What is the difference between passaging and expansion in cell culture?

Passaging and expansion are two important processes in cell culture, but they refer to different stages in the growth of cells. Passaging refers to the process of transferring cells from one culture vessel to another. This is typically done when the cells have grown to a high density in their current vessel and need more room to continue growing. Passaging involves detaching the cells from their current vessel using a trypsin solution, separating them into individual cells, and then adding them to a new vessel with fresh growth medium. Passaging is important to ensure that cells remain healthy and do not become overcrowded, which can lead to cell death or changes in their behavior. Expansion, on the other hand, refers to the process of increasing the number of cells in culture. This can be achieved through passaging, but it also involves other strategies such as increasing the concentration of growth factors or changing the composition of the growth medium. Expansion is important for producing large numbers of cells for experiments or for therapeutic purposes. In summary, passaging and expansion are both important processes in cell culture, but they refer to different stages in the growth of cells. Passaging involves transferring cells to a new vessel, while expansion involves increasing the number of cells in culture.