A fibroblast is a type of cell that mainly responsible for the properties of extracellular matrix by secreting the precursors of all the components of it. Cyagen OriCell Strain ICR Mouse Embryonic Fibroblasts (Irradiated) (MEFs) are derived from ICR mouse embryos (12.5 dpc), cultured as monolayer, and cryopreserved at the first passage after (G)-ray irradiation. OriCell Strain ICR Mouse Embryonic Fibroblasts (Irradiated) are used to culture mouse or human embryonic stem cells while maintaining their undifferentiated states. They have been tested negative for bacteria, fungi and mycoplasma.