Doctors at Columbia University’s Medical Center have been working on 3D-printing a knee joint, or meniscus, using a degradable plastic scaffold as well as a protein growth system. Once the object is printed, it’s transplanted into the body where the protein turns into a knee joint.

The meniscus is a protective lining around the knee; if it’s torn or injured, it may cause long-term complications, including arthritis. Currently, doctors can replace a torn meniscus with a meniscal transplant — using tissues from other parts of the body — but this poses quite a risk of complications.

“At present, there’s little that orthopedists can do to regenerate a torn knee meniscus,” Jeremy Mao, the lead author of the study, said in a press release. “Some small tears can be sewn back in place, but larger tears have to be surgically removed. While removal 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.”

The new procedure, outlined in a study, involves first taking an MRI of the meniscus then converting this to a 3D image. The image is then used to assist the 3D printer in copying the exact shape of the intact meniscus, and print out a scaffold made of polycaprolactone — a biodegradable polymer that can be seamlessly subsumed by the human body. This scaffold also contains two human proteins, connective growth factor (CTGF) and transforming growth factor beta-3 (TGF-beta-3), which helps the new meniscal tissue to grow by attracting stem cells.

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

So far, researchers tested this method in 11 sheep, and came up with successful results. They hope to soon bring this to clinical human trials.