Choosing a CO2 Incubator
To a certain extent, choosing a CO2 incubator is largely a personal preference on the part of the researcher. Many just purchase what they have used in the past or what their old boss used because there was little research involved.
Water Jacket CO2 Incubators
Currently, water-jacked incubators are the more popular choice. A water jacket will hold the temperature longer than an air-jacket when power is lost. This is helpful in many situations; the incubator will be able to “recover” more quickly after a power outage and also get back to temperature more quickly after the door has been opened. This quick recovery is due to the fact that the chamber is surrounded by hot walls, filled with hot water and water holds heat longer than air. The temperature uniformity overall is better, which means less potential for “cool spots” than in an air jacketed incubator.
There are a few downsides to water jacketed incubators—they take longer for the initial set up (since it takes awhile to fill the jacket with water and get the water up to temperature for the first use) and they are also heavier, so more cumbersome to move. In fact, MUST drain the water before moving the unit and this can be very time consuming and the incubator would lose its structural strength if the water were left in.
Forced air CO2 incubator
An alternative to the water-jacketed incubator is the forced air incubator. This type of incubator is easier to set up initially, and will get to its set temperature for the first time more quickly because there is a great volume of air movement. It is also easier (less heavy) to move. A big advantage to the forced air dry wall incubator, which is becoming more popular in recent times, is the fact that it can be self-sterilizing. The user can turn the temperature of the air jacketed incubator up to 180° C (on some models) which will in effect kill any micro-organisms that could be present in the incubator. You could not do this in a water jacketed incubator because it would take days for the hot water to cool down again before use.
The downside to the forced-air air jacketed incubator is that in the event of a power outage, will cool more rapidly, which would likely have a detrimental effect on cell growth. In addition, since the forced air incubator has larger volume of air movement than a water-jacked incubator, there is a greater chance of the dishes within drying out. This may not be as big an issue anymore as most labs have back up power supply, but for those that don’t, it is something to consider.
More Information
Another decision that needs to be made in choosing an incubator is what type of CO2 controller to choose. The less expensive option is a TC (thermal conductivity) control. These are not as common anymore, as this is a less precise method of CO2 control. The TC sensor is an indirect method of CO2 detection, as it measures the level of CO2 by sensing temperature & humidity differences as CO2 is introduced into the chamber.
Far more common these days is the IR (infrared) sensor method of control. This offers a much tighter control, has less variability, and allows the incubator to recalibrate its CO2 more quickly as it does not depend on temperature & humidity. An IR sensor is unaffected by changes in temperature and humidity and is the ideal choice for situations where the incubator door is opened frequently.
Finally
A final consideration when choosing a water jacketed incubator is what type of water to be used in filling the jacket. This will depend on what type of anode the incubator contains. Many incubators are set up to take both tap water and distilled water. However, some do require just distilled water. Since many labs have access to distilled water, this is probably not a major issue, but for small labs with limited space and no distilled water set up, this could be a factor. Under no circumstances should deionized, or ultrapure, water be used, as this can pit the stainless steel structure. To help the preserve the stainless steel interior even better, some labs add a pint of antifreeze or ethylene glycol to the water in the water-jacket.
Once a researcher has chosen what type of incubator best suits his or her lab, the next big decision is where to place it. Incubators should not be placed in direct sunlight, near heat sources (i.e. ovens or autoclaves) or near fast moving air currents, such as heating/cooling ducts or near a door. To optimize air circulation around the unit, the incubator should have a minimum of 4 inches of space between a wall or partition on all sides, as anything closer could obstruct airflow. All units come with leveling feet to insure that the unit sits level and solid on the floor (or on top of another unit, in the case of stacked incubators).
To increase longevity of the lab’s CO2 incubator, it is important to clean and decontaminate regularly. As discussed earlier, a forced air incubator can ‘self-decontaminate’ by turning the heat to 180 ° C. For a water-jacketed incubator, remove all parts, wash with soap and water, and disinfect with 70% alcohol solution. Never use a chlorine based bleach or abrasive cleaner as these will damage the stainless steel finish. For all units, it is recommended that the HEPA and CO2 filters be replaced once a year, though in reality, most labs go longer between changes.
MIDSCI Offers both kinds of Incubators.