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At least 1,099 records · Page 61Linked to original sources
PubMed2006

Direct measurement of the impact of impaired erythrocyte deformability on microvascular network perfusion in a microfluidic device.

The ability of red blood cells (RBCs, erythrocytes) to deform and pass through capillaries is essential for continual flow of blood in the microvasculature, which ensures an adequate supply of oxygen and nutrients, prompt removal of metabolic waste products, transport of drugs and hormones, and traffic of circulating cells to and from all living tissues. This paper presents a novel tool for evaluating the impact of impaired deformability of RBCs on the flow of blood in the microvasculature by directly measuring perfusion of a test microchannel network with dimensions and topology similar to the real microcirculation. The measurement of microchannel network perfusion is compared with RBC filtration -- a conventional assay of RBC deformability. In contrast to RBC filterability, network perfusion depends linearly on RBC deformability modulated by graded exposure to glutaraldehyde, showing a higher sensitivity to small changes of deformability. The direct measurement of microchannel network perfusion represents a new concept for the field of blood rheology and should prove beneficial for basic science and clinical applications.

Erythrocyte Deformability↗
PubMed2006

Electroosmotic flow patterning using microfluidic delay loops.

A theoretical and experimental investigation of alternating electroosmotic flow patterns by means of specially designed delay loops is presented. Using elementary methods of compact network modeling and detailed FEM simulations the flow behavior and, in particular, the rearrangement of sample plugs is modeled. The proposed designs rely on flow splitting in combination with electroosmotic delay loops leading to a runtime difference or phase shift between two sub-streams. Due to this phase shift, a new fluid interface is generated at the merging point. The approach is experimentally validated by injection of a Rhodamine 6G solution into an aqueous sodium tetraborate buffer.

Borates↗
PubMed2006

Integration of microfluidics with biomedical infrared spectroscopy for analytical and diagnostic metabolic profiling.

We describe how infrared spectroscopy of dry films (IRDF) can provide diagnostic information, and how we expect integration with laminar fluid diffusion interface (LFDI) sample pre-processing to generate new analytical and diagnostic tests. LFDI pre-processing provides sample clean-up and analyte separation. The sensitivity of IRDF to certain analytes is enhanced through the depletion of sample constituents that otherwise obscure relevant spectral features, permitting the deposition of films with larger sample volumes and, hence, of greater effective optical pathlength for the targeted analytes. An integrated LFDI-IRDF technology holds promise both as a method for rapid point-of-care quantitative analysis of biological fluids and as the engine of discovery for a wide range of novel diagnostic methods based upon metabolic profiling. In particular, successful integration will provide a versatile and cost effective technology platform that will allow for the accurate quantification of low-concentration analytes that are otherwise inaccessible and will provide the basis for diagnostic and prognostic methods that would otherwise be impossible. The specific question addressed by the proof-of-concept study summarised here is whether the spectra of LFDI processed samples can provide analytical methods that are more accurate than otherwise possible without LFDI pre-processing. The enrichment of serum creatinine is accomplished, with subsequent enhancement of its spectral contribution permitting quantification of this clinically important analyte beyond that achievable with no pre-processing. Finally, to illustrate the potential in diagnostic applications, two recently initiated studies are outlined, one involving chronic kidney disease and the other for chronic and acute coronary artery disease.

Biomarkers↗
PubMed2006

Engineering challenges of BioNEMS: the integration of microfluidics, micro- and nanodevices, models and external control for systems biology.

Systems biology, i.e. quantitative, postgenomic, postproteomic, dynamic, multiscale physiology, addresses in an integrative, quantitative manner the shockwave of genetic and proteomic information using computer models that may eventually have 10(6) dynamic variables with non-linear interactions. Historically, single biological measurements are made over minutes, suggesting the challenge of specifying 10(6) model parameters. Except for fluorescence and micro-electrode recordings, most cellular measurements have inadequate bandwidth to discern the time course of critical intracellular biochemical events. Micro-array expression profiles of thousands of genes cannot determine quantitative dynamic cellular signalling and metabolic variables. Major gaps must be bridged between the computational vision and experimental reality. The analysis of cellular signalling dynamics and control requires, first, micro- and nano-instruments that measure simultaneously multiple extracellular and intracellular variables with sufficient bandwidth; secondly, the ability to open existing internal control and signalling loops; thirdly, external BioMEMS micro-actuators that provide high bandwidth feedback and externally addressable intracellular nano-actuators; and, fourthly, real-time, closed-loop, single-cell control algorithms. The unravelling of the nested and coupled nature of cellular control loops requires simultaneous recording of multiple single-cell signatures. Externally controlled nano-actuators, needed to effect changes in the biochemical, mechanical and electrical environment both outside and inside the cell, will provide a major impetus for nanoscience.

Animals↗
PubMed2004

Introduction: mixing in microfluidics.

In this paper we briefly review the main issues associated with mixing at the microscale and introduce the papers comprising the Theme Issue.

Complex Mixtures↗
PubMed2003

Reaction-diffusion dynamics: confrontation between theory and experiment in a microfluidic reactor.

