In biology

Biology

Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...

, an incubator is a device used to grow and maintain of course microbiological culture

Microbiological culture

A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture media under controlled laboratory conditions. Microbial cultures are used to determine the type of organism, its abundance in the sample being tested,...

s or cell culture

Cell culture

Cell culture is the complex process by which cells are grown under controlled conditions. In practice, the term "cell culture" has come to refer to the culturing of cells derived from singlecellular eukaryotes, especially animal cells. However, there are also cultures of plants, fungi and microbes,...

s. The incubator maintains optimal temperature

Temperature

Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

, humidity

Humidity

Humidity is a term for the amount of water vapor in the air, and can refer to any one of several measurements of humidity. Formally, humid air is not "moist air" but a mixture of water vapor and other constituents of air, and humidity is defined in terms of the water content of this mixture,...

 and other conditions such as the carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 (CO₂) and oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 content of the atmosphere inside. Incubators are essential for a lot of experimental work in cell biology

Cell biology

Cell biology is a scientific discipline that studies cells – their physiological properties, their structure, the organelles they contain, interactions with their environment, their life cycle, division and death. This is done both on a microscopic and molecular level...

, microbiology

Microbiology

Microbiology is the study of microorganisms, which are defined as any microscopic organism that comprises either a single cell , cell clusters or no cell at all . This includes eukaryotes, such as fungi and protists, and prokaryotes...

 and molecular biology

Molecular biology

Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...

 and are used to culture both bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

l as well as eukaryotic

Eukaryote

A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...

 cells. It was invented by Fe Del Mundo

Fe del Mundo

Fe del Mundo was a Filipino pediatrician. The first woman admitted as a student of the Harvard Medical School, she founded the first pediatric hospital in the Philippines...

, the first Filipino, and possibly the first woman to study at Harvard Medical School

Harvard Medical School

Harvard Medical School is the graduate medical school of Harvard University. It is located in the Longwood Medical Area of the Mission Hill neighborhood of Boston, Massachusetts....

.

Incubators are also used in the poultry industry to act as a substitute for hens. This often results in higher hatch rates due to the ability to control both temperature and humidity. Various brands of incubators are commercially available to breeders.

The simplest incubators are insulated boxes with an adjustable heater, typically going up to 60 to 65 °C (140 to 150 °F), though some can go slightly higher (generally to no more than 100 °C). The most commonly used temperature both for bacteria such as the frequently used E. coli

Escherichia coli

Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...

 as well as for mammalian cells is approximately 37 °C, as these organisms grow well under such conditions. For other organisms used in biological experiments, such as the budding yeast Saccharomyces cerevisiae

Saccharomyces cerevisiae

Saccharomyces cerevisiae is a species of yeast. It is perhaps the most useful yeast, having been instrumental to baking and brewing since ancient times. It is believed that it was originally isolated from the skin of grapes...

, a growth temperature of 30 °C is optimal.

More elaborate incubators can also include the ability to lower the temperature (via refrigeration), or the ability to control humidity or CO₂

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 levels. This is important in the cultivation of mammalian cells, where the relative humidity

Humidity

Humidity is a term for the amount of water vapor in the air, and can refer to any one of several measurements of humidity. Formally, humid air is not "moist air" but a mixture of water vapor and other constituents of air, and humidity is defined in terms of the water content of this mixture,...

 is typically >95% and a slightly acidic pH

PH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 is achieved by maintaining a CO₂ level of 5%.

Most incubators include a timer; some can also be programmed to cycle through different temperatures, humidity levels, etc. Incubators can vary in size from tabletop to units the size of small rooms.

There are many other ways to create an incubator. The renowned scientist Louis Pasteur used the small opening underneath his staircase as an incubator.

The maximum temperature for sterilization is 200^oC .

