Biologists and materials scientists are experimenting with a new approach to cartilage replacement. They’ve developed a novel biomaterial that rebuilds damaged cartilage, creating new, high-quality padding for the knee joint. Though the biomaterial has only been tested with sheep, its success so far could allow simple injections to someday supplement or replace conventional joint repair procedures.
Osteoarthritis, or the degeneration of cartilage at the joints, is a painful and physically limiting ailment that afflicts more than three million US adults each year. Without treatment, bone rubs against bone, making it deeply uncomfortable and difficult to move. But today’s go-to treatment isn’t a walk in the park, either. Microfracture surgery, which involves creating tiny holes in the bone, triggers the natural creation of blood clot-induced fibrocartilage, which mainly functions like joint (or articular) cartilage. Recovering from this procedure takes several weeks of physical therapy and months of reduced activity. Patients with particularly advanced osteoarthritis must undergo cartilage replacement surgery, which takes at least six weeks to recover from, or full knee replacements, followed by a year-long recovery period.
In a paper for the Proceedings of the National Academy of Sciences, researchers at Northwestern University introduce “injectable scaffolds”—a custom biomaterial designed to repair damaged joint cartilage. The material consists of a custom iteration on hyaluronic acid (a natural polysaccharide found in cartilage and used in skincare products) and a bioactive peptide that binds with TGFb-1, a protein responsible for cartilage growth. Together, these components create bundles of nanoscale fibers that mimic cartilage’s natural structure while encouraging the body to repair damaged cartilage—and maintain what’s left.
Microstructure of the new bioactive material. Nanofibers are pink; hyaluronic acid is shown in purple.
Credit: Samuel Stupp/Northwestern University
An initial experiment involving sheep yielded promising results. Like humans, sheep possess non-regenerating joint cartilage that, once damaged, makes it difficult to bear weight evenly across the limbs. By partnering with orthopedic veterinarians at the University of Wisconsin-Madison, the team injected their material into the knees of sheep with cartilage defects. The biomaterial “transformed into a rubbery matrix,” filling the gaps in the animals’ damaged cartilage and producing a more resilient scaffold.
“A study on a sheep model is more predictive of how the treatment will work in humans. In other smaller animals, cartilage regeneration occurs much more readily,” said Samuel Stupp, a renowned materials scientist at Northwestern. “Our new therapy can induce repair in a tissue that does not naturally regenerate. We think our treatment could help address a serious, unmet clinical need.”
Stupp’s team envisions a future in which their biomaterial can prevent knee replacement surgeries by repairing damaged tissue before a more invasive procedure is needed. Depending on the results of future tests, the material could also find a place in sports medicine, where cartilage damage can occur after a bad twist or impact-related injury.