We confront, quantitatively, the theoretical description of the reaction-diffusion process of a second-order reaction to experiment. The reaction at work is Ca(2+)/CaGreen, a fluorescent tracer for calcium. The reactor is a T-shaped microchannel, 10 microm deep, 200 microm wide, and 2 cm long. The experimental measurements are compared with the two-dimensional numerical simulation of the reaction-diffusion equations. We find good agreement between theory and experiment. From this study, one may propose a method of measurement of various quantities, such as the kinetic rate of the reaction, in conditions yet inaccessible to conventional methods.

Biophysics↗
PubMedDate not supplied

Optical imaging in microfluidic bioreactors enables oxygen monitoring for continuous cell culture.

For the first time, a fluorescence lifetime calibration method for an oxygen-sensitive dye ruthenium tris(2,2'-dipyridyl) dichloride hexahydrate (RTDP) is applied to image oxygen levels in poly(dimethyl siloxane) (PDMS) bioreactors containing living C2C12 mouse myoblasts. PDMS microsystems are broadly used in bioengineering applications due to their biocompatibility and ease of handling. For these systems, oxygen concentrations are of significance and are likely to play an important role in cell behavior and gene expression. Fluorescence lifetime imaging microscopy (FLIM) bases image contrast on fluorophore excited state lifetimes, which reflect local biochemistry. Unique attributes of the widefield, time-domain FLIM system include tunable excitation (337.1 to 960 nm), large temporal dynamic range (> or =600 ps), high spatial resolution (1.4 microm), calibrated detection (0 to 300+/-8 microM of oxygen), and rapid data acquisition and processing times (10 s). Oxygen levels decrease with increasing cell densities and are consistent with model outcomes obtained by simulating bioreactor oxygen diffusion and cell proliferation. In single bioreactor loops, FLIM detects spatial heterogeneity in oxygen levels with variations as high as 20%. The fluorescence lifetime-based imaging approach we describe avoids intensity-based artifacts (including photobleaching and concentration variations) and provides a technique with high spatial discrimination for oxygen monitoring in continuous cell culture systems.

Animals↗
PubMed2005

Development of a nanoparticle-labeled microfluidic immunoassay for detection of pathogenic microorganisms.

The light-scattering properties of submicroscopic metal particles ranging from 40 to 120 nm in diameter have recently been investigated. These particles scatter incident white light to generate monochromatic light, which can be seen either by the naked eye or by dark-field microscopy. The nanoparticles are well suited for detection in microchannel-based immunoassays. The goal of the present study was to detect Helicobacter pylori- and Escherichia coli O157:H7-specific antigens with biotinylated polyclonal antibodies. Gold particles (diameter, 80 nm) functionalized with a secondary antibiotin antibody were then used as the readout. A dark-field stereomicroscope was used for particle visualization in poly(dimethylsiloxane) microchannels. A colorimetric quantification scheme was developed for the detection of the visual color changes resulting from immune reactions in the microchannels. The microchannel immunoassays reliably detected H. pylori and E. coli O157:H7 antigens in quantities on the order of 10 ng, which provides a sensitivity of detection comparable to those of conventional dot blot assays. In addition, the nanoparticles within the microchannels can be stored for at least 8 months without a loss of signal intensity. This strategy provides a means for the detection of nanoparticles in microchannels without the use of sophisticated equipment. In addition, the approach has the potential for use for further miniaturization of immunoassays and can be used for long-term archiving of immunoassays.

Bacteria↗
PubMed2006

A microfluidics-based mobility shift assay to discover new tyrosine phosphatase inhibitors.

Protein tyrosine phosphatases (PTPs) play key roles in regulating tyrosine phosphorylation levels in cells. Since the discovery of PTP1B as a major drug target for diabetes and obesity, PTPs have emerged as a new and promising class of signaling targets for drug development in a variety of therapeutic areas. The routine use of generic substrate 6,8-difluoro-4-methylumbelliferyl phosphate (DiFMUP) in our hands led to the discovery of very similar and often not very selective molecules. Therefore, to increase the chances to discover novel chemical scaffolds, a side-by-side comparison between the DiFMUP assay and a chip-based mobility shift assay with a specific phosphopeptide was performed, on 1 PTP, using a focused set of compounds. Assay robustness and sensitivity were comparable for both the DiFMUP and mobility shift assays. The off-chip mobility shift assay required a longer development time because of identification, synthesis, and characterization of a specific peptide, and its cost per point was higher. However, although most potent scaffolds found with the DiFMUP assay were confirmed in the mobility shift format, the off-chip mobility shift assay led to the identification of previously unidentified chemical scaffolds with improved druglike properties.

Drug Evaluation, Preclinical↗
PubMed2006

Live cell refractometry using microfluidic devices.

Using Hilbert phase microscopy for extracting quantitative phase images, we measured the average refractive index associated with live cells in culture. To decouple the contributions to the phase signal from the cell refractive index and thickness, we confined the cells in microchannels. The results are confirmed by comparison with measurements of spherical cells in suspension.

Cell Shape↗
PubMed2006

Reversible, room temperature bonding of glass devices for microfluidics.

This chapter describes a procedure for bonding glass microdevice substrates to their top plates by contact alone. This method results in devices that are robustly bonded but that can be separated, cleaned, and reused. For glass chips that have been used for applications involving the transport of hard particles, cells, or other biological material, reversible bonding provides a way of increasing the chip's lifetime and utility. Glass microdevices that are cleaned following this procedure can be successfully used many times for electrophoresis or pressure-driven applications.

Glass↗