There should be i) a or more sources of stem cells that can generate cartilage cellular and extracellular components, ii) guiding scaffolds that can make a preferable shape in vitro, iii) other proliferative or inductive growth factors to get sufficient number of differentiated chondrocytes and iv) provision of appropriate niche including physical stimulation and antioxidants to enhance proper cell differentiation and specific tissue properties.
Start with the following reviews to grasp a full understanding of current status and limitations.
In addition to Dr Lee's very comprehensive comment, I would like to add and highlight the key role of adequate mechanical stimulation and 2D-3D geometries:
Article Mechanical Stimulation of Mesenchymal Stem Cells: Implicatio...
Article The Effect of Two- and Three-Dimensional Cell Culture on the...
Article Enhanced Chondrogenic Differentiation of Human Bone Marrow-D...