Regenerating Torn Cartilage

A new biomaterial could improve knee-cartilage repair surgery.

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.

Knee filler: A biomaterial developed by Cartilix, called ChonDux, could improve current microfracture surgery aimed at repairing damaged knee cartilage. During the procedure, the surgeon applies a bioadhesive (shown in blue) to the cavity where the cartilage is missing. Tiny holes (red) are then drilled in the bone next to the cavity and filled in with hydrogel (wavy lines). UVA light is shined on the material, which causes the polymer to harden from a viscous liquid into a gel (crosshatched lines). Credit: Nature Materials

The minimally invasive knee surgery known as microfracture, in which a surgeon drills holes in the knee to stimulate the regeneration of cartilage lost from wear and tear, has become increasingly popular among athletes in recent years. A number of professional basketball players, including Greg Oden of the Portland Trail Blazers and Amare Stoudemire of the Phoenix Suns, have undergone the procedure, contributing to its rise in popularity. However, the procedure's success rate varies dramatically, says Norman Marcus, an orthopedic surgeon at the Virginia Cartilage Institute, in Springfield, VA. Among young athletes who have small defects in their knee cartilage, microfracture works up to 75 percent of the time. However, that number drops to 50 percent in older patients, Marcus says.

Marcus, who is chief medical officer at Cartilix, and his colleagues hope to improve the procedure and make it more accessible to the larger population of baby boomers. As people age, many are forced to curtail their physical activities due to painful, swollen joints caused by the deterioration of cartilage in the knee that comes with age or results from repetitive stress or injury. Marcus hopes to be able to treat these patients before they develop full-blown osteoarthritis. "The goal is to identify that big population that wants to be active throughout their entire lives," he says.

During microfracture, a surgeon uses a special awl to drill a series of tiny holes into the bone underneath the area of missing cartilage. Bone marrow containing stem cells seeps into the damaged area and forms a clot. The clot releases stem cells, which differentiate into cartilage cells and gradually form new tissue. However, because the new tissue is scar cartilage, not true cartilage, it may not have the same durability and strength as the original tissue--a likely contributor to the high failure rate of microfracture.

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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.