energetic considerations

We have investigated the consequences due to the changes in hydrodynamics above the membrane surface brought about by an oscillatory flow in the crossflow microfiltration (CFMF) of beer on a tubular mineral membrane. Experimental results in oscillatory flow filtration were analysed in terms of membrane resistance to filtration and energy consumption and compared with steady flow filtration. Two types of beers were used: a clarified beer composed of colloids and macromolecular material and a rough beer containing in addition yeast cells. Oscillatory flow was found to decrease membrane fouling resistance (up to 100%) in rough beer filtration in the presence of a yeast cell cake layer on the membrane surface, whereas it has no effect in clarified beer filtration in the presence of membrane clogging. The detrimental effect of transmembrane pressure on membrane resistance (at ΔP>1 bar) has been emphasized in both oscillatory and steady flows. The time-average hydraulic power dissipated by friction in the filtration module, in relation with the absolute value of the time-average flow rate in oscillatory flow, was found to be systematically higher than for steady flow filtration. However, the hydraulic energy per unit volume of permeate in the microfiltration of rough beer under oscillatory flow was close to that in steady flow at a time-average tangential velocity of 3 m/s. By considering the specific energy (per m³ of permeate) related to the kinetic energy applied to fluid in oscillatory and steady flow modes, the system by gas compression in oscillatory flow led to a reduction of specific energy ranging from 15% to 40%. Finally the ratio of hydraulic power consumed in oscillatory and steady flow was compared with a theoretical calculation based on the assumption that the oscillating flow regime is quasi-steady.     

Flux enhancement during dean vortex tubular membrane nanofiltration. 10. Design,construction, and system characterization

Controlled centrifugal instabilities (called Dean vortices) resulting from flow in helical tubes have been used to reduce concentration polarization and membrane fouling during nanofiltration. These vortices enhance back-migration of solute through convective flow away from the membrane–solution interface and allow for increased membrane permeation rates. Based on the theory of Dean vortex flow, a new prototype vortex generating tubular nanofiltration element was designed. Two sets of nanofiltration modules were constructed; a linear module and a new module containing hollow fibers wrapped around rods of small diameter in helical geometry. Optimization of the design is discussed with respect to the diameter and thickness of the hollow fibers. Axial pressure drop and energy consumption measurements for the helical module agreed very well with available correlations for various experimental conditions. Water permeabilities for the helical modules were similar to those of the conventional linear modules. No significant effect of pH was observed on the water permeability.     

Potentiometric flow injection sensing system for determination of heparin based on current-controlled release of protamine

A flow injection system incorporated with a polycation-sensitive polymeric membrane electrode in the flow cell is proposed for potentiometric determination of heparin. An external current in nano-ampere scale is continuously applied across the polymeric membrane for controlled release of protamine from the inner filling solution to the sample solution, which makes the electrode membrane regenerate quickly after each measurement. The protamine released at membrane–sample interface is consumed by heparin injected into the flow cell via their strong electrostatic interaction, thus decreasing the measured potential, by which heparin can be detected. Under optimized conditions, a linear relationship between the potential peak height and the concentration of heparin in the sample solution can be obtained in the range of 0.1–2.0 U mL⁻¹, and the detection limit is 0.06 U mL⁻¹. The proposed potentiometric sensing system has been successfully applied to the determination of heparin in undiluted sheep whole blood.     

On the no-field method for void time determination in flow field-flow fractionation

Elution time measurements of colloidal particles injected in a symmetrical flow field-flow fractionation (flow FFF) system when the inlet and outlet cross-flow connections are closed have been performed. This no-field method has been proposed earlier for void time (and void volume) determination in flow FFF Giddings et al. (1977). The elution times observed were much larger than expected on the basis of the channel geometrical volume and the flow rate. In order to explain these discrepancies, a flow model allowing the carrier liquid to flow through the porous walls toward the reservoirs located behind the porous elements and along these reservoirs was developed. The ratio between the observed elution time and expected one is found to depend only on a parameter which is a function of the effective permeability and thickness of the porous elements and of the channel thickness and length. The permeabilities of the frits used in the system were measured. Their values lead to predicted elution times in reasonable agreement with experimental ones, taking into account likely membrane protrusion inside the channel on system assembly. They comfort the basic feature of the flow model, in the no-field case. The carrier liquid mostly bypasses the channel to flow along the system mainly in the reservoir. It flows through the porous walls toward the reservoirs near channel inlet and again through the porous walls from the reservoirs to the channel near channel outlet before exiting the system. In order to estimate the extent of this bypassing process, it is desirable that the hydrodynamic characteristics of the permeable elements (permeability and thickness) are provided by flow FFF manufacturers. The model applies to symmetrical as well as asymmetrical flow FFF systems.     

SU-8 flow field plates for a micro PEMFC

A SU-8 photoresist microfabrication process was developed for micro proton exchange membrane fuel cell flow structures for both anode and cathode flow field plates with a cross section of 5 cm² (22.5 mm×22.5 mm) and thickness (for a single cell) of about 750 µm. The new design for flow field plates would have SU-8 used as not only a photoresist but also as a microstructure material. A thickness of 30 nm Pt sputter loading deposited onto a Nafion 117 for membrane electrode assembly was made, with both scanning electron microscopy and atomic force microscopy characterization. Air flows were completed in hydrogen fuel cells with air breathing and forced air flows of low input pressure as well as low velocity. Performance tests of polarization curves and power density distribution as well as impendence measurements were conducted and discussed to examine the effects of orientation of the cathode surface with five hydrogen feeding rates as well as different airflow feeding modes.     

