共查询到20条相似文献,搜索用时 31 毫秒
1.
A chemically powered channelless microfluidic device was designed, fabricated, and characterized. The device consists of an
asymmetric silver–gold bimetallic catalytic junction fabricated on a silicon dioxide surface. The decomposition of hydrogen
peroxide at the silver–gold interface generates a proton gradient and an associated electric field which in turn drives electroosmosis
and electrophoresis when a charged particle is present in the vicinity of the field. By engineering an asymmetric device consisting
of an isolated junction, continuous electroosmotic fluid flow across the device has been achieved. In addition, a new device
geometry has been developed which is capable of focusing and directing negatively charged particles along a desired path without
the need of microchannels. The efficiency and ease of the fabrication suggest the possibility of many versatile applications
including biological molecule sorting and manipulation. 相似文献
2.
Even at low Reynolds numbers, momentum can impact the shape of hydrodynamically focused flow. Both theoretical and experimental
characterization of hydrodynamic focusing in microchannels at Reynolds numbers ≤25 revealed the important parameters that
affect the shape of the focused layer. A series of symmetric and asymmetric microfluidic channels with two converging streams
were fabricated with different angles of confluence at the junction. The channels were used to study the characteristics of
Y-type microchannels for flow-focusing. Computational analysis and experimental results gathered using confocal microscopy
and particle image velocimetry indicated that the orientation of the sheath and the sample stream inlets, as well as the absolute
flow velocities, determine the curvature in the concentration distribution of the focused stream. Decreasing the angle of
confluence between sheath and sample, as well as reducing the overall Reynolds number, resulted in a flat interface between
sheath and focused fluids. Alignment of the faster flowing sheath fluid channel with the main channel also reduced the inertial
effects and produced a focused stream with a flat concentration profile. Control over the shape of the focused stream is important
in many biosensors and lab-on-a-chip devices that rely on hydrodynamic focusing for increased detection sensitivity. 相似文献
3.
Milliseconds microfluidic chaotic bubble mixer 总被引:2,自引:2,他引:0
Xiaole Mao Bala Krishna Juluri Michael Ian Lapsley Zackary Stoeri Stratton Tony Jun Huang 《Microfluidics and nanofluidics》2010,8(1):139-144
In this study, we report a rapid microfluidic mixing device based on chaotic advection induced by microbubble–fluid interactions.
The device includes inlets for to-be-mixed fluids and nitrogen gas. A side-by-side laminar flow segmented by monodisperse
microbubbles is generated when the fluids and the nitrogen are co-injected through a flow focusing micro-orifice. The flow
subsequently enters a series of hexagonal expansion chambers, in which the hydrodynamic interaction among the microbubbles
results in the stretch and fold of segmented fluid volumes and rapid mixing and homogenization. We characterize the performance
of the microfluidic mixer and demonstrate rapid mixing within 20 ms. We further show that bubbles can be conveniently removed
from the mixed fluids using a microfluidic comb structure on completion of the mixing. 相似文献
4.
Rapid measurement of fluid viscosity using co-flowing in a co-axial microfluidic device 总被引:2,自引:1,他引:1
This article presents a simple microfluidic method to measure the Newtonian fluid viscosity. This method is carried out in
a co-axial microfluidic device. A stable liquid/liquid annular co-laminar flow in the co-axial microfluidic device has been
realized, which can be described by Navier–Stokes equations. The viscosity of either fluid can be measured based on the equations
when the viscosities of another fluid is known. Proper conditions to form stable annular co-laminar flow for the viscosity
measurement were investigated. Several fluids were tested with viscosity ranging from 0.6 to 40 mPa s. The measured results
fit very well with those measured by a commercial spinning digital viscometer. The novel method is highly controllable and
reliable, and has the advantage of less time and material consumption, as well as easy fabrication of the device. 相似文献
5.
