Pressure as a tool to evaluate cell growth
This application presents a simple method to monitor cell proliferation in microfluidic chips in real time. This is demonstrated experimentally using a custom microfluidic chip. Cell morphology was studied under flowing and static culture condition
This study has been made in collaboration with Taha Messlmani, co-supervised by Fluigent and Anne Le Goff, from the Biomecanic and Bioengineer laboratory (BMBI – UMR CNRS 7338) of Université de Technologie de Compiègne (UTC).
Materials and methods
» Flow-EZ: The Flow EZ is the most advanced flow controller for pressure-based fluid control. It can be combined with a Flow Unit to control pressure or flow rate. A range of 10 – 40 mbar was used during the experiments.
» Flow unit M: A flow sensor that allows real time flow rate measurement up to 80 µL/min. By combining a Flow Unit with the Flow EZ, it is possible to switch from pressure control to flow rate control. (more details on www.fluigent.com/products)
» A microfluidic cell culture chamber chip. At least 2 chips should be used for the first calibration
» Tubing
» Cell culture media
» Cell line
Partial results
Determining cell proliferation within the biochip in real-time
We followed the protocol find the correlation between cell proliferation and the pressure increase for maintaining a steady flow rate. The experiment was repeated on 5 biochips to increase statistical significance. The pressure applied to maintain a flow rate of 10 µL/min as a function of the number of cells (estimated after injection, and counted after 3 days of perfusion) is shown in the figure.
We can observe a good correlation between the pressure applied and cell number for cells cultured during 3 days and counted afterwards. The slope from the curve was determined and lead to a linear function making it possible to estimate the number of cells as a function of the applied pressure under identical conditions.
Cell viability under steady and dynamic flow conditions
To assess the influence of flow rate on cells, cell morphology of cells cultured under dynamic and static conditions was compared (images on the right).
We observe that the actin network is more developed under dynamic conditions compared to static conditions. In fact, under flowing (dynamic) conditions, a low shear is applied on cells. This shear stress tends to elongate cells, and as consequence 2-dimensional cell growth is favored. Under static conditions, 3-dimensional cell growth is favored as no shear is applied. Cells growing 3-dimensionally could lead to increased cellular heterogeneity as they do not have access the same amount of nutrients or oxygen within the microfluidic chamber. Under dynamic conditions, cells are in a favorable growth environment, that is a continuous and homogeneous perfusion culture with a steady and low shear stress applied on cells.
Conclusion
We here demonstrated the use of pressure controllers coupled with flow sensors for determining and estimating cell proliferation within a microfluidic chip in real-time. The user can track in real-time cell
proliferation by simply monitoring pressure increase. This method allows one to estimate cell proliferation kinetics within a chip in an inexpensive fashion. This system shows great advantages as it offers real time information on pressure and flow rate, without requiring the preparation of additional replicates dedicated to monitor proliferation at different time points, hence making it a strong and versatile tool.
References
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- Zhou, Y. et al. Characterizing Deformability and Electrical Impedance of Cancer Cells in a Microfluidic Device. Anal. Chem. 90, 912–919 (2018).
- Cahill, B. P. Optimization of an impedance sensor for droplet-based microfluidic systems. Smart Sensors, Actuators, MEMS V 8066, 80660F (2011).
