Cell culturing involves growing cells outside their natural environment within a controlled laboratory setting. This scientific practice allows researchers to study cells in isolation, providing a clearer view of their behavior and responses. This careful maintenance enables a deeper understanding of cellular processes, which is challenging to achieve within a complex living organism.
The Essential Ingredients for Cell Growth
For cells to thrive in a laboratory, they require a specific “nutrient soup” known as a culture medium. This liquid mixture contains a precise balance of inorganic salts, which maintain osmotic balance and pH, alongside carbohydrates like glucose that serve as the primary energy source for cellular metabolism. Amino acids, the building blocks for proteins, and various vitamins, necessary for normal cell metabolism, are also included in this complex formulation.
A common addition to the culture medium is animal serum, often fetal bovine serum (FBS), at a concentration of 5–10%. Serum provides a rich source of growth factors, hormones, and attachment factors that promote cell proliferation and survival in the artificial environment. Antibiotics, such as penicillin and streptomycin, are frequently incorporated to prevent bacterial or fungal contamination, which can contaminate the culture.
Beyond the nutrient medium, cells need a stable physical environment, provided by a CO2 incubator. This specialized equipment maintains a constant temperature, around 37°C, to mimic the internal conditions of the human body. Inside the incubator, the humidity is kept high, at about 95% relative humidity, to prevent the culture medium from evaporating and causing stress to the cells. A regulated carbon dioxide concentration, 5%, is also maintained to help buffer the pH of the culture medium, ensuring it remains within the narrow physiological range necessary for cell viability.
Types of Cell Cultures
Cell cultures are broadly categorized based on their origin and growth characteristics. Primary cultures consist of cells directly isolated from tissues, such as those obtained from a biopsy. These cells retain many of the original tissue’s characteristics and functions, offering a relevant model for study. However, primary cells have a finite lifespan and a limited capacity to divide, eventually undergoing senescence, which is an irreversible cell cycle arrest.
Conversely, continuous cell lines originate from primary cultures that have undergone a transformation, allowing them to divide indefinitely. These “immortalized” cells can be propagated for many passages, making them a readily available and consistent resource for long-term research. A well-known example is the HeLa cell line, derived from cervical cancer cells in 1951 from Henrietta Lacks. HeLa cells are known for their rapid proliferation and robust nature, making them widely used in various scientific studies, including those on cancer and viral infections.
Cell cultures also differ in their growth patterns within the laboratory vessel. Adherent cultures are composed of cells that require attachment to a surface to grow, forming a single layer or monolayer. Most cells derived from solid tissues, like skin or organ cells, exhibit this adherent behavior. In contrast, suspension cultures involve cells that float freely in the culture medium, without needing to attach to a surface. This growth pattern is for blood cells or certain adapted cell lines, and it offers advantages for large-scale production due to easier handling and scalability.
The Cell Culturing Process
Maintaining cell cultures involves adherence to strict laboratory practices, primarily aseptic technique, to prevent contamination. This technique creates a barrier between microorganisms in the environment and the sterile cell culture, reducing the likelihood of bacterial or fungal growth. Scientists perform cell culture work within a biosafety cabinet, a specialized enclosure that provides a continuous flow of filtered air to maintain a clean workspace. Before and after use, all surfaces within the cabinet are disinfected, with 70% ethanol, and personal hygiene, including wearing gloves and lab coats, is observed.
A routine procedure in cell culturing is “passaging” or “subculturing,” which becomes necessary as cells multiply and reach a high density. When cells become too crowded or deplete their nutrients, their growth slows, and they become unhealthy. During passaging, a portion of the cells from an existing culture is transferred to a new culture vessel containing fresh medium. For adherent cells, this involves detaching them from the surface using enzymes like trypsin before splitting them into new flasks. This process ensures cells have adequate space and nutrients to continue growing exponentially, maintaining their health and proliferative capacity.
Applications in Science and Medicine
Cell culturing has become an important tool with diverse applications across science and medicine. In disease research, cultured cells provide controlled models to investigate the underlying mechanisms of various illnesses. Scientists use cell lines to study how diseases like cancer develop and progress, observing cellular behaviors on a molecular level. Similarly, in Alzheimer’s disease research, cell models allow for the study of protein aggregation and neuronal dysfunction, offering insights into potential therapeutic targets.
Cell cultures are also widely used in drug development, enabling the testing of new compounds for safety and effectiveness before human trials. Researchers can expose cultured human cells to potential drug candidates to observe their effects on cellular processes, identify toxicity, and assess therapeutic responses. This in vitro testing helps to screen numerous compounds efficiently, reducing the reliance on animal testing and streamlining the early stages of pharmaceutical development. For example, liver cell cultures are used to evaluate drug-induced liver injury, a common concern in drug safety.
In vaccine production, cell culture systems are employed to grow large quantities of viruses, which are then used to create vaccines. This method offers a faster and more stable alternative to traditional egg-based production. For instance, cell lines have been used to produce vaccines for diseases such as polio, measles, and influenza. The ability to propagate viruses in a controlled cellular environment ensures consistent and scalable vaccine manufacturing, addressing global health needs.
Cell culturing also holds promise in regenerative medicine, a field focused on repairing or replacing damaged tissues and organs. Through tissue engineering, scientists aim to grow functional tissues and organs in the laboratory for transplantation. This involves culturing various cell types, including stem cells, on scaffolds that guide their growth and differentiation into specific tissues like skin or cartilage. Advances in cell culture techniques, such as induced pluripotent stem cells (iPSCs), offer the potential to create patient-specific tissues, minimizing the risk of immune rejection in future therapeutic applications.