This paper describes two methods for controlling capillary-driven liquid flow on microfluidic channels. Unlike flow driven by external forces, capillary-driven flow is dominated by interfacial phenomena and, therefore, is sensitive to the channel geometry and chemical composition (surface energy) along the channel. The first method to control fluid flow is based on altering surface energy along the channel through regulation of UV irradiation time, which enables adjusting the contact angle along the fluid path. The slowing down (delay) of the liquid flow depends on the stripe length and its position in the channel. Using this technique, we generated flow delays spanning from a second to over 3 min. In the second approach, we manipulated the flow velocity by introducing contractions and expansions in the channel. The methods used herein are inexpensive and can be incorporated to the microfluidic channel fabrication step. They are capable of controlling liquid flow with precise time delays without introducing the foreign matter in the fluidic device. 相似文献
6.
Scale-up and control of droplet production in coupled microfluidic flow-focusing geometries 总被引:1,自引:1,他引:0
A single microfluidic chip consisting of six microfluidic flow-focusing devices operating in parallel was developed to investigate the feasibility of scaling microfluidic droplet generation up to production rates of hundreds of milliliters per hour. The design utilizes a single inlet channel for both the dispersed aqueous phase and the continuous oil phase from which the fluids were distributed to all six flow-focusing devices. The exit tubing for each of the six flow-focusing devices is separate and individually plumbed to each device. Within each flow-focusing device, the droplet size was monodisperse, but some droplet size variations were observed across devices. We show that by modifying the flow resistance in the outlet channel of an individual flow-focusing device it is possible to control both the droplet size and frequency of droplet production. This can be achieved through the use of valves or, as is done in this study, by changing the length of the exit tubing plumbed to the outlet of the each device. Longer exit tubing and larger flow resistance is found to lead to larger droplets and higher production frequencies. The devices can thus be individually tuned to create a monodisperse emulsion or an emulsion with a specific drop size distribution. 相似文献
7.
Ciprian Iliescu Guolin Xu Elena Barbarini Marioara Avram Andrei Avram 《Microsystem Technologies》2009,15(8):1157-1162
This paper presents a microfluidic device for magnetophoretic separation of red blood cells from blood under continuous flow.
The separation method consists of continuous flow of a blood sample (diluted in PBS) through a microfluidic channel which
presents on the bottom “dots” of ferromagnetic layer. By applying a magnetic field perpendicular on the flowing direction,
the ferromagnetic “dots” generate a gradient of magnetic field which amplifies the magnetic force. As a result, the red blood
cells are captured on the bottom of the microfluidic channel while the rest of the blood is collected at the outlet. Experimental
results show that an average of 95% of red blood cells is trapped in the device. 相似文献
8.
Gwendoline M. Toh Naoki Yanagisawa Robert C. Corcoran Debashis Dutta 《Microfluidics and nanofluidics》2010,9(6):1135-1141
In this article, we report a novel approach to fabricating a low molecular weight cut-off membrane that could readily be employed
for several microfluidic applications. The reported structure was created by selectively retaining a precursor solution [5%
(w/v) maleic anhydride, 21% (v/v) (37:1) acrylamide/bisacrylamide, and 0.2% (w/v) VA-086 photoinitiator] in a chosen location
of a microfluidic network via capillary forces and then photo-polymerizing the mixture. The pores in the resulting membrane
were subsequently filled with 3-aminopropyltriethoxysilane, heated, and then treated with sodium silicate solution and heated
again, giving a structure having reduced porosity. The composite membrane thus created has been shown to have a molecular
weight cut-off that is at least an order of magnitude smaller than other photo-polymerized microfluidic membranes reported
in the literature. Moreover, this polymer–silicate structure was observed to be capable of blocking electroosmotic flow, thereby
generating a pressure gradient around its interface with an open microchannel upon application of an electric field across
the microchannel-membrane junction. In this study, a fraction of the resulting hydrodynamic flow was successfully guided to
an electric field free analysis channel to implement a pressure-driven assay. With our current design pressure-driven velocities,
up to 1.8 mm/s was generated in the electric field free analysis channel for an applied voltage of 2 kV in the pumping section.
Finally, the functionality of this integrated microfluidic device was demonstrated by implementing a reverse phase chromatographic
separation using the pressure-driven flow generated on-chip. 相似文献
9.
