Signaling molecules and growth factors
Signaling molecules and growth factors help cells to achieve the chondrogenic differentiation and maintain their phenotype. Since the early periods of cartilage tissue engineering, growth factors such as those in the insulin-like growth factor (IGF) and the TGF-p (Transforming growth factor-beta) family are found to be effective in promoting the chondrogenic differentiation of chondrocytes and stem cells and have thus become a standard in cartilage tissue engineering . A number of transcription factors such as Sox9 and RunX are also found to be effective in regulating the chon- drogenic differentiation of stem cells [36,37].
Culture growth conditions affect cell differentiation in the same profound way as growth factors and signaling molecules. It has been shown that appropriate cell differentiation can be achieved using just the right mechanical properties of scaffolds without the aid of growth factors [36,38]. Several growth conditions have been tested for effectively directing the chondrogenic differentiation of cells. Native cartilage tissue is hypoxic because of its avascular nature. Using the analogy, the hypoxic condition is found to be effective in producing chondrogenic ECM of embryonic stem cells without the aid of growth factors [39-42].