What To Look for in a [CO.sub.2] Incubator.
Although the ultimate goal of maintaining cell culture stocks has not changed, [CO.sub.2] incubators have become more accurate and convenient as reliability, contamination control, and ease of use are the main areas of concern when selecting a [CO.sub.2] incubator. The units range in size from bench-top models ([is less than] 40 L) to large-capacity incubators ([is greater than] 700 L).
[CO.sub.2] levels within a chamber are established with a set point and are controlled to maintain that set point. When the door is opened, [CO.sub.2] escapes and a sensor detects a drop in the [CO.sub.2] level. [CO.sub.2] is automatically injected to raise the level to the set point. Thermal conductivity (TC) and infrared control systems are used to detect changes in [CO.sub.2] levels.
TC systems work by measuring the resistance between two thermistors, one exposed to the chamber environment and the other enclosed. The presence of [CO.sub.2] in the chamber changes the resistance between the two thermistors. The level of [CO.sub.2] is determined by measuring the resistance. A drawback of TC is that changes in temperature and relative humidity, caused by frequent door openings, can affect the accuracy of the sensor.
IR systems, which detect CO: levels with an optical sensor, were developed as an alternative to TC sensors and are a more accurate controller of [CO.sub.2] levels. An air sample from the chamber is passed between an IR emitter (a light source) and the sensor. The sensor detects a reduction in the IR from the emitter as the [CO.sub.2] in the air sample absorbs the IR. The amount of IR absorbed is relative to the levels of CO: in the air sample. IR sensors are not affected by variations in temperature and humidity, so they are more accurate than TC types. However, IR systems are usually more expensive.
Maintaining a constant temperature in the incubator is critical to the health and growth of cultured cells. Water-jacketed and radiant-walled are the two primary heating options to consider when selecting a small to mid-sized [CO.sub.2] incubator.
Water-jacketed incubators maintain temperature by surrounding the interior chamber with heated water in a separate compartment. The water is heated and circulates around the inner chamber via natural convection. The heat from the water radiates to the interior chamber maintaining a constant temperature inside. Water is a particularly effective insulator, and the water-jacket system is considered a more reliable method of heating in case of a power outage. After a power failure, a water-jacketed incubator will hold a set temperature four to five times longer than a radiant-walled unit.
Radiant-walled incubators heat the interior chamber using heaters mounted in the surrounding cavity that radiate heat through to the inside chamber. This system allows for quick recovery of temperature following door openings or changes in temperature settings. They are also simple to use as they don't require filling, monitoring, or emptying of water.
A fan can be mounted outside of the culturing area to help to circulate the air inside the chamber without disturbing cultures. This gentle circulation speeds recovery of internal temperature as well as [CO.sub.2] and humidity levels following door openings.
Maintaining adequate moisture inside the chamber is important to prevent the drying out of cultures. Large [CO.sub.2] 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 levels of 95 to 98%. Some incubators have a humidity reservoir that holds water in a heated pan to increase humidity to 97 to 98%. But these are more complex system as they have more components and may be prone to internal sweating.
Contamination is a major source of frustration in cell culturing. [CO.sub.2] incubator manufacturers have reduced the areas or surfaces where microorganisms can grow and incorporated autodecontamination cycles to combat contamination. Many firms also offer HEPA filters to cut contamination during the incubation cycle. The filters can be used in conjunction with autodecontamination cycles.
Makers have introduced a number of options that reduce fungal growth and other contaminants, such as copper-lined chambers with copper shelves and fixtures as well as removable shelves and crevice-free interiors or coved comers in drawn internal chambers. Companies have also made surface areas more accessible for the use of disinfectants.
A [CO.sub.2] incubator should be easy to use and maintain. With the introduction of microprocessor controls and various accessories, the units are approaching a "set it and forget it" mode of operation. Features such as over-temperature thermostats and alarms, [CO.sub.2] alarms, door opening alarms, password protection of settings, self-calibration, and autodecontamination cycles offer easy operation and security for the user.
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|Comment:||What To Look for in a [CO.sub.2] Incubator.|
|Publication:||R & D|
|Date:||Mar 1, 2000|
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