Healing Knees With Light-Activated Gel

When the knee’s vital cartilage erodes or tears, there isn’t much that doctors can do to save it. Researchers are exploring a new kind of hydrogel that may lead to more optimistic odds of recovery.





Last Sunday, during a playoff loss to the Seattle Seahawks, Washington Redskins quarterback Robert Griffin III crumpled on the field with a knee injury. Griffin reportedly tore ACL and LCL ligaments and may face a year-long recovery following reconstructive surgery today. But as bad as things look for the star rookie QB, things could be worse: A physical therapist told ESPN that Griffin would be looking at even graver recovery challenges had he suffered damage to his knee cartilage. 

That’s because the cartilage that cushions the bones in the knee just doesn’t heal well, and there aren’t any great options for treatment. But today in the journal Science Translational Medicine, scientists, including biomedical engineer Jennifer Elisseeff from Johns Hopkins University, propose a new way to heal knees using a light-activated form of hydrogel—a soft, jelly-like material composed of crisscrossing polymer fibers that soak up water. 

Cartilage doesn’t naturally have a blood supply to help it heal. So a common treatment strategy, called microfracturing, is to drill holes into surrounding tissue and bone. The bleeding helps stem cells recolonize the area and stimulate the development of new cartilage. The problem with this strategy, Elisseeff says, is that the repair tissue doesn’t completely fill in the damaged area, and may fill it with scar tissue instead of real cartilage. 

In their study, Elisseeff and colleagues performed the standard microfracturing technique to repair knee cartilage. On 15 patients, however, the surgeons poured a liquid hydrogel into the torn cartilage. The hydrogel’s polymers had been designed so that when surgeons shined a UV light onto the goop, it hardened into a gelatinous solid, sort of like real cartilage. 

"At the end of the day, it looks like red Jell-O," says Norman Marcus, an orthopedic surgeon on the team. "It wiggles when you touch it." 

The hydrogel goes into the cartilage as a liquid, so it can take on any shape. That’s helpful because the size and shape of the damage varies widely from person to person. Sometimes the rips are round or oblong, other times they’re irregular or even hockey-stick-shaped. Once the gel solidifies, it’s meant to guide tissue regeneration. It provides a physical scaffold for stem cells to attach to, Elisseeff says, and includes chemical and biological factors, such as the chemicals chondroitin sulfate and hylaronic acid, normally found in cartilage, which inhibit the formation of scar tissue. 

In patients who received the hydrogel implant, repair tissue filled 86 percent of the cartilage hole, compared with 64 percent in the three control subjects who received traditional microfracturing treatment. The patients with hydrogel also reported significantly less pain than the controls. 

Gunnar Knutsen, an orthopedic surgeon at the University Hospital North Norway, cautions that it is too soon to tell whether the hydrogel treatment is better than the standard therapy. Larger clinical trials are needed to make that judgment, he says. Paying for those trials would most likely fall on Biomet, the company that owns the rights to the hydrogel. Elisseef and her co-authors claim no financial connections to Biomet; they’ve simply tried to show that the hydrogel treatment is feasible and doesn’t appear to cause harm. 

Farshid Guilak, an orthopedic surgeon at Duke University, called the preliminary results promising, especially when compared to stem cell treatments that would require a biopsy of the patient’s stem cells and then re-injection into the damaged cartilage. "The major advance of this approach is that it can take advantage of the body’s own stem cells that are in the microfracture clot," Guilak says. 

If the hydrogel proves its worth, it could help people with both age-related cartilage degeneration and sports-related injuries to get back on their feet and back into the game. That’s something the current treatments can’t always achieve. "For lesions larger than a centimeter, microfracturing has a 50 percent fail rate," Marcus says. "That’s a very high failure rate. We need something that works 90 percent of the time."