Microcarriers are support matrices that allow for the growth of adherent cells in bioreactors, and can be made from a number of different materials, including glass, polystyrene plastic, acrylamide, collagen, and alginate. They are regularly used to grow protein-producing or virus-generating adherent cell populations in the large-scale production of proteins and vaccines. These microcarriers support the adhesion and expansion of stem cells in their undifferentiated state and directed differentiation into specialized cell types.