For people who suffer chronic back pain from degenerated or diseased spinal discs, there are few options. Surgeons can implant a plastic or metal spinal disc to replace your damaged one. But metal and plastic prosthetics can only do so much; surgeries are costly and recovery times are long.
Now Cornell University engineers in Ithaca and doctors at Weill Cornell Medical College in NYC have come up with a new solution. They've designed replacement spinal discs out of biological materials.
Their findings are published in the latest issue of Proceedings of the National Academy of Sciences.
For many years, surgeons approached this problem by simply removing the affected spinal disc and fusing the remaining vertebral bodies together — a process known as "discectomy." Unfortunately, while this left many patients with much less pain, their mobility was often severely hampered.
In 2005, a surgical procedure was approved by the FDA that foregoes the process of spinal fusion in favor of spinal disc replacement, with surgeons swapping the patient's diseased disc(s) for an implant made out of metal and plastic.
While these implants do a more admirable job of mimicking normal spinal movement than a pair of fused vertebrae, they pose an inherent problem: metal and plastic — inorganic materials that they are — degrade over time, and can give rise to a host of unwanted side effects.
To address these side effects, Drs. Larry Bonassar and Roger Härtl have designed an implant to replace intervertebral discs in the spinal column whose mechanical properties actually improve with time.
"Our implants have maintained 80-90 percent of initial disc height," explained Bonassar. "In fact, the mechanical properties only get better with time."
The secret to the discs is their use of two polymers: collagen, which you can see wrapped around the outside of the artificial disc on the right (the disc on the left is an actual intervertebral disc), and a hydrogel called alginate in the middle. Unlike metal or plastic, these polymers allow the scientists to seed the implants with cells that mature into new, organic tissue. As a result, the structural integrity of the implant actually improves as the cells grow inside the body.
According to Dr. Härtl, the new discs not only offer a "huge advantage" over traditional implants, but also less invasive surgical methods and fewer long-term side effects. The scientists, who so far have performed implantation experiments on rats, intend to swap the discs of larger animals, and eventually humans, meaning we could see biological implants of our very own in the not so distant future.
Research Via PNAS
Image of intervertebral discs via
Image of natural and tissue engineered discs via Cornell's Chronicle Online