Are you talking about Synvisc (AKA hyaluronic acid)? Hyaluronic acid is a gel-like substance that helps cushion the cartilage in your knee when the cartilage is breaking down from a loss of normal lubricating fluid (synovial fluid) in the joint. It's made from chicken combs, and it is very similar to synovial fluid. It takes multiple injections and usually doesn't start working for a few weeks. In my case, it never worked at all. There is a new SynviscOne, which is only 1 injection, takes about a month to kick in and is supposed to last 6 months. This product doesn't create new cartilage, but it does cushion and protect the cartilage you have.
There is another product called Regenexx that is a stem cell product and it does regenerate cartilage. I don't know a lot about it, other than (a) they remove your bone marrow, extract the stem cells from it, and then inject the stem cells into the area needing regeneration and (b) it doesn't work on large areas of damaged cartilage, and my ortho docs don't think it is effective enough to use on knee or hip joints, and being in the middle of nowhere, it is not a technology my organization is likely to have any time soon. Honestly, I've not read all that much about it, other than when I was doing research before I had my second knee done last year.