Problem: Contamination in cell culture is a time-consuming, costly and ongoing problem. Research can be invalidated, valuable cell lines lost and weeks and even months of work ruined. Many labs have rigorous processes in place to protect cells, yet still have occasional problems with contamination. As important as processes are, the incubators used to house cultures should be designed to perform in ways that protect samples and allow them to flourish.
A seamless interior and an inner glass door are features that help maintain a healthy environment for cells in culture. Photo courtesy BINDER Inc.
Solution: It should be noted that concern about contaminants and requirements for level of protection depend on the sample and experiment. Are you culturing pond water for the presence of E. coli, or growing an irreplaceable line of cancer cells? In this article, it will be assumed that the highest level of sample security is required.
Incubator interiors provide an environment in which atmosphere, temperature and humidity interact to provide a suitable place for cells to grow. Unfortunately, the conditions that make research samples happy are also conducive to the growth of contaminants such as mycoplasma.
Seamless interiors are preferred in the incubator’s construction. Seams and rough spots from the manufacturing process provide all that is needed for infectious agents to avoid wipe downs and cleanings and to gain a foothold in the incubator. Shelves, probes, ports and all additions to the interior should be incorporated in a way that makes cleaning easy and leaves little to no room for infections to establish themselves.
HEPA filters do catch some airborne contaminants (although most contaminants are not airborne) but they also harbor the very organisms they snare. They can be expensive and time-consuming to change and disposal can be costly if infectious agents are involved. Consider the level of threat airborne contaminants pose and the ways other incubators deal with this. If your incubator has a HEPA filter, do change it regularly.
The way gases are mixed and introduced can have an impact on environmental conditions throughout the chamber. Premixing before injection provides greater control and distributes gases evenly throughout the chamber. The proper gas mixture is also critical in maintaining pH, a vital factor in cell health.
Interior heating by water or air jackets should provide uniform temperatures throughout the chamber, and maintain temperature consistently. Be wary of units that have hot spots, in which heating elements contact the chamber.
Doors should seal tightly and be easy to open and close. Locks prevent accidental openings. Inner doors should be used to reduce exposure of the chamber to outside conditions. It is helpful to organize and plan the location and number of plates being accessed and what will be done with them before accessing the chamber. This will limit the amount of time the door is open and thus provide a more stable environment.
The CO2 sensor and the technology it uses are extremely important in determining the stability of the environment. Look for a model that provides the desired degree and kind of control; for most cells, more is better. Sensors also help the incubator return to set-point after a door-opening, and thus, sensitivity and responsiveness are paramount.
Humidification is tricky. While cells like varying degrees of humidity, pooled water on culture dishes or in corners of the incubator can play host to unwanted and potentially harmful organisms. It is important that not only is the proper amount of humidity maintained, but that the resulting condensation is controlled. Different incubators try to accomplish this in varying ways, but directing condensation to a pan in the bottom of the unit that is easy to remove, sterilize and replace is optimal.
Available incubators offer various levels of self-cleaning. Disinfection temporarily eliminates or inactivates infectious agents; decontamination is the elimination or irreversible inactivation of all pathogenic germs; sterilization inactivates or eliminates all vital microorganisms. Those incubators that do not offer sterilization cycles will have a decontamination cycle or must be manually disinfected, an imprecise and time-consuming chore. A self-sterilizing incubator offers many and obvious advantages and ensures the best possible conditions for incoming experiments.