Microfluidic chambers for cell culture: How to perform fast medium and drug change?

Ability to switch drugs in seconds or less in microfluidic chambers for cell culture allows to study cell response at cells timescale. There are a lot of applications in microfluidic cell culture where the use of pulseless syringe pumps is relevant. However, these flow control devices are generally not suited for fast flow switch in microfluidic devices due to system compliance. There are several types of microfluidic devices that enable fast flow change (<1 sec) of cell culture media, starting from a single straight PDMS channel to more complex methods like hydrodynamic focusing. In the following review, we will describe the advantages and limitations of each method.

Basic microfluidic cell culture chamber with narrow microchannels

For basic cell culture with medium renewal you can use a pressure pump or a push syringe, rigid tubing and a liquid tank containing the medium or the drug. Eventually, a flow sensor can be added to adapt the pressure depending of the required flow rate.

Advantages of basic microfluidic chambers for cell culture with tight microchannels

• Easy fabrication of the single layer PDMS microfluidic device
• Such microchips are compliant with non adherent cells such as worms, bacteria or yeasts
• This kind of cell culture microfluidic chamber can be used with basic flow control setup

Limitations of basic microfluidic cell culture chamber with tight microchannels

• Not compliant with adherent cells
• Requires precise flow control to reduce the medium switch time without flushing cells
• Injection of cells within microchannels can be stressful for cells
• Medium switch time is between 1 and 10 seconds, depending on the required flow rate. This time can be reduced down to 100 ms using relevant fluidic connections.
• The drug treatment on cells can be non uniform; it depends on the cells density in each microchannel
• Flow rate during flow change can induce mechanical stress on cells

Use of a Multiple inlets microfluidic cell culture chamber with laminar flow

For laminar flow switch, the easiest method is to use a pressure pump with two inlets and two liquid tanks containing the media or the drugs. Pressure patterns (rectangular, sinus ect..) will ease the set-up and flow rates implementation. Eventually, a flow sensor can be added to adapt the pressure depending on the required flow rate.

Two push-syringes can eventually be used but the correlated flow rate settings and especially their coordinated precise modifications may be tricky to apply.

Using three inlets allows to confine the central flow stream between the two side flows. Depending on the flow rate conditions, the central flow stream can be down to 50 nanometers wide. This method, called hydrodynamic focusing, also allows to treat only a given portion of a cell with drugs (PARTCELL method, [1]).

For hydrodynamic flow focusing you can use one pressure controller with three oultets and three liquid tanks containing the media or the drugs. Eventually, a flow sensor can be added to adapt the pressure depending on the required flow rate.

As before, a push-syringe can be used for hydrodynamic focusing but its modification will be more difficult to implement and much less fast and precise.
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Advantages of multiple inlets microfluidic cell culture chip using laminar flow

• Single layer PDMS microfluidic device: easy fabrication
• Those devices are compliant with adherent cells
• Small setup required for flow control
• Medium switch time is around 100 msec

Limitations of multiple inlets microfluidic cell culture chip using laminar flow

• Does not work with non-adherent cells
• Requires precise flow control to maintain laminar frontiers
• Deposition and positioning of cells in channels can be difficult
• Flow on cells can induce mechanical stress

Y-channel microfluidic cell culture chip using laminar flow and narrow microchannels

For laminar flow switch you can use two pressure pumps and two liquid tanks containing the media or the drugs. Eventually, a flow sensor can be added to adapt the pressure depending on the required flow rate.

As before, push-syringes can eventually be used but the correlated flow rate settings and especially their coordinated precise modifications may be tricky to apply.

Advantages of Y-channel microfluidic cell culture chip containing trapped cells and using laminar flow

• Single layer PDMS microfluidic device: Easy fabrication
• Compliant with non adherent cells such as worm, bacteria or yeast
• Small setup required for flow control
• Medium switch time is around 100 ms

Limitations of Y-channel microfluidic cell culture chip containing trapped cells and using laminar flow

• Not compliant with adherent cells
• Requires precise flow control to control the medium switch time without cell flushing and to position precisely the laminar interface
• Injection of cells within microchannels can be stressful for cells
• The drug treatment on cells can be non uniform; it depends on the cells density in each microchannel
• Flow rate during flow change can induce mechanical stress on cells

Drug treatment using diffusion

Another kind type of device also allows this kind of medium change (see below).

For diffusion-based flow switch you can use a single pressure pump, liquid tanks containing the media or drugs and valves. When changing drug, the inlets of the cell chambers have to be blocked using plugs or valves. Eventually, a flow sensor can be added to adapt the pressure depending on the required flow rate.

Advantages of drug treatment using diffusion

• Easy fabrication
• Compliant with non adherent cells such as worm, bacteria or yeast
• No mechanical stress on cells by flow rate
• Medium switch time is around 1 s (depending on the diffusion length)

Limitations of drug treatment using diffusion

• Injection of cells in channels can be stressful for cells
• Medium change speed may be difficult to adjust.

Drug treatment using diffusion and narrow microchannels

For diffusion-based flow switch, you can use a single pressure pump and a liquid tank containing the medium or drugs. When changing drug, outlets of the cell chamber have to be blocked using plugs or valves.

To inject drugs on both sides of the device, we recommend two pressure pumps rather than push-syringe to finely tune the pressures. Eventually, a flow sensor can be added to adapt the pressure depending on the required flow rate.

Advantages of Drug treatment using diffusion and narrow microchannels

• Compliant with non adherent cells such as worm, bacteria or yeasts
• With diffusion by both sides, medium switch can be 4 times faster than by one side
• Medium switch time is around 1 s (Depending on the diffusion length)
• No mechanical stress on cells by flow rate

Limitations of Drug treatment using diffusion and narrow microchannels

• Injection of cells within channels can be stressful for cells
• Requires quite precise flow control to limit medium convection in cells channels leading to cells movements

For more reviews about microfluidics, please visit our other reviews here: «Microfluidics reviews». The photos in this article come from the Elveflow® data bank, Wikipedia or elsewhere if specified. Article written by Guilhem Velvé Casquillas and Timothée Houssin and revised by Lauren Durieux.

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