Tissue engineering is a major topic of research and is one aspect of regenerative medicine when it centers on self-renewal. Tissue engineering is the practicing of combining scaffolds, which are extracellular matrices that support the cells but also relay certain signaling molecules. Tissue engineering can turn cells, and molecules into functional tissues like bone, blood vessels, muscle to restore, maintain, or improve damaged tissues or whole organs.
Tissue engineering works by understanding how cells respond to signals and interact with their environment in order to “organize” into tissues and organism. In regenerative medicine, the scaffolds are created with proteins with the hopes that tissue will regenerate. Or, the cells of a donor organ are stripped and collagen scaffold is used. Scaffolds must be biodegradable in the sense that once the tissue is grown, the scaffold should be absorbed rather than surgically removed.
One exciting application of tissue engineering is cartilage repair for knees, including cartilage repair for knees that have osteoarthritis.
60% of patients who have knee arthroscopy exhibit cartilage damage, and a significant number of individuals over 60 years old have some clinical symptoms of such damage. Without improvements in technology, the self-healing of damaged cartilage is limited.
Many of the ways in which bone tissue have been used for repair, such as autografting and allografting, are limited because of the risk of infection, and potential risk to the donor-site. Bone defects are one of the leading causes of morbidity and disability in elderly patients.
Cartilage repair for osteoarthritis
Growing tissue without instability and imperfections that are dangerous to a patient has been shown to be difficult. Scientists believe that eventually they can regrow cartilage to help with osteoarthritis. One exciting breakthrough comes from scientists at Boston University, who have shown that by adding inactive TGF Beta, a growth factor, instead of active TGF Beta, cartilage can be grown without the typical pathologies that show up in bioengineered cells, albeit somewhat slower.
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FDA Approved Uses of Tissue Regeneration for Knee Cartilage Repair
Currently, the FDA has approved a procedure called Maci, which is the first FDA-approved product applying tissue engineering. Healthy cartilage from the patient’s own knee (“autologous” cartilage) is used to grow cells on scaffolds, in this case, a pig’s collagen membrane. The membrane is then reabsorbed by the body. An implant has 500k-1M cells per cm2. In a study of 144 patients, the safety and long-term efficacy was demonstrated.
Cartilage repair for knees repaired with microfracture surgery
Microfracture surgery is an articular cartilage repair surgical technique used on knees that works by creating tiny fractures in the underlying bone. New cartilage then develops from a “super-clot.” The surgery is quick, minimally invasive, and can have a significantly shorter recovery time than an arthroplasty (the procedure of fixing the surface of a joint through more invasive surgery). 50% of surgeries using “microfracture surgery” in young people with sports injuries have been successful long-term.
Microfracture surgery hasn’t yet been successful with osteoarthritis, but now, a tissue engineer has created a gel that can be injected into cartilage after surgery for regeneration. Injectable hydrogels have been shown to be usable as three-dimensional cell culture scaffolds in cartilage and bone tissue engineering. They have a porous framework for cell transplantation and proliferation, minimal invasive properties, and they can take different shapes.
The scaffolds of both cartilage and bone tissue engineering should be “porous, highly biocompatible, nontoxic, and capable of promoting cell differentiation and new tissue formation; they should also have stable mechanical properties, degrade in response to the formation of new tissue, facilitate the diffusion of nutrients and metabolites, adhere and integrate with the surrounding native tissue, and properly fill the injured site.” Because hydrogels are increasingly fulfilling these conditions, the potential for successful microfracture surgery for cartilage repair for knees is much more likely to occur in the future.
Tissue engineering for treatment of knee injuries and osteoarthritis are increasingly looking possible. Hydrogels will make microfracture surgery tenable for people with osteoarthritis, as well.