23. We qualify the mixing as thorough when the fluorescence appears uniform to within the resolution (∼2 μm) and sensitivity (down to variations of ∼5% of the maximum intensity) of our microscope.
Because there are many possible solutions to a problem; it is important to choose the design requirements and success criteria for the proposed solution. Here the authors describe their design criteria for thoroughly mixing a solution.
Chaotic flows will also exist in the laminar shear flow in the boundary layer of an extended flow over a surface that presents the staggered herringbone structure. This stirring of the boundary layer should enhance the rates of diffusion-limited reactions at surfaces (e.g., electrode reactions) and heat transfer from solids into bulk flows.
Here the authors describe some possible applications that could benefit from this work. One specific application described is diffusion limited reactions which might happen at a surface such as those between an electrode and electrolytes in solution or between immobilized antibodies and antigens in solution. A previous annotation mentions a protein detection mechanism from blood samples which is dependent on a diffusion limited reaction.
offers a general solution to the problem of mixing fluids in microfluidic systems. The simplicity of its design allows it to be integrated easily into microfluidic structures with standard microfabrication techniques.
The authors have proven that they have created a novel mixing technique which is more effective that standard diffusion mixing, easier to integrate into other microfluidic structurers than current mixing techniques, and doesn't require any complicated active device components.
applications
A recent paper has been published (Protein detection in blood with single-molecule imaging) which demonstrates capturing of the target proteins within blood. This increases the effectiveness of their protein detection method.
(of cells)
Many health and biotechnology research and assays depend on the efficient sorting of cells. Microfluidics allows for efficient and accurate cell sorting due to the ability to interact with cells using physical structures and processes occurring on the same scale. This is useful in drug development, disease detection, and cellular research.
In a steady chaotic flow, the stretching and folding of volumes of the fluid proceed exponentially as a function of the axial distance traveled by the volume: Δr = lexp(−Δy/λ), where the initial transverse distance is taken to be l, and λ is a characteristic length determined by the geometry of trajectories in the chaotic flow
Chaotic flow allows for faster mixing as it allows for the fluid components to stretch and fold much sooner along the flow direction. This allows to achieve full mixing within a much smaller channel length.
16. We made the master structures with two-step photolithography in SU-8 photoresist: The first layer of photolithography defined the channel structure; the second layer defined the pattern of ridges. The pattern of ridges was aligned to lie on top of the channel structure in the first layer. We measured the dimensions of the channel and the ridges using a profilometer. We made molds of the structure in PDMS. To close the channel, we exposed the PDMS to a plasma for 1 min and sealed it to a glass cover slip.
Here the authors describe the exact steps that they use to create the devices. The techniques (photolithography) and materials (PDMS) described are commonly used in the fabrication of microfluidic devices.
The micrographs in Fig. 3, A and B, show that for flows with high Péclet number (Pe = 2 × 105), there is negligible mixing in a simple channel (Fig. 3A) and incomplete mixing in a channel with straight ridges (Fig. 3B) after the flow has proceeded 3 cm—the typical dimension of a microfluidic chip—down the channel.
Here the authors describe how they compared the mixing performance of 1) a straight microchannel, 2) a microchannel with straight ridges, and 3) a microchannel with staggered herringbone ridges to prove that their design (staggered herringbone ridges) had the best mixing performance.
26. Recent experimental results confirm that ridges in the floor of a channel do generate transverse components in electroosmotic flows (28).
"Here, the authors note that the ridge structures result in mixing not only in pressure driven flows but also in electroosmotic flows."
22. We have evaluated the extent of the chaotic region in the cross section by numerically integrating an approximate two-dimensional representation of the transverse flow to generate a Poincaré map. The map is dense (no islands) everywhere in the cross section except in a narrow band (<10% of height) at the top of the channel. We have not systematically optimized the design of the mixer with respect to these Δφm and p values.
Here the authors describe the mathematical process of analyzing the data presented in Fig. 2B to determine the extent of the chaotic region.
29. Labeled polymers were prepared by allowing poly(ethylenimine) (molecular weight ∼500,000) to react with fluorocein isothiocyanate. The product was dialyzed for several days. Diffusivities were calculated based on the broadening of fluorescent streams of the dye in confocal images flows of known speed: D = 4 × 10−6 cm2/s in water and D = 2 × 10−8 cm2/s in 80% glycerol/20% water. Flow speeds were measured by weighing the fluid collected at the outlet of the channel. Viscosity of the glycerol/water solution was estimated to be 0.67 g/cm·s by comparing the flow rate to that of water through the same channel with the same applied pressure.
