Introduction to Microfluidics

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A New Standard for Cell Culture

Today, all the major microscope manufacturers offer devices built for live-cell imaging. Many of these systems come complete with computerized incubation chambers and microscope stages that allow multilayered integration of key parameters:
  • Cooling
  • Heating
  • Environmental gases
  • Mineral balance
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The stages, when combined with integrated but often proprietary microscope-controlling and image-acquisition software are beginning to allow researchers some control over the general cell culture environment. This limited environmental control allows them to overcome at least some of extrinsic control elements arising in live cell analysis, but there are issues.

As good as today’s modern cell culture imaging microscope systems are today, many of these devices are extremely expensive and while they offer some basic controls over temperature, humidity, and nutrient, their ability to precisely control the actual microenvironment of the cells is limited.

Controlling Environment vs Microenvironment

Gaining control of cellular behavior, while still having the ability to visualize and track living cells in culture is necessary to have precise, dynamic, environmental control of the cellular microenvironment. Tight and timely control over multiple culture parameters while constantly monitoring culture status would allow for far better manipulation of the microenvironment and would seem to be the experimental ideal.

Microfluidic Control of Assay Environments
The science of Microfluidics started in the printing and inkjet arenas but now as found applications in every major biological and physical science arena. Biologists are examining microfluidic solutions across a wide arena of specialties, including drug discovery and drug delivery, genetics and genetic sequencing challenges such as the typing of single nucleotide polymorphisms, to proteomics, and even to the newly emerging field termed “lab-on-a-chip” solution systems where several different laboratory functions are performed simultaneously.

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Microfluidic technology has the potential to achieve the following:
  • Exploration of single cell behaviors and interactions
  • Adaptable to single molecule biophysics and experimentation
  • Miniaturization and portability of chemical and biological assays
  • Exquisite control & manipulation of micro environments and fluid controlled experiments
  • Cost savings through minimal reagent use
  • Potential for massively-parallel and high-throughput biochemical analyses
  • High adaptability to robotic and instrumental control and data collection
 

Biological Microfluidics

Biological microfluidics is an emerging multidisciplinary science that intersects the fields of biotechnology, biochemistry, chemistry, nanotechnology and physics to create devices that control the cell culture microenvironment. Diffusion in a microfluidic environment can be tightly controlled, making addition and removal of cell culture chamber materials (extrinsic factors) much easier.

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Biological microfluidic systems work because such microfluidic environments are sub-millimeter (channel diameters of around 100 nanometers to several hundred micrometers are common). At that size, the microfluidic behavior of fluids changes in comparison to what we observe in the macro scale. For instance, in a microfluidic environment a fluid’s Reynolds number (a measure of its viscosity) often drops to very low or near zero. This means that fluids do not mix; that diffusion is halted or vastly decreased likely because of the molecular tension of the molecules within the fluid itself. These microfluidic devices and their channels can be passively or actively controlled and continuous or discontinuous in fluid dynamics with additional versions being developed every year.

For a list of microfluidics research groups, click here!

See how microfluidics has been applied to controlling cell culture microenvironments using the CellASIC® ONIX platform.
Merck:/Freestyle/BI-Bioscience/Cell-Culture/cellASIC/cd-cell-culture.jpg 
An example of 3D cell culture used to assess drug-induced cell death.

In Vivo-Like Cell Culture

Microfluidic systems provide many advantages for live cell imaging, including improved cell culture micro-environments. The tight control of fluid flows assists in creating and maintaining more predictive cell cultures, including mixed cultures, 3D and 4D cultures. Current strategies for 3D cell culture include growing cells in hanging drops, in a natural or synthetic 3D matrix on biodegradable polymers in a cross-linked hydrogel or in porous synthetic scaffolds. Even in these advanced platforms, if subjected to static conditions of gas, nutrient medium and waste buildup, they are limited by the inefficient mass transport between the inside and outside of the 3D cell structures. Microfluidic control of microenvironments is being used increasingly to overcome the challenges of mass transport in 3D culture.

Merck:/Freestyle/BI-Bioscience/Cell-Culture/cellASIC/CellASIC_Cell-Migration_EM-1-cover.jpgThree-dimensional culture and assessment of drug-induced cell death using the CellASIC® ONIX Microfluidic Platform

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8 Critical cell culture parameters that can be controlled by microfluidics in combination with a closed culture system

ParameterSome Effects of Deficient valuesSome Effects of Excessive values
Temperature Decreased cell response Increased respiration/ protein damage
Oxygen Level Decreased pH/increased glycolysis Increased ROS, Membrane damage
Growth Factors Increased apoptosis/ decreased protein synthesis Increased angiogenesis and cell division
Humidity Increased  osmolarity/ cell metabolism / increase oxidative stress No significant changes
pH Increased Alkalosis and dehydration Protein and membrane denaturation
Osmolarity Decreased cell division / increased autophagic proteolysis Increased oxidative stress, DNA breakage, and nutrient digestion
Glucose Decreased autophagy and metabolism Increased Apoptosis and ROS
ECM and Adhesion Decreased angiogenesis / aberrant differentiation Increased cell adhesion, chemotaxis, proliferation