![]() ![]() When one of the boundaries of a system is removed, a larger liquid-gas interface results, which enables liquid-gas reactions. Open microfluidics also allows simplicity of fabrication thus eliminating the need to bond surfaces. One of the main advantages of open microfluidics is ease of accessibility which enables intervention (i.e., for adding or removing reagents) to the flowing liquid in the system. The fabrication of a V-groove is more difficult than a U-groove as it poses a higher risk for faulty construction, since the corner has to be tightly sealed. The narrower the V-groove is, the better the capillary flow of liquids is even for highly viscous liquids such as blood this effect has been used to produce an autonomous assay. The width of the groove plays an important role in controlling the fluid flow. In a perfect inner corner of a V-groove, the filament will advance indefinitely in the groove allowing the formation of capillary filament depending on the wetting conditions. V-grooves with sharp groove angle result in the interface curvature at the corners explained by reduced Concus-Finn conditions. V-groove, unlike U-groove, allows for a variety of velocities depending on the groove angle. SCF in U-groove (left) U-groove open microfluidic channel SCF (right) The geometry of the channels dictates the flow along the interior walls fabricated with various ever-evolving processes. The dynamics of capillary-driven flow in open microfluidics are highly reliant on two types of geometric channels commonly known as either rectangular U-grooves or triangular V-grooves. The elimination of and infusion source reduces the size of the device and associated apparatus, along with other aspects that could obstruct their use. ![]() Rather than rely on using pumps or syringes to maintain flow, open capillary microfluidics uses surface tension to facilitate the flow. Open capillary microfluidics are channels that expose fluids to open air by excluding the ceiling and/or floor of the channel. Capillary filaments in open microfluidics Thread-based microfluidics has been applied to 3D tissue engineering and analyte analysis. Threads are also relatively strong and difficult to break from handling which makes them stable over time and easy to transport. Additionally, two or more threads can converge together in a knot bringing two separate ‘streams’ of fluid together as a reagent mixing method. Threads are versatile because they can be woven to form specific patterns. Common thread materials include nitrocellulose, rayon, nylon, hemp, wool, polyester, and silk. Thread-based microfluidics, an offshoot from paper-based microfluidics, utilizes the same capillary based wicking capabilities. Disadvantages include difficulty of fluid retention and high limits of detection. Lateral flow immunoassays, such as those used in pregnancy tests, are one example of the application of paper for point of care or home-based diagnostics. ![]() Cell culture methods within paper have also been developed. The application of paper as a diagnostic tool has shown to be powerful because it has successfully been used to detect glucose levels, bacteria, viruses, and other components in whole blood. In some cases, dissolvable barriers have been used to create boundaries on the paper and control the fluid flow. Coatings such as wax have been used to guide flow in paper microfluidics. Paper is also versatile because it is available in various thicknesses and pore sizes. Paper-based microfluidics is an attractive method because paper is cheap, easily accessible, and has a low environmental impact. Paper-based microfluidics utilizes the wicking ability of paper for functional readouts. #Pdms scaffold meaning free#Where pf is the free perimeter of the channel (i.e., the interface not in contact with the channel wall), and pw is the wetted perimeter (i.e., the walls in contact with the fluid), and θ is the contact angle of the fluid on the material of the device. The geometry of the channel and contact angle of fluids has been shown to produce SCF if the following equation is true. SCF occurs when the pressure at the advancing meniscus is negative. In open-channel microfluidics, a surface tension-driven capillary flow occurs and is referred to as spontaneous capillary flow (SCF). Some examples of these subsets include open-channel microfluidics, paper-based, and thread-based microfluidics. Open microfluidics can be categorized into various subsets.
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