Tips for Choosing the Right Incubator

The CO₂ incubator is a key piece of laboratory equipment designed to provide a sterile, humidified, and pH optimized in vitro environment for the culture of living tissues or cells. There are generally two main types of incubators, direct heat and water jacket, each with significant advantages and drawbacks. To determine which type of incubator best suits the needs of your lab, a careful assessment of long-term usage should be performed taking into account placement of the incubator and cell types to be incubated. Different cell types have varying sensitivities to conditions such as temperature fluctuations, vibrations, and hypoxia, which are critical to know before deciding on an incubator. Once it is determined where the incubator will be placed within the lab and the ideal living conditions for your cells, use the tips below to choose the right incubator.

Know the advantages and drawbacks of direct heat vs. water jacket incubators—As the name suggests, water jacket incubators have a water-filled container surrounding the growth chamber, which heats or cools the temperature inside by conduction through the inner walls. Water within the jacket circulates and results in a generally uniform interior temperature and thermal buffer against outside air fluctuations. This buffer can be especially useful in the event of a power outage, as water jacket incubators are able to hold heat up to five times longer than direct heat units. The water jacket also dampens vibrations, which can be a valuable feature when working with sensitive cells. Buyers should also consider that water jacket incubators are very heavy when filled and can take as long as 24 hours before a stable operating temperature is reached when first started up. Additionally, they are not designed to operate at temperatures high enough for decontamination or sterilization. Instead, gas decontamination may be required.

Direct heat incubators also heat the inner chamber through conduction, however the inner walls have direct contact with heating coils instead of a water jacket. This results in relatively fast temperature changes with setup taking only eight hours. In addition, the heating coils can reach temperatures required for efficient decontamination making sterilization easy. Unfortunately, because the heating coils have discrete contact points within the walls, direct heat incubators are less uniformly heated within the inner chamber. However, this effect can be mitigated with proper internal airflow. It is also important to consider that the inner chamber of direct heat incubators are more susceptible to temperature fluctuations with changing ambient air temperature. If temperature stability is critical, a water jacket incubator may be more suitable.

Determine where within the lab the incubator will be located—The environment surrounding the incubator will play a large part in determining your incubator needs. A water jacket incubator may be the best choice if the incubator is in a hot spot and requires refrigeration or if the ambient temperature changes frequently. The water is much more resistant to external temperature changes compared to the coils of a direct heat incubator. The water also minimizes vibrations within the incubator, which can be necessary if the incubator is placed near other equipment with heavy vibrations such as a centrifuge. Determining where your incubator will be located before purchasing will help you decide on the best suited incubator.

Assess the humidity controls of the incubator—Maintaining the ideal humidification within an incubator is essential because it prevents evaporation from the cell cultures. Water evaporation from the media will increase the concentration of salts, metabolites, and amino acids and cause osmotic pressure to rise, which can damage cells. Incubator humidification controls are important for mitigating evaporation, but the amount and type of airflow that occurs within the chamber also greatly affects the rate of evaporation. Some manufacturers have introduced systems to slow the airflow, which minimizes evaporation to avoid drying out cell cultures. Look for the number of air exchanges over time within the inner chamber when comparing incubators.

Decide if hypoxic control is necessary and determine accuracy of gas sensors—Preserving a healthy CO₂ level within the incubator is important as the CO₂ interacts with the buffering system of the cell culture media to determine the media’s pH. While many incubators use the more traditional thermal conductivity (TC) sensor, the newer type of infrared (IR) sensor is often more effective as it is not as sensitive to chamber humidity and temperature. O₂ levels can also have drastic effects on the growth of some cultures such as stem cells or primary tissues. A hypoxic environment is more similar to conditions within a living body. An incubator with O₂ controls uses nitrogen gas to effectively lower the concentration of O₂ within the growth chamber. Assessing gas control needs for your lab’s long-term usage of the incubator is crucial.

Consider options for constant contamination control—Contaminations can be introduced into the incubator by simply opening the door. Incubators maintained with positive pressure within the growth chamber minimize airflow into the chamber and can prevent airborne contaminants from entering. Internal air then typically flows through a HEPA filter to provide an extra layer of sterilization. HEPA filters that are inside the growth chamber can cause problems if the blower motor stops and static pressure is lost causing contaminants from the filter to fall freely on your cultures. An externally mounted HEPA filter keeps contaminants far away from cells and also makes it easy to service. When choosing an incubator, it is worthwhile to carefully research the contamination controls as sterility of cultures is a top priority in cell culture.