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In microbiology an incubator is a device for controlling temperature, humidity, and other conditions under which a microbiological culture is being grown. The simplest incubators are insulated boxes with an adjustable heater, typically going up to approx. 65 °C. Some incubators can go slightly higher but generally to no more than 100 °C. More advanced incubators may have the ability to lower the temperature (via refrigeration), and/or the ability to control humidity or CO2 levels. This feature is specifically designed for cell growth.
Most incubators provide inner and outer glass doors for transparency. The main controller includes a timer. Some can also be programmed to cycle through different temperatures, humidity levels, etc. Incubators can vary in size from tabletops units to units the size of small rooms. Incubators may also provide special features such as regulation of shake speed.
As for temperature, 37°C is a commonly used temperature in incubators being the normal human body temperature. Most bacteria, especially the frequently used E. Coli, grows well under such conditions. For other applications lower temperatures are required, (for fish cells a growth temperature of 25°C is optimal).
Most standard incubator units are designed with outside air intake through a filter followed by heating and uniform distribution of the air throughout the chamber. This ensures even impact on samples placed on (often times) perforated shelves anywhere in chamber volume. Exhaust air is vented to the outside through a port at the top of the unit. The only parameter of interest is temperature and the temperature range is typically +25 to +70°C. Samples are often placed in closed containers so no cross contamination is possible.
Biological incubators are more complex in design as not only temperature but also humidity and CO2 are monitored and controlled. Air is still introduced from the outside but now through a sterile filter and mixed with a sterile supply of CO2. To increase humidity levels above normal ambience, a water reservoir is fitted at the bottom and to secure homogeneity throughout the chamber typically a fan is pushing the air around in laminar flow. Biological incubators are primarily used for stabilization of bacteria and cells in open containers (petri dishes). CO2 interaction with the suspension media adjusts the PH level for optimal growth. High humidity levels typically around 95-98% RH prevent samples from concentrating or completely drying out during incubation which can last for several days or even weeks. Typically controlled parameters in biological incubators are :
- Temperature +25°C to +60°C (+/-2°C)
- Humidity 95-98% (+/- 2%)
- CO2 level 3-7% (+/- 0.3%)
Usually validation of incubators doesn't pose any special challenges because the parameters to be controlled are relatively easy to match. The temperatures are modest and no pressure measurements are needed. The range of Ellab's temperature and temperature/RH% LAB data loggers can be used. To simplify the operation, the LED indicators on the LAB sensors will provide the operator with instant information on logger status. The LAB loggers can be matched with the SKY option for real time data transmission. For very small and low volume incubators that include an access port(s), using thermocouples could be advantageous to reduce impact and ensure chamber integrity.
The Current Good Manufacturing Practice formanufacturing, processing, packing or holding of drugs and Current Good Manufacturing Practice for finished pharmaceuticals is described in 21 CFR Parts 210 and 211. Subpart D describes handling of equipment (that it shall be routinely calibrated, inspected or checked according to a written program designed to assure proper performance). Furthermore, DIN 12880-2 specifies performance requirements and tests for heating cabinets and incubators in laboratories. The standard applies for cabinets and incubators with a working temperature range from -10°C to 300°C and includes shaking incubators.
Validation of an incubator consists of various steps regarding Installation Qualification (IQ), Operational Qualifications (OQ) and Performance Qualifications (PQ).
The IQ is conducted to demonstrate that the incubator is inspected and contains all the required parts to ensure functionality.
In the OQ, the performance of the incubator and its operational procedure is verified. The OQ consists of temperature mapping of the empty chamber and is performed to confirm that the empty chamber works within the specified limits throughout the chamber. The OQ also contains information about the calibration of measuring equipment and defines the location of the thermocouples and /or data loggers in the incubator.
The PQ verifies that the loaded incubator chamber is capable of reaching and maintaining the target temperature range. The effect of opening doors for different lengths of time is tested and the effect of a power failure on the incubator's ability to get back into the temperature profile is also evaluated.
The typical number of measuring points is 5 (4 corners + center) on the lower and top shelf. During OQ these are fixed directly on the shelves in an empty chamber and during PQ they are placed into loaded samples. For larger chambers it is recommended to place 5 measuring points on a minimum of 3 layers or on each layer with sample readings every 1- 5 minutes for 24, 48 or 72 hours.
Ellab’s wireless loggers are ideal for such qualifications. Even most standard incubators provide access port(s) the cable feed through could disturb the integrity of the chamber atmosphere. For example, the acceptance criteria for a standard incubator with a set point of +37°C, is that all measurements throughout the chamber do not individually differ by more than 2°C and all measurements maintain temperature within 32°C to 37°C.
With biological incubators the temperature validation is similar to above whereas the number of relative humidity measuring points is dependent on the chamber design (the ability to circulate air typically performed by a fan). Often a minimum of 2-3 RH sensors are placed throughout the chamber and the same is valid for CO2 measurement.
For most pharmaceutical and medical device applications, this will require the use of Ellab’s advanced software ValSuite™ Pro with its 21 CFR Part 11 compliance and sophisticated reports/features. For validation purposes, creating a Unit that demonstrates the exact position of each measuring point is advantageous when handling many sample points. Furthermore, creating a Profile which includes a Limit Report and a Statistical Report is useful and produces time savings.
At the end of each study, report(s) can be signed by Electronic Signature(s), stored, printed and distributed in a secure and locked PDF format. If not requirering electronic records, ValSuite™ Basic can provide all the necessary functionality. ValSuite™ Basic provides the same Statistical analysis and Limit report options but without the Part 11 compliance.
Using the built-in calibration functionality, users can calibrate the Ellab sensors at regular intervals. The ValSuite™ Pro software generates an easy to read calibration report that includes all measurements and tolerances that are defined by the user. It is recommended that Ellab sensors and probes are sent in at least once a year for factory calibration (which includes a traceable calibration certificate).