Continuous generation of hydrogel beads and encapsulation of biological materials using a microfluidic droplet-merging channel 总被引:1,自引:0,他引:1
In this paper, we describe a method for encapsulation of biomaterials in hydrogel beads using a microfluidic droplet-merging
channel. We devised a double T-junction in a microfluidic channel for alternate injection of aqueous fluids inside a droplet
unit carried within immiscible oil. With this device, hydrogel beads with diameter <100 μm are produced, and various solutions
containing cells, proteins and reagents for gelation could merge with the gel droplets with high efficiency in the broad range
of flow rates. Mixing of reagents and reactions inside the hydrogel beads are continuously observed in a microchannel through
a microscope. By enabling serial injection of each liquid with the dispersed gel droplets after they are produced from the
oil-focusing channel, the device simplifies the sample preparation process, and gel-bead fabrication can be coupled with further
assay continuously in a single channel. Instantaneous reactions of enzyme inside hydrogel and in-situ formation of cell-containing
beads with high viability are demonstrated in this report. 相似文献
10.
Taotao Fu Youguang Ma Denis Funfschilling Huai Z. Li 《Microfluidics and nanofluidics》2011,10(5):1135-1140
This communication describes the gas–liquid two-phase flow patterns and the formation of bubbles in non-Newtonian fluids in
microfluidic flow-focusing devices. Experiments were conducted in two different polymethyl methacrylate (PMMA) square microchannels
of, respectively, 600 × 600 and 400 × 400 μm. N2 bubbles were generated in non-Newtonian polyacrylamide (PAAm) solutions of different concentrations. Slug bubble, missile
bubble, annular and intermittent flow patterns were observed at the cross-junction by varying gas and liquid flow rates. Gas
and liquid flow rates, concentration of PAAm solutions, and channel size were varied to investigate their effect on the mechanism
of bubble formation. The bubble size was proportional to the ratio of gas/liquid flow rate for slug bubbles and could be scaled
with the ratio of gas/liquid flow rate as a power–law relationship for missile bubbles under wide experimental conditions. 相似文献
11.
Liang-Liang Fan Yu Han Xu-Kun He Liang Zhao Jiang Zhe 《Microfluidics and nanofluidics》2014,17(4):639-646
A new microfluidic device for fast and high-throughput particle focusing is reported. The particle focusing is based on the combination of inertial lift force effect and centrifugal force effect generated in a microchannel with a series of repeated asymmetric sharp corners on one side of the channel wall. The inertial lift force induces two focused particle streams in the microchannel, and the centrifugal force generated at the sharp corner structures tends to drive the particles laterally away from the corner. With the use of a series of repeated asymmetric sharp corner structures, a single and highly focused particle stream was achieved near the straight channel wall at a wide range of flow rate. In comparison with other hydrodynamic particle focusing methods, this method is less sensitive to the flow rate and can work at a higher flow rate (up to 700 μL/min) and Reynolds number (Re = 129.5). With its simple structure and operation, and high throughput, this method can be potentially used in particle focusing processes in a variety of lab-on-a-chip applications. 相似文献
12.
A fast microfluidic mixer based on acoustically driven sidewall-trapped microbubbles 总被引:1,自引:1,他引:0
Daniel Ahmed Xiaole Mao Bala Krishna Juluri Tony Jun Huang 《Microfluidics and nanofluidics》2009,7(5):727-731
Due to the low Reynolds number associated with microscale fluid flow, it is difficult to rapidly and homogenously mix two
fluids. In this letter, we report a fast and homogenized mixing device through the use of a bubble-based microfluidic structure.
This micromixing device worked by trapping air bubbles within the pre-designed grooves on the sidewalls of the channel. When
acoustically driven, the membranes (liquid/air interfaces) of these trapped bubbles started to oscillate. The bubble oscillation
resulted in a microstreaming phenomenon—strong pressure and velocity fluctuations in the bulk liquid, thus giving rise to
fast and homogenized mixing of two side-by-side flowing fluids. The performance of the mixer was characterized by mixing deionized
water and ink at different flow rates. The mixing time was measured to be as small as 120 ms. 相似文献
13.
Magnetophoretic isolation of biological cells in a microfluidic environment has strong relevance in biomedicine and biotechnology.
