Pumps or perfusion in organ on a chip
Many organ on a chip systems use pumps to perfuse the micro-tissues they model, or in engineering terms, they have “flow” in the system. But you pay a price here: adding perfusion makes the system more complex! So, you really need to think:
Do I really need perfusion in my organ on a chip?
To help you answer this question, we discuss possible reasons you may need perfusion:
1. Mechanical Stimuli
Many cells in the body experience forces, usually shear stress, from the fluid around them. Take the vasculature, the blood flows in the vessels and exerts a force on endothelial cells. If you want model it outside the body, you need to pump the medium on the cells to mimic the physiological conditions. That is why you may need perfusion in vascular models.
Other examples of the tissues that experience mechanical stimulus are
2. Automation
Think about
- refreshing medium automatically, or
- plan adding a reagent, e.g. drugs, to the medium in intervals,
- or sampling automatically at a specific time point.
For all these circumstances, you need to refresh medium in the chip automatically, which means that you need a pump, and possibly extra components, to perfuse fresh media into the system.
3. Connecting organ models
If you want to study cross-talk of multiple organ models cultured in different chambers, you need a pump, internal or external, to transfer medium from one to the other.
4. Biochemical gradients
If you look at gradients in Transwell models, for example, you see that the gradient diminishes relatively fast (usually hours). To keep the gradients in place, e.g. for an intestinal barrier, and organ on a chip can be connected to a pump to refresh media continuously or at intervals.
5. Circulating cells
The title says it all! To circulate cells in organ on a chip, a pump is needed that is suitable for perfusing circulating cells.
Different types of pumps
After you are sure that you need perfusion in your organ on a chip system, you need to choose a pump. Let us have an overview of different pumps and compare them. First, definition of different pumping mechanisms:
- “Flow driven” pump: such as syringe and peristaltic pumps; you set a flow rate, you get that flow rate
- “Pressure driven” pump: You set a pressure, based on the fluid path you get different flow rates
PLEASE note that this table only gives a general overview for organ on a chip systems and requires detailed and exhaustive analysis for every organ or application.
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