What is animal cell culture?
Animal cell culture means growing cells taken from an animal or a human outside the body, in a closed, clean container. It is also called in vitro culture, which means "in glass".
Animal cells are harder to grow than bacteria or plant cells. They need:
- A sterile place: work is done in a laminar air-flow hood (a clean-air cabinet), with sterile tools.
- A medium: a liquid food with glucose (sugar), amino acids, salts, vitamins and often serum (the liquid part of blood, for example fetal bovine serum) that gives growth factors. Antibiotics may be added to stop germs.
- The right conditions: 37 °C (body heat), pH about 7.2–7.4, and 5% carbon dioxide in the incubator. The CO2 works with the bicarbonate in the medium to keep the pH steady.
Most cells from tissues are adherent: they must stick to a surface to grow. Blood cells and some others grow floating in the liquid; this is a suspension culture.
Culture methods: primary culture, subculture and cell lines
Primary culture
A small piece of tissue is cut up and treated with an enzyme such as trypsin or collagenase. This loosens the cells. The cells are put into a flask with medium. This first culture, made straight from the tissue, is the primary culture.
Growth and confluence
The cells stick, spread and divide. When they cover the whole floor in a single layer (a monolayer), they are confluent. Normal cells then stop dividing because they touch each other. This is contact inhibition.
Subculture (passage)
To keep the cells growing, we loosen them with trypsin and share them into new flasks with fresh medium. Each split is one passage.
Cell lines
- Finite cell line: normal cells divide only a limited number of times (about 40–60 divisions) and then stop. This limit is called the Hayflick limit.
- Continuous (immortal) cell line: cells that can divide without end, often cancer cells or changed cells. The famous HeLa line came from a cervical cancer in 1951 and is still used in labs all over the world.
Cells can be frozen in liquid nitrogen (−196 °C) and woken up years later. This is cryopreservation.
Uses of animal cell culture
- Vaccines: viruses grow only inside living cells, so vaccines for polio, rabies, measles and others are made in cultured cells.
- Medicines (recombinant proteins): cells such as CHO cells are given a human gene and then make proteins like clotting factors, erythropoietin or interferon.
- Monoclonal antibodies: a hybridoma (an antibody-making cell joined to a cancer cell) grows forever and makes one pure antibody, used in tests and cancer treatment.
- Testing drugs and chemicals: scientists test if a new drug or cosmetic harms cells, so fewer animals are used.
- Tissue engineering: skin cells are grown in sheets to cover serious burns; cartilage and other tissues are being grown too.
- Research and diagnosis: studying cancer, ageing and viruses; checking chromosomes of an unborn baby (amniocentesis cells are cultured).
- IVF: an egg and sperm meet in a dish and the early embryo grows in culture medium for a few days.
Stem cell technology
A stem cell is an unspecialised cell. It has two powers: it can self-renew (make copies of itself) and it can differentiate (turn into special cells like nerve, muscle or blood cells).
- Embryonic stem cells come from a very early embryo (about 5 days old). They are pluripotent: they can become almost any cell of the body.
- Adult stem cells are found in bone marrow, skin, fat and other tissues. They are multipotent: they make a few related kinds of cells. Bone marrow stem cells make all blood cells.
- Umbilical cord blood is rich in blood stem cells. Some families store it in cord blood banks.
- Induced pluripotent stem (iPS) cells: in 2006 scientists added a few genes to ordinary skin cells and turned them back into pluripotent cells. This avoids using embryos.
Uses: bone marrow transplants for leukaemia and thalassaemia, repairing the cornea, research on diseases like Parkinson's and diabetes, and testing drugs on human cells. Concerns: using embryos raises ethical questions, and grown stem cells can sometimes form tumours, so treatments must be tested carefully.
Key formulas and definitions
- Cells after n doublings = starting cells × 2ⁿ
- Number of doublings n = time ÷ doubling time
- Conditions: 37 °C, pH ≈ 7.4, 5% CO2, sterile medium
- Primary culture → subculture (passage) → finite or continuous cell line
Worked examples
1. A flask has 50 000 cells. The doubling time is 24 hours. How many cells after 3 days?
3 days = 72 h = 3 doublings. 50 000 × 2³ = 50 000 × 8 = 400 000 cells.
2. Cells double every 20 hours. How long to go from 1 × 10⁵ to 1.6 × 10⁶ cells?
1.6 × 10⁶ ÷ 1 × 10⁵ = 16 = 2⁴, so 4 doublings. 4 × 20 h = 80 hours.
3. A confluent flask holds 2 × 10⁶ cells. You split it 1:4. How many cells go into each new flask?
2 × 10⁶ ÷ 4 = 5 × 10⁵ cells per flask.
Common mistakes
- Thinking animal cells can grow on plain sugar water. They need amino acids, vitamins, salts, growth factors (serum) and a steady pH.
- Mixing up primary culture and cell line. Primary culture comes straight from tissue; a cell line is what keeps growing after subculture.
- Thinking CO2 is food for animal cells. The 5% CO2 only keeps the pH of the medium steady.
- Thinking all stem cells can make any cell. Only pluripotent cells (embryonic, iPS) can; adult stem cells make only a few kinds.