Bioengineer here able to chime in with niche expertise. Cartilage is and has been a holy grail in biomedical engineering but is very difficult to grow and transplant. There have been some successful neo-cartilage projects but integrating that into a defect and successfully integrating with host cartilage is the problem. The boundary of the defect actually has electronegative components that actively oppose integration of host and transplant (synthetic) cartilage. I think the most likely solution won't be a tissue-engineered transplant but rather an active cellular component that appropriately responds, and builds upon, this negative feedback cycle via cellular programming.