Techniques for restoring cartilage

The general methods for restoring cartilage, the surface cover of our joints, involve using materials that are either already there or bringing new materials to the repair site. The cells that we are born with are called chondrocytes. One technique, called autologous cell implntation, uses a small biospy of these cells and then expands them in the lab- cloning- only to reimplant them later. Other methods try to take advantage of the body's stem cells, which fortunately are in the bone marrow just below the joint surface. How do these cells (sometimes) know to mkae new cartilage? That is the dilemma- and the possible cure- for many types of cartilage loss.
other issues have to do with the cost of these procedures. It sure would be better to use cells ( adult stem cells) that are alreay present, if you could just convert them into the cartilage that is needed. Many experiments using growth factor proteins are trying to accomplish just that.