Fetal Bovine Serum (FBS) is a liquid component of blood derived from a bovine fetus. It is the most common supplement added to basal growth media for cultivating eukaryotic cells in a laboratory setting. This amber-colored fraction is used in cell and tissue culture technology to support the proliferation and survival of cells outside of a living organism, a process known as in vitro culture. FBS is important to a wide range of scientific disciplines, including biomedical research, pharmaceutical development, and vaccine manufacture.
The Role of FBS in Scientific Research
The widespread use of Fetal Bovine Serum in laboratories stems from its unique and complex biochemical composition, making it an effective growth supplement. It contains a dense mixture of macronutrients, hormones, and proteins required for cell maintenance and function. Specifically, FBS provides essential growth factors, such as insulin-like growth factors (IGFs) and fibroblast growth factors (FGFs), that signal cells to divide and proliferate.
The serum also includes attachment factors that help cells adhere to the plastic surfaces of culture dishes, which is necessary for many cell types to grow properly. Bovine Serum Albumin (BSA) is a major protein component that helps maintain the correct osmotic balance and acts as a carrier for various molecules within the culture medium. Researchers typically add FBS to a basal medium at a concentration of 5–10% by volume because it promotes rapid cell growth and is non-toxic to a wide range of cell lines.
The Source of the Serum
Fetal Bovine Serum is a co-product of the global meat industry, derived from the blood of bovine fetuses collected at commercial slaughterhouses. The process begins when pregnant cows are processed, either for meat or culled from the dairy industry. The fetus is then removed from the uterus, and its blood is harvested.
The fetal source is chosen over adult bovine serum due to differences in blood composition that enhance cell culture success. Fetal blood naturally contains a high concentration of growth factors and is relatively low in immunoglobulins (antibodies). The low antibody count minimizes the risk of immunological reactions that could interfere with the growth of cultured cells.
Utilizing fetal blood also minimizes the presence of complement proteins that might otherwise lyse the cultured mammalian cells. The high demand for FBS means that hundreds of thousands of liters of serum are required globally each year by the scientific community.
The Collection and Processing Method
The procedure for obtaining Fetal Bovine Serum is a standardized, multi-step industrial process designed to ensure sterility and quality control. Once the fetus is removed from the slaughtered dam, the blood is typically collected via cardiac puncture. This involves aseptically inserting a needle into the heart of the fetus and drawing the blood into a sterile container or blood bag through a closed system.
This collection method is preferred because it minimizes the risk of contamination from microorganisms found on the fetus or in the environment. After collection, the blood is allowed to clot naturally, often under refrigeration, to separate the liquid serum component from the solid cellular components and fibrin. Within about 24 hours, the clotted blood is subjected to centrifugation, which spins the blood at high speeds to further separate the clear, straw-colored serum from the remaining red blood cells and the clot.
The raw serum is then pooled into large batches and subjected to rigorous quality testing for parameters like pH, osmolality, and hemoglobin content. To ensure the final product is sterile and free of potential contaminants, the serum is passed through a sequence of membrane filters. The final step in this filtration train involves passing the serum through a filter with a pore size of 0.1 micrometers, which is small enough to remove bacteria and other biological agents, including mycoplasma. After sterile filtration, the finished FBS is quick-frozen, usually at or below -20°C, to preserve the activity of the growth factors and other components until laboratory use.
Ethical Considerations and Alternative Options
The collection method for Fetal Bovine Serum has generated considerable ethical debate within the scientific and animal welfare communities. The primary concern centers on the use of cardiac puncture to harvest blood from the fetus without anesthesia. Although industry guidelines often require a delay after the mother’s slaughter to ensure the fetus has lost consciousness, many animal welfare advocates argue that the fetus may still experience pain or distress during the procedure.
These welfare concerns, coupled with scientific issues like batch-to-batch variability in FBS composition, have driven the search for alternatives. One substitute is Human Platelet Lysate (HPL), derived from donated human blood, which offers an animal-free option effective for culturing certain human cells. Another approach uses chemically defined media, which are synthetic mixtures of known components that eliminate the variability associated with a biological product like serum.
While these alternatives offer a more defined composition and address ethical concerns, they are not universally compatible with all cell lines. Researchers must often accept trade-offs, as serum-free media may be more expensive or require extensive optimization to achieve the same growth rates and cell viability seen with FBS.