October 05, 2008
Polymer Hydrogel Improves Knee Surgery Outcomes

A new biomaterial boosts success rates when using the microfracture technique to restore knee cartilage.

A new biomaterial developed by Cartilix, a biotech startup based in Foster City, CA, could dramatically improve the success rate of knee-cartilage repair surgery, making the procedure more accessible to patients with bad knees. The new material, called ChonDux, consists of a polymer hydrogel that, when injected into the knee during surgery, guides the regeneration of cartilage by stimulating repair cells in the body.

So far the technique has been tested on animals and on a small human group in Europe. So you can't get this treatment unless you can get yourself enrolled in a coming US clinical trial.

This hydrogel enhances an existing knee surgery repair technique called microfracture. The microfracture approach involves drilling lots of small holes in bone where the cartilage is missing. A blood clot formed in that area signals stem cells to rush in and do repair. This new enhancement of that approach reduces the amount of scar tissue that forms and increases cartilage formation.

ChonDux consists of a hydrogel made of polyethylene glycol--a polymer commonly used in a variety of medical products--and a bioadhesive to keep the hydrogel in place after injection. First, the surgeon coats the inside of the cavity where the cartilage is missing with the bioadhesive and then, as in microfracture, drills tiny holes into the bone next to the cavity. Then the surgeon fills the empty space with the hydrogel and shines UVA light on the material, which causes the polymer to harden from a viscous liquid into a gel.The blood clot that forms from the microfracture then gets trapped in the hydrogel.

The bioadhesive in this case is chondroitin sulfate which many people take as a supplement to reduce joint pain.

One of the biggest problems with transplanting biomaterials is getting the mostly aqueous material to stick in a very slippery space, says Jennifer Elisseeff, a biomedical engineer at Johns Hopkins University, who developed ChonDux and cofounded Cartilix. The adhesive in this case consists of chondroitin sulfate--a natural component of cartilage that is chemically modified to bind to the healthy cartilage surrounding the defect, as well as to the hydrogel. "It acts like a primer that helps paint stick to the wall," Elisseeff said at a panel at the recent EmTech conference in Cambridge, MA. The adhesive prevents scar formation between the new and old cartilage.

This approach is fairly low tech. The researchers didn't grow up stem cells for injection into the knee. They also didn't use gene therapy to instruct cells to do repair. Yet those higher tech methods are needed. The existing microfracture technique has a much lower success rate in older people - probably because their stem cells are less vigorous. Younger stem cells or stem cells primed up to do repair could boost success rates.

The drilling of holes in bone as a way to stimulate repair seems crude. We need ways to coat a surface with repair stimulating materials without causing damage. Simulate the damage biochemically rather than cause real damage. Those techniques will come as the compounds that stimulate repair become better understood and more manipulable.

Share |      Randall Parker, 2008 October 05 02:53 PM  Biotech Tissue Engineering

dougb said at October 5, 2008 5:18 PM:

I'm 32. I have idiopathic systemic joint pain. Developed after a knee injury. Modern medicine doesnt seem to have any answers for me. So this has been a area ive been keeping my eye on considering how I could progress later in life (and to try to figure out what has been going on with me). Joints are going to be one of the harder problems to solve regarding aging. Evolution knits us together like a sweater....one thread cut...and the dominos start falling. Even if we solve cartilage issues what about tendons. Even in perfectly normal people there feet flaten out as they age as their tendons lose strength. How would you shink the tendon/ligament back to its proper length and elasticity while its still in the body? That is one thing I'd like to see progress on. Glad to hear progress is being made though.

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