A numerical analysis of magnetophoretic cell separation using magnetic microspheres in a straight and a T-shaped microfluidic
channel under the influence of a line dipole is presented. The effect of coupled particle–fluid interactions on the fluid
flow and particle trajectories are investigated under different particle loading and dipole strengths. Microchannel flow and
particle trajectories are simulated for different values of dipole strength and position, particle diameter and magnetic susceptibility,
fluid viscosity and flow velocity in both the microchannel configurations. Residence times of the captured particles within
the channel are also computed. The capture efficiency is found to be a function of two nondimensional parameters, α and β.
The first parameter denotes the ratio of magnetic to viscous forces, while the second one represents the ratio of channel
height to the distance of the dipole from the channel wall. Two additional nondimensional parameters γ (representing the inverse
of normalized offset distance of the dipole from the line of symmetry) and σ (representing the inverse of normalized width
of the outlet limbs) are found to influence the capture efficiency in the T-channel. Results of this investigation can be
applied for the selection of a wide range of operating and design parameters for practical microfluidic cell separators. 相似文献
14.
Robert Copperwhite Mary O’Sullivan Catherine Boothman Arnaud Gorin Colette McDonagh Mohamed Oubaha 《Microfluidics and nanofluidics》2011,11(3):283-296
This article reports on a detailed investigation of sol–gel processed hybrid organic–inorganic materials for use in lab-on-a-chip
(LoC) applications. A particular focus on this research was the implementation of integrated microfluidic circuitry in waveguide-based
photonic sensing platforms. This objective is not possible using other fabrication technologies that are typically used for
microfluidic platforms. Significant results on the surface characterisation of hybrid sol–gel processed materials have been
obtained which highlight the ability to tune the hydrophilicity of the materials by careful adjustment of material constituents
and processing conditions. A proof-of-principle microfluidic platform was designed and a fabrication process was established
which addressed requirements for refractive index tuning (essential for waveguiding), bonding of a transparent cover layer
to the device, optimized sol–gel deposition process, and a photolithography process to form the microchannels. Characterisation
of fluid flow in the resulting microchannels revealed volumetric flow rates between 0.012 and 0.018 μl/min which is characteristic
of capillary-driven fluid flow. As proof of the integration of optical and microfluidic functionality, a microchannel was
fabricated crossing an optical waveguide which demonstrated that the presence of optical waveguides does not significantly
disrupt capillary-driven fluid flow. These results represent the first comprehensive evaluation of photocurable hybrid sol–gel
materials for use in waveguide-based photonic platforms for lab-on-a-chip applications. 相似文献
15.
Shih Hao Huang Hwa Seng Khoo Shang Yu ChangChien Fan Gang Tseng 《Microfluidics and nanofluidics》2008,5(4):459-468
Monodisperse copolymer particles carrying surface carboxyl groups in the range of 50–200 μm were prepared by in situ UV polymerization
of ethyleneglycol dimethacrylate (EGDMA) with acrylic acid (AA) via a microfluidic flow-focusing device (MFFD). The design
of the coaxial orifices in the MFFD enables the confinement of the comonomer liquid thread to the central axis of the microchannel,
which can avoid the wetting problem of comonomer liquid with the microchannel and can successfully produce monodisperse copolymer
microspheres with coefficient of variance below 5%. The effects of concentration of EGDMA and AA on droplet diameters and
the distribution of carboxyl group on particle surfaces were examined. It has been found that, increasing the concentration
of AA would decrease particle sizes, but increase the distribution of carboxyl group on particle surfaces. Bioconjugation
of the carboxylated copolymer particles with the anti-rabbit IgG–Cy3 conjugates was successfully demonstrated. By increasing
the concentration of AA accompanied with decreasing the particle sizes, high efficiency of bioconjugation on carboxylated
copolymer particles was achieved. The rapid continuous synthesis of carboxylated copolymer particles via a microfluidic device
provides a reliable control of particle sizes and composition for massive production in biotechnological applications. 相似文献
16.
