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Microfluidic Channels (microfluidic + channel)

Distribution by Scientific Domains

Polymers and Materials Science	41%
Life Sciences	41%
Engineering	6%

Selected Abstracts

Fabrication of lab-on chip platforms by hot embossing and photo patterning

BIOTECHNOLOGY JOURNAL, Issue 11 2007
Devendra K. Maurya
Abstract In this paper, we review the approaches developed in our laboratory to fabricate polymer-based microfluidic devices to suit a range of applications in bio- or chemical analysis. Thermoplastic materials such as polycarbonate (PC) and poly(methyl methacrylate) (PMMA) are used to fabricate microfluidic devices via hot embossing. To emboss microchannels, we use hard stamps fabricated in silicon or soft stamps molded on poly(dimethylsiloxane) (PDMS). Hard stamps are fabricated on silicon wafers through photolithography and deep reactive ion etching (DRIE). Soft stamps are fabricated by casting PDMS prepolymer on silicon molds. To enclose the fluidic channels, direct fusion bonding was found to produce the highest bond strength with minimal structural deformation. One-step photolithographic methods have also been explored to produce via photochemical patterning microfluidic structures in photocurable materials. We use the photocurable capabilities of a PDMS copolymer, which incorporates a methacrylate crosslinker. Microfluidic channels are produced via one step-photopatterning processes by crosslinking the prepolymer mixture through a photomask. The smaller feature size attainable was 100 ,m. Structures with higher spatial resolution are fabricated through a photoimprinting process whereby a mold is pressed against the precured mixture during UV crosslinking exposure. The application of the fabricated fluidic devices in electrophoretic ion analysis is also presented. [source]

Rapid Generation of Biologically Relevant Hydrogels Containing Long-Range Chemical Gradients

ADVANCED FUNCTIONAL MATERIALS, Issue 1 2010
Jiankang He
Abstract Many biological processes are regulated by gradients of bioactive chemicals. Thus, the generation of materials with embedded chemical gradients may be beneficial for understanding biological phenomena and generating tissue-mimetic constructs. Here a simple and versatile method to rapidly generate materials containing centimeter-long gradients of chemical properties in a microfluidic channel is described. The formation of a chemical gradient is initiated by a passive-pump-induced forward flow and further developed during an evaporation-induced backward flow. The gradient is spatially controlled by the backward flow time and the hydrogel material containing the gradient is synthesized via photopolymerization. Gradients of a cell-adhesion ligand, Arg-Gly-Asp-Ser (RGDS), are incorporated in poly(ethylene glycol)-diacrylate (PEG-DA) hydrogels to test the response of endothelial cells. The cells attach and spread along the hydrogel material in a manner consistent with the RGDS-gradient profile. A hydrogel containing a PEG-DA concentration gradient and constant RGDS concentration is also shown. The morphology of cells cultured on such hydrogel changes from round in the lower PEG-DA concentration regions to well-spread in the higher PEG-DA concentration regions. This approach is expected to be a valuable tool to investigate the cell,material interactions in a simple and high-throughput manner and to design graded biomimetic materials for tissue engineering applications. [source]

Solvent-Resistant PDMS Microfluidic Devices with Hybrid Inorganic/Organic Polymer Coatings

ADVANCED FUNCTIONAL MATERIALS, Issue 23 2009
Bo-Yeol Kim
Abstract This study presents a method for the fabrication of solvent-resistant poly(dimethylsiloxane) (PDMS) microfluidic devices by coating the microfluidic channel with a hybrid inorganic/organic polymer (HR4). This modification dramatically increases the resistance of PDMS microfluidic channels to various solvents, because it leads to a significant reduction in the rate of solvent absorption and consequent swelling. The compatibility of modified PDMS with a wide range of solvents is investigated by evaluating the swelling ratio measured through weight changes in a standard block. The HR4-modified PDMS microfluidic device can be applied to the formation of water-in-oil (W/O) and oil-in-water (O/W) emulsions. The generation of organic solvent droplets with high monodispersity in the microfluidic device without swelling problems is demonstrated. The advantage of this proposed method is that it can be used to rapidly fabricate microfluidic devices using the bulk properties of PDMS, while also increasing their resistance to various organic solvents. This high compatibility with a variety of solvents of HR4-modified PDMS can expand the application of microfluidic systems to many research fields. [source]

