By Pat Anson, PNN Editor

Clinical trials on humans may begin as soon as next year on an experimental hydrogel designed to replace damaged cartilage in arthritic knees, according to researchers at Duke University, who say the gel is up to three times stronger than natural cartilage.   

Implants made of the material are currently being tested on sheep by Sparta Biomedical, a medical device company that is developing a line of synthetic cartilage.

“If everything goes according to plan, the clinical trial should start as soon as April 2023,”  Benjamin Wiley, PhD, Sparta’s chief technology officer and a Duke chemistry professor, said in a press release. “I think this will be a dramatic change in treatment for people.”

Wiley says hydrogel implants could someday be used as an alternative to total knee replacement surgery, one of the fastest growing elective procedures in the United States. About one in six adults suffer from knee osteoarthritis, a painful disorder that leads to thinning of cartilage and progressive joint damage.

Often considered the treatment of last resort, knee replacement surgery can be problematic. Studies have found that about a third of the patients who have their knees replaced continue to experience chronic pain. The artificial joints also have a limited life span and sometimes need to be replaced after a few years.   

“There's just not very good options out there,” said Wiley.

To make the hydrogel, Wiley and his team took thin sheets of cellulose fibers and infused them with a water absorbing polymer, creating a Jello-like material that is surprisingly strong. The cellulose fibers act like the collagen in natural cartilage, giving the gel strength when pulled or stretched.

Natural cartilage can withstand up to 8,500 pounds per inch of tugging and squishing before reaching a breaking point. The hydrogel can handle even more pressure and is 66% stronger than cartilage when compressed, the equivalent of parking a car on a postage stamp.

“It’s really off the charts in terms of hydrogel strength,” Wiley says.

Duke researchers first reported in 2020 that they had developed a hydrogel strong enough for knees, but using it to replace cartilage presented some design challenges. Hydrogels are difficult to attach directly to bone or cartilage to keep them from breaking loose or sliding off during intense activities.

They got around that problem by cementing and clamping the hydrogel to a titanium base, which is then anchored into a small hole where the damaged cartilage used to be. Tests showed the design stays fastened 68% more firmly than natural cartilage on bone.

In wear tests, the researchers took the hydrogel and natural cartilage and spun them against each other a million times, with a pressure similar to what the knee experiences during walking. Using high-resolution X-ray imaging, they found that the artificial cartilage held up three times better than the real thing.

And because the hydrogel mimics the smooth and cushiony nature of real cartilage, it protects other joint surfaces from being damaged as they slide against the implant. Other researchers have tried replacing cartilage with implants made of metal or polyethylene, but because those materials are stiffer than cartilage, they can chafe against other parts of the knee.

The research study, published in the journal Advanced Functional Materials, was funded by Sparta Biomedical and Duke University.

An experimental gel also shows promise as a treatment for low back pain caused by degenerative disc disease, according to a recent small study. Hydrafil – an injectable gel developed by ReGelTec – fills in cracks and tears in damaged discs, restoring the disc’s structural integrity. The injection procedure is minimally invasive and only takes about 30 minutes.