Ulrich A. Kleβinger Bernhard K. Wunderlich Andreas R. Bausch 《Microfluidics and nanofluidics》2013,15(4):533-540
The ongoing development of microfluidic devices involves the use of highly complex fluids, even of multiphase systems. Despite the great achievements in the development of numerous applications, there is still a lack in the complete understanding of the underlying physics of the observed macroscopic effects. One prominent example is the flow through benchmark contractions where micro- and even macroscopic explanations of some of the occurring flow patterns are still missing. Here, we study the development of the flow profiles of shear thinning semi-dilute polymer solutions in microfluidic planar abrupt contraction geometries. Flow profiles along the narrow channel part are obtained by μ-PIV measurements, whereby the pressure drop along the microfluidic channel as well as the local transient viscosities downstream to the orifice are computed. A relaxation process of the flow profiles from an initially parabolic shape to the flattened steady-state flow profile is observed and traced back to the polymer relaxation. 相似文献
17.
Yu-An Chen Zi-Wei Huang Fang-Sheng Tsai Chang-Yu Chen Cheng-Ming Lin Andrew M. Wo 《Microfluidics and nanofluidics》2011,10(1):59-67
A home-use device that allows rapid and quantitative sperm quality analysis is desirable but not yet fully realized. To aid
this effort, this article presents a microfluidic device capable of quantifying sperm quality in terms of two critical fertility-related
parameters—motile sperm concentration and motility. The microdevice produces flow field for sperms to swim against, and sperms
that overcame the flow within a specified time are propelled along in a separate channel and counted via resistive pulse technique.
Data are compared to two control methods clinically utilized for sperm quality exam—hemocytometer and the sperm quality analyzer.
Results reveal the numbers of pulses generated by passage of sperms correlates strongly with the two control methods: pulse
number from 0 to 335 corresponds to progressively motile sperm concentrations from 0 to 19 × 106/ml (hemocytometer) and Sperm Motility Index from 0 to 204 (sperm quality analyzer). The microdevice should be applicable
to facilitate self-assessment of sperm quality at home. 相似文献
18.
Davide Ciceri Jilska M. Perera Geoffrey W. Stevens 《Microfluidics and nanofluidics》2011,11(5):593-600
The diffusion behaviour of Co(II) ion in an aqueous homogeneous system and that of 8-hydroxyquinoline (8HQ) in a heterogeneous
liquid–liquid system was measured in a Y–Y shaped microfluidic device. We propose a modified version of a previously published
equation for a static system to describe the diffusion behaviour of chemical species in this microfluidic device. Specific
adaptations of the original equation to the micro environment are illustrated and discussed. The model proposed successfully
fitted the diffusion of Co(II) in a homogeneous system (aqueous solutions) and 8HQ across a water/oil interface. We envisage
the application of the proposed equation for the discrimination of the diffusion contribution in solvent extraction kinetic
studies. 相似文献
19.
We experimentally study the transport properties of threads made of high-viscosity fluids flowing in a sheath of miscible, low-viscosity fluids in bifurcating microchannels. A viscous filament is generated using a square hydrodynamic focusing section by injecting a ‘thick’ fluid into the central channel and a ‘thin’ fluid from the side channels. This method allows us to produce miscible fluid threads of various sizes and lateral positions in a straight channel and enables the systematic study of the downstream thread’s response to flow partitioning in branching microfluidic networks at low Reynolds numbers. A phase diagram detailing the various flow patterns observed at the first bifurcation, including thread folding, transport, and fouling, is presented along with transition lines. We also examine the role of viscous buckling instabilities on thread behavior and the formation of complex viscous mixtures and stratifications at the small scale. This work shows the possibility to finely control thread trajectory and stability as well as manipulate the structural arrangement of high-viscosity multiphase flows in complex microfluidic systems. 相似文献
20.
Roberto L. C. Cisne Jr. Talita F. Vasconcelos Eric J. R. Parteli Jos�� S. Andrade Jr. 《Microfluidics and nanofluidics》2011,10(3):543-550
We present a fluidic device that shows ratchet-like characteristics for particle transport at low Reynolds. The ratchet consists
of a two-dimensional saw-tooth channel, within which a laminar flow is generated by imposing a longitudinal pressure gradient.
Particle trajectories are calculated by solving the continuity and Navier–Stokes equations for the fluid flow and the equations
for particle transport in both flow directions. The ratchet-like effect is connected with a large asymmetry in the mean transit
time, with regard to flow direction, due to particle motion within zones of low flow velocity near the asymmetric wall profile.
We show how to obtain ratchet of particles with select Stokes under given flow conditions by adjusting the geometry of the
ratchet channel. 相似文献