Tissue Engineering

In cell culture, hESCs can spontaneously differentiate into cells of the three germ layers [82]. Perhaps, the biggest challenge in the clinical use of ESCs is the lack of knowledge of how to predictably direct their differentiation. For example, although ESCs can generate cells of hematopoietic, endothelial, cardiac, neural, osteogenic, hepatic, and pancreatic tissues, it has been very difficult to achieve directed differentiation into these tissues. The lack of homogeneous differentiation may be attributed to the intrinsic property of ESCs of differentiating stochastically in the absence of proper temporal and spatial signals from the surrounding microenvironment. Various techniques have been employed to control the differentiation of hESCs and to isolate a specific germ layer for tissue regeneration applications. The limitation of current techniques used for controlled differentiation is the low transformation efficiency, which results in a cell population containing ectoderm and mesoderm germ layers. The segregation of these germ layers can be achieved by using appropriate differentiation protocols. In this section, we describe some of the current approaches used to direct the differentiation of ESCs and give examples of their use.