Capillary Force Lithography: A Versatile Tool for Structured Biomaterials Interface Towards Cell and Tissue Engineering,

ADVANCED FUNCTIONAL MATERIALS, Issue 17 2009
Kahp-Yang Suh
Abstract This Feature Article aims to provide an in-depth overview of the recently developed molding technologies termed capillary force lithography (CFL) that can be used to control the cellular microenvironment towards cell and tissue engineering. Patterned polymer films provide a fertile ground for controlling various aspects of the cellular microenvironment such as cell,substrate and cell,cell interactions at the micro- and nanoscale. Patterning thin polymer films by molding typically involves several physical forces such as capillary, hydrostatic, and dispersion forces. If these forces are precisely controlled, the polymer films can be molded into the features of a polymeric mold with high pattern fidelity and physical integrity. The patterns can be made either with the substrate surface clearly exposed or unexposed depending on the pattern size and material properties used in the patterning. The former (exposed substrate) can be used to adhere proteins or cells on pre-defined locations of a substrate or within a microfluidic channel using an adhesion-repelling polymer such as poly(ethylene glycol) (PEG)-based polymer and hyaluronic acid (HA). Also, the patterns can be used to co-culture different cells types with molding-assisted layer-by-layer deposition. In comparison, the latter (unexposed substrate) can be used to control the biophysical surrounding of a cell with tailored mechanical properties of the material. The surface micropatterns can be used to engineer cellular and multi-cellular architecture, resulting in changes of the cell shape and the cytoskeletal structures. Also, the nanoscale patterns can be used to affect various aspects of the cellular behavior, such as adhesion, proliferation, migration, and differentiation. [source]

Highly sensitive spin-valve devices for chip-cytometers

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2009
Jong Wook Roh
Abstract The highly sensitive spin-valve devices integrated with a microfluidic channel have been studied for cell counting in a chip-cytometer. The presence or absence of a single magnetic bead was successfully detected by direct measurement of fringe fields emanating from magnetic beads using spin-valve devices. The real-time detection was also successfully confirmed by the direct measurement of magnetic fields generated from the magnetic beads passing an active sensing area of a spin-valve device integrated with a microfluidic channel. Our results show the possibility of implementing a chip-cytometer for biological applications using the highly sensitive spin-valve devices integrated with a microfluidic device. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Cell Detachment Model for an Antibody-Based Microfluidic Cancer Screening System

BIOTECHNOLOGY PROGRESS, Issue 5 2006
Swapnil P. Wankhede
We consider cells bound to the floor of a microfluidic channel and present a model of their flow-induced detachment. We approximate hydrodynamic force and cell elastic response using static finite-element simulation of a single cell. Detachment is assumed to occur when hydrodynamic and adhesive forces are roughly equal. The result is extended to multiple cells at the device level using a sigmoidal curve fit. The model is applied to a microfluidic cancer-screening device that discriminates between normal epithelial cells and cells infected with human papillomavirus (HPV), on the basis of increased expression of the transmembrane protein ,6 integrin in the latter. Here, the cells to be tested are bound to a microchannel floor coated with anti ,6 integrin antibodies. In an appropriate flow rate range, normal cells are washed away while HPV-infected cells remain bound. The model allows interpolation between data points to choose the optimal flow rate and provides insight into interaction of cell mechanical properties and the flow-induced detachment mechanism. Notably, the results suggest a significant influence of cell elastic response on detachment. [source]

Regeneration-type nerve electrode using bundled microfluidic channels

ELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 4 2009
Takafumi Suzuki
Abstract Neural interface devices that will allow signals from the human nervous system to control external equipment are extremely important for the next generation of prosthetic systems. A novel multichannel regeneration-type nerve electrode designed to record from and stimulate peripheral nerves has been developed to allow the control of artificial hands and to generate artificial sensations. In this study a novel flexible regeneration microelectrode based on the nerve regeneration principle was designed and fabricated using MEMS technologies. The electrode, which was fabricated on a 25-µm-thick parylene C substrate, has multiple fluidic channels. Each fluidic channel was 100µm wide×30µm high×1500µm long and featured multiple electrodes inside them as recording and stimulating sites. They also served as guidance channels for the regenerating axons. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(4): 29,34, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10059 [source]

