In stem cell research, in vitro culture is essential for obtaining large numbers of cells. The condition of the surface on which the cells grow plays a key role in helping cells to proliferate and – more importantly – retain their stem cell-like phenotype.
In an organism, most mature cell types spend nearly all their time anchored to the extracellular matrix of the tissue they reside in. When grown in vitro, these cells also require a tissue-culture treated surface to adhere to, such as glass or plastic, in order to survive and proliferate.
In stem cell culture, the stability of the cells phenotype is a key aspect for successful, reproducible results. Conventional growth surfaces, such as tissue culture-treated polystyrene, are often not suitable for stem cell culture as they can cause random differentiation into other cell types or even cell death, due to the absence of factors that are essential for stem cell survival and proliferation1.
Therefore, several different methods of modifying surfaces prior to stem cell seeding have been developed in order to maintain phenotypic stability. These methods can be subdivided into three categories: feeder cells, biological coatings and synthetic coatings.
When Thomson et al.2 cultured the first human embryonic stem cells in vitro, they seeded their cells onto a layer of feeder cells. Different types of terminally differentiated cells can serve as a feeder layer for stem cells, with many researchers using fibroblasts. Before seeding, feeder cells have to be irradiated with gamma rays or treated with other reagents (e.g. Mitomycin-C) to prevent them from proliferating.
A feeder layer supports stem cells by producing both soluble and insoluble factors. Extracellular matrix proteins provide anchorage points and the complex mix of secreted soluble compounds plays a role in maintaining a stem cell phenotype. However, the question of which combination of soluble factors is responsible for phenotypic stability remains to be answered.