Incubator

If a hot room is not available, it may be necessary to buy an equivalent dry incubator. Even with a hot room, it is sometimes convenient to have another incubator close to the hood for trypsinization. The incubator should be large enough, ∼50–200 L (1.5–6 ft³) per person, and should have forced-air circulation, temperature control to within ±0.2 °C, and a safety thermostat that cuts off if the incubator overheats or, better, that regulates the incubator if the first thermostat fails. The incubator should be resistant to corrosion (e.g., stainless steel, although anodized aluminum is acceptable for a dry incubator) and easily cleaned. A double chamber, or two incubators stacked, one above the other, independently regulated, is preferable to one large incubator because it can accommodate more cultures with better temperature control, and if one half fails or needs to be cleaned, the other can still be used.
Many incubators have a heated water jacket to distribute heat evenly around the cabinet, thus avoiding the formation of cold spots. These incubators also hold their temperature longer in the event of a heater failure or cut in power. However, new high-efficiency insulation and diffuse surface heater elements have all but eliminated the need for a water jacket and make moving the incubator much simpler. (A water jacket generally needs to be emptied if the incubator is to be moved.)
Incubator shelving is usually perforated to facilitate the circulation of air. However, the perforations can lead to irregularities in cell distribution in monolayer cultures, with variations in cell density following the pattern of spacing on the shelves. The variations may be due to convection currents generated over points of contact relative to holes in the shelf, or they may be related to areas that cool down more quickly when the door is opened. Although no problem may arise in routine maintenance, flasks and dishes should be placed on an insulated tile or metal tray in experiments in which uniform density is important.

Trypsinization
Trypsinization is the process of using trypsin, a proteolytic enzyme which breaks down proteins, to dissociate adherent cells from the vessel in which they are being cultured. When added to a cell culture, trypsin breaks down the proteins which enable the cells to adhere to the vessel. Trypsinization is often used to passage cells to a new vessel.
For experimental purposes, cells are often cultivated in containers that take the form of plastic flasks or plates. In such flasks, cells are provided with growth medium comprising the essential nutrients required for proliferation, and the cells adhere to the container and each other as they grow.
This process of cell culture or tissue culture requires a method to dissociate the cells from the container and each other. Trypsin, an enzyme commonly found in the digestive tract, can be used to "digest" the proteins that facilitate adhesion to the container and between cells.
Trypsinization is often done to permit passage of the cells to a new container, observation for experimentation, or reduction of the degree of confluency in the flask by removal of a percentage of the cells.

Humid CO₂ Incubator

Although cultures can be incubated in sealed flasks in a regular dry incubator or a hot room, some vessels, e.g., Petri dishes or multiwell plates, require a controlled atmosphere with high humidity and elevated CO2 tension. The cheapest way of controlling the gas phase is to place the cultures in a plastic box, or chamber (Bellco, MP Biomedicals): Gas the container with the correct CO2 mixture and then seal it. If the container is not completely filled with dishes, include an open dish of water to increase the humidity inside the chamber.
CO2 incubators are more expensive, but their ease of use and superior control of CO2 tension and temperature (anaerobic jars and desiccators take longer to warm up) justify the expenditure. A controlled atmosphere is achieved by using a humidifying tray (Fig 5.16) and controlling the CO2 tension with a CO2-monitoring device, which draws air from the incubator into a sample chamber, determines the concentration of CO2, and injects pure CO2 into the incubator to make up any deficiency. Air is circulated around the incubator by natural convection or by using a fan to keep both the CO2 level and the temperature uniform. It is claimed that fan-circulated incubators recover faster after opening, although natural convection incubators can still have a quick recovery and greatly reduce the risks of contamination.
Dry, heated wall incubators also encourage less fungal contamination on the walls, as the walls tend to remain dry, even at high relative humidity. Some CO2 controllers need to be calibrated every few months, but the use of gold wire or infrared detectors minimizes drift and many models reset the zero of the CO2 detector automatically.
The size of incubator required will depend on usage, both the numbers of people using it and the types of cultures. Five people using only microtitration plates could have 1000 plates (∼100,000 individual cultures) or 10 experiments each in a modest-sized incubator, while one person doing cell cloning could fill one shelf with one or two experiments. Flask cultures, especially large flasks, are not an economical use of CO2 incubators. They are better incubated in a regular incubator or hot room. If CO2 is required, flasks can be gassed from a cylinder or CO2 supply.

Trypsinization
Trypsinization is the process of using trypsin, a proteolytic enzyme which breaks down proteins, to dissociate adherent cells from the vessel in which they are being cultured. When added to a cell culture, trypsin breaks down the proteins which enable the cells to adhere to the vessel. Trypsinization is often used to passage cells to a new vessel.
For experimental purposes, cells are often cultivated in containers that take the form of plastic flasks or plates. In such flasks, cells are provided with growth medium comprising the essential nutrients required for proliferation, and the cells adhere to the container and each other as they grow.
This process of cell culture or tissue culture requires a method to dissociate the cells from the container and each other. Trypsin, an enzyme commonly found in the digestive tract, can be used to "digest" the proteins that facilitate adhesion to the container and between cells.
Trypsinization is often done to permit passage of the cells to a new container, observation for experimentation, or reduction of the degree of confluency in the flask by removal of a percentage of the cells.