Suspension methods refer to techniques used to culture cells in a liquid medium without the need for attachment to a solid surface, such as the plastic of a tissue culture flask or a microcarrier. Suspension cultures are commonly used for growing cells that can proliferate in a free-floating state, such as many types of mammalian cells, insect cells, and microorganisms like bacteria and yeast.

There are several advantages to using suspension methods:

1. Scalability: Suspension cultures can be easily scaled up to produce large quantities of cells or cellular products, such as recombinant proteins or viral vectors, by simply increasing the volume of the culture medium. This makes suspension methods suitable for large-scale industrial production.
2. Homogeneity: Since cells in suspension are evenly distributed throughout the culture medium, they are exposed to a consistent environment, including nutrients, gas exchange, and waste removal. This can result in more uniform cell growth and product quality.
3. Ease of handling: Suspension cultures can be more straightforward to handle and maintain compared to adherent cell cultures, as they do not require enzymatic treatments, such as trypsinization, to detach the cells from the culture surface for passaging or harvesting.

Several types of equipment and techniques are used for suspension cultures:

1. Shaker flasks: Cells are cultured in flasks placed on an orbital shaker, which agitates the culture medium to keep the cells suspended and promote gas exchange. Shaker flasks are suitable for small-scale suspension cultures and can be used for the initial stages of cell line adaptation to suspension growth.
2. Spinner flasks: These flasks contain a magnetic stir bar or impeller that rotates to keep the cells suspended in the medium. Spinner flasks are useful for intermediate-scale suspension cultures and can be used to grow cells for protein production or other applications.
3. Bioreactors and fermenters: Bioreactors are controlled systems used for large-scale suspension cultures. They provide precise control over environmental conditions, such as temperature, pH, dissolved oxygen, and nutrient levels, and can be used to grow mammalian, insect, bacterial, or yeast cells for the production of recombinant proteins, monoclonal antibodies, or other cellular products. Stirred-tank bioreactors and airlift bioreactors are examples of bioreactor systems used for suspension cultures.

Adapting adherent cells to suspension growth can be challenging and may require changes in the culture medium, growth factors, or other culture conditions. However, suspension methods offer several advantages for cell culture, particularly for large-scale production and bioprocessing applications.