Warming Trends: CO2 Incubators for Cell Culture

Date: October 11, 1999Table of CO2 Incubators VWRbrand large-capacity CO2 incubator, model 1927 There would the new "golden age of biology" be without the millions of cells that are used to unlock the mysteries of life? Maintaining cell culture stocks is essential and cannot be accomplished without the proper environmental controls. Once the cells are fed and properly seeded to the correct density, they require precise heat, humidity, and gas levels to thrive. Investigators sleep at night entrusting their livelihoods to the faithful CO2 incubators back in the lab. In general, mammalian cells achieve optimal growth in culture at a temperature of 37°C (25-27°C for insect cells) and under conditions of 80-95 percent relative humidity (RH) and 5 percent CO2. Cell culture incubators control these environmental conditions in several ways and come in either water-jacketed or air-jacketed (also called radiant wall or dry wall depending on the manufacturer) varieties. Water-jacketed incubators are surrounded by water on five sides and are usually made no larger than 5-6 cubic ft. in chamber volume. Thermal autodecontamination cycles are not possible in these units, because heating causes expansion and compromises the integrity of the incubator. Water-jacketed incubators take longer to reach the set temperature and stabilize, but have the advantage of maintaining temperature for five to six hours in the event of a power loss. Labs without a backup generator should consider this option. An air-jacketed incubator is capable of reaching the set temperature quickly but does not maintain this temperature without the heat source. These incubators have a larger size range (up to 40 cubic ft.) and weigh considerably less than a comparably sized water-jacketed incubator. They also have faster recovery times for temperature and humidity--an important consideration if the unit will have frequent door openings. Once the choice of water versus air jacketing is made, one must consider the merits of automatic versus manual features. Automatic incubators are controlled through a microprocessor, which maintains the temperature, CO2 level, and humidity (optional). CO2 levels are maintained with a single tank. Manual control (also called flow-through) requires two tanks, one for CO2 and the second for air. Gas valves are set to achieve the proper mix of gases in the chamber and are monitored with flow meters. The next decision concerns CO2 control--options include thermal conductivity (TC) or infrared (IR) sensor control. TC sensors control CO2 levels by sensing changes in conductivity induced by alterations in environmental conditions and can be affected by RH and temperature fluctuations. To eliminate RH and temperature as sources of variation, manufacturers developed IR sensors. IR sensors measure the absorbance of the light from an infrared lamp of a specific wavelength over a fixed distance. Since only CO2 absorbs light at the wavelength selected, the sensor functions independently of both temperature and humidity. For CO2 incubators that are frequently opened, an IR sensor will offer greater measurement accuracy and improved CO2 control. However, IR-monitored incubators cannot be used for temperatures above 55°C. One ongoing concern in cell culture is contamination. Several companies have addressed this by adding a HEPA filter that can filter out 99.97 percent of contaminants larger than 0.3 µm. Air is circulated continuously through the filter to prevent contamination after the opening of the door. Some manufacturers offer copper shelves and inner walls to minimize fungal growth on the inside of the incubator. Additionally, a decontamination cycle with either dry or wet heat is available in some models. CEDCO's line of CO2 incubators is water jacketed and microprocessor controlled. The Standard Series includes either IR or TC sensors, safety monitors/alarms, a heated outer door to prevent condensation, and an 18-month warranty. The Advanced series also includes an automatic tank cylinder switch (switches from an empty to a full tank), a digital display of the relative humidity, and a printer port. Both the Standard and Advanced series can be purchased with a single or dual chamber. LabLine air-jacketed automatic CO2 incubator, model 495 Incubators from Forma Scientific utilize the effects of various airflow patterns and velocities to help maintain a sterile culture environment. Forma incubators are warm air-jacketed to provide uniform heating throughout the chamber and therefore are not prone to internal condensation, which can be a breeding site for airborne contaminants. The humidity supply system is located outside of the chamber on some models and can be filled through an external port. Other models permit selection of two ranges of humidity settings (82-87 percent or 91-96 percent). Water-jacketed models are HEPA filtered and have optional copper shelves, ductwork, and humidity pans. Lastly, Forma markets a wide temperature range incubator that can be programmed for 0 to 60°C. Air-jacketed CO2 incubators from Hotpack feature a self-decontamination cycle that can be programmed to clean the incubator between