Of all the parts of the human body, the 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 jellylike 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, a biomedical engineer at the University of Pennsylvania.
But nature's design, though rugged, does not last forever. With age, nearly everyone's spinal discs degenerate to a degree. Lower-back pain was the world's leading cause of disability in 2017, said the Institute for Health Metrics and Evaluation at the University of Washington. In severe cases, patients have vertebrae fused together, but they lose flexibility and one-third come back for repeat surgery.
A team at Penn has 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. "It's a living structure," Smith said.
It has taken more than a dozen years for the 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.
Some of their funding came from the U.S. Department of Veterans Affairs because members of the military suffer especially high rates of disc degeneration and back pain, Mauck said.