Temperature control for microscopy imaging : micro perfusion system
Using microscopy imaging to address cell biology questions requires maintaining the cells in a physiological-like environment. There are several temperature controllers available on the market; all have positive and negative features and depending on users needs some might be better suited than others. Micro perfusion systems are commonly used to control sample temperature at the microscope stage.
Micro-perfusion systems are composed of a culture chamber connected to a perfusion system allowing fluid renewal in the chamber. There are open or closed chambers. Open chamber allow a direct access to the cells, and are convenient for cells injection. Closed chambers prevent medium evaporation and better-controlled environmental parameters (gas, pH); they are more appropriate for long-term imaging. Micro perfusion systems provide fast temperature switch and the possibility to renew medium during the experiment.
Speed of the temperature switch (~1 min)
Since temperature controlled micro perfusion systems directly thermalize the sample by changing the cell culture medium, temperature switch can be achieved in less than 1 min when extreme flows are generated around the sample.
Efficient thermal transfer
Forced liquid convection is efficient for thermal transfer. Hence, temperature-controlled micro perfusion systems provide a good temperature uniformity across the sample. It also reduces the increase in temperature when turning on DIC illumination or during extended observations with epi-fluorescence.
Medium renewal, drug injection
Temperature controlled micro perfusion systems are based on medium renewal with the possibility to inject drugs. In this system the cells are kept in a physiological-like environment. They are particularly suited for long-term imaging.
High shear stress
Because temperature-controlled micro perfusion systems generate strong flow rate on the cells, they induce high shear stress on them. Moreover, because of fluid flow-rate chemical signaling molecules can be washed out too quickly from cells environment. Finally, cells in suspension, loosely adherent cells or very sensitive cells such as stem cells might be simply washed out or suffer to much mechanical stress from the flow-rate.
Mono temperature control
Only one temperature can be set on the microscope stage temperature controller. While other system allows to set two temperatures at once and shift from one to the other ultra-rapidly
Requires an objective collar
Using immersion objectives will require additional temperature controlled objectives collar to reduce the temperature gradient between observation zone and the rest of the biological sample.
Ambient and above
Most of the micro perfusion systems work on a temperature range from ambiant to 50°C, some of them can be completed by a cooling system to reach 0 C but they require a specific additional cooling microscope stage adapter.
Requires experimented users
Temperature-controlled micro-perfusion systems are best for experimented users as it requires a strong knowledge to make the system works correctly.