Parameters governing reproducibility of flow properties of porous monoliths photopatterned within microfluidic channels

ELECTROPHORESIS, Issue 14 2010
Mei He
Abstract We report the patternability as well as the reproducibility and stability of flow resistance of polymer monolithic beds photopatterned within microfluidic channels as a function of initial reagent composition and preparation conditions. 2-Hydroxyethyl methacrylate and ethylene dimethacrylate-based polymer monoliths were selectively photopatterned within microchannels and their flow resistance was evaluated using a photobleaching, TOF linear flow rate measurement method developed in our lab. This measurement technique was found to be significantly more informative for columns formed in microfluidic channels compared with bulk monolith characterization by mercury intrusion porosimetry. 1-Octanol was determined to provide sharp bed edge formation and relatively low flow resistance by photopatterning relative to other porogenic solvents. Compared with literature formulations which did not achieve good flow stability and reproducibility from batch to batch, using 2-hydroxyethyl methacrylate, ethylene dimethacrylate and 1-octanol as porogenic solvents, less than 4% RSD was achieved in flow stability over 7 days for monoliths prepared with 60,80% crosslinker(monomer+crosslinker) ratio. Column-to-column variation of 5% RSD was obtained in this composition range. These results demonstrate that photopatterning of uniform polymer monolithic beds, which is critical for applications in multiplexed microfluidic systems, requires careful attention to the parameters that affect reproducibility, specifically the porogenic solvent choice and the crosslinker to monomer ratio. [source]

Cover Picture: Electrophoresis 3'2010

ELECTROPHORESIS, Issue 3 2010
Article first published online: 29 JAN 2010
Issue no. 3 is a regular issue with Emphasis on "Proteins and Proteomics". The first part has 8 articles on proteins and proteomics covering various topics, e.g. preparative divergent flow IEF, multichannel gel electrophoresis, capillary gel electrophoresis, nanoparticle-based CE of proteins, 2-DE in a radial gel format, depletion of high abundance proteins, and proteomic investigation of fetal brain and lentil seed. The remaining 10 articles are concerned with nucleic acids, gene expression, methodologies and application. Featured articles include: Preparative divergent flow IEF without carrier ampholytes for separation of complex biological samples ((10.1002/elps.200900484)) SDS-PAGE and two-dimensional maps in a radial gel format ((10.1002/elps.200900526)) Analysis of Effect of Electrolyte Types on Electrokinetic Energy Conversion in Nanoscale Capillaries ((10.1002/elps.200900409)) A simple method to determine the surface charge in microfluidic channels ((10.1002/elps.200900603)) [source]

Confinement effects on the morphology of photopatterned porous polymer monoliths for capillary and microchip electrophoresis of proteins

ELECTROPHORESIS, Issue 14 2008
Mei He
Abstract We find that the morphology of porous polymer monoliths photopatterned within capillaries and microchannels is substantially influenced by the dimensions of confinement. Porous polymer monoliths were prepared by UV-initiated free-radical polymerization using either the hydrophilic or hydrophobic monomers 2-hydroxyethyl methacrylate or butyl methacrylate, cross-linker ethylene dimethacrylate and different porogenic solvents to produce bulk pore diameters between 3.2 and 0.4,µm. The extent of deformation from the bulk porous structure under confinement strongly depends on the ratio of characteristic length of the confined space to the monolith pore size. The effects are similar in cylindrical capillaries and D-shaped microfluidic channels. Bulk-like porosity is observed for a confinement dimension to pore size ratio >10, and significant deviation is observed for a ratio <5. At the extreme limit of deformation a smooth polymer layer ,300 nm thick is formed on the surface of the capillary or microchannel. Surface tension or wetting also plays a role, with greater wetting enhancing deformation of the bulk structure. The films created by extreme deformation provide a rapid and effective strategy to create robust wall coatings, with the ability to photograft various surface chemistries onto the coating. This approach is demonstrated through cationic films used for electroosmotic flow control and neutral hydrophilic coatings for electrophoresis of proteins. [source]

