The beauty of human bones is that when broken, they fix themselves. But sometimes bones deteriorate in such a way that they can't repair themselves effectively.
Bone grafts are currently the preferred solution, but they pose problems of their own. A team of Penn researchers has come up with a better cure: artificial bone with a heart of glass.
The artificial bone overcomes instances when patients don't have enough bone suitable for grafting, and instances when grafts fail to attach themselves properly or even become infected.
Paul Ducheyne with femur and model of the molecular structure of bone tissue
Photo by Candace diCarlo
Professor of Bioengineering Paul Ducheyne and Assistant Professor of Orthopedic Surgery Johnathan Garino have spent the past several years growing bone tissue on a special type of ceramic material that, unlike most ceramics, is chemically reactive. That means that molecules can adhere to and release from the glass surface, when immersed in a solution.
To create the artifical bone tissue, Ducheyne and Garino seeded molecules of a substance called fibromectin onto the glass surface. "Fibromectin is a very important molecule in creating osteoblasts," which manufacture bone tissue, Ducheyne explained. The fibromectin turns the glass substrate into a core around which new bone tissue can grow.
Bone marrow cells extracted from animals, once attached to the glass substrate via the fibromectin links, start to replicate themselves and manufacture bone tissue. "With these reactive ceramics, we set the sequence of reactions that is part and parcel of the cells into motion and do that very, very quickly," Ducheyne said.
The ceramic material is already being used in human bone repair to stimulate cell activity within existing bone tissue. Ducheyne and Garino are now taking the process a step further: using the ceramic base as a "seed culture" for manufacturing bone tissue in vitro, then implanting the tissue in animals to function as filler and eventually become extensions of the existing bone.
In experiments with rats, the researchers found that tissue synthesized over two weeks before implanting became as strong as intact bone after only two weeks in the rat - twice as fast as untreated bone tissue or synthetic tissue developed from a ceramic seed implanted directly.
While research into this procedure using human bone tissue has yet to be approved, Ducheyne estimates that synthesized bone tissue implanted in human subjects would reach the same level of strength in about four to six weeks.
Ducheyne said that this synthesized bone tissue could become valuable as a tool to restore bones that have deteriorated after the installation of hip implants or similar prostheses. "There is a lot of bone erosion in these cases, and we have to reconstruct that bone," he said. "And that's where we think our concept here in which we seed the cells could be very useful.
"If you can come up with a substitute that functions as well as an allograft, or nearly as well, and you get repair of the bone, it costs less, and it doesn't create [infections], that's great."
Originally published on January 14, 1999