Liquid Stirring Solutions
Fluid agitation is a common step in many microfluidic applications. During sample preparation, it allows for the dissolution, mixing, or dispersing of reagents. Continuous stirring is required during specific experiments to maintain mass transfer, emulsion, or suspension in heterogeneous mixtures. Fluigent provides different solutions to best fit your liquid stirring specifications.
This technology can be integrated in any custom project. Benefit from the best performance and Fluigent expertise for your project.
- Tailor-made: different types of motion, intensities of stress, volumes handled
- Compatible with temperature control: stirring and heating/cooling modules are easily combined
- Versatile: can be integrated into Fluigent’s protocols and communicate with other microfluidic setup modules
Liquid stirring modules: technology description
Fluigent has developed fluid agitation solutions that use different technologies. The stirring module can be coupled to a temperature control module, as they both require a platform to which the reservoirs are attached. As they are integrated in the software, Fluigent allows the user to play on certain parameters. For example, three different speeds can be implemented, allowing for different ranges of liquid stirring with the same module.
Magnetic induction stirrer: a motor-less agitation method
Fluigent’s designed technology works similarly to standard magnetic stirrers generally used in chemistry applications. It’s composed of two elements: a magnetic stir bar (immersed in the fluid) and a coil (placed under the container, off-center). When AC current flows through the coil, the magnetic field alternatively generated, turned off, and inverted leads the stir bar to vibrate or spin, thus stirring the liquid in the sample. By adjusting the current, this method provides gentle to strong agitation. This magnetic induction stirrer presents various advantages compared to usual motorized magnetic stirrers: it does not generate heat that may impede temperature sensitive experiments and it’s quiet and compact, making it adaptable to volumes used in microfluidics. It is the preferred technology to integrate fluid stirring in a very compact system.
Orbital shaker: a stable platform for consistent vial-to-vial homogeneity
Fluigent also developed contactless fluid agitation technologies. Orbital shakers usually consist of a large plate that provides soft orbital motion in a horizontal plane. However, the movement could be implemented differently so that the platform oscillates with any trajectory. Unlike the magnetic stirrer, this solution is non-intrusive and can consistently handle multiple reservoirs with the same device. The benefits of the orbital shaker compared to other shakers like the platform shaker or the vortexer are that it generates no vibrations, produces less heat, and is able to aerate the samples and evenly distribute cells. This technology has been developed for customers who do not need much capacity but external sterile liquid stirring that avoids sedimentation and cell damage. The platform is also optimized to integrate temperature control.
Vortex mixer: a solution for intense shear stress
The vortex mixer is similar to the orbital shaker in terms of motion. The differences are orbital diameter, agitation frequency range and means of contact. While the orbital shaker usually has a bigger diameter and a lower frequency, the vortex mixer usually has a smaller diameter and a higher frequency. Thus, the latter allows a more intense liquid stirring. Moreover, vials are placed on a plate on an orbital shaker whereas the vortexer has a cup-shaped, slightly off-centered rubber piece vertically attached to the motor drive shaft that transmits its rotative movement to the vial or the foam rack with several tubes attached to it. This creates a vortex in the liquid.
Comparison between liquid stirring technologies
Each method has its own advantages that make it more adapted for certain applications. Here are some variables that may be taken into account when choosing the best liquid stirring solution for your project: 
|Magnetic stirrer||Orbital plate||Vortex mixer|
|Agitation level||Locally gentle to intense shear||Intermediate-level stress||Most intense overall stress|
|Frequency range (rpm)||60-1400||60-300||500-3200|
|Invasiveness||Invasive but the stir bar is coated (PTFE) to be chemically inert||Non invasive||Non invasive|
|Durability||No moving external part subject to break or wear out||Motorized mechanical device||Motorized mechanical device|
|Volume||Compact, adapted to small volumes due to the size of the bar and the absence of a motor||Plate of adjustable size that can fit multiple reservoirs||Rack of adjustable size that can fit multiple reservoirs|
|What to use it for?||Low-viscosity laboratory mixing||Homogeneous distribution of cells and nutrients throughout the flask||Vigorous mixing, resuspension of samples|
Microfluidic related applications to liquid stirring
- Drug production
Homogeneous mixing is a prerequisite in biopharmaceutical manufacturing operations like drug production. They are performed in stirred vessels that use magnetic stirrers because they are gentle enough to prevent protein damage in spite of the shear stress they can cause. Magnetic stirring can also be used to produce drug nanosuspensions to enhance its dissolution rate and improve safety for the patient. 
The cultivation of mammalian cells in suspension is essential for protein synthesis in clinical and pharmaceutical research. The classical way to cultivate them involves spinner flasks, but they require much work to clean and sterilize. Another approach is to agitate Erlenmeyer flasks or a multiwell plate on an orbital shaker. It allows superior cell growth, high reproducibility in performance, good cell viability, low cost, and easy cleaning and handling of the bottles, which makes it a viable liquid stirring solution for the culture of mammalian cells in suspension. 
- DNA extraction for PCR
Many applications of DNA technology such as the detection of fungal pathogens by PCR need extraction methods that isolate uncontaminated DNA suitable for amplifications. Several methods to perform this exist and most of them have a reagents’ mixing step with a vortex mixer for maximum efficiency. 
 G. Bai, J. S. Bee, J. G. Biddlecombe, Q. Chen, W. T. Leach, “Computational fluid dynamics (CFD) insights into agitation stress methods in biopharmaceutical development”, International Journal of Pharmaceutics, 2012
 T. Ladner, S. Odenwald, K. Kerls, G. Zieres, A. Boillon, J. Boeuf, “CFD Supported Investigation of Shear Induced by Bottom-Mounted Magnetic Stirrer in Monoclonal Antibody Formulation”, Pharmaceutical Research, 2018
 P. Kocbek, S. Baumgartner, J. Kristl, “Preparation and evalutation of nanosuspensions for enhancing the dissolution of poorly soluble drugs”, International Journal of Pharmaceutics, 2006
 M. Micheletti, T. Barrett, S. D. Doig, F. Baganz, M. S. Levy, J. M. Woodley, G. J. Lye, “Fluid mixing in shaken bioreactors: Implications for scale-up predictions from microlitre-scale microbial and mammalian cell cultures”, Chemical Engineering Science, 2006
 N. Muller, P. Girard, D. L. Hacker, M. Jordan, F. M. Wurm, “Orbital Shaker Technology for the Cultivation of Mammalian Cells in Suspension”, Biotechnology and Bioengineering, 2005
 J. C. Colosi, B. A. Schaal, “Tissue grinding with ball bearings and vortex mixer for DNA extraction”, Nucleic Acids research, 1993
 D. N. Fredricks, C. Smith, A. Meier, “Comparison of Six DNA Methods for Recovery of Fungal DNA as Assessed by Quantitative PCR”, Journal of Clinical Microbiology, 2005
Expertise and resources
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