Assessment of Joule heating and its effects on electroosmotic flow and electrophoretic transport of solutes in microfluidic channels

ELECTROPHORESIS, Issue 3 2006
Gongyue Tang
Abstract Joule heating is inevitable when an electric field is applied across a conducting medium. It would impose limitations on the performance of electrokinetic microfluidic devices. This article presents a 3-D mathematical model for Joule heating and its effects on the EOF and electrophoretic transport of solutes in microfluidic channels. The governing equations were numerically solved using the finite-volume method. Experiments were carried out to investigate the Joule heating associated phenomena and to verify the numerical models. A rhodamine,B-based thermometry technique was employed to measure the solution temperature distributions in microfluidic channels. The microparticle image velocimetry technique was used to measure the velocity profiles of EOF under the influence of Joule heating. The numerical solutions were compared with experimental results, and reasonable agreement was found. It is found that with the presence of Joule heating, the EOF velocity deviates from its normal "plug-like" profile. The numerical simulations show that Joule heating not only accelerates the sample transport but also distorts the shape of the sample band. [source]

A polymeric master replication technology for mass fabrication of poly(dimethylsiloxane) microfluidic devices

ELECTROPHORESIS, Issue 9 2005
Hai-Fang Li
Abstract A protocol of producing multiple polymeric masters from an original glass master mold has been developed, which enables the production of multiple poly(dimethylsiloxane) (PDMS)-based microfluidic devices in a low-cost and efficient manner. Standard wet-etching techniques were used to fabricate an original glass master with negative features, from which more than 50 polymethylmethacrylate (PMMA) positive replica masters were rapidly created using the thermal printing technique. The time to replicate each PMMA master was as short as 20 min. The PMMA replica masters have excellent structural features and could be used to cast PDMS devices for many times. An integration geometry designed for laser-induced fluorescence (LIF) detection, which contains normal deep microfluidic channels and a much deeper optical fiber channel, was successfully transferred into PDMS devices. The positive relief on seven PMMA replica masters is replicated with regard to the negative original glass master, with a depth average variation of 0.89% for 26 ,m deep microfluidic channels and 1.16% for the 90 ,m deep fiber channel. The imprinted positive relief in PMMA from master-to-master is reproducible with relative standard deviations (RSDs) of 1.06% for the maximum width and 0.46% for depth in terms of the separation channel. The PDMS devices fabricated from the PMMA replica masters were characterized and applied to the separation of a fluorescein isothiocyanate (FITC)-labeled epinephrine sample. [source]

Microfluidic device for capillary electrochromatography-mass spectrometry

ELECTROPHORESIS, Issue 21 2003
Iulia M. Lazar
Abstract A novel microfabricated device that integrates a monolithic polymeric separation channel, an injector, and an interface for electrospray ionization-mass spectrometry detection (ESI-MS) was devised. Microfluidic propulsion was accomplished using electrically driven fluid flows. The methacrylate-based monolithic separation medium was prepared by photopolymerization and had a positively derivatized surface to ensure electroosmotic flow (EOF) generation for separation of analytes in a capillary electrochromatography (CEC) format. The injector operation was optimized to perform under conditions of nonuniform EOF within the microfluidic channels. The ESI interface allowed hours of stable operation at the flow rates generated by the monolithic column. The dimensions of one processing line were sufficiently small to enable the integration of 4,8 channel multiplexed structures on a single substrate. Standard protein digests were utilized to evaluate the performance of this microfluidic chip. Low- or sub-fmol amounts were injected and detected with this arrangement. [source]

Solvent-Resistant PDMS Microfluidic Devices with Hybrid Inorganic/Organic Polymer Coatings

