Embryonic stem cells, or ES cells, are pluripotent stem cells, differentiating into the primary germ layers, ectoderm, endoderm, and mesoderm- and eventually the rest of the cell types in the body. ES cells are isolated from the inner cell mass of a blastocyst, an early-stage embryo. Human embryos are obtained from in vitro fertilization procedure surpluses and donated by donors with consent. The sizes of human ES cells are about 14 μm, and mouse ES cells about 8 μm. Methods for propagating embryonic stem cell lines in culture are also well established and are a common source of pluripotent ES cells. The plasticity and self-renewal of ES cells offer many applications in a variety of research areas, namely regenerative medicine and biotechnology.