Posted on 08/11/2022 1:19:16 PM PDT by Red Badger
A hydrogel-based implant could replace worn-out cartilage and alleviate knee pain without replacing the entire joint. Credit: Benjamin Wiley, Duke University.
Over-the-counter pain relievers, physical therapy, steroid injections—some people have tried it all and are still dealing with knee pain.
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. 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.
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.
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.
Implants made of the material are currently being developed by Sparta Biomedical and tested in sheep. Researchers are gearing up to begin clinical trials in humans next year.
"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.
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.
The cellulose fibers act like the collagen fibers in natural cartilage, Wiley said—they give the gel strength when stretched. The polyvinyl alcohol helps it return to its original shape. The result is a Jello-like material, 60% water, which is supple yet surprisingly strong.
Natural cartilage can withstand a whopping 5,800 to 8,500 pounds per inch of tugging and squishing, respectively, before reaching its breaking point. Their lab-made version is the first hydrogel that can handle even more. 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.
"It's really off the charts in terms of hydrogel strength," Wiley said.
The team has already made hydrogels with remarkable properties. 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.
Putting the gel to practical use as a cartilage replacement, however, presented additional design challenges. One was achieving the upper limits of cartilage's strength. 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. But the tissue can take up to four times that before it breaks.
"We knew there was room for improvement," Wiley said.
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. In the new study, instead of freezing and thawing the hydrogel, the researchers used a heat treatment called annealing to coax even more crystals to form within the polymer network.
By increasing the crystal content, the researchers were able to produce a gel that can withstand five times as much stress from pulling and nearly twice as much squeezing relative to freeze-thaw methods.
The improved strength of the annealed gel also helped solve a second design challenge: securing it to the joint and getting it to stay put.
Cartilage forms a thin layer that covers the ends of bones so they don't grind against one another. Previous studies haven't been able to attach hydrogels directly to bone or cartilage with sufficient strength to keep them from breaking loose or sliding off. So the Duke team came up with a different approach.
Their method of attachment involves cementing and clamping the hydrogel to a titanium base. This is then pressed and anchored into a hole where the damaged cartilage used to be. Tests show the design stays fastened 68% more firmly than natural cartilage on bone.
"Another concern for knee implants is wear over time, both of the implant itself and the opposing cartilage," Wiley said.
Other researchers have tried replacing damaged cartilage with knee implants made of metal or polyethylene, but because these materials are stiffer than cartilage they can chafe against other parts of the knee.
In wear tests, the researchers took artificial cartilage and natural cartilage and spun them against each other a million times, with a pressure similar to what the knee experiences during walking. Using a high-resolution X-ray scanning technique called micro-computed tomography (micro-CT), the scientists found that the surface of their lab-made version held up three times better than the real thing. Yet because the hydrogel mimics the smooth, slippery, cushiony nature of real cartilage, it protects other joint surfaces from friction as they slide against the implant.
Natural cartilage is remarkably durable stuff. But once damaged, it has limited ability to heal because it doesn't have any blood vessels, Wiley said.
In the United States, osteoarthritis is twice as common today than it was a century ago. Surgery is an option when conservative treatments fail. Over the decades surgeons have developed a number of minimally invasive approaches, such as removing loose cartilage, or making holes to stimulate new growth, or transplanting healthy cartilage from a donor. But all of these methods require months of rehab, and some percentage of them fail over time.
Generally considered a last resort, total knee replacement is a proven way to relieve pain. But artificial joints don't last forever, either. Particularly for younger patients who want to avoid major surgery for a device that will only need to be replaced again down the line, Wiley said, "there's just not very good options out there."
"I think this will be a dramatic change in treatment for people at this stage," Wiley said.
Explore further
From the lab, the first cartilage-mimicking gel that's strong enough for knees More information: Jiacheng Zhao et al, A Synthetic Hydrogel Composite with a Strength and Wear Resistance Greater than Cartilage, Advanced Functional Materials (2022). DOI: 10.1002/adfm.202205662 Journal information: Advanced Functional Materials Provided by Duke University
Doc, will I be able to ski?
Of course.
Great, because I really never did get the hang of it.
Stammen, Jason A., Stephen Williams, David N. Ku, and Robert E. Guldberg. “Mechanical properties of a novel PVA hydrogel in shear and unconfined compression.” Biomaterials 22, no. 8 (2001): 799-806.
Our company actually worked on a product using polyvinyl alcohol gels. The group that published the paper above came up with the gel (polyvinyl alcohol, for use as cartilage replacement); we paid them money for their biocompatibility data.
My job was to extrude the gel into a long string of various diameters to be cut up and used as a plug. So I used a freezing anti-solvent as a coagulation bath. The result was a string so strong you could not break it (PVA hydrogen bonds like crazy).
This was sometime around 2004 or 2005. As you see the publication was from 2001.
It would be quite something if this new polyvinyl alcohol gel described here makes it to the market. All kinds of snags lie along the way: marketing, product durability under load, chronic toxicity, physician acceptance, etc.
By the way neither the Georgia Tech group nor our company ever marketed the gel. Now our company is in a completely different area of medicine.
Now, if this could have applications for ACL replacements...
This is then pressed and anchored into a hole where the damaged cartilage used to be.
= = =
So they still cut and pry and jab and drill and stuff.
Ouch.
My Ortho Dr. Linsey Rolston of New Castle Indiana has been doing Partial Knee Replacement for many years. He is the Inventer of this process. This not a new technique.
My wife used a product called gelone
Insurance refused to pay for prescription
We paid out of pocket around 400 dllrs
3 months now and pretty much knee pain not an issue
bump
Wow. I was thinking about this possibility last night as an alternative to joint replacements. I hope this works out.
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If it was available right now, it would be 15 years too late for my wife...
I have so many check engine lights that come on in my body that knee pain would just be a drop in the bucket. Aging is not for wimps.
Some time ago I watched a knee replacement live on public television.
It was all drills, hammers, saws, screws, bolts, and nuts.
It wasn’t medicine, it was carpentry.
LOL - So true. Saw such a video also.
😀😁😂🤣😃😄
I will be plagiarising that at the family joint Thanksgiving & my 89th birthday dinner this November just before I blow out the candles on my cake...
Not a word about how the body will respond to the chemicals in the gel.
It wasn’t medicine, it was carpentry.
One of the most skilled orthopedic surgeons I over met received a B.Sc. in mechanical engineering and then decided to go to medical school. That guy can d the prettiest joint replacements I’ve ever seen.
I had bilateral total knee replacement surgeries in June, two weeks apart. Pretty devastating for the first week or so but now after a couple months of physical therapy i can walk better than i have in years. If this new polymer ever gets approved i think id still go with replacement. Literally lik starting over again
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