Reversibly Deformable and Mechanically Tunable Fluidic Antennas

ADVANCED FUNCTIONAL MATERIALS, Issue 22 2009
Ju-Hee So
Abstract This paper describes the fabrication and characterization of fluidic dipole antennas that are reconfigurable, reversibly deformable, and mechanically tunable. The antennas consist of a fluid metal alloy injected into microfluidic channels comprising a silicone elastomer. By employing soft lithographic, rapid prototyping methods, the fluidic antennas are easier to fabricate than conventional copper antennas. The fluidic dipole radiates with ,90% efficiency over a broad frequency range (1910,1990,MHz), which is equivalent to the expected efficiency for a similar dipole with solid metallic elements such as copper. The metal, eutectic gallium indium (EGaIn), is a low-viscosity liquid at room temperature and possesses a thin oxide skin that provides mechanical stability to the fluid within the elastomeric channels. Because the conductive element of the antenna is a fluid, the mechanical properties and shape of the antenna are defined by the elastomeric channels, which are composed of polydimethylsiloxane (PDMS). The antennas can withstand mechanical deformation (stretching, bending, rolling, and twisting) and return to their original state after removal of an applied stress. The ability of the fluid metal to flow during deformation of the PDMS ensures electrical continuity. The shape and thus, the function of the antenna, is reconfigurable. The resonant frequency can be tuned mechanically by elongating the antenna via stretching without any hysteresis during strain relaxation, and the measured resonant frequency as a function of strain shows excellent agreement (±0.1,0.3% error) with that predicted by theoretical finite element modeling. The antennas are therefore sensors of strain. The fluid metal also facilitates self-healing in response to sharp cuts through the antenna. [source]

Eutectic Gallium-Indium (EGaIn): A Liquid Metal Alloy for the Formation of Stable Structures in Microchannels at Room Temperature,

ADVANCED FUNCTIONAL MATERIALS, Issue 7 2008
Michael D. Dickey
Abstract This paper describes the rheological behavior of the liquid metal eutectic gallium-indium (EGaIn) as it is injected into microfluidic channels to form stable microstructures of liquid metal. EGaIn is well- ;suited for this application because of its rheological properties at room temperature: it behaves like an elastic material until it experiences a critical surface stress, at which point it yields and flows readily. These properties allow EGaIn to fill microchannels rapidly when sufficient pressure is applied to the inlet of the channels, yet maintain structural stability within the channels once ambient pressure is restored. Experiments conducted in microfluidic channels, and in a parallel-plate rheometer, suggest that EGaIn's behavior is dictated by the properties of its surface (predominantly gallium oxide, as determined by Auger measurement s); these two experiments both yield approximately the same number for the critical surface stress required to induce EGaIn to flow (,0 .5,N/m). This analysis,which shows that the pressure that must be exceeded for EGaIn to flow through a microchannel is inversely proportional to the critical (i.e., smallest) dimension of the channel,is useful to guide future fabrication of microfluidic channels to mold EGaIn into functional microstructures. [source]

Addressable Protein Patterning via Switchable Superhydrophobic Microarrays,

ADVANCED FUNCTIONAL MATERIALS, Issue 15 2007
J.-Y. Shiu
Abstract We report on a simple process to create a switchable superhydrophobic surface where the water contact angle can be switched from a superhydrophobic state (ca.,167°) to a completely wetted state (<,10°). In the superhydrophobic state, the switchable superhydrophobic surface was resistant to the adsorption of proteins. However, once converted to a wetted state, the same surface promoted protein adsorption. We have developed a novel multicomponent protein-patterning technique based on this unique property of the switchable superhydrophobic surface. It is demonstrated that up to 100,×,100 protein spots can be created within one second. Each element on the switchable superhydrophobic microarray can be addressed individually and different types of biomolecules can be selectively deposited on the microarray without losing their activity. When integrated with microfluidic channels, the switchable superhydrophobic surface allows the parallel patterning of protein molecules to be carried out without cross contamination. [source]

Microfluidics: Surface-Treatment-Induced Three-Dimensional Capillary Morphogenesis in a Microfluidic Platform (Adv. Mater.

ADVANCED MATERIALS, Issue 47 2009
47/2009)
The cover shows confocal images of 3D sprouting into matrix material in microfluidic channels. Roger Kamm and co-workers report on p. 4863 that robust induction of realistic angiogenesis into the 3D matrix material under simultaneous imaging and a stably controlled concentration gradient of chemoattractants can be achieved. The formation of a 3D vascular network is demonstrated to be a direct consequence of surface treatment of the region of the device-containing matrix material. [source]

Shrink-Induced Nanowrinkles: Tunable Nanowrinkles on Shape Memory Polymer Sheets (Adv. Mater.

