The challenge in tissue engineering lies in recreating the precise structure of the extracellular matrix observed in natural cartilage. Without that correct structure all that results is a sloppy gel of cartilage cells rather than a useful load-bearing tissue, and that sloppy gel was the only outcome of early attempts to grow cartilage. In recent years progress has been made towards getting the structure right, either through better approaches to growing cartilage cells or through decellularization of existing donor cartilage. In recent news, researchers have claimed sufficient progress in growing cartilage from a patient's own cells to move forward into human trials:
Cartilage injuries and diseases are very common. About 40 percent of adults over 65 years old have osteoarthritis. Cartilage has no nerves and so does not cause pain until the cartilage is gone and the bone underneath starts to be affected. Cartilage also has no blood vessels and therefore cannot heal on its own once injured. In the worst case, the knee joint has to be replaced by an artificial joint. Currently, the clinical gold standard for repairing cartilage is a surgical procedure known as osteochondral autograft transplantation. It involves harvesting a graft from one part of the joint and transplanting it to replace the damaged cartilage. However, this procedure leaves the autograft donor sites injured and may lead to chronic pain and degeneration. An alternative is to use the patients' own cells such as stem cells and grow them into a three dimensional tissue-like structure until it becomes at least partially functional, before replacing the defective tissue.
Over the last eight years, researchers have developed several technologies enabling the growth of complex tissues consisting of multiple tissue components. The core technology is to grow cartilage tissues complete with underlying bone tissues in vitro using the patient's own stem cells isolated from clinically accessible sources such as bone marrow. This 'complex tissue plug' mimics the structural organization of native cartilage-bone tissues. Animal studies in rabbits have shown that replacing defects in knee joint cartilage with these tissue engineered cartilage-bone tissue plugs gives rapid and sustained regeneration of high quality cartilage with structure, composition and mechanical properties comparable to that of the clinical gold standard autografts. The use of these regenerative complex tissue plugs allows surgeons to use the same autograft surgical procedure to repair cartilage damage without the need to hurt the patients' own cartilage. Currently, by working with orthopaedic surgeons, the research team is preparing to translate this technology for human applications.