Of all the parts of the human body, the stubby little discs between the bones in the spine represent one of the more remarkable feats of nature’s design.
Consisting of tough, rubbery rings of collagen with jelly-like centers, they compress with every step we take. They twist. They flex. Over a lifetime of wear and tear, they replenish their supportive matrix of collagen despite having no internal blood supply.
“It is really a marvel of engineering,” said Robert L. Mauck, who as a biomedical engineer at the University of Pennsylvania, has the chops to say that.
So naturally, Mauck and a team of colleagues have attempted to recreate it in the lab.
That’s because nature’s design, though impressively rugged, does not last forever. With age, nearly everyone’s spinal discs degenerate to a degree, in some cases causing terrible pain. Lower -back pain was the world’s leading cause of disability in 2017, according to the Institute for Health Metrics and Evaluation at the University of Washington. In severe cases, patients resort to having vertebrae fused together, but they lose flexibility and often are not satisfied with the result. One-third come back for repeat surgery.
In late 2018, the Penn team published a promising study of what they hope is a better option: replacement discs made from a combination of synthetic materials and living cells.
So far, the researchers have implanted their discs only in rats and goats, but they appear to behave much like the real thing, said Penn Medicine orthopedic surgeon Harvey E. Smith, the clinical leader of the effort.
“It’s a living structure,” Smith said.
The results have impressed other researchers who are working on the same challenge, among them Lawrence J. Bonassar, a Cornell University biomedical engineering professor.
“Clearly, there is more work to do, but obviously these results are incredibly encouraging,” said Bonassar, whose team has reported success with implanting a different type of replacement disc in dogs.
It has taken more than a dozen years for the Penn team to get to this point, and a lot of varied expertise. In addition to engineers and orthopedists, the group includes veterinarian Thomas P. Schaer, a research director at Penn’s New Bolton Center, who joins Smith in implanting the experimental discs in the necks of goats.
Most of the study authors also are affiliated with the Crescenz VA Medical Center in Philadelphia, such as biomedical engineer Sarah Gullbrand, the lead author of the study, and some of their funding came from the U.S. Department of Veterans Affairs. That is because members of the military suffer especially high rates of disc degeneration and back pain, whether from combat injury or operating large machinery, Mauck said.
Bus and truck drivers also may be at higher risk of disc degeneration, as are cigarette smokers — likely because smoking harms blood vessels, and therefore discs, among many other body parts.
When a disc ruptures or collapses, pain can arise in several ways, though the cause is not always clear.