ADVANCED MATERIALS, Issue 44 2009
44/2009)
By leveraging the mismatch in stiffness between a stiff thin metal film and heat-induced shrinkage of prestressed polystyrene sheets, Michelle Khine and co-workers can rapidly and controllably create tunable nanowrinkles of various sizes and shapes for surface-enhanced sensing applications, as reported on p. 4472. Because the wrinkles are robustly embedded into the plastic, nanostructures can be integrated into microfluidic channels within minutes. Cover design by Libre Design. [source]

Rapid Microfluidic Generation of Patterned Aldehydes from Hydroxy-Terminated Self-Assembled Monolayers for Ligand and Cell Immobilization on Optically Transparent Indium Tin Oxide Surfaces

ADVANCED MATERIALS, Issue 30 2009
Abigail Pulsipher
Selective immobilization of a wide range of ligands on an indium tin oxide (ITO) surface is demonstrated. A chemoselective immobilization strategy to tailor ITO surfaces is developed by selectively oxidizing hydroxyl-terminated phosphonate self-assembled monolayers (SAMs) to aldehyde-presenting SAMs using microfluidic channels and then reacting with oxyamine-containing ligands , all on a chip. [source]

Coupled lattice-Boltzmann and finite-difference simulation of electroosmosis in microfluidic channels

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2004
Dzmitry Hlushkou
Abstract In this article we are concerned with an extension of the lattice-Boltzmann method for the numerical simulation of three-dimensional electroosmotic flow problems in porous media. Our description is evaluated using simple geometries as those encountered in open-channel microfluidic devices. In particular, we consider electroosmosis in straight cylindrical capillaries with a (non)uniform zeta-potential distribution for ratios of the capillary inner radius to the thickness of the electrical double layer from 10 to 100. The general case of heterogeneous zeta-potential distributions at the surface of a capillary requires solution of the following coupled equations in three dimensions: Navier,Stokes equation for liquid flow, Poisson equation for electrical potential distribution, and the Nernst,Planck equation for distribution of ionic species. The hydrodynamic problem has been treated with high efficiency by code parallelization through the lattice-Boltzmann method. For validation velocity fields were simulated in several microcapillary systems and good agreement with results predicted either theoretically or obtained by alternative numerical methods could be established. Results are also discussed with respect to the use of a slip boundary condition for the velocity field at the surface. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Electrode Grids for ITO Free Organic Photovoltaic Devices,

ADVANCED MATERIALS, Issue 19 2007
K. Tvingstedt
Silver grids are utilized to exclude the expensive use of indium tin oxide (ITO) in conjugated polymer photovoltaic devices. The grids are generated by electroless deposition from elastomeric microfluidic channels onto transparent substrates. The organic photovoltaic devices demonstrated here, with minimized series resistance, are confirmed to have characteristics comparable to devices exploiting ITO. [source]

Fabrication of Photonic/Microfluidic Integrated Devices Using an Epoxy Photoresist

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 6 2010
Thomas Kowpak
Abstract Using a single layer of SU-8 photoresist to fabricate optical waveguide cores and microfluidic channels on Pyrex glass is an ideal way to achieve photonic/microfluidic integration on a single chip. To address the problem of poor bonding, a thin nanoscale intermediate polymer layer was applied to reduce the stress generated from the material processing while maintaining strong adhesion between the patterning polymer layer and Pyrex. It was found that a 186,600,nm thick intermediate layer of a specialty epoxy photoresist effectively served the purpose without deteriorating the optical performance of the involved waveguides. Quality photonic/microfluidic integrated devices with satisfied optical performance were fabricated. [source]

Diffractive imaging for periodic samples: retrieving one-dimensional concentration profiles across microfluidic channels

