In the past, researchers attempting to create stronger hydrogels used a freeze-thaw process to produce crystals within the gel, which drive out water and help hold the polymer chains together. “We knew there was room for improvement,” Wiley said. But the tissue can take up to four times that before it breaks. Activities like hopping, lunging, or climbing stairs put some 10 Megapascals of pressure on the cartilage in the knee, or about 1,400 pounds per square inch. One was achieving the upper limits of cartilage’s strength. Putting the gel to practical use as a cartilage replacement, however, presented additional design challenges. In 2020, they reported that they had created the first hydrogel strong enough for knees, which feel the force of two to three times body weight with each step. The team has already made hydrogels with remarkable properties. “It’s really off the charts in terms of hydrogel strength,” Wiley said. It is 26% stronger than natural cartilage in tension, something like suspending seven grand pianos from a key ring, and 66% stronger in compression - which would be like parking a car on a postage stamp. Their lab-made version is the first hydrogel that can handle even more. Natural cartilage can withstand a whopping 5,800 to 8,500 pounds per inch of tugging and squishing, respectively, before reaching its breaking point. The result is a Jello-like material, 60% water, which is supple yet surprisingly strong. The polyvinyl alcohol helps it return to its original shape. The cellulose fibers act like the collagen fibers in natural cartilage, Wiley said - they give the gel strength when stretched. To make this material, the Duke team took thin sheets of cellulose fibers and infused them with a polymer called polyvinyl alcohol - a viscous goo consisting of stringy chains of repeating molecules - to form a gel. “If everything goes according to plan, the clinical trial should start as soon as April 2023,” said Duke chemistry professor Benjamin Wiley, who led the research along with Duke mechanical engineering and materials science professor Ken Gall. Researchers are gearing up to begin clinical trials in humans next year. Implants made of the material are currently being developed by Sparta Biomedical and tested in sheep. Mechanical testing reveals that the Duke team’s hydrogel - a material made of water-absorbing polymers - can be pressed and pulled with more force than natural cartilage, and is three times more resistant to wear and tear. Writing in the journal Advanced Functional Materials, a Duke University-led team says they have created the first gel-based cartilage substitute that is even stronger and more durable than the real thing. To be notified when clinical trials start, sign up for updates at. For those who want to avoid replacing the entire knee joint, there may soon be another option that could help patients get back on their feet fast, pain-free, and stay that way. Often knee pain comes from the progressive wear and tear of cartilage known as osteoarthritis, which affects nearly one in six adults - 867 million people - worldwide. Over-the-counter pain relievers, physical therapy, steroid injections - some people have tried it all and are still dealing with knee pain.
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