Patient-specific 3D-printed scaffolds infused with human growth factors could radically change the way in which a torn knee meniscus is repaired. Researchers at Columbia University Medical Center (New York) have successfully tested the procedure on sheep and published a paper about the project in the online edition of Science Translational Medicine.

Approximately one million patients undergo surgery to repair a damaged meniscus, the knee's protective lining, in the United States each year. Small tears can be sewn back in place, but larger tears have to be surgically removed, says study leader Jeremy Mao, DDS, PhD, the Edwin S. Robinson Professor of Dentistry (in Orthopedic Surgery) at the medical center.

"While removal [of a damaged meniscus] helps reduce pain and swelling, it leaves the knee without the natural shock absorber between the femur and tibia, which greatly increases the risk of arthritis," says Mao. Meniscal transplants using tissues harvested from other parts of the patient's body or cadavers are another option, but the procedure has a low success rate and carries significant risks. The therapy developed by Mao and his team could provide the first effective, long-lasting repair of damaged menisci, according to a press release published by the medical center.

Mao's approach starts with MRI scans of the intact meniscus in the undamaged knee, which are converted into a 3D image. The data are used to 3D print a scaffold in the exact shape of the meniscus, down to a resolution of 10 microns. The scaffold, which takes about 30 minutes to print, is made of polycaprolactone, a biodegradable polymer that is also used to make surgical sutures.

The scaffold is infused with two recombinant human proteins to attract existing stem cells from the body and induce them to form meniscal tissue. To be successful, the proteins must be released in specific areas of the scaffold in a specific order. This is accomplished by encapsulating the proteins in two types of slow-dissolving polymeric microspheres. Finally, the protein-infused scaffold is inserted into the knee. In sheep, the meniscus regenerates in about four to six weeks. Eventually, the scaffold dissolves and is eliminated by the body.

"This is a departure from classic tissue engineering, in which stems cells are harvested from the body, manipulated in the laboratory, and then returned to the patient—an approach that has met with limited success," says Mao. "In contrast, we're jumpstarting the process within the body, using factors that promote endogenous stem cells for tissue regeneration."

Ultimately, the entire process, from initial scan to delivery of the personalized meniscal scaffold, could be accomplished in days.

The researchers hope to begin clinical trials once funding is in place.

The video below shows an accelerated version of meniscus scaffolding being 3D printed.