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2007
Oliver Bunk
A technique has been developed that allows determination of the concentration profiles of colloidal solutions or any kind of fluid under confinement. Currently, submicrometre-wide channels are sampled with a resolution in the 10,nm range. The method comprises regular arrays of microfluidic channels and one-dimensional X-ray phase-retrieval techniques for the analysis of small-angle X-ray diffraction from the array structures. Recording the X-ray diffraction data requires a low dose on each individual channel since the sum of the signals from all channels is detected. The determined concentration profiles represent the ensemble average rather than individual entities and are obtained in a model-independent way. As an example, amplitude and phase of the exit field and concentration profiles for a colloidal fluid within confining channels of different widths are shown. [source]

A microfluidic bioreactor with integrated transepithelial electrical resistance (TEER) measurement electrodes for evaluation of renal epithelial cells

BIOTECHNOLOGY & BIOENGINEERING, Issue 4 2010
Nicholas Ferrell
Abstract We have developed a bilayer microfluidic system with integrated transepithelial electrical resistance (TEER) measurement electrodes to evaluate kidney epithelial cells under physiologically relevant fluid flow conditions. The bioreactor consists of apical and basolateral fluidic chambers connected via a transparent microporous membrane. The top chamber contains microfluidic channels to perfuse the apical surface of the cells. The bottom chamber acts as a reservoir for transport across the cell layer and provides support for the membrane. TEER electrodes were integrated into the device to monitor cell growth and evaluate cell,cell tight junction integrity. Immunofluorescence staining was performed within the microchannels for ZO-1 tight junction protein and acetylated ,-tubulin (primary cilia) using human renal epithelial cells (HREC) and MDCK cells. HREC were stained for cytoskeletal F-actin and exhibited disassembly of cytosolic F-actin stress fibers when exposed to shear stress. TEER was monitored over time under normal culture conditions and after disruption of the tight junctions using low Ca2+ medium. The transport rate of a fluorescently labeled tracer molecule (FITC-inulin) was measured before and after Ca2+ switch and a decrease in TEER corresponded with a large increase in paracellular inulin transport. This bioreactor design provides an instrumented platform with physiologically meaningful flow conditions to study various epithelial cell transport processes. Biotechnol. Bioeng. 2010;107:707,716. © 2010 Wiley Periodicals, Inc. [source]

Multienzyme catalysis in microfluidic biochips

BIOTECHNOLOGY & BIOENGINEERING, Issue 1 2003
Moo-Yeal Lee
Abstract The attachment of enzymes to glass microfluidic channels has been achieved using a highly reactive poly(maleic anhydride- alt -,-olefin) (PMA)-based coating that is supplied to the microchannel in a toluene solution. The PMA reacts with 3-aminopropyltriethoxysilane groups linked to the glass surface to form a matrix that enables additional maleic anhydride groups to react with free amino groups on enzymes to give a mixed covalent,noncovalent immobilization support. Using a simple T-channel microfluidic design, with reaction channel dimensions of 200 ,m wide (at the center), 15 ,m deep, and 30 mm long giving a reaction volume of 90 nL, soybean peroxidase (SBP) was attached at an amount up to 0.6 ,g/channel. SBP-catalyzed oxidation of p -cresol was performed in aqueous buffer (with 20% [v/v], dimethylformamide) containing H2O2, with microfluidic transport enabled by electroosmotic flow (EOF). Michaelis,Menten kinetics were obtained with Km and Vmax values of 0.98 mM and 0.21 ,mol H2O2 converted/mg SBP per minute, respectively. These values are nearly identical to nonimmobilized SBP kinetics in aqueous,DMF solutions in 20-,L volumes in 384-well plates and 5-mL reaction volumes in 20-mL scintillation vials. These results indicate that SBP displays intrinsically native activity even in the immobilized form at the microscale, and further attests to the mild immobilization conditions afforded by PMA. Bienzymic and trienzymic reactions were also performed in the microfluidic biochip. Specifically, a combined Candida antarctica lipase B,SBP bienzymic system was used to convert tolyl acetate into poly(p -cresol), and an invertase,glucose oxidase SBP trienzymic system was used to take sucrose and generate H2O2 for SBP-catalyzed synthesis of poly(p -cresol). © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 83: 20,28, 2003. [source]