Cellular-based therapies for cartilage tissue engineering have evolved quite significantly in the past decades. The realization that such an endeavor requires the acquisition of an adequate stem or progenitor cell population, techniques to effectively maintain or induce the desired phenotype and efficient culturing and implantation conditions have led researchers to develop a wide variety of protocols to approach the issue. Originally, cells taken from donor grafts of healthy cartilage were used as the cell source for tissue engineering constructs. Since then, however, researchers have moved on to cells from the adipose tissue, embryonic tissues, bone marrow and other sources. Similarly, as the potential for different cell sources to generate functional mesenchymal lineage tissues are discovered, several differentiation and phenotypic maintainance stimuli have been explored to optimize the resulting grafts. Physical stimuli in the form of mechanical compression as well as chemical stimuli in the form of growth factor cocktails have all proven effective in the induction of cells into the chondrogenic lineage to varying degrees. Finally, substrate expansion of these cells in materials ranging from naturally occuring ploymers such as fibrin, to synthetic and micro-fabricated structures is an active field of research. This review will discuss the most recent methods being utilized for the initiation of chondrogenesis from various stem cell sources as well as some methods being explored in our laboratory.
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