Flow injection potentiometric detection of trimethylamine in seafood using tungsten oxide electrode

A simple flow injection gas/diffusion method for the determination of trimethylamine (TMA) in seafood with potentiometric detection using tungsten oxide electrode has been developed. The method is based on the diffusion of TMA through a PTFE membrane from a sodium hydroxide donor stream to a phosphate buffer acceptor stream. The TMA in the acceptor stream passes through an electrochemical flow cell containing a tungsten oxide wire and a silver/silver chloride electrode, where TMA was sensitively detected. The parameters affecting the sensitivity of the electrode such as sodium hydroxide concentration, buffer concentration, pH, flow rate and injected volume were studied in details. The electrode response was linear in the concentration range from 1 to 10 μg ml⁻¹ TMA with a correlation coefficient (R²) of 0.991 and a detection limit of 0.05 μg ml⁻¹ TMA. The intra- and inter-days precision (R.S.D.) was found to be, respectively, 1.20 and 1.6% (n=6). The method was applied to the determination of TMA in fish tissue and recoveries of 99-100% were obtained for fish extracts. Results were in close agreement with those obtained by the existing classical official method. Common interference from those species that can diffuse through the membrane were removed by the addition of formaldehyde to the seafood extract. The method is simple, feasible with satisfactory accuracy and precision and thus, could be used for monitoring seafood quality with a sampling rate of 20±2 sample h⁻¹.     

Thickness decrease of a grafted polyelectrolyte membrane exposed to shear flow

The effect of the shear flow on the thickness change of a polyelectrolyte membrane grafted onto a glass substrate was directly investigated with a flow cell combined with a confocal laser scanning microscope. The membrane thickness decreased proportionally to an increase in the shear stress of the flow when the shear rate exceeded a critical value of 1 s^?1. The higher the ionic strength was of the fluid, the greater the thinning effect was. The correlation between the critical shear rate and the relaxation of the polymer in the gel membrane was examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2808–2815, 2003     

Determination of 2-ethylhexyl 4-(dimethylamino) benzoate using membrane-assisted liquid–liquid extraction and gas chromatography-mass spectrometric detection

A flow-cell for micro-porous membrane liquid–liquid extraction with a sheet membrane was used to extract 2-ethylhexyl 4-(dimethylamino) benzoate (EDB) from urine of solar-cream users and spiked wine samples. The cell enabled the target analyte to be extracted from 7.9 mL of donor solution into 200 μL of acceptor solution (decane). After extraction, the acceptor solution was transferred to a micro-vial for GC-MS analysis without derivation. In this work, variables affecting the enrichment factor were also studied, such as organic solvent, extraction time, recirculation flow of the donor solution through the donor chamber, presence of potassium chloride and ethanol in the donor solution and pH. The method has been evaluated in terms of linearity, sensitivity, precision, limits of detection and quantification and extraction efficiency. Limits of quantification were 1 and 3 μg L⁻¹ EDB for urine and wine, respectively. Quantitative analysis has been carried out by applying the method of standard additions. Within- and between-day relative standard deviations were lower than 12% and 20%, respectively. EDB was found in the urine of users of cream containing EDB in the concentration interval 1.2–7.2 μg L⁻¹. Therefore, this provides evidence of EDB dermal absorption and subsequent excretion through the urinary tract. EDB was not found in the analysed wine samples.     

High-performance collection of palladium ions in acidic media using nucleic-acid-base-immobilized porous hollow-fiber membranes

We prepared nucleic-acid-base-immobilized porous membranes of a hollow-fiber form with pore size, porosity, and thickness of 0.2 μm, 70%, and approximately 0.7 mm, respectively. Glycidyl methacrylate was graft-polymerized onto a polyethylene-made porous hollow-fiber membrane, followed by ring-opening of the epoxy group with the amino groups of adenine, guanine, and cytosine. The collection of palladium ions was achievable during the permeation of palladium chloride solution through the adenine-immobilized porous hollow-fiber membrane. The diffusional mass-transfer resistance of palladium ion to immobilized adenine was negligible because palladium ion was transported by permeative flow through the pores. The adenine-immobilized porous membrane with an immobilization density of 0.85 mol/kg of the membrane exhibited the highest molar binding ratio of palladium ion to immobilized adenine of 0.31 in 1 M hydrochloric acid. In addition, a quantitative elution with 4 M hydrochloric acid was experimentally demonstrated.     

Characteristic simulation with various anode support thicknesses of membrane electrode assembly in SOFC

This study focuses on the research of solid oxide fuel cell (SOFC) and proposes reasonably practical designs, analyses, and numerical analyses with coupling software in physics, COMSOL Multiphysics, as the analysis tool to discuss the effects on the SOFC performance. This research applies the design of electrode support (anode support) to substitute the original electrolyte support, Yttria-stabilized zirconia, so that the electrolyte membrane could form a membrane to reduce ohmic resistance and increase power density. This study further discusses the effects of various flow fields (counterflow and co-flow) on internal mass transfer and SOFC performance. The findings show that the cell performance of SOFC with co-flow is better than counterpart with counterflow under anode support thickness 1,000 μm. Regarding the analyses of porosity effect with the porosity 0.7 and tortuosity 4.5, the power density reaches the maximum that could enhance the cell performance.     

An on-line method for determining ATPase bioactivity and its application to human umbilical vein endothelial cell membrane

Based on the determination of inorganic phosphate (the product of ATP dephosphorylation by ATPase), a method for on-line determination of bioactivity of ATPase on cell membrane is presented, in which on-line sampling of cell membrane and separation of inorganic phosphate is employed in a flow injection system. The method has been successfully applied to the investigation of variation of ATPase from human umbilical vein endothelial cell membrane; the results show that ATPase activity decreases with elapsed time studied, which may supply important information for the pertinent studies on cell membrane enzymes bioactivity.