Managing Real-State on Centrifugal Microfluidic Platforms

admin — Wed, 24 Apr 2019 13:43:37 +0000

Centrifugal microfluidic platforms, also called compact microfluidic biodisks or compact disks (CD), have been around for almost four decades and have seen a surge in technology advancement in the last decade¹. CDs are used in rapid immunoassaying and clinical biochemistry for blood diagnostics. They are used as micro total analysis systems (μTAS), in which several individual assays are embedded and run simultaneously on a single chip. They operate on simple inexpensive motors programmed for hands-free control and do not require external actuators such as magnets or surface treatments. Basically, CDs are great, and this article should end here. Unfortunately, there is a catch: due to unidirectional (radial) centrifugal forces, CDs run out of real estate faster than non-rotating microfluidic devices.

Schematic highlighting various body forces applicable to a radial column of water inside the channel of a CD. Notice the radially outward-acting centrifugal force which is crucial to moving the fluid towards the edge of the disc.

Fluids only move radially outwards, limiting the number of analytical steps a CD can perform. In 2010, Gorkin et al.² released one of the earlier papers where the authors suggest pneumatic pumping to counter the unidirectionality of CDs.Their idea was to store the centrifugal energy as compression energy and release it when needed to launch the fluid towards the center. Gorkin et al. conducted a series of experiments, to understand the correlation between a certain rotational speed and the corresponding amount of compression energy storage-Higher rotational speeds cause more compression energy storage.

Photo of the CD used by Gorkin et al. and the 5 stages of pneumatic pumping in the CD. Compression of the air in the compression sub-compartment happens because of the disc rotation. The final relaxation stage is attained by slowing the disc rotation.

Experiments are at the core of designing microfluidic devices. But conducting enough experiments and maintaining a perfect control environment for each experiment can become prohibitive. Complex designs require complex experimental setups and analysis. Can modeling share some burden of the experiments? The answer to that question is yes, based on the sequence of images below. Quantitatively, an excellent correlation (R²>0.99) exists between the experimental and the FLOW-3D simulation results.

Top row: Images of the section of the CD rotating at different speeds. Bottom row: Simulation counterpart for each rotational speed used in the experiments.

The real-estate management of uni-directional flow devices such as centrifugal microfluidic platforms is difficult but attainable. Innovative ideas such as pneumatic pumping, followed by experiments and supported by accurate simulations, alleviate the major limitation- available real estate – of centrifugal microfluidic platforms while maintaining the benefits of these devices.

^{1. Bithi, S. S. & Vanapalli, S. A. Microfluidic cell isolation technology for drug testing of single tumor cells and their clusters. Scientific Reports 7, 41707, doi:10.1038/srep41707 (2017).}
^{2. Park, I. S. et al. Real-Time Analysis of Cellular Response to Small-Molecule Drugs within a Microfluidic Dielectrophoresis Device. Anal Chem 87, 5914-5920, doi:10.1021/ac5041549 (2015).}

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Adwaith Gupta

Adwaith Gupta is a Senior Computational Fluid Dynamics Engineer at Flow Science Inc and an independent Artificial Intelligence Engineer. At Flow Science, he is an active member of the product development team; leads the academic programs; oversees the development of state-of-art optimization software; and spearheads the expansion of FLOW-3D (Flow Science’s multiphysics modelling software) into the microfluidics industry. He obtained his MS from Stanford University majoring in Fluid Mechanics with a focus on computational modelling and scientific computing.

The post Managing Real-State on Centrifugal Microfluidic Platforms appeared first on The MicroFluidic Circle.

Two Reasons to Integrate Simulations into Your Microfluidics Workflow, Now

admin — Wed, 06 Dec 2017 14:32:51 +0000

Over the last two years, I have seen an increased interest in using simulation software to better understand microfluidics processes. The two most common and important reasons for considering integration of simulation software into microfluidics processes have been to reduce device cost and improve quality control.

Microfluidics processes are truly multiphysics in nature, requiring a robust simulation tool to accurately capture all of the physics involved. Certain physics like surface tension become more prominent at the micro scales at which microfluidics processes work. Coupled to surface tension are other physics in play, such as electro-osmosis, electro-kinetics and visco-elasticity. In short, microfluidic simulations can be very complex. An accurate simulation tool can provide insights to the designer about the microfluidic device and help him develop a more efficient and better design. One such example is analyzing an acoustophoretic particle focusing device that removes a variety of objects from solutions in a microfluidic channel. The process is applicable to malignant cell removal, nanoparticle separation, and sequestration of suspended liquids. Another application is to understand the dynamics that govern the formation of lenses using fluids (optofluidics) in microfluidic channels. Optofluidics combines elements of optics and microfluidics and finds applications in biosensors, displays, lab-on-chip devices, molecular imaging and lenses.

Going back to the acoustophoretic particle focusing device, using inappropriate control parameters such as acoustic wave frequency can lead to forces that may cause some malignant cells to avoid getting separated from the bloodstream. The animation below shows an acoustophoretic device that focuses all the representative malignant particles to the middle of the device, which can then be safely extracted from the solution.

Simulation of an acoustophoretic device where particles enter the computational domain at an off-center location in a microchannel of 500μm height and 2mm length. Under the influence of a standing acoustic wave at a frequency of 1Mhz, the particles are focused in the middle of the channel.

Similarly for the optofluidics device, hydraulic parameters such as flow rates can alter the shape of the lens significantly. Understanding how flow rates affect the shape of a lens ensures the proper illumination of cell bodies in a solution, making it easy to study their behaviour. Also, using simulation the shape of the microfluidics channels can be optimized to produce the desired lens shapes with minimum material, saving on the cost of manufacturing. This animation shows an optofluidic device forming different lens shapes.

Simulation showing lens formations for different flow rate combinations. In this case different lens types are formed, such as bi-convex, plano-convex and meniscus.

The microfluidics industry is currently on the so-called slope of enlightenment of the Gartner Hype Cycle curve for emerging technologies, thanks to the increased research into microfluidics processes and applications. An important aspect of microfluidics processes is the “precise” control and manipulation of fluids that can be attained by thorough experimentation complimented by accurate simulations. Integration of simulation software in your workflow can provide precise control over a microfluidics process while maintaining the economic viability and the reliability of the device.

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Adwaith Gupta

The post Two Reasons to Integrate Simulations into Your Microfluidics Workflow, Now appeared first on The MicroFluidic Circle.

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Managing Real-State on Centrifugal Microfluidic Platforms

Adwaith Gupta

Two Reasons to Integrate Simulations into Your Microfluidics Workflow, Now

Adwaith Gupta