Here the authors provide a description of the fluorescent streams used in the first 3 figures and how they were prepared.
Within the limits of our simple model of mixing (13), we estimate from the linear portion of the plot in Fig. 3E that λ is on the order of a few millimeters; the average width of the filaments of unmixed fluid decreases by a factor of ∼3 as the fluid travels this axial distance. This estimate agrees qualitatively with the evolution seen in Fig. 3C.
When possible it is important to compare the data gathered experimentally with the expected result (determined logically or mathematically) to make sure that the experiments are valid and accurate within an acceptable range of error. Here the authors state that their experimental data qualitatively agrees with their mathematical model.
aqueous buffer
Aqueous buffer is a solution of weak acid and its conjugate base which provides a degree of stability to prevent the rapid fluctuation in pH when a small amount of strong acid or base is added.
biology and biotechnology;
Recently, this technology has been used to create a new method for the molecular profiling of circulating tumor cells (Covalent chemistry on nanostructured substrates enables noninvasive quantification of gene rearrangements in circulating tumor cells). This method would allow for noninvasive monitoring of disease progression and treatment guidance.
type of structure can be fabricated
Learning Standard: Scientific Investigations Use a Variety of Methods (NS1). New technologies advance scientific knowledge. (HS-LS1-2). Without technologies such as photolithography or advanced microscopy the devices and methods utilized in this paper would not be possible.
uniaxial flows,
Flows constrained along a single dimension such as those found in the microchannels of microfluidic devices.
DOI 10.1126/science.1066238
Digital Object Identifier (DOI) is a standardized method for uniquely referencing digital documents with the aim of easily leading to the documents location. Almost all published academic journal articles as well as research reports and data sets have an assigned DOI.
homogenize
To make uniform or similar.
30. Supported by Defense Advanced Research Projects Agency grants NSF ECS-9729405 and NSF DMR-9809363 Materials Research Science and Engineering Center (A.D.S., S.K.W.D., H.A.S., and G.M.W.); NIH grant GM51559 (A.D.S., S.K.W.D, and G.M.W.); Army Research Office grant DAAG55-97-1-0114 (H.A.S.); and NSF-9875933, NSF DMS-9803555, and a Sloan Foundation Fellowship (I.M.). S.K.W.D. thanks the Deutsche Forschungsgemeinschaft for a research fellowship.
Here the authors list where the funding for the research came from. A lot of academic research is funded through government grants (DARPA, NSF, NIH, Military, etc.).
analysis (of DNA and proteins)
Microfluidics offers the potential for rapid and efficient analysis of DNA and proteins at a lower cost then traditional analysis. This is perhaps one of the most widely used commercial applications of microfluidics and has recently been seen most prominently in SARS-CoV-2 and other immunology testing tasks.
Typical uses of microfluidic devices (e.g., chemical analysis in the field) require that these systems be inexpensive and simple to operate; microfluidic components that operate with pressure flow and few moving parts are desirable.
Learning Standard: Constructing Evidence and Designing Solutions (SEP6). This standard states that there is a range of possible engineering solutions and the best is dependent upon the design requirements and the criteria used for evaluation. The authors list the design requirements of microfluidics as inexpensive, easy to operate, with few moving parts.
The ability to generate transverse flows in microchannels makes it possible to design steady chaotic flows for use in microfluidic systems. A mixer based on patterns of grooves on the floor of the channel is shown schematically in Fig. 2A; we refer to this design as the staggered herringbone mixer (SHM)
Learning Standard ETS1.C: Optimizing the Design Solution. The authors optimized the mixing design by changing the mixing elements to a staggered herringbone pattern.
It is difficult to mix solutions in microchannels.
Learning Standard ETS1.A: Defining and Delimiting an Engineering Problem. This standard requires students to accurately recognize and define an engineering problem. In this paper the authors are addressing a difficult problem, mixing fluids at the microscale.
transverse
Perpendicular to the direction of the flow along the channel
kinematic viscosity
The measurement of a fluid's internal resistance to flow
orthogonal
At a right angle, perpendicular
turbulent
Fluid flow that is subject to chaotic changes in velocity and pressure. The opposite of laminar flow.
Poiseuille flows
Steady viscous (thick) fluid flow driven by an effective pressure gradient established between the two ends of a long straight pipe of uniform circular cross-section
sorting
Startup Outset Medical (https://www.outsetmedical.com/) has created a portable dialysis machine which utilizes the microfluidic technology discussed in this paper.
chromatography
Chemical analysis technique involving the separation of components in a mixture by passing it through a material in which the components move at different rates.
[Chromatography basics video] https://www.youtube.com/watch?v=XfSopnqrHOs)