7 Questions to Ask Before Buying a CO₂ Incubator:

• What size CO₂ incubator do you require?
• What type of CO₂ sensor do you require?
• Do you need a water-jacketed or air-jacketed incubator?
• What uniformity and accuracy do you need?
• What humidity range do you require?
• What features are included to remove or prevent contamination?
• Do you need O₂ control for your environment?

3 General Sizes:

There are many different sizes available, but all can be grouped into 3 categories:

• Benchtop = under 6.5 cu.ft. Ideal for individual use and completely isolating separate cultures.
• Floor standing = between 6.5 to 11 cu.ft. Ideal for multiple users and often large enough to isolate different cultures within the same unit for different viral studies, pathogenic studies or stem cell applications.
• Reach In = over 11 cu.ft. Ideal for large groups with substantial room to isolate cultures.

Types of CO₂ Sensors:

• IR (Infrared): the most accurate controller of CO₂ levels, detecting CO₂ with an optical sensor. Chamber air passes over an IR emitter (a light source) and the sensor detects a reduction in the IR as the CO₂ in the chamber air absorbs the IR. The amount of IR absorbed is relative to the levels of CO₂ in the chamber air. The IR sensor is not affected by temperature and humidity fluctuations, so it is more accurate than the TC sensor, especially following door openings.
• TC (Thermal conductivity): measures the resistance between two thermistors, one exposed to the chamber and the other enclosed. The presence of CO₂ in the chamber changes the resistance between the two thermistors. Changes in temperature and humidity can affect the accuracy of the sensor.

Temperature Control:

There are 3 options for temperature control:

• Water-jacketed: consists of a separate enclosure around 5 sides of the incubator (everywhere but the door) that is filled with heated water. The heated water is circulated inside the enclosure, to maintain a consistent temperature inside the incubator. One of the benefits of choosing a water-jacketed model is that the water within the jacket not only provides heat, but also acts as an insulator. This means that during frequent door openings or power outages, samples will remain protected at the set temperature.
• Air-jacketed: the incubator is heated using a separate isolated air jacket on the 5 walls of the incubator. Some have a heated air chamber on the door as well, creating a full 6-sided heat source. The air inside the jacket is often circulated using a series of small fans. One advantage of an air jacketed system is that if the temperature drops below the set point, the unit can ramp back up to its set temperature quickly. Air-jacketed incubators do not require much in the way of maintenance, as there are no water reservoirs to fill. Air jacketed systems are also lighter in weight than other systems, making them easier to move around the lab if needed.
• Direct Heat: since there is no jacket, direct heat incubators offer larger internal capacity in a smaller footprint than an air or water-jacketed system. They are often priced lower than a jacketed system. Heating comes from all six sides of the incubator, including the door, which allows for convection circulation and temperature uniformity without the need for fans.

Why is humidity important?

It is important to maintain adequate moisture inside the chamber to prevent the drying out of cultures. Humidity, temperature, and gas uniformity within a CO₂ incubator are the three most important factors to ensuring high yields in cell culture. When humidity is not properly circulated or generated evenly throughout the chamber, the effects can include decreases in cell weight, cell morphology variability, nutrient over-digestion, and decreased protein production. Large CO₂ incubators may use steam-generators or atomizers to control relative humidity levels but most small to mid-sized incubators use humidity pans to produce humidity through evaporation. Humidity pans produce relative humidity levels between 95-98%.

Contamination:

Contamination is a major source of frustration in cell culturing. Many manufacturers offer HEPA filters in CO₂ incubators to reduce contamination during the incubation cycle. Copper-lined chambers with copper shelves and fixtures, removable shelves and coved corners all reduce fungal growth. Some CO₂ incubators also have auto-decontamination cycles that decontaminate the internal chamber in between incubation cycles. Auto-decontamination works by raising the internal temperature to +90°C for several hours. The auto-decontamination cycle, used in conjunction with HEPA filters, greatly reduces contamination.

Maintenance:

CO₂ Incubators should have a regular maintenance schedule to avoid unscheduled down-time and potential loss of product. Components of the incubator such as the CO₂ sensor and temperature controller need to be calibrated on a regular basis. HEPA filters, and anodes should be replaced regularly. Decontamination of the incubator needs to occur on a frequent basis.

Six Month Check:

• Check all filters for discolouration. Replace if discoloured.
• Check gas lines and CO₂ regulator for leaks.
• Check air flow or fan blade for rotation and discoloration. This depends on manufacturer and model.
• Check CO₂ tank switcher for proper operation.

 Other Considerations Before Buying:

• Future needs
• The lab environment (foot traffic, space, sample throughput needs)
• Is the system easy and intuitive to use without a manual?