Injectable Gel Could Help Knee Cartilage Heal

By Pat Anson, Editor

With the number of knee replacement surgeries soaring in the United States, researchers at the University of Iowa are working on an injectable gel that could repair damaged cartilage and make many knee surgeries unnecessary.

"We are creating an [injectable, bioactive] hydrogel that can repair cartilage damage, regenerate stronger cartilage, and hopefully delay or eliminate the development of osteoarthritis and eliminate the need for total knee replacement," says Yin Yu, a graduate student at the University of Iowa (UI) whose study is featured in the journal Arthritis and Rheumatology.

Osteoarthritis (OA) is a joint disorder that leads to thinning of cartilage and progressive joint damage. Nearly 40 percent of Americans over the age of 45 have some degree of knee OA, and those numbers are expected to grow as the population ages.

About 600,000 knee replacement surgeries are performed annually in the U.S. – about twice the number performed 20 years ago. Recent studies have questioned whether many of the surgeries are appropriate.

UI researchers have previously identified precursor cells in healthy cartilage that can mature into new cartilage tissue – a surprising development given the long-held assumption that cartilage is one of the few tissues in the body that cannot repair itself.

The researchers also identified molecular signals that encourage precursor cells to migrate out of healthy tissue and into damaged areas – stimulating the development of new cartilage. One of the signals, called stromal cell-derived factor 1 (SDF1), acts like a “homing beacon” for the precursor cells.

In an experimental model of cartilage injury, Yu loaded the hydrogel with SDF1 and injected it into holes punched into the model cartilage. The precursor cells migrated toward the SDF1 infused gel and filled in the injury site. Subsequent application of a growth factor caused the cells to mature into normal cartilage that repaired the injury.

The new tissue is not as strong as normal cartilage, but researchers think it could be strengthened through physical therapy and exercise.

"There's really no cure for osteoarthritis except for total joint replacement, which is not particularly suitable for younger patients because the artificial joints wear out and need to be replaced multiple times," said James Martin, PhD, a UI assistant professor of orthopedics and rehabilitation who leads the research team.

"Our approach aims to leverage the body's own capacity for repair, and what we've shown is that cartilage does have regenerative potential; you just have to manipulate it just right."

UI Researchers are now looking at different ways to include the growth factor in the hydrogel – possibly by using nano-size plasmids that carry genetic instructions for the growth factor or microspheres loaded with the substance.

Yu and Martin plan to start animal trials within a year and, if the results are promising, begin human trials in about five years.

Injections of platelet rich plasma (PRP) into the knee also show promise in the treatment of osteoarthritis, according to a recent study published in The Journal of the American Osteopathic Association (JAOA).

Only a few small clinical trials have been conducted on the effectiveness of PRP therapy. Researchers at the University of Miami Miller School of Medicine analyzed those trials and found that patients with knee osteoarthritis and other musculoskeletal injuries showed significant improvements as long as two years after PRP injections.

The procedure involves withdrawing blood from the patient and then spinning it to produce a high concentration of platelet cells. The plasma is then injected back into the patient at the injury site, speeding up the healing process. Several top athletes, including Kobe Bryant and Peyton Manning, have used a form of PRP therapy to help them recover from injuries.