experiments automatically. The decontamination cycle can last from four to seven hours and eliminates the accumulation of bacteria and fungi. Clean humidity is provided by an external steam generator, which boils the water outside of the chamber. The microprocessor control mechanism uses individual modules for CO2, temperature, humidity, and decontamination. Units are also stackable, conserving valuable lab space. Kendro Laboratory Products (the union of Sorvall and Heraeus) offers the BBD6220, the BB6060/BB6220, and the HERAcell CO2 incubators. The BBD6220 features hot air (180°C) disinfection and sterilization of water before the working chamber is humidified. The TC sensor is placed under tight control through periodic auto-zero testing and compensation for the humidity level. The BB6060/BB6220 models offer decontamination control via UV light (optional), copper shelves, and a copper interior chamber. A trough at the bottom of the workspace permits heat from the heating system to be transferred directly to the water; this humidifies more rapidly than a pan. Optional gas-tight screens (six individual doors) seal off the workspace and allow access to individual compartments. The HERAcell features ContraCon decontamination (humid heat at 90°C), which disinfects the entire interior, including fittings and sensors. The water reservoir in the HERAcell is found in the tilted inner casing, eliminating the need for a humidity pan. A convenient pull-out storage tray can be used for placement of cultures or for the jotting of notes. Several varieties of CO2 incubators are designed by LabLine (now partnered with Barnstead/Thermolyne). Air- and water-jacketed automatic models use a DECONTAM cycle (TC sensor models only) that heats the chamber to 100°C for 12 hours. The standard SMARTGAS system feature allows fast recovery rates and more accurate control of CO2. LabLine incubators have security password protection, which prevents unauthorized users from changing the set points. Compact automatic models have seamless copper chambers and the SMARTGAS system. Additionally, LabLine offers economical, compact, air-jacketed, wall and flow-through CO2 incubators. For those labs in need of more culture space, LabLine makes 34 cubic ft. automatic and flow-through models. Water-jacketed CO2 incubators made by NAPCO (now partnered with Precision Scientific, a division of Jouan) are microprocessor controlled, allowing relative humidity levels to be maintained as high as 98 percent through a patented integral vapor generator and do not require pans. A HEPA filter cleanses contaminants from the gas, and all shelves and supports are fully removable and autoclavable to help ensure complete decontamination. Incubators are available with either TC or IR CO2 sensors. The NAPCO 6500 is a new design, introduced this year, that features a chamber with coved corners, and a simple, easy-to-remove shelf system. By eliminating all fans, sensors, ducts, and fan housings from the chamber, NAPCO has produced a CO2 incubator that is hard to contaminate and easy to clean. AutoFlow CO2 incubators from NuAire are water jacketed and microprocessor controlled, with HEPA filters standard on all models. CO2 is monitored with IR or timed-sequence gas control. An optional humidity sensor that activates an independent recirculation pump controls humidity in some models. The pump draws in chamber air and pushes it through the HEPA filter and finally through a humidified, heated enclosure before it is returned to the chamber. Some models are equipped with "fuzzy logic," which provides quick adaptive control of chamber temperature, CO2, humidity levels, and door temperature. Revco's entries into the ring are the Ultima and Elite series models. Both are water jacketed, microprocessor controlled (IntrLogic™), and are available in standard and compact midi sizes. The Elite series features a stainless steel interior, whereas the Ultima comes in stainless steel or copper. An optional HEPA filter cleans the chamber without high-velocity airflow, which can be detrimental to the "still air" cell culture technique. IR and TC CO2 control systems are offered as well. Sheldon Manufacting produces benchtop and floor model IR CO2 incubators. Incubators are available with water jackets and are microprocessor controlled to minimize CO2 consumption. Water-jacketed models with TC sensors come in benchtop and floor models as well. Reach-in 40 cubic ft. air-jacketed models with IR sensors are also available. VWRbrand (manufactured by Sheldon for VWR) offers water- and air-jacketed automatic and manual CO2 incubators. Most are equipped with microprocessor temperature control and either TC or IR CO2 sensors. Incubators are available in sizes from 2 to 40 cubic ft. and come with a 24-month warranty. A good incubator is like a faithful pet--always ready to do your bidding when you need it, never complaining if properly taken care of. A good quality incubator will last at least 10 years, with many lasting 15 to 20 years if properly maintained. Michelle Vettese-Dadey can be contacted at dadey@rcn.com. Table of CO2 Incubators

Warming Trends: CO2 Incubators for Cell Culture

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